Merge remote-tracking branch 'upstream/master' into 503-hover-doc-links

.cargo/config

@@ -3,3 +3,6 @@ xtask = "run --package xtask --bin xtask --"
 install-ra = "run --package xtask --bin xtask -- install" # for backwards compat
 tq = "test -- -q"
 qt = "tq"
+
+[target.x86_64-pc-windows-msvc]
+linker = "rust-lld"

.gitattributes

@@ -1,5 +1,5 @@
 * text=auto eol=lf
-crates/ra_syntax/test_data/** -text eof=LF
+crates/syntax/test_data/** -text eof=LF
 # Older git versions try to fix line endings on images, this prevents it.
 *.png binary
 *.jpg binary

.github/FUNDING.yml

@@ -1,12 +1,2 @@
-# These are supported funding model platforms
-
-github: # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
-patreon: # Replace with a single Patreon username
+github: rust-analyzer
 open_collective: rust-analyzer
-ko_fi: # Replace with a single Ko-fi username
-tidelift: # Replace with a single Tidelift platform-name/package-name e.g., npm/babel
-community_bridge: # Replace with a single Community Bridge project-name e.g., cloud-foundry
-liberapay: # Replace with a single Liberapay username
-issuehunt: # Replace with a single IssueHunt username
-otechie: # Replace with a single Otechie username
-custom: # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']

.github/workflows/ci.yaml

@@ -16,20 +16,6 @@ env:
   RUSTUP_MAX_RETRIES: 10
 
 jobs:
-  # rust-audit:
-  #   name: Audit Rust vulnerabilities
-  #   runs-on: ubuntu-latest
-  #   steps:
-  #   - name: Checkout repository
-  #     uses: actions/checkout@v2
-
-  #   - uses: actions-rs/install@v0.1
-  #     with:
-  #       crate: cargo-audit
-  #       use-tool-cache: true
-
-  #   - run: cargo audit
-
   rust:
     name: Rust
     runs-on: ${{ matrix.os }}
@@ -84,15 +70,14 @@ jobs:
     - name: Prepare cache
       run: cargo xtask pre-cache
 
-    - name: Prepare cache 2
-      if: matrix.os == 'windows-latest'
-      run: Remove-Item ./target/debug/xtask.exe, ./target/debug/deps/xtask.exe
-
-  # Weird target to catch non-portable code
-  rust-power:
-    name: Rust Power
+  # Weird targets to catch non-portable code
+  rust-cross:
+    name: Rust Cross
     runs-on: ubuntu-latest
 
+    env:
+      targets: "powerpc-unknown-linux-gnu x86_64-unknown-linux-musl"
+
     steps:
     - name: Checkout repository
       uses: actions/checkout@v2
@@ -103,7 +88,9 @@ jobs:
         toolchain: stable
         profile: minimal
         override: true
-        target: 'powerpc-unknown-linux-gnu'
+
+    - name: Install Rust targets
+      run: rustup target add ${{ env.targets }}
 
     - name: Cache cargo directories
       uses: actions/cache@v2
@@ -114,14 +101,17 @@ jobs:
         key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
 
     - name: Check
-      run: cargo check --target=powerpc-unknown-linux-gnu --all-targets
+      run: |
+        for target in ${{ env.targets }}; do
+          cargo check --target=$target --all-targets
+        done
 
   typescript:
     name: TypeScript
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, windows-latest, macos-latest]
+        os: [ubuntu-latest, windows-latest]
 
     runs-on: ${{ matrix.os }}
 

Cargo.toml

@@ -2,37 +2,34 @@
 members = [ "crates/*", "xtask/" ]
 
 [profile.dev]
-# disabling debug info speeds up builds a bunch,
+# Disabling debug info speeds up builds a bunch,
 # and we don't rely on it for debugging that much.
 debug = 0
 
+[profile.dev.package]
+# These speed up local tests.
+rowan.opt-level = 3
+rustc-hash.opt-level = 3
+smol_str.opt-level = 3
+text-size.opt-level = 3
+# This speeds up `cargo xtask dist`.
+miniz_oxide.opt-level = 3
+
 [profile.release]
 incremental = true
-debug = 0 # set this to 1 or 2 to get more useful backtraces in debugger
+debug = 0 # Set this to 1 or 2 to get more useful backtraces in debugger.
 
-# ideally, we would use `build-override` here, but some crates are also
-# needed at run-time and we end up compiling them twice
-[profile.release.package.proc-macro2]
-opt-level = 0
-[profile.release.package.quote]
-opt-level = 0
-[profile.release.package.syn]
-opt-level = 0
-[profile.release.package.serde_derive]
-opt-level = 0
-[profile.release.package.chalk-derive]
-opt-level = 0
-[profile.release.package.salsa-macros]
-opt-level = 0
-[profile.release.package.tracing-attributes]
-opt-level = 0
-[profile.release.package.xtask]
-opt-level = 0
-
-# Gzipping the artifacts is up to 10 times faster with optimizations (`cargo xtask dist`).
-# `miniz_oxide` is the direct dependency of `flate2` which does all the heavy lifting
-[profile.dev.package.miniz_oxide]
-opt-level = 3
+# Ideally, we would use `build-override` here, but some crates are also
+# needed at run-time and we end up compiling them twice.
+[profile.release.package]
+chalk-derive.opt-level = 0
+proc-macro2.opt-level = 0
+quote.opt-level = 0
+salsa-macros.opt-level = 0
+serde_derive.opt-level = 0
+syn.opt-level = 0
+tracing-attributes.opt-level = 0
+xtask.opt-level = 0
 
 [patch.'crates-io']
 # rowan = { path = "../rowan" }

README.md

@@ -39,7 +39,7 @@ https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Frls-2.2E0
 
 * Website: https://rust-analyzer.github.io/
 * Metrics: https://rust-analyzer.github.io/metrics/
-* API docs: https://rust-analyzer.github.io/rust-analyzer/ra_ide/
+* API docs: https://rust-analyzer.github.io/rust-analyzer/ide/
 
 ## License
 

bors.toml

@@ -1,9 +1,8 @@
 status = [
     "Rust (ubuntu-latest)",
     "Rust (windows-latest)",
-    "Rust (macos-latest)",
+    # "Rust (macos-latest)",
     "TypeScript (ubuntu-latest)",
     "TypeScript (windows-latest)",
-    "TypeScript (macos-latest)",
 ]
 delete_merged_branches = true

crates/arena/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "arena"
+version = "0.0.0"
+license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false

crates/assists/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "assists"
+version = "0.0.0"
+license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false
+
+[dependencies]
+rustc-hash = "1.1.0"
+itertools = "0.9.0"
+either = "1.5.3"
+
+stdx = { path = "../stdx" }
+syntax = { path = "../syntax" }
+text_edit = { path = "../text_edit" }
+profile = { path = "../profile" }
+base_db = { path = "../base_db" }
+ide_db = { path = "../ide_db" }
+hir = { path = "../hir" }
+test_utils = { path = "../test_utils" }

crates/assists/src/assist_context.rs

@@ -0,0 +1,293 @@
+//! See `AssistContext`
+
+use std::mem;
+
+use algo::find_covering_element;
+use base_db::{FileId, FileRange};
+use hir::Semantics;
+use ide_db::{
+    label::Label,
+    source_change::{SourceChange, SourceFileEdit},
+    RootDatabase,
+};
+use syntax::{
+    algo::{self, find_node_at_offset, SyntaxRewriter},
+    AstNode, SourceFile, SyntaxElement, SyntaxKind, SyntaxToken, TextRange, TextSize,
+    TokenAtOffset,
+};
+use text_edit::{TextEdit, TextEditBuilder};
+
+use crate::{
+    assist_config::{AssistConfig, SnippetCap},
+    Assist, AssistId, AssistKind, GroupLabel, ResolvedAssist,
+};
+
+/// `AssistContext` allows to apply an assist or check if it could be applied.
+///
+/// Assists use a somewhat over-engineered approach, given the current needs.
+/// The assists workflow consists of two phases. In the first phase, a user asks
+/// for the list of available assists. In the second phase, the user picks a
+/// particular assist and it gets applied.
+///
+/// There are two peculiarities here:
+///
+/// * first, we ideally avoid computing more things then necessary to answer "is
+///   assist applicable" in the first phase.
+/// * second, when we are applying assist, we don't have a guarantee that there
+///   weren't any changes between the point when user asked for assists and when
+///   they applied a particular assist. So, when applying assist, we need to do
+///   all the checks from scratch.
+///
+/// To avoid repeating the same code twice for both "check" and "apply"
+/// functions, we use an approach reminiscent of that of Django's function based
+/// views dealing with forms. Each assist receives a runtime parameter,
+/// `resolve`. It first check if an edit is applicable (potentially computing
+/// info required to compute the actual edit). If it is applicable, and
+/// `resolve` is `true`, it then computes the actual edit.
+///
+/// So, to implement the original assists workflow, we can first apply each edit
+/// with `resolve = false`, and then applying the selected edit again, with
+/// `resolve = true` this time.
+///
+/// Note, however, that we don't actually use such two-phase logic at the
+/// moment, because the LSP API is pretty awkward in this place, and it's much
+/// easier to just compute the edit eagerly :-)
+pub(crate) struct AssistContext<'a> {
+    pub(crate) config: &'a AssistConfig,
+    pub(crate) sema: Semantics<'a, RootDatabase>,
+    pub(crate) frange: FileRange,
+    source_file: SourceFile,
+}
+
+impl<'a> AssistContext<'a> {
+    pub(crate) fn new(
+        sema: Semantics<'a, RootDatabase>,
+        config: &'a AssistConfig,
+        frange: FileRange,
+    ) -> AssistContext<'a> {
+        let source_file = sema.parse(frange.file_id);
+        AssistContext { config, sema, frange, source_file }
+    }
+
+    pub(crate) fn db(&self) -> &RootDatabase {
+        self.sema.db
+    }
+
+    pub(crate) fn source_file(&self) -> &SourceFile {
+        &self.source_file
+    }
+
+    // NB, this ignores active selection.
+    pub(crate) fn offset(&self) -> TextSize {
+        self.frange.range.start()
+    }
+
+    pub(crate) fn token_at_offset(&self) -> TokenAtOffset<SyntaxToken> {
+        self.source_file.syntax().token_at_offset(self.offset())
+    }
+    pub(crate) fn find_token_at_offset(&self, kind: SyntaxKind) -> Option<SyntaxToken> {
+        self.token_at_offset().find(|it| it.kind() == kind)
+    }
+    pub(crate) fn find_node_at_offset<N: AstNode>(&self) -> Option<N> {
+        find_node_at_offset(self.source_file.syntax(), self.offset())
+    }
+    pub(crate) fn find_node_at_offset_with_descend<N: AstNode>(&self) -> Option<N> {
+        self.sema.find_node_at_offset_with_descend(self.source_file.syntax(), self.offset())
+    }
+    pub(crate) fn covering_element(&self) -> SyntaxElement {
+        find_covering_element(self.source_file.syntax(), self.frange.range)
+    }
+    // FIXME: remove
+    pub(crate) fn covering_node_for_range(&self, range: TextRange) -> SyntaxElement {
+        find_covering_element(self.source_file.syntax(), range)
+    }
+}
+
+pub(crate) struct Assists {
+    resolve: bool,
+    file: FileId,
+    buf: Vec<(Assist, Option<SourceChange>)>,
+    allowed: Option<Vec<AssistKind>>,
+}
+
+impl Assists {
+    pub(crate) fn new_resolved(ctx: &AssistContext) -> Assists {
+        Assists {
+            resolve: true,
+            file: ctx.frange.file_id,
+            buf: Vec::new(),
+            allowed: ctx.config.allowed.clone(),
+        }
+    }
+
+    pub(crate) fn new_unresolved(ctx: &AssistContext) -> Assists {
+        Assists {
+            resolve: false,
+            file: ctx.frange.file_id,
+            buf: Vec::new(),
+            allowed: ctx.config.allowed.clone(),
+        }
+    }
+
+    pub(crate) fn finish_unresolved(self) -> Vec<Assist> {
+        assert!(!self.resolve);
+        self.finish()
+            .into_iter()
+            .map(|(label, edit)| {
+                assert!(edit.is_none());
+                label
+            })
+            .collect()
+    }
+
+    pub(crate) fn finish_resolved(self) -> Vec<ResolvedAssist> {
+        assert!(self.resolve);
+        self.finish()
+            .into_iter()
+            .map(|(label, edit)| ResolvedAssist { assist: label, source_change: edit.unwrap() })
+            .collect()
+    }
+
+    pub(crate) fn add(
+        &mut self,
+        id: AssistId,
+        label: impl Into<String>,
+        target: TextRange,
+        f: impl FnOnce(&mut AssistBuilder),
+    ) -> Option<()> {
+        if !self.is_allowed(&id) {
+            return None;
+        }
+        let label = Label::new(label.into());
+        let assist = Assist { id, label, group: None, target };
+        self.add_impl(assist, f)
+    }
+
+    pub(crate) fn add_group(
+        &mut self,
+        group: &GroupLabel,
+        id: AssistId,
+        label: impl Into<String>,
+        target: TextRange,
+        f: impl FnOnce(&mut AssistBuilder),
+    ) -> Option<()> {
+        if !self.is_allowed(&id) {
+            return None;
+        }
+        let label = Label::new(label.into());
+        let assist = Assist { id, label, group: Some(group.clone()), target };
+        self.add_impl(assist, f)
+    }
+
+    fn add_impl(&mut self, assist: Assist, f: impl FnOnce(&mut AssistBuilder)) -> Option<()> {
+        let source_change = if self.resolve {
+            let mut builder = AssistBuilder::new(self.file);
+            f(&mut builder);
+            Some(builder.finish())
+        } else {
+            None
+        };
+
+        self.buf.push((assist, source_change));
+        Some(())
+    }
+
+    fn finish(mut self) -> Vec<(Assist, Option<SourceChange>)> {
+        self.buf.sort_by_key(|(label, _edit)| label.target.len());
+        self.buf
+    }
+
+    fn is_allowed(&self, id: &AssistId) -> bool {
+        match &self.allowed {
+            Some(allowed) => allowed.iter().any(|kind| kind.contains(id.1)),
+            None => true,
+        }
+    }
+}
+
+pub(crate) struct AssistBuilder {
+    edit: TextEditBuilder,
+    file_id: FileId,
+    is_snippet: bool,
+    change: SourceChange,
+}
+
+impl AssistBuilder {
+    pub(crate) fn new(file_id: FileId) -> AssistBuilder {
+        AssistBuilder {
+            edit: TextEdit::builder(),
+            file_id,
+            is_snippet: false,
+            change: SourceChange::default(),
+        }
+    }
+
+    pub(crate) fn edit_file(&mut self, file_id: FileId) {
+        self.file_id = file_id;
+    }
+
+    fn commit(&mut self) {
+        let edit = mem::take(&mut self.edit).finish();
+        if !edit.is_empty() {
+            let new_edit = SourceFileEdit { file_id: self.file_id, edit };
+            assert!(!self.change.source_file_edits.iter().any(|it| it.file_id == new_edit.file_id));
+            self.change.source_file_edits.push(new_edit);
+        }
+    }
+
+    /// Remove specified `range` of text.
+    pub(crate) fn delete(&mut self, range: TextRange) {
+        self.edit.delete(range)
+    }
+    /// Append specified `text` at the given `offset`
+    pub(crate) fn insert(&mut self, offset: TextSize, text: impl Into<String>) {
+        self.edit.insert(offset, text.into())
+    }
+    /// Append specified `snippet` at the given `offset`
+    pub(crate) fn insert_snippet(
+        &mut self,
+        _cap: SnippetCap,
+        offset: TextSize,
+        snippet: impl Into<String>,
+    ) {
+        self.is_snippet = true;
+        self.insert(offset, snippet);
+    }
+    /// Replaces specified `range` of text with a given string.
+    pub(crate) fn replace(&mut self, range: TextRange, replace_with: impl Into<String>) {
+        self.edit.replace(range, replace_with.into())
+    }
+    /// Replaces specified `range` of text with a given `snippet`.
+    pub(crate) fn replace_snippet(
+        &mut self,
+        _cap: SnippetCap,
+        range: TextRange,
+        snippet: impl Into<String>,
+    ) {
+        self.is_snippet = true;
+        self.replace(range, snippet);
+    }
+    pub(crate) fn replace_ast<N: AstNode>(&mut self, old: N, new: N) {
+        algo::diff(old.syntax(), new.syntax()).into_text_edit(&mut self.edit)
+    }
+    pub(crate) fn rewrite(&mut self, rewriter: SyntaxRewriter) {
+        let node = rewriter.rewrite_root().unwrap();
+        let new = rewriter.rewrite(&node);
+        algo::diff(&node, &new).into_text_edit(&mut self.edit);
+    }
+
+    // FIXME: kill this API
+    /// Get access to the raw `TextEditBuilder`.
+    pub(crate) fn text_edit_builder(&mut self) -> &mut TextEditBuilder {
+        &mut self.edit
+    }
+
+    fn finish(mut self) -> SourceChange {
+        self.commit();
+        let mut change = mem::take(&mut self.change);
+        if self.is_snippet {
+            change.is_snippet = true;
+        }
+        change
+    }
+}

crates/assists/src/ast_transform.rs

@@ -0,0 +1,200 @@
+//! `AstTransformer`s are functions that replace nodes in an AST and can be easily combined.
+use rustc_hash::FxHashMap;
+
+use hir::{HirDisplay, PathResolution, SemanticsScope};
+use syntax::{
+    algo::SyntaxRewriter,
+    ast::{self, AstNode},
+};
+
+pub fn apply<'a, N: AstNode>(transformer: &dyn AstTransform<'a>, node: N) -> N {
+    SyntaxRewriter::from_fn(|element| match element {
+        syntax::SyntaxElement::Node(n) => {
+            let replacement = transformer.get_substitution(&n)?;
+            Some(replacement.into())
+        }
+        _ => None,
+    })
+    .rewrite_ast(&node)
+}
+
+pub trait AstTransform<'a> {
+    fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode>;
+
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a>;
+    fn or<T: AstTransform<'a> + 'a>(self, other: T) -> Box<dyn AstTransform<'a> + 'a>
+    where
+        Self: Sized + 'a,
+    {
+        self.chain_before(Box::new(other))
+    }
+}
+
+struct NullTransformer;
+
+impl<'a> AstTransform<'a> for NullTransformer {
+    fn get_substitution(&self, _node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        None
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        other
+    }
+}
+
+pub struct SubstituteTypeParams<'a> {
+    source_scope: &'a SemanticsScope<'a>,
+    substs: FxHashMap<hir::TypeParam, ast::Type>,
+    previous: Box<dyn AstTransform<'a> + 'a>,
+}
+
+impl<'a> SubstituteTypeParams<'a> {
+    pub fn for_trait_impl(
+        source_scope: &'a SemanticsScope<'a>,
+        // FIXME: there's implicit invariant that `trait_` and  `source_scope` match...
+        trait_: hir::Trait,
+        impl_def: ast::Impl,
+    ) -> SubstituteTypeParams<'a> {
+        let substs = get_syntactic_substs(impl_def).unwrap_or_default();
+        let generic_def: hir::GenericDef = trait_.into();
+        let substs_by_param: FxHashMap<_, _> = generic_def
+            .params(source_scope.db)
+            .into_iter()
+            // this is a trait impl, so we need to skip the first type parameter -- this is a bit hacky
+            .skip(1)
+            // The actual list of trait type parameters may be longer than the one
+            // used in the `impl` block due to trailing default type parameters.
+            // For that case we extend the `substs` with an empty iterator so we
+            // can still hit those trailing values and check if they actually have
+            // a default type. If they do, go for that type from `hir` to `ast` so
+            // the resulting change can be applied correctly.
+            .zip(substs.into_iter().map(Some).chain(std::iter::repeat(None)))
+            .filter_map(|(k, v)| match v {
+                Some(v) => Some((k, v)),
+                None => {
+                    let default = k.default(source_scope.db)?;
+                    Some((
+                        k,
+                        ast::make::ty(
+                            &default
+                                .display_source_code(source_scope.db, source_scope.module()?.into())
+                                .ok()?,
+                        ),
+                    ))
+                }
+            })
+            .collect();
+        return SubstituteTypeParams {
+            source_scope,
+            substs: substs_by_param,
+            previous: Box::new(NullTransformer),
+        };
+
+        // FIXME: It would probably be nicer if we could get this via HIR (i.e. get the
+        // trait ref, and then go from the types in the substs back to the syntax).
+        fn get_syntactic_substs(impl_def: ast::Impl) -> Option<Vec<ast::Type>> {
+            let target_trait = impl_def.trait_()?;
+            let path_type = match target_trait {
+                ast::Type::PathType(path) => path,
+                _ => return None,
+            };
+            let generic_arg_list = path_type.path()?.segment()?.generic_arg_list()?;
+
+            let mut result = Vec::new();
+            for generic_arg in generic_arg_list.generic_args() {
+                match generic_arg {
+                    ast::GenericArg::TypeArg(type_arg) => result.push(type_arg.ty()?),
+                    ast::GenericArg::AssocTypeArg(_)
+                    | ast::GenericArg::LifetimeArg(_)
+                    | ast::GenericArg::ConstArg(_) => (),
+                }
+            }
+
+            Some(result)
+        }
+    }
+    fn get_substitution_inner(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        let type_ref = ast::Type::cast(node.clone())?;
+        let path = match &type_ref {
+            ast::Type::PathType(path_type) => path_type.path()?,
+            _ => return None,
+        };
+        let resolution = self.source_scope.speculative_resolve(&path)?;
+        match resolution {
+            hir::PathResolution::TypeParam(tp) => Some(self.substs.get(&tp)?.syntax().clone()),
+            _ => None,
+        }
+    }
+}
+
+impl<'a> AstTransform<'a> for SubstituteTypeParams<'a> {
+    fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        self.get_substitution_inner(node).or_else(|| self.previous.get_substitution(node))
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        Box::new(SubstituteTypeParams { previous: other, ..self })
+    }
+}
+
+pub struct QualifyPaths<'a> {
+    target_scope: &'a SemanticsScope<'a>,
+    source_scope: &'a SemanticsScope<'a>,
+    previous: Box<dyn AstTransform<'a> + 'a>,
+}
+
+impl<'a> QualifyPaths<'a> {
+    pub fn new(target_scope: &'a SemanticsScope<'a>, source_scope: &'a SemanticsScope<'a>) -> Self {
+        Self { target_scope, source_scope, previous: Box::new(NullTransformer) }
+    }
+
+    fn get_substitution_inner(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        // FIXME handle value ns?
+        let from = self.target_scope.module()?;
+        let p = ast::Path::cast(node.clone())?;
+        if p.segment().and_then(|s| s.param_list()).is_some() {
+            // don't try to qualify `Fn(Foo) -> Bar` paths, they are in prelude anyway
+            return None;
+        }
+        let resolution = self.source_scope.speculative_resolve(&p)?;
+        match resolution {
+            PathResolution::Def(def) => {
+                let found_path = from.find_use_path(self.source_scope.db.upcast(), def)?;
+                let mut path = path_to_ast(found_path);
+
+                let type_args = p
+                    .segment()
+                    .and_then(|s| s.generic_arg_list())
+                    .map(|arg_list| apply(self, arg_list));
+                if let Some(type_args) = type_args {
+                    let last_segment = path.segment().unwrap();
+                    path = path.with_segment(last_segment.with_type_args(type_args))
+                }
+
+                Some(path.syntax().clone())
+            }
+            PathResolution::Local(_)
+            | PathResolution::TypeParam(_)
+            | PathResolution::SelfType(_) => None,
+            PathResolution::Macro(_) => None,
+            PathResolution::AssocItem(_) => None,
+        }
+    }
+}
+
+impl<'a> AstTransform<'a> for QualifyPaths<'a> {
+    fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+        self.get_substitution_inner(node).or_else(|| self.previous.get_substitution(node))
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        Box::new(QualifyPaths { previous: other, ..self })
+    }
+}
+
+pub(crate) fn path_to_ast(path: hir::ModPath) -> ast::Path {
+    let parse = ast::SourceFile::parse(&path.to_string());
+    parse
+        .tree()
+        .syntax()
+        .descendants()
+        .find_map(ast::Path::cast)
+        .unwrap_or_else(|| panic!("failed to parse path {:?}, `{}`", path, path))
+}

crates/assists/src/handlers/add_custom_impl.rs

@@ -0,0 +1,208 @@
+use itertools::Itertools;
+use syntax::{
+    ast::{self, AstNode},
+    Direction, SmolStr,
+    SyntaxKind::{IDENT, WHITESPACE},
+    TextRange, TextSize,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    AssistId, AssistKind,
+};
+
+// Assist: add_custom_impl
+//
+// Adds impl block for derived trait.
+//
+// ```
+// #[derive(Deb<|>ug, Display)]
+// struct S;
+// ```
+// ->
+// ```
+// #[derive(Display)]
+// struct S;
+//
+// impl Debug for S {
+//     $0
+// }
+// ```
+pub(crate) fn add_custom_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let attr = ctx.find_node_at_offset::<ast::Attr>()?;
+    let input = attr.token_tree()?;
+
+    let attr_name = attr
+        .syntax()
+        .descendants_with_tokens()
+        .filter(|t| t.kind() == IDENT)
+        .find_map(|i| i.into_token())
+        .filter(|t| *t.text() == "derive")?
+        .text()
+        .clone();
+
+    let trait_token =
+        ctx.token_at_offset().find(|t| t.kind() == IDENT && *t.text() != attr_name)?;
+
+    let annotated = attr.syntax().siblings(Direction::Next).find_map(ast::Name::cast)?;
+    let annotated_name = annotated.syntax().text().to_string();
+    let start_offset = annotated.syntax().parent()?.text_range().end();
+
+    let label =
+        format!("Add custom impl `{}` for `{}`", trait_token.text().as_str(), annotated_name);
+
+    let target = attr.syntax().text_range();
+    acc.add(AssistId("add_custom_impl", AssistKind::Refactor), label, target, |builder| {
+        let new_attr_input = input
+            .syntax()
+            .descendants_with_tokens()
+            .filter(|t| t.kind() == IDENT)
+            .filter_map(|t| t.into_token().map(|t| t.text().clone()))
+            .filter(|t| t != trait_token.text())
+            .collect::<Vec<SmolStr>>();
+        let has_more_derives = !new_attr_input.is_empty();
+
+        if has_more_derives {
+            let new_attr_input = format!("({})", new_attr_input.iter().format(", "));
+            builder.replace(input.syntax().text_range(), new_attr_input);
+        } else {
+            let attr_range = attr.syntax().text_range();
+            builder.delete(attr_range);
+
+            let line_break_range = attr
+                .syntax()
+                .next_sibling_or_token()
+                .filter(|t| t.kind() == WHITESPACE)
+                .map(|t| t.text_range())
+                .unwrap_or_else(|| TextRange::new(TextSize::from(0), TextSize::from(0)));
+            builder.delete(line_break_range);
+        }
+
+        match ctx.config.snippet_cap {
+            Some(cap) => {
+                builder.insert_snippet(
+                    cap,
+                    start_offset,
+                    format!("\n\nimpl {} for {} {{\n    $0\n}}", trait_token, annotated_name),
+                );
+            }
+            None => {
+                builder.insert(
+                    start_offset,
+                    format!("\n\nimpl {} for {} {{\n\n}}", trait_token, annotated_name),
+                );
+            }
+        }
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn add_custom_impl_for_unique_input() {
+        check_assist(
+            add_custom_impl,
+            "
+#[derive(Debu<|>g)]
+struct Foo {
+    bar: String,
+}
+            ",
+            "
+struct Foo {
+    bar: String,
+}
+
+impl Debug for Foo {
+    $0
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn add_custom_impl_for_with_visibility_modifier() {
+        check_assist(
+            add_custom_impl,
+            "
+#[derive(Debug<|>)]
+pub struct Foo {
+    bar: String,
+}
+            ",
+            "
+pub struct Foo {
+    bar: String,
+}
+
+impl Debug for Foo {
+    $0
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn add_custom_impl_when_multiple_inputs() {
+        check_assist(
+            add_custom_impl,
+            "
+#[derive(Display, Debug<|>, Serialize)]
+struct Foo {}
+            ",
+            "
+#[derive(Display, Serialize)]
+struct Foo {}
+
+impl Debug for Foo {
+    $0
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_ignore_derive_macro_without_input() {
+        check_assist_not_applicable(
+            add_custom_impl,
+            "
+#[derive(<|>)]
+struct Foo {}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_ignore_if_cursor_on_param() {
+        check_assist_not_applicable(
+            add_custom_impl,
+            "
+#[derive<|>(Debug)]
+struct Foo {}
+            ",
+        );
+
+        check_assist_not_applicable(
+            add_custom_impl,
+            "
+#[derive(Debug)<|>]
+struct Foo {}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_ignore_if_not_derive() {
+        check_assist_not_applicable(
+            add_custom_impl,
+            "
+#[allow(non_camel_<|>case_types)]
+struct Foo {}
+            ",
+        )
+    }
+}

crates/assists/src/handlers/add_explicit_type.rs

@@ -0,0 +1,211 @@
+use hir::HirDisplay;
+use syntax::{
+    ast::{self, AstNode, LetStmt, NameOwner},
+    TextRange,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: add_explicit_type
+//
+// Specify type for a let binding.
+//
+// ```
+// fn main() {
+//     let x<|> = 92;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     let x: i32 = 92;
+// }
+// ```
+pub(crate) fn add_explicit_type(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let let_stmt = ctx.find_node_at_offset::<LetStmt>()?;
+    let module = ctx.sema.scope(let_stmt.syntax()).module()?;
+    let expr = let_stmt.initializer()?;
+    // Must be a binding
+    let pat = match let_stmt.pat()? {
+        ast::Pat::IdentPat(bind_pat) => bind_pat,
+        _ => return None,
+    };
+    let pat_range = pat.syntax().text_range();
+    // The binding must have a name
+    let name = pat.name()?;
+    let name_range = name.syntax().text_range();
+    let stmt_range = let_stmt.syntax().text_range();
+    let eq_range = let_stmt.eq_token()?.text_range();
+    // Assist should only be applicable if cursor is between 'let' and '='
+    let let_range = TextRange::new(stmt_range.start(), eq_range.start());
+    let cursor_in_range = let_range.contains_range(ctx.frange.range);
+    if !cursor_in_range {
+        return None;
+    }
+    // Assist not applicable if the type has already been specified
+    // and it has no placeholders
+    let ascribed_ty = let_stmt.ty();
+    if let Some(ty) = &ascribed_ty {
+        if ty.syntax().descendants().find_map(ast::InferType::cast).is_none() {
+            return None;
+        }
+    }
+    // Infer type
+    let ty = ctx.sema.type_of_expr(&expr)?;
+
+    if ty.contains_unknown() || ty.is_closure() {
+        return None;
+    }
+
+    let inferred_type = ty.display_source_code(ctx.db(), module.into()).ok()?;
+    acc.add(
+        AssistId("add_explicit_type", AssistKind::RefactorRewrite),
+        format!("Insert explicit type `{}`", inferred_type),
+        pat_range,
+        |builder| match ascribed_ty {
+            Some(ascribed_ty) => {
+                builder.replace(ascribed_ty.syntax().text_range(), inferred_type);
+            }
+            None => {
+                builder.insert(name_range.end(), format!(": {}", inferred_type));
+            }
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    #[test]
+    fn add_explicit_type_target() {
+        check_assist_target(add_explicit_type, "fn f() { let a<|> = 1; }", "a");
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_simple_expr() {
+        check_assist(add_explicit_type, "fn f() { let a<|> = 1; }", "fn f() { let a: i32 = 1; }");
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_underscore() {
+        check_assist(
+            add_explicit_type,
+            "fn f() { let a<|>: _ = 1; }",
+            "fn f() { let a: i32 = 1; }",
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_nested_underscore() {
+        check_assist(
+            add_explicit_type,
+            r#"
+            enum Option<T> {
+                Some(T),
+                None
+            }
+
+            fn f() {
+                let a<|>: Option<_> = Option::Some(1);
+            }"#,
+            r#"
+            enum Option<T> {
+                Some(T),
+                None
+            }
+
+            fn f() {
+                let a: Option<i32> = Option::Some(1);
+            }"#,
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_macro_call() {
+        check_assist(
+            add_explicit_type,
+            r"macro_rules! v { () => {0u64} } fn f() { let a<|> = v!(); }",
+            r"macro_rules! v { () => {0u64} } fn f() { let a: u64 = v!(); }",
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_macro_call_recursive() {
+        check_assist(
+            add_explicit_type,
+            r#"macro_rules! u { () => {0u64} } macro_rules! v { () => {u!()} } fn f() { let a<|> = v!(); }"#,
+            r#"macro_rules! u { () => {0u64} } macro_rules! v { () => {u!()} } fn f() { let a: u64 = v!(); }"#,
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_ty_not_inferred() {
+        check_assist_not_applicable(add_explicit_type, "fn f() { let a<|> = None; }");
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_ty_already_specified() {
+        check_assist_not_applicable(add_explicit_type, "fn f() { let a<|>: i32 = 1; }");
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_specified_ty_is_tuple() {
+        check_assist_not_applicable(add_explicit_type, "fn f() { let a<|>: (i32, i32) = (3, 4); }");
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_cursor_after_equals() {
+        check_assist_not_applicable(
+            add_explicit_type,
+            "fn f() {let a =<|> match 1 {2 => 3, 3 => 5};}",
+        )
+    }
+
+    #[test]
+    fn add_explicit_type_not_applicable_if_cursor_before_let() {
+        check_assist_not_applicable(
+            add_explicit_type,
+            "fn f() <|>{let a = match 1 {2 => 3, 3 => 5};}",
+        )
+    }
+
+    #[test]
+    fn closure_parameters_are_not_added() {
+        check_assist_not_applicable(
+            add_explicit_type,
+            r#"
+fn main() {
+    let multiply_by_two<|> = |i| i * 3;
+    let six = multiply_by_two(2);
+}"#,
+        )
+    }
+
+    #[test]
+    fn default_generics_should_not_be_added() {
+        check_assist(
+            add_explicit_type,
+            r#"
+struct Test<K, T = u8> {
+    k: K,
+    t: T,
+}
+
+fn main() {
+    let test<|> = Test { t: 23u8, k: 33 };
+}"#,
+            r#"
+struct Test<K, T = u8> {
+    k: K,
+    t: T,
+}
+
+fn main() {
+    let test: Test<i32> = Test { t: 23u8, k: 33 };
+}"#,
+        );
+    }
+}

crates/assists/src/handlers/add_missing_impl_members.rs

@@ -0,0 +1,766 @@
+use hir::HasSource;
+use syntax::{
+    ast::{
+        self,
+        edit::{self, AstNodeEdit, IndentLevel},
+        make, AstNode, NameOwner,
+    },
+    SmolStr,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
+    utils::{get_missing_assoc_items, render_snippet, resolve_target_trait, Cursor},
+    AssistId, AssistKind,
+};
+
+#[derive(PartialEq)]
+enum AddMissingImplMembersMode {
+    DefaultMethodsOnly,
+    NoDefaultMethods,
+}
+
+// Assist: add_impl_missing_members
+//
+// Adds scaffold for required impl members.
+//
+// ```
+// trait Trait<T> {
+//     Type X;
+//     fn foo(&self) -> T;
+//     fn bar(&self) {}
+// }
+//
+// impl Trait<u32> for () {<|>
+//
+// }
+// ```
+// ->
+// ```
+// trait Trait<T> {
+//     Type X;
+//     fn foo(&self) -> T;
+//     fn bar(&self) {}
+// }
+//
+// impl Trait<u32> for () {
+//     fn foo(&self) -> u32 {
+//         ${0:todo!()}
+//     }
+// }
+// ```
+pub(crate) fn add_missing_impl_members(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    add_missing_impl_members_inner(
+        acc,
+        ctx,
+        AddMissingImplMembersMode::NoDefaultMethods,
+        "add_impl_missing_members",
+        "Implement missing members",
+    )
+}
+
+// Assist: add_impl_default_members
+//
+// Adds scaffold for overriding default impl members.
+//
+// ```
+// trait Trait {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl Trait for () {
+//     Type X = ();
+//     fn foo(&self) {}<|>
+//
+// }
+// ```
+// ->
+// ```
+// trait Trait {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl Trait for () {
+//     Type X = ();
+//     fn foo(&self) {}
+//
+//     $0fn bar(&self) {}
+// }
+// ```
+pub(crate) fn add_missing_default_members(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    add_missing_impl_members_inner(
+        acc,
+        ctx,
+        AddMissingImplMembersMode::DefaultMethodsOnly,
+        "add_impl_default_members",
+        "Implement default members",
+    )
+}
+
+fn add_missing_impl_members_inner(
+    acc: &mut Assists,
+    ctx: &AssistContext,
+    mode: AddMissingImplMembersMode,
+    assist_id: &'static str,
+    label: &'static str,
+) -> Option<()> {
+    let _p = profile::span("add_missing_impl_members_inner");
+    let impl_def = ctx.find_node_at_offset::<ast::Impl>()?;
+    let impl_item_list = impl_def.assoc_item_list()?;
+
+    let trait_ = resolve_target_trait(&ctx.sema, &impl_def)?;
+
+    let def_name = |item: &ast::AssocItem| -> Option<SmolStr> {
+        match item {
+            ast::AssocItem::Fn(def) => def.name(),
+            ast::AssocItem::TypeAlias(def) => def.name(),
+            ast::AssocItem::Const(def) => def.name(),
+            ast::AssocItem::MacroCall(_) => None,
+        }
+        .map(|it| it.text().clone())
+    };
+
+    let missing_items = get_missing_assoc_items(&ctx.sema, &impl_def)
+        .iter()
+        .map(|i| match i {
+            hir::AssocItem::Function(i) => ast::AssocItem::Fn(i.source(ctx.db()).value),
+            hir::AssocItem::TypeAlias(i) => ast::AssocItem::TypeAlias(i.source(ctx.db()).value),
+            hir::AssocItem::Const(i) => ast::AssocItem::Const(i.source(ctx.db()).value),
+        })
+        .filter(|t| def_name(&t).is_some())
+        .filter(|t| match t {
+            ast::AssocItem::Fn(def) => match mode {
+                AddMissingImplMembersMode::DefaultMethodsOnly => def.body().is_some(),
+                AddMissingImplMembersMode::NoDefaultMethods => def.body().is_none(),
+            },
+            _ => mode == AddMissingImplMembersMode::NoDefaultMethods,
+        })
+        .collect::<Vec<_>>();
+
+    if missing_items.is_empty() {
+        return None;
+    }
+
+    let target = impl_def.syntax().text_range();
+    acc.add(AssistId(assist_id, AssistKind::QuickFix), label, target, |builder| {
+        let n_existing_items = impl_item_list.assoc_items().count();
+        let source_scope = ctx.sema.scope_for_def(trait_);
+        let target_scope = ctx.sema.scope(impl_item_list.syntax());
+        let ast_transform = QualifyPaths::new(&target_scope, &source_scope)
+            .or(SubstituteTypeParams::for_trait_impl(&source_scope, trait_, impl_def));
+        let items = missing_items
+            .into_iter()
+            .map(|it| ast_transform::apply(&*ast_transform, it))
+            .map(|it| match it {
+                ast::AssocItem::Fn(def) => ast::AssocItem::Fn(add_body(def)),
+                ast::AssocItem::TypeAlias(def) => ast::AssocItem::TypeAlias(def.remove_bounds()),
+                _ => it,
+            })
+            .map(|it| edit::remove_attrs_and_docs(&it));
+        let new_impl_item_list = impl_item_list.append_items(items);
+        let first_new_item = new_impl_item_list.assoc_items().nth(n_existing_items).unwrap();
+
+        let original_range = impl_item_list.syntax().text_range();
+        match ctx.config.snippet_cap {
+            None => builder.replace(original_range, new_impl_item_list.to_string()),
+            Some(cap) => {
+                let mut cursor = Cursor::Before(first_new_item.syntax());
+                let placeholder;
+                if let ast::AssocItem::Fn(func) = &first_new_item {
+                    if let Some(m) = func.syntax().descendants().find_map(ast::MacroCall::cast) {
+                        if m.syntax().text() == "todo!()" {
+                            placeholder = m;
+                            cursor = Cursor::Replace(placeholder.syntax());
+                        }
+                    }
+                }
+                builder.replace_snippet(
+                    cap,
+                    original_range,
+                    render_snippet(cap, new_impl_item_list.syntax(), cursor),
+                )
+            }
+        };
+    })
+}
+
+fn add_body(fn_def: ast::Fn) -> ast::Fn {
+    if fn_def.body().is_some() {
+        return fn_def;
+    }
+    let body = make::block_expr(None, Some(make::expr_todo())).indent(IndentLevel(1));
+    fn_def.with_body(body)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_add_missing_impl_members() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Foo {
+    type Output;
+
+    const CONST: usize = 42;
+
+    fn foo(&self);
+    fn bar(&self);
+    fn baz(&self);
+}
+
+struct S;
+
+impl Foo for S {
+    fn bar(&self) {}
+<|>
+}"#,
+            r#"
+trait Foo {
+    type Output;
+
+    const CONST: usize = 42;
+
+    fn foo(&self);
+    fn bar(&self);
+    fn baz(&self);
+}
+
+struct S;
+
+impl Foo for S {
+    fn bar(&self) {}
+
+    $0type Output;
+
+    const CONST: usize = 42;
+
+    fn foo(&self) {
+        todo!()
+    }
+
+    fn baz(&self) {
+        todo!()
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_copied_overriden_members() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Foo {
+    fn foo(&self);
+    fn bar(&self) -> bool { true }
+    fn baz(&self) -> u32 { 42 }
+}
+
+struct S;
+
+impl Foo for S {
+    fn bar(&self) {}
+<|>
+}"#,
+            r#"
+trait Foo {
+    fn foo(&self);
+    fn bar(&self) -> bool { true }
+    fn baz(&self) -> u32 { 42 }
+}
+
+struct S;
+
+impl Foo for S {
+    fn bar(&self) {}
+
+    fn foo(&self) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_empty_impl_def() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Foo { fn foo(&self); }
+struct S;
+impl Foo for S { <|> }"#,
+            r#"
+trait Foo { fn foo(&self); }
+struct S;
+impl Foo for S {
+    fn foo(&self) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn fill_in_type_params_1() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Foo<T> { fn foo(&self, t: T) -> &T; }
+struct S;
+impl Foo<u32> for S { <|> }"#,
+            r#"
+trait Foo<T> { fn foo(&self, t: T) -> &T; }
+struct S;
+impl Foo<u32> for S {
+    fn foo(&self, t: u32) -> &u32 {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn fill_in_type_params_2() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Foo<T> { fn foo(&self, t: T) -> &T; }
+struct S;
+impl<U> Foo<U> for S { <|> }"#,
+            r#"
+trait Foo<T> { fn foo(&self, t: T) -> &T; }
+struct S;
+impl<U> Foo<U> for S {
+    fn foo(&self, t: U) -> &U {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_cursor_after_empty_impl_def() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Foo { fn foo(&self); }
+struct S;
+impl Foo for S {}<|>"#,
+            r#"
+trait Foo { fn foo(&self); }
+struct S;
+impl Foo for S {
+    fn foo(&self) {
+        ${0:todo!()}
+    }
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_qualify_path_1() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod foo {
+    pub struct Bar;
+    trait Foo { fn foo(&self, bar: Bar); }
+}
+struct S;
+impl foo::Foo for S { <|> }"#,
+            r#"
+mod foo {
+    pub struct Bar;
+    trait Foo { fn foo(&self, bar: Bar); }
+}
+struct S;
+impl foo::Foo for S {
+    fn foo(&self, bar: foo::Bar) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_generic() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod foo {
+    pub struct Bar<T>;
+    trait Foo { fn foo(&self, bar: Bar<u32>); }
+}
+struct S;
+impl foo::Foo for S { <|> }"#,
+            r#"
+mod foo {
+    pub struct Bar<T>;
+    trait Foo { fn foo(&self, bar: Bar<u32>); }
+}
+struct S;
+impl foo::Foo for S {
+    fn foo(&self, bar: foo::Bar<u32>) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_and_substitute_param() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod foo {
+    pub struct Bar<T>;
+    trait Foo<T> { fn foo(&self, bar: Bar<T>); }
+}
+struct S;
+impl foo::Foo<u32> for S { <|> }"#,
+            r#"
+mod foo {
+    pub struct Bar<T>;
+    trait Foo<T> { fn foo(&self, bar: Bar<T>); }
+}
+struct S;
+impl foo::Foo<u32> for S {
+    fn foo(&self, bar: foo::Bar<u32>) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_substitute_param_no_qualify() {
+        // when substituting params, the substituted param should not be qualified!
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod foo {
+    trait Foo<T> { fn foo(&self, bar: T); }
+    pub struct Param;
+}
+struct Param;
+struct S;
+impl foo::Foo<Param> for S { <|> }"#,
+            r#"
+mod foo {
+    trait Foo<T> { fn foo(&self, bar: T); }
+    pub struct Param;
+}
+struct Param;
+struct S;
+impl foo::Foo<Param> for S {
+    fn foo(&self, bar: Param) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_associated_item() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod foo {
+    pub struct Bar<T>;
+    impl Bar<T> { type Assoc = u32; }
+    trait Foo { fn foo(&self, bar: Bar<u32>::Assoc); }
+}
+struct S;
+impl foo::Foo for S { <|> }"#,
+            r#"
+mod foo {
+    pub struct Bar<T>;
+    impl Bar<T> { type Assoc = u32; }
+    trait Foo { fn foo(&self, bar: Bar<u32>::Assoc); }
+}
+struct S;
+impl foo::Foo for S {
+    fn foo(&self, bar: foo::Bar<u32>::Assoc) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_nested() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod foo {
+    pub struct Bar<T>;
+    pub struct Baz;
+    trait Foo { fn foo(&self, bar: Bar<Baz>); }
+}
+struct S;
+impl foo::Foo for S { <|> }"#,
+            r#"
+mod foo {
+    pub struct Bar<T>;
+    pub struct Baz;
+    trait Foo { fn foo(&self, bar: Bar<Baz>); }
+}
+struct S;
+impl foo::Foo for S {
+    fn foo(&self, bar: foo::Bar<foo::Baz>) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_fn_trait_notation() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod foo {
+    pub trait Fn<Args> { type Output; }
+    trait Foo { fn foo(&self, bar: dyn Fn(u32) -> i32); }
+}
+struct S;
+impl foo::Foo for S { <|> }"#,
+            r#"
+mod foo {
+    pub trait Fn<Args> { type Output; }
+    trait Foo { fn foo(&self, bar: dyn Fn(u32) -> i32); }
+}
+struct S;
+impl foo::Foo for S {
+    fn foo(&self, bar: dyn Fn(u32) -> i32) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_empty_trait() {
+        check_assist_not_applicable(
+            add_missing_impl_members,
+            r#"
+trait Foo;
+struct S;
+impl Foo for S { <|> }"#,
+        )
+    }
+
+    #[test]
+    fn test_ignore_unnamed_trait_members_and_default_methods() {
+        check_assist_not_applicable(
+            add_missing_impl_members,
+            r#"
+trait Foo {
+    fn (arg: u32);
+    fn valid(some: u32) -> bool { false }
+}
+struct S;
+impl Foo for S { <|> }"#,
+        )
+    }
+
+    #[test]
+    fn test_with_docstring_and_attrs() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+#[doc(alias = "test alias")]
+trait Foo {
+    /// doc string
+    type Output;
+
+    #[must_use]
+    fn foo(&self);
+}
+struct S;
+impl Foo for S {}<|>"#,
+            r#"
+#[doc(alias = "test alias")]
+trait Foo {
+    /// doc string
+    type Output;
+
+    #[must_use]
+    fn foo(&self);
+}
+struct S;
+impl Foo for S {
+    $0type Output;
+
+    fn foo(&self) {
+        todo!()
+    }
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_default_methods() {
+        check_assist(
+            add_missing_default_members,
+            r#"
+trait Foo {
+    type Output;
+
+    const CONST: usize = 42;
+
+    fn valid(some: u32) -> bool { false }
+    fn foo(some: u32) -> bool;
+}
+struct S;
+impl Foo for S { <|> }"#,
+            r#"
+trait Foo {
+    type Output;
+
+    const CONST: usize = 42;
+
+    fn valid(some: u32) -> bool { false }
+    fn foo(some: u32) -> bool;
+}
+struct S;
+impl Foo for S {
+    $0fn valid(some: u32) -> bool { false }
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_generic_single_default_parameter() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Foo<T = Self> {
+    fn bar(&self, other: &T);
+}
+
+struct S;
+impl Foo for S { <|> }"#,
+            r#"
+trait Foo<T = Self> {
+    fn bar(&self, other: &T);
+}
+
+struct S;
+impl Foo for S {
+    fn bar(&self, other: &Self) {
+        ${0:todo!()}
+    }
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_generic_default_parameter_is_second() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Foo<T1, T2 = Self> {
+    fn bar(&self, this: &T1, that: &T2);
+}
+
+struct S<T>;
+impl Foo<T> for S<T> { <|> }"#,
+            r#"
+trait Foo<T1, T2 = Self> {
+    fn bar(&self, this: &T1, that: &T2);
+}
+
+struct S<T>;
+impl Foo<T> for S<T> {
+    fn bar(&self, this: &T, that: &Self) {
+        ${0:todo!()}
+    }
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_assoc_type_bounds_are_removed() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Tr {
+    type Ty: Copy + 'static;
+}
+
+impl Tr for ()<|> {
+}"#,
+            r#"
+trait Tr {
+    type Ty: Copy + 'static;
+}
+
+impl Tr for () {
+    $0type Ty;
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_whitespace_fixup_preserves_bad_tokens() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Tr {
+    fn foo();
+}
+
+impl Tr for ()<|> {
+    +++
+}"#,
+            r#"
+trait Tr {
+    fn foo();
+}
+
+impl Tr for () {
+    fn foo() {
+        ${0:todo!()}
+    }
+    +++
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_whitespace_fixup_preserves_comments() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Tr {
+    fn foo();
+}
+
+impl Tr for ()<|> {
+    // very important
+}"#,
+            r#"
+trait Tr {
+    fn foo();
+}
+
+impl Tr for () {
+    fn foo() {
+        ${0:todo!()}
+    }
+    // very important
+}"#,
+        )
+    }
+}

crates/assists/src/handlers/add_turbo_fish.rs

@@ -0,0 +1,164 @@
+use ide_db::defs::{classify_name_ref, Definition, NameRefClass};
+use syntax::{ast, AstNode, SyntaxKind, T};
+use test_utils::mark;
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    AssistId, AssistKind,
+};
+
+// Assist: add_turbo_fish
+//
+// Adds `::<_>` to a call of a generic method or function.
+//
+// ```
+// fn make<T>() -> T { todo!() }
+// fn main() {
+//     let x = make<|>();
+// }
+// ```
+// ->
+// ```
+// fn make<T>() -> T { todo!() }
+// fn main() {
+//     let x = make::<${0:_}>();
+// }
+// ```
+pub(crate) fn add_turbo_fish(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let ident = ctx.find_token_at_offset(SyntaxKind::IDENT).or_else(|| {
+        let arg_list = ctx.find_node_at_offset::<ast::ArgList>()?;
+        if arg_list.args().count() > 0 {
+            return None;
+        }
+        mark::hit!(add_turbo_fish_after_call);
+        arg_list.l_paren_token()?.prev_token().filter(|it| it.kind() == SyntaxKind::IDENT)
+    })?;
+    let next_token = ident.next_token()?;
+    if next_token.kind() == T![::] {
+        mark::hit!(add_turbo_fish_one_fish_is_enough);
+        return None;
+    }
+    let name_ref = ast::NameRef::cast(ident.parent())?;
+    let def = match classify_name_ref(&ctx.sema, &name_ref)? {
+        NameRefClass::Definition(def) => def,
+        NameRefClass::ExternCrate(_) | NameRefClass::FieldShorthand { .. } => return None,
+    };
+    let fun = match def {
+        Definition::ModuleDef(hir::ModuleDef::Function(it)) => it,
+        _ => return None,
+    };
+    let generics = hir::GenericDef::Function(fun).params(ctx.sema.db);
+    if generics.is_empty() {
+        mark::hit!(add_turbo_fish_non_generic);
+        return None;
+    }
+    acc.add(
+        AssistId("add_turbo_fish", AssistKind::RefactorRewrite),
+        "Add `::<>`",
+        ident.text_range(),
+        |builder| match ctx.config.snippet_cap {
+            Some(cap) => builder.insert_snippet(cap, ident.text_range().end(), "::<${0:_}>"),
+            None => builder.insert(ident.text_range().end(), "::<_>"),
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+    use test_utils::mark;
+
+    #[test]
+    fn add_turbo_fish_function() {
+        check_assist(
+            add_turbo_fish,
+            r#"
+fn make<T>() -> T {}
+fn main() {
+    make<|>();
+}
+"#,
+            r#"
+fn make<T>() -> T {}
+fn main() {
+    make::<${0:_}>();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn add_turbo_fish_after_call() {
+        mark::check!(add_turbo_fish_after_call);
+        check_assist(
+            add_turbo_fish,
+            r#"
+fn make<T>() -> T {}
+fn main() {
+    make()<|>;
+}
+"#,
+            r#"
+fn make<T>() -> T {}
+fn main() {
+    make::<${0:_}>();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn add_turbo_fish_method() {
+        check_assist(
+            add_turbo_fish,
+            r#"
+struct S;
+impl S {
+    fn make<T>(&self) -> T {}
+}
+fn main() {
+    S.make<|>();
+}
+"#,
+            r#"
+struct S;
+impl S {
+    fn make<T>(&self) -> T {}
+}
+fn main() {
+    S.make::<${0:_}>();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn add_turbo_fish_one_fish_is_enough() {
+        mark::check!(add_turbo_fish_one_fish_is_enough);
+        check_assist_not_applicable(
+            add_turbo_fish,
+            r#"
+fn make<T>() -> T {}
+fn main() {
+    make<|>::<()>();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn add_turbo_fish_non_generic() {
+        mark::check!(add_turbo_fish_non_generic);
+        check_assist_not_applicable(
+            add_turbo_fish,
+            r#"
+fn make() -> () {}
+fn main() {
+    make<|>();
+}
+"#,
+        );
+    }
+}

crates/assists/src/handlers/apply_demorgan.rs

@@ -0,0 +1,93 @@
+use syntax::ast::{self, AstNode};
+
+use crate::{utils::invert_boolean_expression, AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: apply_demorgan
+//
+// Apply https://en.wikipedia.org/wiki/De_Morgan%27s_laws[De Morgan's law].
+// This transforms expressions of the form `!l || !r` into `!(l && r)`.
+// This also works with `&&`. This assist can only be applied with the cursor
+// on either `||` or `&&`, with both operands being a negation of some kind.
+// This means something of the form `!x` or `x != y`.
+//
+// ```
+// fn main() {
+//     if x != 4 ||<|> !y {}
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     if !(x == 4 && y) {}
+// }
+// ```
+pub(crate) fn apply_demorgan(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let expr = ctx.find_node_at_offset::<ast::BinExpr>()?;
+    let op = expr.op_kind()?;
+    let op_range = expr.op_token()?.text_range();
+    let opposite_op = opposite_logic_op(op)?;
+    let cursor_in_range = op_range.contains_range(ctx.frange.range);
+    if !cursor_in_range {
+        return None;
+    }
+
+    let lhs = expr.lhs()?;
+    let lhs_range = lhs.syntax().text_range();
+    let not_lhs = invert_boolean_expression(lhs);
+
+    let rhs = expr.rhs()?;
+    let rhs_range = rhs.syntax().text_range();
+    let not_rhs = invert_boolean_expression(rhs);
+
+    acc.add(
+        AssistId("apply_demorgan", AssistKind::RefactorRewrite),
+        "Apply De Morgan's law",
+        op_range,
+        |edit| {
+            edit.replace(op_range, opposite_op);
+            edit.replace(lhs_range, format!("!({}", not_lhs.syntax().text()));
+            edit.replace(rhs_range, format!("{})", not_rhs.syntax().text()));
+        },
+    )
+}
+
+// Return the opposite text for a given logical operator, if it makes sense
+fn opposite_logic_op(kind: ast::BinOp) -> Option<&'static str> {
+    match kind {
+        ast::BinOp::BooleanOr => Some("&&"),
+        ast::BinOp::BooleanAnd => Some("||"),
+        _ => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    #[test]
+    fn demorgan_turns_and_into_or() {
+        check_assist(apply_demorgan, "fn f() { !x &&<|> !x }", "fn f() { !(x || x) }")
+    }
+
+    #[test]
+    fn demorgan_turns_or_into_and() {
+        check_assist(apply_demorgan, "fn f() { !x ||<|> !x }", "fn f() { !(x && x) }")
+    }
+
+    #[test]
+    fn demorgan_removes_inequality() {
+        check_assist(apply_demorgan, "fn f() { x != x ||<|> !x }", "fn f() { !(x == x && x) }")
+    }
+
+    #[test]
+    fn demorgan_general_case() {
+        check_assist(apply_demorgan, "fn f() { x ||<|> x }", "fn f() { !(!x && !x) }")
+    }
+
+    #[test]
+    fn demorgan_doesnt_apply_with_cursor_not_on_op() {
+        check_assist_not_applicable(apply_demorgan, "fn f() { <|> !x || !x }")
+    }
+}

crates/assists/src/handlers/change_return_type_to_result.rs

@@ -0,0 +1,998 @@
+use std::iter;
+
+use syntax::{
+    ast::{self, make, BlockExpr, Expr, LoopBodyOwner},
+    AstNode, SyntaxNode,
+};
+use test_utils::mark;
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: change_return_type_to_result
+//
+// Change the function's return type to Result.
+//
+// ```
+// fn foo() -> i32<|> { 42i32 }
+// ```
+// ->
+// ```
+// fn foo() -> Result<i32, ${0:_}> { Ok(42i32) }
+// ```
+pub(crate) fn change_return_type_to_result(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let ret_type = ctx.find_node_at_offset::<ast::RetType>()?;
+    // FIXME: extend to lambdas as well
+    let fn_def = ret_type.syntax().parent().and_then(ast::Fn::cast)?;
+
+    let type_ref = &ret_type.ty()?;
+    let ret_type_str = type_ref.syntax().text().to_string();
+    let first_part_ret_type = ret_type_str.splitn(2, '<').next();
+    if let Some(ret_type_first_part) = first_part_ret_type {
+        if ret_type_first_part.ends_with("Result") {
+            mark::hit!(change_return_type_to_result_simple_return_type_already_result);
+            return None;
+        }
+    }
+
+    let block_expr = &fn_def.body()?;
+
+    acc.add(
+        AssistId("change_return_type_to_result", AssistKind::RefactorRewrite),
+        "Wrap return type in Result",
+        type_ref.syntax().text_range(),
+        |builder| {
+            let mut tail_return_expr_collector = TailReturnCollector::new();
+            tail_return_expr_collector.collect_jump_exprs(block_expr, false);
+            tail_return_expr_collector.collect_tail_exprs(block_expr);
+
+            for ret_expr_arg in tail_return_expr_collector.exprs_to_wrap {
+                let ok_wrapped = make::expr_call(
+                    make::expr_path(make::path_unqualified(make::path_segment(make::name_ref(
+                        "Ok",
+                    )))),
+                    make::arg_list(iter::once(ret_expr_arg.clone())),
+                );
+                builder.replace_ast(ret_expr_arg, ok_wrapped);
+            }
+
+            match ctx.config.snippet_cap {
+                Some(cap) => {
+                    let snippet = format!("Result<{}, ${{0:_}}>", type_ref);
+                    builder.replace_snippet(cap, type_ref.syntax().text_range(), snippet)
+                }
+                None => builder
+                    .replace(type_ref.syntax().text_range(), format!("Result<{}, _>", type_ref)),
+            }
+        },
+    )
+}
+
+struct TailReturnCollector {
+    exprs_to_wrap: Vec<ast::Expr>,
+}
+
+impl TailReturnCollector {
+    fn new() -> Self {
+        Self { exprs_to_wrap: vec![] }
+    }
+    /// Collect all`return` expression
+    fn collect_jump_exprs(&mut self, block_expr: &BlockExpr, collect_break: bool) {
+        let statements = block_expr.statements();
+        for stmt in statements {
+            let expr = match &stmt {
+                ast::Stmt::ExprStmt(stmt) => stmt.expr(),
+                ast::Stmt::LetStmt(stmt) => stmt.initializer(),
+                ast::Stmt::Item(_) => continue,
+            };
+            if let Some(expr) = &expr {
+                self.handle_exprs(expr, collect_break);
+            }
+        }
+
+        // Browse tail expressions for each block
+        if let Some(expr) = block_expr.expr() {
+            if let Some(last_exprs) = get_tail_expr_from_block(&expr) {
+                for last_expr in last_exprs {
+                    let last_expr = match last_expr {
+                        NodeType::Node(expr) => expr,
+                        NodeType::Leaf(expr) => expr.syntax().clone(),
+                    };
+
+                    if let Some(last_expr) = Expr::cast(last_expr.clone()) {
+                        self.handle_exprs(&last_expr, collect_break);
+                    } else if let Some(expr_stmt) = ast::Stmt::cast(last_expr) {
+                        let expr_stmt = match &expr_stmt {
+                            ast::Stmt::ExprStmt(stmt) => stmt.expr(),
+                            ast::Stmt::LetStmt(stmt) => stmt.initializer(),
+                            ast::Stmt::Item(_) => None,
+                        };
+                        if let Some(expr) = &expr_stmt {
+                            self.handle_exprs(expr, collect_break);
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fn handle_exprs(&mut self, expr: &Expr, collect_break: bool) {
+        match expr {
+            Expr::BlockExpr(block_expr) => {
+                self.collect_jump_exprs(&block_expr, collect_break);
+            }
+            Expr::ReturnExpr(ret_expr) => {
+                if let Some(ret_expr_arg) = &ret_expr.expr() {
+                    self.exprs_to_wrap.push(ret_expr_arg.clone());
+                }
+            }
+            Expr::BreakExpr(break_expr) if collect_break => {
+                if let Some(break_expr_arg) = &break_expr.expr() {
+                    self.exprs_to_wrap.push(break_expr_arg.clone());
+                }
+            }
+            Expr::IfExpr(if_expr) => {
+                for block in if_expr.blocks() {
+                    self.collect_jump_exprs(&block, collect_break);
+                }
+            }
+            Expr::LoopExpr(loop_expr) => {
+                if let Some(block_expr) = loop_expr.loop_body() {
+                    self.collect_jump_exprs(&block_expr, collect_break);
+                }
+            }
+            Expr::ForExpr(for_expr) => {
+                if let Some(block_expr) = for_expr.loop_body() {
+                    self.collect_jump_exprs(&block_expr, collect_break);
+                }
+            }
+            Expr::WhileExpr(while_expr) => {
+                if let Some(block_expr) = while_expr.loop_body() {
+                    self.collect_jump_exprs(&block_expr, collect_break);
+                }
+            }
+            Expr::MatchExpr(match_expr) => {
+                if let Some(arm_list) = match_expr.match_arm_list() {
+                    arm_list.arms().filter_map(|match_arm| match_arm.expr()).for_each(|expr| {
+                        self.handle_exprs(&expr, collect_break);
+                    });
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn collect_tail_exprs(&mut self, block: &BlockExpr) {
+        if let Some(expr) = block.expr() {
+            self.handle_exprs(&expr, true);
+            self.fetch_tail_exprs(&expr);
+        }
+    }
+
+    fn fetch_tail_exprs(&mut self, expr: &Expr) {
+        if let Some(exprs) = get_tail_expr_from_block(expr) {
+            for node_type in &exprs {
+                match node_type {
+                    NodeType::Leaf(expr) => {
+                        self.exprs_to_wrap.push(expr.clone());
+                    }
+                    NodeType::Node(expr) => {
+                        if let Some(last_expr) = Expr::cast(expr.clone()) {
+                            self.fetch_tail_exprs(&last_expr);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
+enum NodeType {
+    Leaf(ast::Expr),
+    Node(SyntaxNode),
+}
+
+/// Get a tail expression inside a block
+fn get_tail_expr_from_block(expr: &Expr) -> Option<Vec<NodeType>> {
+    match expr {
+        Expr::IfExpr(if_expr) => {
+            let mut nodes = vec![];
+            for block in if_expr.blocks() {
+                if let Some(block_expr) = block.expr() {
+                    if let Some(tail_exprs) = get_tail_expr_from_block(&block_expr) {
+                        nodes.extend(tail_exprs);
+                    }
+                } else if let Some(last_expr) = block.syntax().last_child() {
+                    nodes.push(NodeType::Node(last_expr));
+                } else {
+                    nodes.push(NodeType::Node(block.syntax().clone()));
+                }
+            }
+            Some(nodes)
+        }
+        Expr::LoopExpr(loop_expr) => {
+            loop_expr.syntax().last_child().map(|lc| vec![NodeType::Node(lc)])
+        }
+        Expr::ForExpr(for_expr) => {
+            for_expr.syntax().last_child().map(|lc| vec![NodeType::Node(lc)])
+        }
+        Expr::WhileExpr(while_expr) => {
+            while_expr.syntax().last_child().map(|lc| vec![NodeType::Node(lc)])
+        }
+        Expr::BlockExpr(block_expr) => {
+            block_expr.expr().map(|lc| vec![NodeType::Node(lc.syntax().clone())])
+        }
+        Expr::MatchExpr(match_expr) => {
+            let arm_list = match_expr.match_arm_list()?;
+            let arms: Vec<NodeType> = arm_list
+                .arms()
+                .filter_map(|match_arm| match_arm.expr())
+                .map(|expr| match expr {
+                    Expr::ReturnExpr(ret_expr) => NodeType::Node(ret_expr.syntax().clone()),
+                    Expr::BreakExpr(break_expr) => NodeType::Node(break_expr.syntax().clone()),
+                    _ => match expr.syntax().last_child() {
+                        Some(last_expr) => NodeType::Node(last_expr),
+                        None => NodeType::Node(expr.syntax().clone()),
+                    },
+                })
+                .collect();
+
+            Some(arms)
+        }
+        Expr::BreakExpr(expr) => expr.expr().map(|e| vec![NodeType::Leaf(e)]),
+        Expr::ReturnExpr(ret_expr) => Some(vec![NodeType::Node(ret_expr.syntax().clone())]),
+
+        Expr::CallExpr(_)
+        | Expr::Literal(_)
+        | Expr::TupleExpr(_)
+        | Expr::ArrayExpr(_)
+        | Expr::ParenExpr(_)
+        | Expr::PathExpr(_)
+        | Expr::RecordExpr(_)
+        | Expr::IndexExpr(_)
+        | Expr::MethodCallExpr(_)
+        | Expr::AwaitExpr(_)
+        | Expr::CastExpr(_)
+        | Expr::RefExpr(_)
+        | Expr::PrefixExpr(_)
+        | Expr::RangeExpr(_)
+        | Expr::BinExpr(_)
+        | Expr::MacroCall(_)
+        | Expr::BoxExpr(_) => Some(vec![NodeType::Leaf(expr.clone())]),
+        _ => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn change_return_type_to_result_simple() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i3<|>2 {
+                let test = "test";
+                return 42i32;
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let test = "test";
+                return Ok(42i32);
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_return_type() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let test = "test";
+                return 42i32;
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let test = "test";
+                return Ok(42i32);
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_return_type_bad_cursor() {
+        check_assist_not_applicable(
+            change_return_type_to_result,
+            r#"fn foo() -> i32 {
+                let test = "test";<|>
+                return 42i32;
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_return_type_already_result_std() {
+        check_assist_not_applicable(
+            change_return_type_to_result,
+            r#"fn foo() -> std::result::Result<i32<|>, String> {
+                let test = "test";
+                return 42i32;
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_return_type_already_result() {
+        mark::check!(change_return_type_to_result_simple_return_type_already_result);
+        check_assist_not_applicable(
+            change_return_type_to_result,
+            r#"fn foo() -> Result<i32<|>, String> {
+                let test = "test";
+                return 42i32;
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_cursor() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> <|>i32 {
+                let test = "test";
+                return 42i32;
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let test = "test";
+                return Ok(42i32);
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -><|> i32 {
+                let test = "test";
+                42i32
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let test = "test";
+                Ok(42i32)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_only() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                42i32
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                Ok(42i32)
+            }"#,
+        );
+    }
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                if true {
+                    42i32
+                } else {
+                    24i32
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                if true {
+                    Ok(42i32)
+                } else {
+                    Ok(24i32)
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_nested_if() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                if true {
+                    if false {
+                        1
+                    } else {
+                        2
+                    }
+                } else {
+                    24i32
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                if true {
+                    if false {
+                        Ok(1)
+                    } else {
+                        Ok(2)
+                    }
+                } else {
+                    Ok(24i32)
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_await() {
+        check_assist(
+            change_return_type_to_result,
+            r#"async fn foo() -> i<|>32 {
+                if true {
+                    if false {
+                        1.await
+                    } else {
+                        2.await
+                    }
+                } else {
+                    24i32.await
+                }
+            }"#,
+            r#"async fn foo() -> Result<i32, ${0:_}> {
+                if true {
+                    if false {
+                        Ok(1.await)
+                    } else {
+                        Ok(2.await)
+                    }
+                } else {
+                    Ok(24i32.await)
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_array() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> [i32;<|> 3] {
+                [1, 2, 3]
+            }"#,
+            r#"fn foo() -> Result<[i32; 3], ${0:_}> {
+                Ok([1, 2, 3])
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_cast() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -<|>> i32 {
+                if true {
+                    if false {
+                        1 as i32
+                    } else {
+                        2 as i32
+                    }
+                } else {
+                    24 as i32
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                if true {
+                    if false {
+                        Ok(1 as i32)
+                    } else {
+                        Ok(2 as i32)
+                    }
+                } else {
+                    Ok(24 as i32)
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like_match() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                match my_var {
+                    5 => 42i32,
+                    _ => 24i32,
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let my_var = 5;
+                match my_var {
+                    5 => Ok(42i32),
+                    _ => Ok(24i32),
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_loop_with_tail() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                loop {
+                    println!("test");
+                    5
+                }
+
+                my_var
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let my_var = 5;
+                loop {
+                    println!("test");
+                    5
+                }
+
+                Ok(my_var)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_loop_in_let_stmt() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = let x = loop {
+                    break 1;
+                };
+
+                my_var
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let my_var = let x = loop {
+                    break 1;
+                };
+
+                Ok(my_var)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like_match_return_expr() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                let res = match my_var {
+                    5 => 42i32,
+                    _ => return 24i32,
+                };
+
+                res
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let my_var = 5;
+                let res = match my_var {
+                    5 => 42i32,
+                    _ => return Ok(24i32),
+                };
+
+                Ok(res)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                let res = if my_var == 5 {
+                    42i32
+                } else {
+                    return 24i32;
+                };
+
+                res
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let my_var = 5;
+                let res = if my_var == 5 {
+                    42i32
+                } else {
+                    return Ok(24i32);
+                };
+
+                Ok(res)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like_match_deeper() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                match my_var {
+                    5 => {
+                        if true {
+                            42i32
+                        } else {
+                            25i32
+                        }
+                    },
+                    _ => {
+                        let test = "test";
+                        if test == "test" {
+                            return bar();
+                        }
+                        53i32
+                    },
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let my_var = 5;
+                match my_var {
+                    5 => {
+                        if true {
+                            Ok(42i32)
+                        } else {
+                            Ok(25i32)
+                        }
+                    },
+                    _ => {
+                        let test = "test";
+                        if test == "test" {
+                            return Ok(bar());
+                        }
+                        Ok(53i32)
+                    },
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like_early_return() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i<|>32 {
+                let test = "test";
+                if test == "test" {
+                    return 24i32;
+                }
+                53i32
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let test = "test";
+                if test == "test" {
+                    return Ok(24i32);
+                }
+                Ok(53i32)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_closure() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -><|> u32 {
+                let true_closure = || {
+                    return true;
+                };
+                if the_field < 5 {
+                    let mut i = 0;
+
+
+                    if true_closure() {
+                        return 99;
+                    } else {
+                        return 0;
+                    }
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, ${0:_}> {
+                let true_closure = || {
+                    return true;
+                };
+                if the_field < 5 {
+                    let mut i = 0;
+
+
+                    if true_closure() {
+                        return Ok(99);
+                    } else {
+                        return Ok(0);
+                    }
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> u32<|> {
+                let true_closure = || {
+                    return true;
+                };
+                if the_field < 5 {
+                    let mut i = 0;
+
+
+                    if true_closure() {
+                        return 99;
+                    } else {
+                        return 0;
+                    }
+                }
+                let t = None;
+
+                t.unwrap_or_else(|| the_field)
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, ${0:_}> {
+                let true_closure = || {
+                    return true;
+                };
+                if the_field < 5 {
+                    let mut i = 0;
+
+
+                    if true_closure() {
+                        return Ok(99);
+                    } else {
+                        return Ok(0);
+                    }
+                }
+                let t = None;
+
+                Ok(t.unwrap_or_else(|| the_field))
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_weird_forms() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let test = "test";
+                if test == "test" {
+                    return 24i32;
+                }
+                let mut i = 0;
+                loop {
+                    if i == 1 {
+                        break 55;
+                    }
+                    i += 1;
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let test = "test";
+                if test == "test" {
+                    return Ok(24i32);
+                }
+                let mut i = 0;
+                loop {
+                    if i == 1 {
+                        break Ok(55);
+                    }
+                    i += 1;
+                }
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let test = "test";
+                if test == "test" {
+                    return 24i32;
+                }
+                let mut i = 0;
+                loop {
+                    loop {
+                        if i == 1 {
+                            break 55;
+                        }
+                        i += 1;
+                    }
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let test = "test";
+                if test == "test" {
+                    return Ok(24i32);
+                }
+                let mut i = 0;
+                loop {
+                    loop {
+                        if i == 1 {
+                            break Ok(55);
+                        }
+                        i += 1;
+                    }
+                }
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i3<|>2 {
+                let test = "test";
+                let other = 5;
+                if test == "test" {
+                    let res = match other {
+                        5 => 43,
+                        _ => return 56,
+                    };
+                }
+                let mut i = 0;
+                loop {
+                    loop {
+                        if i == 1 {
+                            break 55;
+                        }
+                        i += 1;
+                    }
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, ${0:_}> {
+                let test = "test";
+                let other = 5;
+                if test == "test" {
+                    let res = match other {
+                        5 => 43,
+                        _ => return Ok(56),
+                    };
+                }
+                let mut i = 0;
+                loop {
+                    loop {
+                        if i == 1 {
+                            break Ok(55);
+                        }
+                        i += 1;
+                    }
+                }
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> u32<|> {
+                if the_field < 5 {
+                    let mut i = 0;
+                    loop {
+                        if i > 5 {
+                            return 55u32;
+                        }
+                        i += 3;
+                    }
+
+                    match i {
+                        5 => return 99,
+                        _ => return 0,
+                    };
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, ${0:_}> {
+                if the_field < 5 {
+                    let mut i = 0;
+                    loop {
+                        if i > 5 {
+                            return Ok(55u32);
+                        }
+                        i += 3;
+                    }
+
+                    match i {
+                        5 => return Ok(99),
+                        _ => return Ok(0),
+                    };
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> u3<|>2 {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    match i {
+                        5 => return 99,
+                        _ => return 0,
+                    }
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, ${0:_}> {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    match i {
+                        5 => return Ok(99),
+                        _ => return Ok(0),
+                    }
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> u32<|> {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    if i == 5 {
+                        return 99
+                    } else {
+                        return 0
+                    }
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, ${0:_}> {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    if i == 5 {
+                        return Ok(99)
+                    } else {
+                        return Ok(0)
+                    }
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> <|>u32 {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    if i == 5 {
+                        return 99;
+                    } else {
+                        return 0;
+                    }
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, ${0:_}> {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    if i == 5 {
+                        return Ok(99);
+                    } else {
+                        return Ok(0);
+                    }
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+    }
+}

crates/assists/src/handlers/change_visibility.rs

@@ -0,0 +1,200 @@
+use syntax::{
+    ast::{self, NameOwner, VisibilityOwner},
+    AstNode,
+    SyntaxKind::{CONST, ENUM, FN, MODULE, STATIC, STRUCT, TRAIT, VISIBILITY},
+    T,
+};
+use test_utils::mark;
+
+use crate::{utils::vis_offset, AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: change_visibility
+//
+// Adds or changes existing visibility specifier.
+//
+// ```
+// <|>fn frobnicate() {}
+// ```
+// ->
+// ```
+// pub(crate) fn frobnicate() {}
+// ```
+pub(crate) fn change_visibility(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    if let Some(vis) = ctx.find_node_at_offset::<ast::Visibility>() {
+        return change_vis(acc, vis);
+    }
+    add_vis(acc, ctx)
+}
+
+fn add_vis(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let item_keyword = ctx.token_at_offset().find(|leaf| {
+        matches!(
+            leaf.kind(),
+            T![const] | T![static] | T![fn] | T![mod] | T![struct] | T![enum] | T![trait]
+        )
+    });
+
+    let (offset, target) = if let Some(keyword) = item_keyword {
+        let parent = keyword.parent();
+        let def_kws = vec![CONST, STATIC, FN, MODULE, STRUCT, ENUM, TRAIT];
+        // Parent is not a definition, can't add visibility
+        if !def_kws.iter().any(|&def_kw| def_kw == parent.kind()) {
+            return None;
+        }
+        // Already have visibility, do nothing
+        if parent.children().any(|child| child.kind() == VISIBILITY) {
+            return None;
+        }
+        (vis_offset(&parent), keyword.text_range())
+    } else if let Some(field_name) = ctx.find_node_at_offset::<ast::Name>() {
+        let field = field_name.syntax().ancestors().find_map(ast::RecordField::cast)?;
+        if field.name()? != field_name {
+            mark::hit!(change_visibility_field_false_positive);
+            return None;
+        }
+        if field.visibility().is_some() {
+            return None;
+        }
+        (vis_offset(field.syntax()), field_name.syntax().text_range())
+    } else if let Some(field) = ctx.find_node_at_offset::<ast::TupleField>() {
+        if field.visibility().is_some() {
+            return None;
+        }
+        (vis_offset(field.syntax()), field.syntax().text_range())
+    } else {
+        return None;
+    };
+
+    acc.add(
+        AssistId("change_visibility", AssistKind::RefactorRewrite),
+        "Change visibility to pub(crate)",
+        target,
+        |edit| {
+            edit.insert(offset, "pub(crate) ");
+        },
+    )
+}
+
+fn change_vis(acc: &mut Assists, vis: ast::Visibility) -> Option<()> {
+    if vis.syntax().text() == "pub" {
+        let target = vis.syntax().text_range();
+        return acc.add(
+            AssistId("change_visibility", AssistKind::RefactorRewrite),
+            "Change Visibility to pub(crate)",
+            target,
+            |edit| {
+                edit.replace(vis.syntax().text_range(), "pub(crate)");
+            },
+        );
+    }
+    if vis.syntax().text() == "pub(crate)" {
+        let target = vis.syntax().text_range();
+        return acc.add(
+            AssistId("change_visibility", AssistKind::RefactorRewrite),
+            "Change visibility to pub",
+            target,
+            |edit| {
+                edit.replace(vis.syntax().text_range(), "pub");
+            },
+        );
+    }
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::mark;
+
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn change_visibility_adds_pub_crate_to_items() {
+        check_assist(change_visibility, "<|>fn foo() {}", "pub(crate) fn foo() {}");
+        check_assist(change_visibility, "f<|>n foo() {}", "pub(crate) fn foo() {}");
+        check_assist(change_visibility, "<|>struct Foo {}", "pub(crate) struct Foo {}");
+        check_assist(change_visibility, "<|>mod foo {}", "pub(crate) mod foo {}");
+        check_assist(change_visibility, "<|>trait Foo {}", "pub(crate) trait Foo {}");
+        check_assist(change_visibility, "m<|>od {}", "pub(crate) mod {}");
+        check_assist(change_visibility, "unsafe f<|>n foo() {}", "pub(crate) unsafe fn foo() {}");
+    }
+
+    #[test]
+    fn change_visibility_works_with_struct_fields() {
+        check_assist(
+            change_visibility,
+            r"struct S { <|>field: u32 }",
+            r"struct S { pub(crate) field: u32 }",
+        );
+        check_assist(change_visibility, r"struct S ( <|>u32 )", r"struct S ( pub(crate) u32 )");
+    }
+
+    #[test]
+    fn change_visibility_field_false_positive() {
+        mark::check!(change_visibility_field_false_positive);
+        check_assist_not_applicable(
+            change_visibility,
+            r"struct S { field: [(); { let <|>x = ();}] }",
+        )
+    }
+
+    #[test]
+    fn change_visibility_pub_to_pub_crate() {
+        check_assist(change_visibility, "<|>pub fn foo() {}", "pub(crate) fn foo() {}")
+    }
+
+    #[test]
+    fn change_visibility_pub_crate_to_pub() {
+        check_assist(change_visibility, "<|>pub(crate) fn foo() {}", "pub fn foo() {}")
+    }
+
+    #[test]
+    fn change_visibility_const() {
+        check_assist(change_visibility, "<|>const FOO = 3u8;", "pub(crate) const FOO = 3u8;");
+    }
+
+    #[test]
+    fn change_visibility_static() {
+        check_assist(change_visibility, "<|>static FOO = 3u8;", "pub(crate) static FOO = 3u8;");
+    }
+
+    #[test]
+    fn change_visibility_handles_comment_attrs() {
+        check_assist(
+            change_visibility,
+            r"
+            /// docs
+
+            // comments
+
+            #[derive(Debug)]
+            <|>struct Foo;
+            ",
+            r"
+            /// docs
+
+            // comments
+
+            #[derive(Debug)]
+            pub(crate) struct Foo;
+            ",
+        )
+    }
+
+    #[test]
+    fn not_applicable_for_enum_variants() {
+        check_assist_not_applicable(
+            change_visibility,
+            r"mod foo { pub enum Foo {Foo1} }
+              fn main() { foo::Foo::Foo1<|> } ",
+        );
+    }
+
+    #[test]
+    fn change_visibility_target() {
+        check_assist_target(change_visibility, "<|>fn foo() {}", "fn");
+        check_assist_target(change_visibility, "pub(crate)<|> fn foo() {}", "pub(crate)");
+        check_assist_target(change_visibility, "struct S { <|>field: u32 }", "field");
+    }
+}

crates/assists/src/handlers/early_return.rs

@@ -0,0 +1,515 @@
+use std::{iter::once, ops::RangeInclusive};
+
+use syntax::{
+    algo::replace_children,
+    ast::{
+        self,
+        edit::{AstNodeEdit, IndentLevel},
+        make,
+    },
+    AstNode,
+    SyntaxKind::{FN, LOOP_EXPR, L_CURLY, R_CURLY, WHILE_EXPR, WHITESPACE},
+    SyntaxNode,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    utils::invert_boolean_expression,
+    AssistId, AssistKind,
+};
+
+// Assist: convert_to_guarded_return
+//
+// Replace a large conditional with a guarded return.
+//
+// ```
+// fn main() {
+//     <|>if cond {
+//         foo();
+//         bar();
+//     }
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     if !cond {
+//         return;
+//     }
+//     foo();
+//     bar();
+// }
+// ```
+pub(crate) fn convert_to_guarded_return(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
+    if if_expr.else_branch().is_some() {
+        return None;
+    }
+
+    let cond = if_expr.condition()?;
+
+    // Check if there is an IfLet that we can handle.
+    let if_let_pat = match cond.pat() {
+        None => None, // No IfLet, supported.
+        Some(ast::Pat::TupleStructPat(pat)) if pat.fields().count() == 1 => {
+            let path = pat.path()?;
+            match path.qualifier() {
+                None => {
+                    let bound_ident = pat.fields().next().unwrap();
+                    Some((path, bound_ident))
+                }
+                Some(_) => return None,
+            }
+        }
+        Some(_) => return None, // Unsupported IfLet.
+    };
+
+    let cond_expr = cond.expr()?;
+    let then_block = if_expr.then_branch()?;
+
+    let parent_block = if_expr.syntax().parent()?.ancestors().find_map(ast::BlockExpr::cast)?;
+
+    if parent_block.expr()? != if_expr.clone().into() {
+        return None;
+    }
+
+    // check for early return and continue
+    let first_in_then_block = then_block.syntax().first_child()?;
+    if ast::ReturnExpr::can_cast(first_in_then_block.kind())
+        || ast::ContinueExpr::can_cast(first_in_then_block.kind())
+        || first_in_then_block
+            .children()
+            .any(|x| ast::ReturnExpr::can_cast(x.kind()) || ast::ContinueExpr::can_cast(x.kind()))
+    {
+        return None;
+    }
+
+    let parent_container = parent_block.syntax().parent()?;
+
+    let early_expression: ast::Expr = match parent_container.kind() {
+        WHILE_EXPR | LOOP_EXPR => make::expr_continue(),
+        FN => make::expr_return(),
+        _ => return None,
+    };
+
+    if then_block.syntax().first_child_or_token().map(|t| t.kind() == L_CURLY).is_none() {
+        return None;
+    }
+
+    then_block.syntax().last_child_or_token().filter(|t| t.kind() == R_CURLY)?;
+
+    let target = if_expr.syntax().text_range();
+    acc.add(
+        AssistId("convert_to_guarded_return", AssistKind::RefactorRewrite),
+        "Convert to guarded return",
+        target,
+        |edit| {
+            let if_indent_level = IndentLevel::from_node(&if_expr.syntax());
+            let new_block = match if_let_pat {
+                None => {
+                    // If.
+                    let new_expr = {
+                        let then_branch =
+                            make::block_expr(once(make::expr_stmt(early_expression).into()), None);
+                        let cond = invert_boolean_expression(cond_expr);
+                        make::expr_if(make::condition(cond, None), then_branch)
+                            .indent(if_indent_level)
+                    };
+                    replace(new_expr.syntax(), &then_block, &parent_block, &if_expr)
+                }
+                Some((path, bound_ident)) => {
+                    // If-let.
+                    let match_expr = {
+                        let happy_arm = {
+                            let pat = make::tuple_struct_pat(
+                                path,
+                                once(make::ident_pat(make::name("it")).into()),
+                            );
+                            let expr = {
+                                let name_ref = make::name_ref("it");
+                                let segment = make::path_segment(name_ref);
+                                let path = make::path_unqualified(segment);
+                                make::expr_path(path)
+                            };
+                            make::match_arm(once(pat.into()), expr)
+                        };
+
+                        let sad_arm = make::match_arm(
+                            // FIXME: would be cool to use `None` or `Err(_)` if appropriate
+                            once(make::wildcard_pat().into()),
+                            early_expression,
+                        );
+
+                        make::expr_match(cond_expr, make::match_arm_list(vec![happy_arm, sad_arm]))
+                    };
+
+                    let let_stmt = make::let_stmt(
+                        make::ident_pat(make::name(&bound_ident.syntax().to_string())).into(),
+                        Some(match_expr),
+                    );
+                    let let_stmt = let_stmt.indent(if_indent_level);
+                    replace(let_stmt.syntax(), &then_block, &parent_block, &if_expr)
+                }
+            };
+            edit.replace_ast(parent_block, ast::BlockExpr::cast(new_block).unwrap());
+
+            fn replace(
+                new_expr: &SyntaxNode,
+                then_block: &ast::BlockExpr,
+                parent_block: &ast::BlockExpr,
+                if_expr: &ast::IfExpr,
+            ) -> SyntaxNode {
+                let then_block_items = then_block.dedent(IndentLevel(1));
+                let end_of_then = then_block_items.syntax().last_child_or_token().unwrap();
+                let end_of_then =
+                    if end_of_then.prev_sibling_or_token().map(|n| n.kind()) == Some(WHITESPACE) {
+                        end_of_then.prev_sibling_or_token().unwrap()
+                    } else {
+                        end_of_then
+                    };
+                let mut then_statements = new_expr.children_with_tokens().chain(
+                    then_block_items
+                        .syntax()
+                        .children_with_tokens()
+                        .skip(1)
+                        .take_while(|i| *i != end_of_then),
+                );
+                replace_children(
+                    &parent_block.syntax(),
+                    RangeInclusive::new(
+                        if_expr.clone().syntax().clone().into(),
+                        if_expr.syntax().clone().into(),
+                    ),
+                    &mut then_statements,
+                )
+            }
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn convert_inside_fn() {
+        check_assist(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                bar();
+                if<|> true {
+                    foo();
+
+                    //comment
+                    bar();
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                bar();
+                if !true {
+                    return;
+                }
+                foo();
+
+                //comment
+                bar();
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn convert_let_inside_fn() {
+        check_assist(
+            convert_to_guarded_return,
+            r#"
+            fn main(n: Option<String>) {
+                bar();
+                if<|> let Some(n) = n {
+                    foo(n);
+
+                    //comment
+                    bar();
+                }
+            }
+            "#,
+            r#"
+            fn main(n: Option<String>) {
+                bar();
+                let n = match n {
+                    Some(it) => it,
+                    _ => return,
+                };
+                foo(n);
+
+                //comment
+                bar();
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn convert_if_let_result() {
+        check_assist(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                if<|> let Ok(x) = Err(92) {
+                    foo(x);
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                let x = match Err(92) {
+                    Ok(it) => it,
+                    _ => return,
+                };
+                foo(x);
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn convert_let_ok_inside_fn() {
+        check_assist(
+            convert_to_guarded_return,
+            r#"
+            fn main(n: Option<String>) {
+                bar();
+                if<|> let Ok(n) = n {
+                    foo(n);
+
+                    //comment
+                    bar();
+                }
+            }
+            "#,
+            r#"
+            fn main(n: Option<String>) {
+                bar();
+                let n = match n {
+                    Ok(it) => it,
+                    _ => return,
+                };
+                foo(n);
+
+                //comment
+                bar();
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn convert_inside_while() {
+        check_assist(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                while true {
+                    if<|> true {
+                        foo();
+                        bar();
+                    }
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                while true {
+                    if !true {
+                        continue;
+                    }
+                    foo();
+                    bar();
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn convert_let_inside_while() {
+        check_assist(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                while true {
+                    if<|> let Some(n) = n {
+                        foo(n);
+                        bar();
+                    }
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                while true {
+                    let n = match n {
+                        Some(it) => it,
+                        _ => continue,
+                    };
+                    foo(n);
+                    bar();
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn convert_inside_loop() {
+        check_assist(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                loop {
+                    if<|> true {
+                        foo();
+                        bar();
+                    }
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                loop {
+                    if !true {
+                        continue;
+                    }
+                    foo();
+                    bar();
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn convert_let_inside_loop() {
+        check_assist(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                loop {
+                    if<|> let Some(n) = n {
+                        foo(n);
+                        bar();
+                    }
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                loop {
+                    let n = match n {
+                        Some(it) => it,
+                        _ => continue,
+                    };
+                    foo(n);
+                    bar();
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn ignore_already_converted_if() {
+        check_assist_not_applicable(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                if<|> true {
+                    return;
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn ignore_already_converted_loop() {
+        check_assist_not_applicable(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                loop {
+                    if<|> true {
+                        continue;
+                    }
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn ignore_return() {
+        check_assist_not_applicable(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                if<|> true {
+                    return
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn ignore_else_branch() {
+        check_assist_not_applicable(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                if<|> true {
+                    foo();
+                } else {
+                    bar()
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn ignore_statements_aftert_if() {
+        check_assist_not_applicable(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                if<|> true {
+                    foo();
+                }
+                bar();
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn ignore_statements_inside_if() {
+        check_assist_not_applicable(
+            convert_to_guarded_return,
+            r#"
+            fn main() {
+                if false {
+                    if<|> true {
+                        foo();
+                    }
+                }
+            }
+            "#,
+        );
+    }
+}

crates/assists/src/handlers/expand_glob_import.rs

@@ -0,0 +1,385 @@
+use either::Either;
+use hir::{AssocItem, MacroDef, ModuleDef, Name, PathResolution, ScopeDef, SemanticsScope};
+use ide_db::{
+    defs::{classify_name_ref, Definition, NameRefClass},
+    RootDatabase,
+};
+use syntax::{algo, ast, match_ast, AstNode, SyntaxNode, SyntaxToken, T};
+
+use crate::{
+    assist_context::{AssistBuilder, AssistContext, Assists},
+    AssistId, AssistKind,
+};
+
+// Assist: expand_glob_import
+//
+// Expands glob imports.
+//
+// ```
+// mod foo {
+//     pub struct Bar;
+//     pub struct Baz;
+// }
+//
+// use foo::*<|>;
+//
+// fn qux(bar: Bar, baz: Baz) {}
+// ```
+// ->
+// ```
+// mod foo {
+//     pub struct Bar;
+//     pub struct Baz;
+// }
+//
+// use foo::{Baz, Bar};
+//
+// fn qux(bar: Bar, baz: Baz) {}
+// ```
+pub(crate) fn expand_glob_import(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let star = ctx.find_token_at_offset(T![*])?;
+    let mod_path = find_mod_path(&star)?;
+    let module = match ctx.sema.resolve_path(&mod_path)? {
+        PathResolution::Def(ModuleDef::Module(it)) => it,
+        _ => return None,
+    };
+
+    let source_file = ctx.source_file();
+    let scope = ctx.sema.scope_at_offset(source_file.syntax(), ctx.offset());
+
+    let defs_in_mod = find_defs_in_mod(ctx, scope, module)?;
+    let name_refs_in_source_file =
+        source_file.syntax().descendants().filter_map(ast::NameRef::cast).collect();
+    let used_names = find_used_names(ctx, defs_in_mod, name_refs_in_source_file);
+
+    let parent = star.parent().parent()?;
+    acc.add(
+        AssistId("expand_glob_import", AssistKind::RefactorRewrite),
+        "Expand glob import",
+        parent.text_range(),
+        |builder| {
+            replace_ast(builder, &parent, mod_path, used_names);
+        },
+    )
+}
+
+fn find_mod_path(star: &SyntaxToken) -> Option<ast::Path> {
+    star.ancestors().find_map(|n| ast::UseTree::cast(n).and_then(|u| u.path()))
+}
+
+#[derive(PartialEq)]
+enum Def {
+    ModuleDef(ModuleDef),
+    MacroDef(MacroDef),
+}
+
+impl Def {
+    fn name(&self, db: &RootDatabase) -> Option<Name> {
+        match self {
+            Def::ModuleDef(def) => def.name(db),
+            Def::MacroDef(def) => def.name(db),
+        }
+    }
+}
+
+fn find_defs_in_mod(
+    ctx: &AssistContext,
+    from: SemanticsScope<'_>,
+    module: hir::Module,
+) -> Option<Vec<Def>> {
+    let module_scope = module.scope(ctx.db(), from.module());
+
+    let mut defs = vec![];
+    for (_, def) in module_scope {
+        match def {
+            ScopeDef::ModuleDef(def) => defs.push(Def::ModuleDef(def)),
+            ScopeDef::MacroDef(def) => defs.push(Def::MacroDef(def)),
+            _ => continue,
+        }
+    }
+
+    Some(defs)
+}
+
+fn find_used_names(
+    ctx: &AssistContext,
+    defs_in_mod: Vec<Def>,
+    name_refs_in_source_file: Vec<ast::NameRef>,
+) -> Vec<Name> {
+    let defs_in_source_file = name_refs_in_source_file
+        .iter()
+        .filter_map(|r| classify_name_ref(&ctx.sema, r))
+        .filter_map(|rc| match rc {
+            NameRefClass::Definition(Definition::ModuleDef(def)) => Some(Def::ModuleDef(def)),
+            NameRefClass::Definition(Definition::Macro(def)) => Some(Def::MacroDef(def)),
+            _ => None,
+        })
+        .collect::<Vec<Def>>();
+
+    defs_in_mod
+        .iter()
+        .filter(|def| {
+            if let Def::ModuleDef(ModuleDef::Trait(tr)) = def {
+                for item in tr.items(ctx.db()) {
+                    if let AssocItem::Function(f) = item {
+                        if defs_in_source_file.contains(&Def::ModuleDef(ModuleDef::Function(f))) {
+                            return true;
+                        }
+                    }
+                }
+            }
+
+            defs_in_source_file.contains(def)
+        })
+        .filter_map(|d| d.name(ctx.db()))
+        .collect()
+}
+
+fn replace_ast(
+    builder: &mut AssistBuilder,
+    node: &SyntaxNode,
+    path: ast::Path,
+    used_names: Vec<Name>,
+) {
+    let replacement: Either<ast::UseTree, ast::UseTreeList> = match used_names.as_slice() {
+        [name] => Either::Left(ast::make::use_tree(
+            ast::make::path_from_text(&format!("{}::{}", path, name)),
+            None,
+            None,
+            false,
+        )),
+        names => Either::Right(ast::make::use_tree_list(names.iter().map(|n| {
+            ast::make::use_tree(ast::make::path_from_text(&n.to_string()), None, None, false)
+        }))),
+    };
+
+    let mut replace_node = |replacement: Either<ast::UseTree, ast::UseTreeList>| {
+        algo::diff(node, &replacement.either(|u| u.syntax().clone(), |ut| ut.syntax().clone()))
+            .into_text_edit(builder.text_edit_builder());
+    };
+
+    match_ast! {
+        match node {
+            ast::UseTree(use_tree) => {
+                replace_node(replacement);
+            },
+            ast::UseTreeList(use_tree_list) => {
+                replace_node(replacement);
+            },
+            ast::Use(use_item) => {
+                builder.replace_ast(use_item, ast::make::use_(replacement.left_or_else(|ut| ast::make::use_tree(path, Some(ut), None, false))));
+            },
+            _ => {},
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn expanding_glob_import() {
+        check_assist(
+            expand_glob_import,
+            r"
+mod foo {
+    pub struct Bar;
+    pub struct Baz;
+    pub struct Qux;
+
+    pub fn f() {}
+}
+
+use foo::*<|>;
+
+fn qux(bar: Bar, baz: Baz) {
+    f();
+}
+",
+            r"
+mod foo {
+    pub struct Bar;
+    pub struct Baz;
+    pub struct Qux;
+
+    pub fn f() {}
+}
+
+use foo::{Baz, Bar, f};
+
+fn qux(bar: Bar, baz: Baz) {
+    f();
+}
+",
+        )
+    }
+
+    #[test]
+    fn expanding_glob_import_with_existing_explicit_names() {
+        check_assist(
+            expand_glob_import,
+            r"
+mod foo {
+    pub struct Bar;
+    pub struct Baz;
+    pub struct Qux;
+
+    pub fn f() {}
+}
+
+use foo::{*<|>, f};
+
+fn qux(bar: Bar, baz: Baz) {
+    f();
+}
+",
+            r"
+mod foo {
+    pub struct Bar;
+    pub struct Baz;
+    pub struct Qux;
+
+    pub fn f() {}
+}
+
+use foo::{Baz, Bar, f};
+
+fn qux(bar: Bar, baz: Baz) {
+    f();
+}
+",
+        )
+    }
+
+    #[test]
+    fn expanding_nested_glob_import() {
+        check_assist(
+            expand_glob_import,
+            r"
+mod foo {
+    mod bar {
+        pub struct Bar;
+        pub struct Baz;
+        pub struct Qux;
+
+        pub fn f() {}
+    }
+
+    mod baz {
+        pub fn g() {}
+    }
+}
+
+use foo::{bar::{*<|>, f}, baz::*};
+
+fn qux(bar: Bar, baz: Baz) {
+    f();
+    g();
+}
+",
+            r"
+mod foo {
+    mod bar {
+        pub struct Bar;
+        pub struct Baz;
+        pub struct Qux;
+
+        pub fn f() {}
+    }
+
+    mod baz {
+        pub fn g() {}
+    }
+}
+
+use foo::{bar::{Baz, Bar, f}, baz::*};
+
+fn qux(bar: Bar, baz: Baz) {
+    f();
+    g();
+}
+",
+        )
+    }
+
+    #[test]
+    fn expanding_glob_import_with_macro_defs() {
+        check_assist(
+            expand_glob_import,
+            r"
+//- /lib.rs crate:foo
+#[macro_export]
+macro_rules! bar {
+    () => ()
+}
+
+pub fn baz() {}
+
+//- /main.rs crate:main deps:foo
+use foo::*<|>;
+
+fn main() {
+    bar!();
+    baz();
+}
+",
+            r"
+use foo::{bar, baz};
+
+fn main() {
+    bar!();
+    baz();
+}
+",
+        )
+    }
+
+    #[test]
+    fn expanding_glob_import_with_trait_method_uses() {
+        check_assist(
+            expand_glob_import,
+            r"
+//- /lib.rs crate:foo
+pub trait Tr {
+    fn method(&self) {}
+}
+impl Tr for () {}
+
+//- /main.rs crate:main deps:foo
+use foo::*<|>;
+
+fn main() {
+    ().method();
+}
+",
+            r"
+use foo::Tr;
+
+fn main() {
+    ().method();
+}
+",
+        )
+    }
+
+    #[test]
+    fn expanding_is_not_applicable_if_cursor_is_not_in_star_token() {
+        check_assist_not_applicable(
+            expand_glob_import,
+            r"
+    mod foo {
+        pub struct Bar;
+        pub struct Baz;
+        pub struct Qux;
+    }
+
+    use foo::Bar<|>;
+
+    fn qux(bar: Bar, baz: Baz) {}
+    ",
+        )
+    }
+}

crates/assists/src/handlers/extract_struct_from_enum_variant.rs

@@ -0,0 +1,322 @@
+use base_db::FileId;
+use hir::{EnumVariant, Module, ModuleDef, Name};
+use ide_db::{defs::Definition, search::Reference, RootDatabase};
+use rustc_hash::FxHashSet;
+use syntax::{
+    algo::find_node_at_offset,
+    ast::{self, edit::IndentLevel, ArgListOwner, AstNode, NameOwner, VisibilityOwner},
+    SourceFile, TextRange, TextSize,
+};
+
+use crate::{
+    assist_context::AssistBuilder, utils::insert_use_statement, AssistContext, AssistId,
+    AssistKind, Assists,
+};
+
+// Assist: extract_struct_from_enum_variant
+//
+// Extracts a struct from enum variant.
+//
+// ```
+// enum A { <|>One(u32, u32) }
+// ```
+// ->
+// ```
+// struct One(pub u32, pub u32);
+//
+// enum A { One(One) }
+// ```
+pub(crate) fn extract_struct_from_enum_variant(
+    acc: &mut Assists,
+    ctx: &AssistContext,
+) -> Option<()> {
+    let variant = ctx.find_node_at_offset::<ast::Variant>()?;
+    let field_list = match variant.kind() {
+        ast::StructKind::Tuple(field_list) => field_list,
+        _ => return None,
+    };
+    let variant_name = variant.name()?.to_string();
+    let variant_hir = ctx.sema.to_def(&variant)?;
+    if existing_struct_def(ctx.db(), &variant_name, &variant_hir) {
+        return None;
+    }
+    let enum_ast = variant.parent_enum();
+    let visibility = enum_ast.visibility();
+    let enum_hir = ctx.sema.to_def(&enum_ast)?;
+    let variant_hir_name = variant_hir.name(ctx.db());
+    let enum_module_def = ModuleDef::from(enum_hir);
+    let current_module = enum_hir.module(ctx.db());
+    let target = variant.syntax().text_range();
+    acc.add(
+        AssistId("extract_struct_from_enum_variant", AssistKind::RefactorRewrite),
+        "Extract struct from enum variant",
+        target,
+        |builder| {
+            let definition = Definition::ModuleDef(ModuleDef::EnumVariant(variant_hir));
+            let res = definition.usages(&ctx.sema).all();
+            let start_offset = variant.parent_enum().syntax().text_range().start();
+            let mut visited_modules_set = FxHashSet::default();
+            visited_modules_set.insert(current_module);
+            for reference in res {
+                let source_file = ctx.sema.parse(reference.file_range.file_id);
+                update_reference(
+                    ctx,
+                    builder,
+                    reference,
+                    &source_file,
+                    &enum_module_def,
+                    &variant_hir_name,
+                    &mut visited_modules_set,
+                );
+            }
+            extract_struct_def(
+                builder,
+                &enum_ast,
+                &variant_name,
+                &field_list.to_string(),
+                start_offset,
+                ctx.frange.file_id,
+                &visibility,
+            );
+            let list_range = field_list.syntax().text_range();
+            update_variant(builder, &variant_name, ctx.frange.file_id, list_range);
+        },
+    )
+}
+
+fn existing_struct_def(db: &RootDatabase, variant_name: &str, variant: &EnumVariant) -> bool {
+    variant
+        .parent_enum(db)
+        .module(db)
+        .scope(db, None)
+        .into_iter()
+        .any(|(name, _)| name.to_string() == variant_name.to_string())
+}
+
+fn insert_import(
+    ctx: &AssistContext,
+    builder: &mut AssistBuilder,
+    path: &ast::PathExpr,
+    module: &Module,
+    enum_module_def: &ModuleDef,
+    variant_hir_name: &Name,
+) -> Option<()> {
+    let db = ctx.db();
+    let mod_path = module.find_use_path(db, enum_module_def.clone());
+    if let Some(mut mod_path) = mod_path {
+        mod_path.segments.pop();
+        mod_path.segments.push(variant_hir_name.clone());
+        insert_use_statement(
+            path.syntax(),
+            &mod_path.to_string(),
+            ctx,
+            builder.text_edit_builder(),
+        );
+    }
+    Some(())
+}
+
+// FIXME: this should use strongly-typed `make`, rather than string manipulation.
+fn extract_struct_def(
+    builder: &mut AssistBuilder,
+    enum_: &ast::Enum,
+    variant_name: &str,
+    variant_list: &str,
+    start_offset: TextSize,
+    file_id: FileId,
+    visibility: &Option<ast::Visibility>,
+) -> Option<()> {
+    let visibility_string = if let Some(visibility) = visibility {
+        format!("{} ", visibility.to_string())
+    } else {
+        "".to_string()
+    };
+    let indent = IndentLevel::from_node(enum_.syntax());
+    let struct_def = format!(
+        r#"{}struct {}{};
+
+{}"#,
+        visibility_string,
+        variant_name,
+        list_with_visibility(variant_list),
+        indent
+    );
+    builder.edit_file(file_id);
+    builder.insert(start_offset, struct_def);
+    Some(())
+}
+
+fn update_variant(
+    builder: &mut AssistBuilder,
+    variant_name: &str,
+    file_id: FileId,
+    list_range: TextRange,
+) -> Option<()> {
+    let inside_variant_range = TextRange::new(
+        list_range.start().checked_add(TextSize::from(1))?,
+        list_range.end().checked_sub(TextSize::from(1))?,
+    );
+    builder.edit_file(file_id);
+    builder.replace(inside_variant_range, variant_name);
+    Some(())
+}
+
+fn update_reference(
+    ctx: &AssistContext,
+    builder: &mut AssistBuilder,
+    reference: Reference,
+    source_file: &SourceFile,
+    enum_module_def: &ModuleDef,
+    variant_hir_name: &Name,
+    visited_modules_set: &mut FxHashSet<Module>,
+) -> Option<()> {
+    let path_expr: ast::PathExpr = find_node_at_offset::<ast::PathExpr>(
+        source_file.syntax(),
+        reference.file_range.range.start(),
+    )?;
+    let call = path_expr.syntax().parent().and_then(ast::CallExpr::cast)?;
+    let list = call.arg_list()?;
+    let segment = path_expr.path()?.segment()?;
+    let module = ctx.sema.scope(&path_expr.syntax()).module()?;
+    let list_range = list.syntax().text_range();
+    let inside_list_range = TextRange::new(
+        list_range.start().checked_add(TextSize::from(1))?,
+        list_range.end().checked_sub(TextSize::from(1))?,
+    );
+    builder.edit_file(reference.file_range.file_id);
+    if !visited_modules_set.contains(&module) {
+        if insert_import(ctx, builder, &path_expr, &module, enum_module_def, variant_hir_name)
+            .is_some()
+        {
+            visited_modules_set.insert(module);
+        }
+    }
+    builder.replace(inside_list_range, format!("{}{}", segment, list));
+    Some(())
+}
+
+fn list_with_visibility(list: &str) -> String {
+    list.split(',')
+        .map(|part| {
+            let index = if part.chars().next().unwrap() == '(' { 1usize } else { 0 };
+            let mut mod_part = part.trim().to_string();
+            mod_part.insert_str(index, "pub ");
+            mod_part
+        })
+        .collect::<Vec<String>>()
+        .join(", ")
+}
+
+#[cfg(test)]
+mod tests {
+
+    use crate::{
+        tests::{check_assist, check_assist_not_applicable},
+        utils::FamousDefs,
+    };
+
+    use super::*;
+
+    #[test]
+    fn test_extract_struct_several_fields() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            "enum A { <|>One(u32, u32) }",
+            r#"struct One(pub u32, pub u32);
+
+enum A { One(One) }"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_struct_one_field() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            "enum A { <|>One(u32) }",
+            r#"struct One(pub u32);
+
+enum A { One(One) }"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_struct_pub_visibility() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            "pub enum A { <|>One(u32, u32) }",
+            r#"pub struct One(pub u32, pub u32);
+
+pub enum A { One(One) }"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_struct_with_complex_imports() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            r#"mod my_mod {
+    fn another_fn() {
+        let m = my_other_mod::MyEnum::MyField(1, 1);
+    }
+
+    pub mod my_other_mod {
+        fn another_fn() {
+            let m = MyEnum::MyField(1, 1);
+        }
+
+        pub enum MyEnum {
+            <|>MyField(u8, u8),
+        }
+    }
+}
+
+fn another_fn() {
+    let m = my_mod::my_other_mod::MyEnum::MyField(1, 1);
+}"#,
+            r#"use my_mod::my_other_mod::MyField;
+
+mod my_mod {
+    use my_other_mod::MyField;
+
+    fn another_fn() {
+        let m = my_other_mod::MyEnum::MyField(MyField(1, 1));
+    }
+
+    pub mod my_other_mod {
+        fn another_fn() {
+            let m = MyEnum::MyField(MyField(1, 1));
+        }
+
+        pub struct MyField(pub u8, pub u8);
+
+        pub enum MyEnum {
+            MyField(MyField),
+        }
+    }
+}
+
+fn another_fn() {
+    let m = my_mod::my_other_mod::MyEnum::MyField(MyField(1, 1));
+}"#,
+        );
+    }
+
+    fn check_not_applicable(ra_fixture: &str) {
+        let fixture =
+            format!("//- /main.rs crate:main deps:core\n{}\n{}", ra_fixture, FamousDefs::FIXTURE);
+        check_assist_not_applicable(extract_struct_from_enum_variant, &fixture)
+    }
+
+    #[test]
+    fn test_extract_enum_not_applicable_for_element_with_no_fields() {
+        check_not_applicable("enum A { <|>One }");
+    }
+
+    #[test]
+    fn test_extract_enum_not_applicable_if_struct_exists() {
+        check_not_applicable(
+            r#"struct One;
+        enum A { <|>One(u8) }"#,
+        );
+    }
+}

crates/assists/src/handlers/extract_variable.rs

@@ -0,0 +1,588 @@
+use stdx::format_to;
+use syntax::{
+    ast::{self, AstNode},
+    SyntaxKind::{
+        BLOCK_EXPR, BREAK_EXPR, CLOSURE_EXPR, COMMENT, LOOP_EXPR, MATCH_ARM, PATH_EXPR, RETURN_EXPR,
+    },
+    SyntaxNode,
+};
+use test_utils::mark;
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: extract_variable
+//
+// Extracts subexpression into a variable.
+//
+// ```
+// fn main() {
+//     <|>(1 + 2)<|> * 4;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     let $0var_name = (1 + 2);
+//     var_name * 4;
+// }
+// ```
+pub(crate) fn extract_variable(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    if ctx.frange.range.is_empty() {
+        return None;
+    }
+    let node = ctx.covering_element();
+    if node.kind() == COMMENT {
+        mark::hit!(extract_var_in_comment_is_not_applicable);
+        return None;
+    }
+    let to_extract = node.ancestors().find_map(valid_target_expr)?;
+    let anchor = Anchor::from(&to_extract)?;
+    let indent = anchor.syntax().prev_sibling_or_token()?.as_token()?.clone();
+    let target = to_extract.syntax().text_range();
+    acc.add(
+        AssistId("extract_variable", AssistKind::RefactorExtract),
+        "Extract into variable",
+        target,
+        move |edit| {
+            let field_shorthand =
+                match to_extract.syntax().parent().and_then(ast::RecordExprField::cast) {
+                    Some(field) => field.name_ref(),
+                    None => None,
+                };
+
+            let mut buf = String::new();
+
+            let var_name = match &field_shorthand {
+                Some(it) => it.to_string(),
+                None => "var_name".to_string(),
+            };
+            let expr_range = match &field_shorthand {
+                Some(it) => it.syntax().text_range().cover(to_extract.syntax().text_range()),
+                None => to_extract.syntax().text_range(),
+            };
+
+            if let Anchor::WrapInBlock(_) = anchor {
+                format_to!(buf, "{{ let {} = ", var_name);
+            } else {
+                format_to!(buf, "let {} = ", var_name);
+            };
+            format_to!(buf, "{}", to_extract.syntax());
+
+            if let Anchor::Replace(stmt) = anchor {
+                mark::hit!(test_extract_var_expr_stmt);
+                if stmt.semicolon_token().is_none() {
+                    buf.push_str(";");
+                }
+                match ctx.config.snippet_cap {
+                    Some(cap) => {
+                        let snip = buf
+                            .replace(&format!("let {}", var_name), &format!("let $0{}", var_name));
+                        edit.replace_snippet(cap, expr_range, snip)
+                    }
+                    None => edit.replace(expr_range, buf),
+                }
+                return;
+            }
+
+            buf.push_str(";");
+
+            // We want to maintain the indent level,
+            // but we do not want to duplicate possible
+            // extra newlines in the indent block
+            let text = indent.text();
+            if text.starts_with('\n') {
+                buf.push_str("\n");
+                buf.push_str(text.trim_start_matches('\n'));
+            } else {
+                buf.push_str(text);
+            }
+
+            edit.replace(expr_range, var_name.clone());
+            let offset = anchor.syntax().text_range().start();
+            match ctx.config.snippet_cap {
+                Some(cap) => {
+                    let snip =
+                        buf.replace(&format!("let {}", var_name), &format!("let $0{}", var_name));
+                    edit.insert_snippet(cap, offset, snip)
+                }
+                None => edit.insert(offset, buf),
+            }
+
+            if let Anchor::WrapInBlock(_) = anchor {
+                edit.insert(anchor.syntax().text_range().end(), " }");
+            }
+        },
+    )
+}
+
+/// Check whether the node is a valid expression which can be extracted to a variable.
+/// In general that's true for any expression, but in some cases that would produce invalid code.
+fn valid_target_expr(node: SyntaxNode) -> Option<ast::Expr> {
+    match node.kind() {
+        PATH_EXPR | LOOP_EXPR => None,
+        BREAK_EXPR => ast::BreakExpr::cast(node).and_then(|e| e.expr()),
+        RETURN_EXPR => ast::ReturnExpr::cast(node).and_then(|e| e.expr()),
+        BLOCK_EXPR => {
+            ast::BlockExpr::cast(node).filter(|it| it.is_standalone()).map(ast::Expr::from)
+        }
+        _ => ast::Expr::cast(node),
+    }
+}
+
+enum Anchor {
+    Before(SyntaxNode),
+    Replace(ast::ExprStmt),
+    WrapInBlock(SyntaxNode),
+}
+
+impl Anchor {
+    fn from(to_extract: &ast::Expr) -> Option<Anchor> {
+        to_extract.syntax().ancestors().find_map(|node| {
+            if let Some(expr) =
+                node.parent().and_then(ast::BlockExpr::cast).and_then(|it| it.expr())
+            {
+                if expr.syntax() == &node {
+                    mark::hit!(test_extract_var_last_expr);
+                    return Some(Anchor::Before(node));
+                }
+            }
+
+            if let Some(parent) = node.parent() {
+                if parent.kind() == MATCH_ARM || parent.kind() == CLOSURE_EXPR {
+                    return Some(Anchor::WrapInBlock(node));
+                }
+            }
+
+            if let Some(stmt) = ast::Stmt::cast(node.clone()) {
+                if let ast::Stmt::ExprStmt(stmt) = stmt {
+                    if stmt.expr().as_ref() == Some(to_extract) {
+                        return Some(Anchor::Replace(stmt));
+                    }
+                }
+                return Some(Anchor::Before(node));
+            }
+            None
+        })
+    }
+
+    fn syntax(&self) -> &SyntaxNode {
+        match self {
+            Anchor::Before(it) | Anchor::WrapInBlock(it) => it,
+            Anchor::Replace(stmt) => stmt.syntax(),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::mark;
+
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn test_extract_var_simple() {
+        check_assist(
+            extract_variable,
+            r#"
+fn foo() {
+    foo(<|>1 + 1<|>);
+}"#,
+            r#"
+fn foo() {
+    let $0var_name = 1 + 1;
+    foo(var_name);
+}"#,
+        );
+    }
+
+    #[test]
+    fn extract_var_in_comment_is_not_applicable() {
+        mark::check!(extract_var_in_comment_is_not_applicable);
+        check_assist_not_applicable(extract_variable, "fn main() { 1 + /* <|>comment<|> */ 1; }");
+    }
+
+    #[test]
+    fn test_extract_var_expr_stmt() {
+        mark::check!(test_extract_var_expr_stmt);
+        check_assist(
+            extract_variable,
+            r#"
+fn foo() {
+    <|>1 + 1<|>;
+}"#,
+            r#"
+fn foo() {
+    let $0var_name = 1 + 1;
+}"#,
+        );
+        check_assist(
+            extract_variable,
+            "
+fn foo() {
+    <|>{ let x = 0; x }<|>
+    something_else();
+}",
+            "
+fn foo() {
+    let $0var_name = { let x = 0; x };
+    something_else();
+}",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_part_of_expr_stmt() {
+        check_assist(
+            extract_variable,
+            "
+fn foo() {
+    <|>1<|> + 1;
+}",
+            "
+fn foo() {
+    let $0var_name = 1;
+    var_name + 1;
+}",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_last_expr() {
+        mark::check!(test_extract_var_last_expr);
+        check_assist(
+            extract_variable,
+            r#"
+fn foo() {
+    bar(<|>1 + 1<|>)
+}
+"#,
+            r#"
+fn foo() {
+    let $0var_name = 1 + 1;
+    bar(var_name)
+}
+"#,
+        );
+        check_assist(
+            extract_variable,
+            r#"
+fn foo() {
+    <|>bar(1 + 1)<|>
+}
+"#,
+            r#"
+fn foo() {
+    let $0var_name = bar(1 + 1);
+    var_name
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn test_extract_var_in_match_arm_no_block() {
+        check_assist(
+            extract_variable,
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        true => (<|>2 + 2<|>, true)
+        _ => (0, false)
+    };
+}
+",
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        true => { let $0var_name = 2 + 2; (var_name, true) }
+        _ => (0, false)
+    };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_in_match_arm_with_block() {
+        check_assist(
+            extract_variable,
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        true => {
+            let y = 1;
+            (<|>2 + y<|>, true)
+        }
+        _ => (0, false)
+    };
+}
+",
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        true => {
+            let y = 1;
+            let $0var_name = 2 + y;
+            (var_name, true)
+        }
+        _ => (0, false)
+    };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_in_closure_no_block() {
+        check_assist(
+            extract_variable,
+            "
+fn main() {
+    let lambda = |x: u32| <|>x * 2<|>;
+}
+",
+            "
+fn main() {
+    let lambda = |x: u32| { let $0var_name = x * 2; var_name };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_in_closure_with_block() {
+        check_assist(
+            extract_variable,
+            "
+fn main() {
+    let lambda = |x: u32| { <|>x * 2<|> };
+}
+",
+            "
+fn main() {
+    let lambda = |x: u32| { let $0var_name = x * 2; var_name };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_path_simple() {
+        check_assist(
+            extract_variable,
+            "
+fn main() {
+    let o = <|>Some(true)<|>;
+}
+",
+            "
+fn main() {
+    let $0var_name = Some(true);
+    let o = var_name;
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_path_method() {
+        check_assist(
+            extract_variable,
+            "
+fn main() {
+    let v = <|>bar.foo()<|>;
+}
+",
+            "
+fn main() {
+    let $0var_name = bar.foo();
+    let v = var_name;
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_return() {
+        check_assist(
+            extract_variable,
+            "
+fn foo() -> u32 {
+    <|>return 2 + 2<|>;
+}
+",
+            "
+fn foo() -> u32 {
+    let $0var_name = 2 + 2;
+    return var_name;
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_does_not_add_extra_whitespace() {
+        check_assist(
+            extract_variable,
+            "
+fn foo() -> u32 {
+
+
+    <|>return 2 + 2<|>;
+}
+",
+            "
+fn foo() -> u32 {
+
+
+    let $0var_name = 2 + 2;
+    return var_name;
+}
+",
+        );
+
+        check_assist(
+            extract_variable,
+            "
+fn foo() -> u32 {
+
+        <|>return 2 + 2<|>;
+}
+",
+            "
+fn foo() -> u32 {
+
+        let $0var_name = 2 + 2;
+        return var_name;
+}
+",
+        );
+
+        check_assist(
+            extract_variable,
+            "
+fn foo() -> u32 {
+    let foo = 1;
+
+    // bar
+
+
+    <|>return 2 + 2<|>;
+}
+",
+            "
+fn foo() -> u32 {
+    let foo = 1;
+
+    // bar
+
+
+    let $0var_name = 2 + 2;
+    return var_name;
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_break() {
+        check_assist(
+            extract_variable,
+            "
+fn main() {
+    let result = loop {
+        <|>break 2 + 2<|>;
+    };
+}
+",
+            "
+fn main() {
+    let result = loop {
+        let $0var_name = 2 + 2;
+        break var_name;
+    };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_extract_var_for_cast() {
+        check_assist(
+            extract_variable,
+            "
+fn main() {
+    let v = <|>0f32 as u32<|>;
+}
+",
+            "
+fn main() {
+    let $0var_name = 0f32 as u32;
+    let v = var_name;
+}
+",
+        );
+    }
+
+    #[test]
+    fn extract_var_field_shorthand() {
+        check_assist(
+            extract_variable,
+            r#"
+struct S {
+    foo: i32
+}
+
+fn main() {
+    S { foo: <|>1 + 1<|> }
+}
+"#,
+            r#"
+struct S {
+    foo: i32
+}
+
+fn main() {
+    let $0foo = 1 + 1;
+    S { foo }
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn test_extract_var_for_return_not_applicable() {
+        check_assist_not_applicable(extract_variable, "fn foo() { <|>return<|>; } ");
+    }
+
+    #[test]
+    fn test_extract_var_for_break_not_applicable() {
+        check_assist_not_applicable(extract_variable, "fn main() { loop { <|>break<|>; }; }");
+    }
+
+    // FIXME: This is not quite correct, but good enough(tm) for the sorting heuristic
+    #[test]
+    fn extract_var_target() {
+        check_assist_target(extract_variable, "fn foo() -> u32 { <|>return 2 + 2<|>; }", "2 + 2");
+
+        check_assist_target(
+            extract_variable,
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        true => (<|>2 + 2<|>, true)
+        _ => (0, false)
+    };
+}
+",
+            "2 + 2",
+        );
+    }
+}

crates/assists/src/handlers/fill_match_arms.rs

@@ -0,0 +1,747 @@
+use std::iter;
+
+use hir::{Adt, HasSource, ModuleDef, Semantics};
+use ide_db::RootDatabase;
+use itertools::Itertools;
+use syntax::ast::{self, make, AstNode, MatchArm, NameOwner, Pat};
+use test_utils::mark;
+
+use crate::{
+    utils::{render_snippet, Cursor, FamousDefs},
+    AssistContext, AssistId, AssistKind, Assists,
+};
+
+// Assist: fill_match_arms
+//
+// Adds missing clauses to a `match` expression.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         <|>
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         $0Action::Move { distance } => {}
+//         Action::Stop => {}
+//     }
+// }
+// ```
+pub(crate) fn fill_match_arms(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let match_expr = ctx.find_node_at_offset::<ast::MatchExpr>()?;
+    let match_arm_list = match_expr.match_arm_list()?;
+
+    let expr = match_expr.expr()?;
+
+    let mut arms: Vec<MatchArm> = match_arm_list.arms().collect();
+    if arms.len() == 1 {
+        if let Some(Pat::WildcardPat(..)) = arms[0].pat() {
+            arms.clear();
+        }
+    }
+
+    let module = ctx.sema.scope(expr.syntax()).module()?;
+
+    let missing_arms: Vec<MatchArm> = if let Some(enum_def) = resolve_enum_def(&ctx.sema, &expr) {
+        let variants = enum_def.variants(ctx.db());
+
+        let mut variants = variants
+            .into_iter()
+            .filter_map(|variant| build_pat(ctx.db(), module, variant))
+            .filter(|variant_pat| is_variant_missing(&mut arms, variant_pat))
+            .map(|pat| make::match_arm(iter::once(pat), make::expr_empty_block()))
+            .collect::<Vec<_>>();
+        if Some(enum_def) == FamousDefs(&ctx.sema, module.krate()).core_option_Option() {
+            // Match `Some` variant first.
+            mark::hit!(option_order);
+            variants.reverse()
+        }
+        variants
+    } else if let Some(enum_defs) = resolve_tuple_of_enum_def(&ctx.sema, &expr) {
+        // Partial fill not currently supported for tuple of enums.
+        if !arms.is_empty() {
+            return None;
+        }
+
+        // We do not currently support filling match arms for a tuple
+        // containing a single enum.
+        if enum_defs.len() < 2 {
+            return None;
+        }
+
+        // When calculating the match arms for a tuple of enums, we want
+        // to create a match arm for each possible combination of enum
+        // values. The `multi_cartesian_product` method transforms
+        // Vec<Vec<EnumVariant>> into Vec<(EnumVariant, .., EnumVariant)>
+        // where each tuple represents a proposed match arm.
+        enum_defs
+            .into_iter()
+            .map(|enum_def| enum_def.variants(ctx.db()))
+            .multi_cartesian_product()
+            .map(|variants| {
+                let patterns =
+                    variants.into_iter().filter_map(|variant| build_pat(ctx.db(), module, variant));
+                ast::Pat::from(make::tuple_pat(patterns))
+            })
+            .filter(|variant_pat| is_variant_missing(&mut arms, variant_pat))
+            .map(|pat| make::match_arm(iter::once(pat), make::expr_empty_block()))
+            .collect()
+    } else {
+        return None;
+    };
+
+    if missing_arms.is_empty() {
+        return None;
+    }
+
+    let target = match_expr.syntax().text_range();
+    acc.add(
+        AssistId("fill_match_arms", AssistKind::QuickFix),
+        "Fill match arms",
+        target,
+        |builder| {
+            let new_arm_list = match_arm_list.remove_placeholder();
+            let n_old_arms = new_arm_list.arms().count();
+            let new_arm_list = new_arm_list.append_arms(missing_arms);
+            let first_new_arm = new_arm_list.arms().nth(n_old_arms);
+            let old_range = match_arm_list.syntax().text_range();
+            match (first_new_arm, ctx.config.snippet_cap) {
+                (Some(first_new_arm), Some(cap)) => {
+                    let extend_lifetime;
+                    let cursor =
+                        match first_new_arm.syntax().descendants().find_map(ast::WildcardPat::cast)
+                        {
+                            Some(it) => {
+                                extend_lifetime = it.syntax().clone();
+                                Cursor::Replace(&extend_lifetime)
+                            }
+                            None => Cursor::Before(first_new_arm.syntax()),
+                        };
+                    let snippet = render_snippet(cap, new_arm_list.syntax(), cursor);
+                    builder.replace_snippet(cap, old_range, snippet);
+                }
+                _ => builder.replace(old_range, new_arm_list.to_string()),
+            }
+        },
+    )
+}
+
+fn is_variant_missing(existing_arms: &mut Vec<MatchArm>, var: &Pat) -> bool {
+    existing_arms.iter().filter_map(|arm| arm.pat()).all(|pat| {
+        // Special casee OrPat as separate top-level pats
+        let top_level_pats: Vec<Pat> = match pat {
+            Pat::OrPat(pats) => pats.pats().collect::<Vec<_>>(),
+            _ => vec![pat],
+        };
+
+        !top_level_pats.iter().any(|pat| does_pat_match_variant(pat, var))
+    })
+}
+
+fn does_pat_match_variant(pat: &Pat, var: &Pat) -> bool {
+    let first_node_text = |pat: &Pat| pat.syntax().first_child().map(|node| node.text());
+
+    let pat_head = match pat {
+        Pat::IdentPat(bind_pat) => {
+            if let Some(p) = bind_pat.pat() {
+                first_node_text(&p)
+            } else {
+                return false;
+            }
+        }
+        pat => first_node_text(pat),
+    };
+
+    let var_head = first_node_text(var);
+
+    pat_head == var_head
+}
+
+fn resolve_enum_def(sema: &Semantics<RootDatabase>, expr: &ast::Expr) -> Option<hir::Enum> {
+    sema.type_of_expr(&expr)?.autoderef(sema.db).find_map(|ty| match ty.as_adt() {
+        Some(Adt::Enum(e)) => Some(e),
+        _ => None,
+    })
+}
+
+fn resolve_tuple_of_enum_def(
+    sema: &Semantics<RootDatabase>,
+    expr: &ast::Expr,
+) -> Option<Vec<hir::Enum>> {
+    sema.type_of_expr(&expr)?
+        .tuple_fields(sema.db)
+        .iter()
+        .map(|ty| {
+            ty.autoderef(sema.db).find_map(|ty| match ty.as_adt() {
+                Some(Adt::Enum(e)) => Some(e),
+                // For now we only handle expansion for a tuple of enums. Here
+                // we map non-enum items to None and rely on `collect` to
+                // convert Vec<Option<hir::Enum>> into Option<Vec<hir::Enum>>.
+                _ => None,
+            })
+        })
+        .collect()
+}
+
+fn build_pat(db: &RootDatabase, module: hir::Module, var: hir::EnumVariant) -> Option<ast::Pat> {
+    let path = crate::ast_transform::path_to_ast(module.find_use_path(db, ModuleDef::from(var))?);
+
+    // FIXME: use HIR for this; it doesn't currently expose struct vs. tuple vs. unit variants though
+    let pat: ast::Pat = match var.source(db).value.kind() {
+        ast::StructKind::Tuple(field_list) => {
+            let pats = iter::repeat(make::wildcard_pat().into()).take(field_list.fields().count());
+            make::tuple_struct_pat(path, pats).into()
+        }
+        ast::StructKind::Record(field_list) => {
+            let pats = field_list.fields().map(|f| make::ident_pat(f.name().unwrap()).into());
+            make::record_pat(path, pats).into()
+        }
+        ast::StructKind::Unit => make::path_pat(path),
+    };
+
+    Some(pat)
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::mark;
+
+    use crate::{
+        tests::{check_assist, check_assist_not_applicable, check_assist_target},
+        utils::FamousDefs,
+    };
+
+    use super::fill_match_arms;
+
+    #[test]
+    fn all_match_arms_provided() {
+        check_assist_not_applicable(
+            fill_match_arms,
+            r#"
+            enum A {
+                As,
+                Bs{x:i32, y:Option<i32>},
+                Cs(i32, Option<i32>),
+            }
+            fn main() {
+                match A::As<|> {
+                    A::As,
+                    A::Bs{x,y:Some(_)} => {}
+                    A::Cs(_, Some(_)) => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn tuple_of_non_enum() {
+        // for now this case is not handled, although it potentially could be
+        // in the future
+        check_assist_not_applicable(
+            fill_match_arms,
+            r#"
+            fn main() {
+                match (0, false)<|> {
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn partial_fill_record_tuple() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A {
+                As,
+                Bs { x: i32, y: Option<i32> },
+                Cs(i32, Option<i32>),
+            }
+            fn main() {
+                match A::As<|> {
+                    A::Bs { x, y: Some(_) } => {}
+                    A::Cs(_, Some(_)) => {}
+                }
+            }
+            "#,
+            r#"
+            enum A {
+                As,
+                Bs { x: i32, y: Option<i32> },
+                Cs(i32, Option<i32>),
+            }
+            fn main() {
+                match A::As {
+                    A::Bs { x, y: Some(_) } => {}
+                    A::Cs(_, Some(_)) => {}
+                    $0A::As => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn partial_fill_or_pat() {
+        check_assist(
+            fill_match_arms,
+            r#"
+enum A { As, Bs, Cs(Option<i32>) }
+fn main() {
+    match A::As<|> {
+        A::Cs(_) | A::Bs => {}
+    }
+}
+"#,
+            r#"
+enum A { As, Bs, Cs(Option<i32>) }
+fn main() {
+    match A::As {
+        A::Cs(_) | A::Bs => {}
+        $0A::As => {}
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn partial_fill() {
+        check_assist(
+            fill_match_arms,
+            r#"
+enum A { As, Bs, Cs, Ds(String), Es(B) }
+enum B { Xs, Ys }
+fn main() {
+    match A::As<|> {
+        A::Bs if 0 < 1 => {}
+        A::Ds(_value) => { let x = 1; }
+        A::Es(B::Xs) => (),
+    }
+}
+"#,
+            r#"
+enum A { As, Bs, Cs, Ds(String), Es(B) }
+enum B { Xs, Ys }
+fn main() {
+    match A::As {
+        A::Bs if 0 < 1 => {}
+        A::Ds(_value) => { let x = 1; }
+        A::Es(B::Xs) => (),
+        $0A::As => {}
+        A::Cs => {}
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn partial_fill_bind_pat() {
+        check_assist(
+            fill_match_arms,
+            r#"
+enum A { As, Bs, Cs(Option<i32>) }
+fn main() {
+    match A::As<|> {
+        A::As(_) => {}
+        a @ A::Bs(_) => {}
+    }
+}
+"#,
+            r#"
+enum A { As, Bs, Cs(Option<i32>) }
+fn main() {
+    match A::As {
+        A::As(_) => {}
+        a @ A::Bs(_) => {}
+        A::Cs(${0:_}) => {}
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_empty_body() {
+        check_assist(
+            fill_match_arms,
+            r#"
+enum A { As, Bs, Cs(String), Ds(String, String), Es { x: usize, y: usize } }
+
+fn main() {
+    let a = A::As;
+    match a<|> {}
+}
+"#,
+            r#"
+enum A { As, Bs, Cs(String), Ds(String, String), Es { x: usize, y: usize } }
+
+fn main() {
+    let a = A::As;
+    match a {
+        $0A::As => {}
+        A::Bs => {}
+        A::Cs(_) => {}
+        A::Ds(_, _) => {}
+        A::Es { x, y } => {}
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_tuple_of_enum() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A { One, Two }
+            enum B { One, Two }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match (a<|>, b) {}
+            }
+            "#,
+            r#"
+            enum A { One, Two }
+            enum B { One, Two }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match (a, b) {
+                    $0(A::One, B::One) => {}
+                    (A::One, B::Two) => {}
+                    (A::Two, B::One) => {}
+                    (A::Two, B::Two) => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_tuple_of_enum_ref() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A { One, Two }
+            enum B { One, Two }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match (&a<|>, &b) {}
+            }
+            "#,
+            r#"
+            enum A { One, Two }
+            enum B { One, Two }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match (&a, &b) {
+                    $0(A::One, B::One) => {}
+                    (A::One, B::Two) => {}
+                    (A::Two, B::One) => {}
+                    (A::Two, B::Two) => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_tuple_of_enum_partial() {
+        check_assist_not_applicable(
+            fill_match_arms,
+            r#"
+            enum A { One, Two }
+            enum B { One, Two }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match (a<|>, b) {
+                    (A::Two, B::One) => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_tuple_of_enum_not_applicable() {
+        check_assist_not_applicable(
+            fill_match_arms,
+            r#"
+            enum A { One, Two }
+            enum B { One, Two }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match (a<|>, b) {
+                    (A::Two, B::One) => {}
+                    (A::One, B::One) => {}
+                    (A::One, B::Two) => {}
+                    (A::Two, B::Two) => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_single_element_tuple_of_enum() {
+        // For now we don't hande the case of a single element tuple, but
+        // we could handle this in the future if `make::tuple_pat` allowed
+        // creating a tuple with a single pattern.
+        check_assist_not_applicable(
+            fill_match_arms,
+            r#"
+            enum A { One, Two }
+
+            fn main() {
+                let a = A::One;
+                match (a<|>, ) {
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn test_fill_match_arm_refs() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A { As }
+
+            fn foo(a: &A) {
+                match a<|> {
+                }
+            }
+            "#,
+            r#"
+            enum A { As }
+
+            fn foo(a: &A) {
+                match a {
+                    $0A::As => {}
+                }
+            }
+            "#,
+        );
+
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A {
+                Es { x: usize, y: usize }
+            }
+
+            fn foo(a: &mut A) {
+                match a<|> {
+                }
+            }
+            "#,
+            r#"
+            enum A {
+                Es { x: usize, y: usize }
+            }
+
+            fn foo(a: &mut A) {
+                match a {
+                    $0A::Es { x, y } => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_target() {
+        check_assist_target(
+            fill_match_arms,
+            r#"
+            enum E { X, Y }
+
+            fn main() {
+                match E::X<|> {}
+            }
+            "#,
+            "match E::X {}",
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_trivial_arm() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum E { X, Y }
+
+            fn main() {
+                match E::X {
+                    <|>_ => {}
+                }
+            }
+            "#,
+            r#"
+            enum E { X, Y }
+
+            fn main() {
+                match E::X {
+                    $0E::X => {}
+                    E::Y => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_qualifies_path() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            mod foo { pub enum E { X, Y } }
+            use foo::E::X;
+
+            fn main() {
+                match X {
+                    <|>
+                }
+            }
+            "#,
+            r#"
+            mod foo { pub enum E { X, Y } }
+            use foo::E::X;
+
+            fn main() {
+                match X {
+                    $0X => {}
+                    foo::E::Y => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_preserves_comments() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A { One, Two }
+            fn foo(a: A) {
+                match a {
+                    // foo bar baz<|>
+                    A::One => {}
+                    // This is where the rest should be
+                }
+            }
+            "#,
+            r#"
+            enum A { One, Two }
+            fn foo(a: A) {
+                match a {
+                    // foo bar baz
+                    A::One => {}
+                    // This is where the rest should be
+                    $0A::Two => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_preserves_comments_empty() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A { One, Two }
+            fn foo(a: A) {
+                match a {
+                    // foo bar baz<|>
+                }
+            }
+            "#,
+            r#"
+            enum A { One, Two }
+            fn foo(a: A) {
+                match a {
+                    // foo bar baz
+                    $0A::One => {}
+                    A::Two => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_placeholder() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A { One, Two, }
+            fn foo(a: A) {
+                match a<|> {
+                    _ => (),
+                }
+            }
+            "#,
+            r#"
+            enum A { One, Two, }
+            fn foo(a: A) {
+                match a {
+                    $0A::One => {}
+                    A::Two => {}
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn option_order() {
+        mark::check!(option_order);
+        let before = r#"
+fn foo(opt: Option<i32>) {
+    match opt<|> {
+    }
+}
+"#;
+        let before = &format!("//- /main.rs crate:main deps:core{}{}", before, FamousDefs::FIXTURE);
+
+        check_assist(
+            fill_match_arms,
+            before,
+            r#"
+fn foo(opt: Option<i32>) {
+    match opt {
+        Some(${0:_}) => {}
+        None => {}
+    }
+}
+"#,
+        );
+    }
+}

crates/assists/src/handlers/fix_visibility.rs

@@ -0,0 +1,607 @@
+use base_db::FileId;
+use hir::{db::HirDatabase, HasSource, HasVisibility, PathResolution};
+use syntax::{ast, AstNode, TextRange, TextSize};
+
+use crate::{utils::vis_offset, AssistContext, AssistId, AssistKind, Assists};
+use ast::VisibilityOwner;
+
+// FIXME: this really should be a fix for diagnostic, rather than an assist.
+
+// Assist: fix_visibility
+//
+// Makes inaccessible item public.
+//
+// ```
+// mod m {
+//     fn frobnicate() {}
+// }
+// fn main() {
+//     m::frobnicate<|>() {}
+// }
+// ```
+// ->
+// ```
+// mod m {
+//     $0pub(crate) fn frobnicate() {}
+// }
+// fn main() {
+//     m::frobnicate() {}
+// }
+// ```
+pub(crate) fn fix_visibility(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    add_vis_to_referenced_module_def(acc, ctx)
+        .or_else(|| add_vis_to_referenced_record_field(acc, ctx))
+}
+
+fn add_vis_to_referenced_module_def(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let path: ast::Path = ctx.find_node_at_offset()?;
+    let path_res = ctx.sema.resolve_path(&path)?;
+    let def = match path_res {
+        PathResolution::Def(def) => def,
+        _ => return None,
+    };
+
+    let current_module = ctx.sema.scope(&path.syntax()).module()?;
+    let target_module = def.module(ctx.db())?;
+
+    let vis = target_module.visibility_of(ctx.db(), &def)?;
+    if vis.is_visible_from(ctx.db(), current_module.into()) {
+        return None;
+    };
+
+    let (offset, current_visibility, target, target_file, target_name) =
+        target_data_for_def(ctx.db(), def)?;
+
+    let missing_visibility =
+        if current_module.krate() == target_module.krate() { "pub(crate)" } else { "pub" };
+
+    let assist_label = match target_name {
+        None => format!("Change visibility to {}", missing_visibility),
+        Some(name) => format!("Change visibility of {} to {}", name, missing_visibility),
+    };
+
+    acc.add(AssistId("fix_visibility", AssistKind::QuickFix), assist_label, target, |builder| {
+        builder.edit_file(target_file);
+        match ctx.config.snippet_cap {
+            Some(cap) => match current_visibility {
+                Some(current_visibility) => builder.replace_snippet(
+                    cap,
+                    current_visibility.syntax().text_range(),
+                    format!("$0{}", missing_visibility),
+                ),
+                None => builder.insert_snippet(cap, offset, format!("$0{} ", missing_visibility)),
+            },
+            None => match current_visibility {
+                Some(current_visibility) => {
+                    builder.replace(current_visibility.syntax().text_range(), missing_visibility)
+                }
+                None => builder.insert(offset, format!("{} ", missing_visibility)),
+            },
+        }
+    })
+}
+
+fn add_vis_to_referenced_record_field(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let record_field: ast::RecordExprField = ctx.find_node_at_offset()?;
+    let (record_field_def, _) = ctx.sema.resolve_record_field(&record_field)?;
+
+    let current_module = ctx.sema.scope(record_field.syntax()).module()?;
+    let visibility = record_field_def.visibility(ctx.db());
+    if visibility.is_visible_from(ctx.db(), current_module.into()) {
+        return None;
+    }
+
+    let parent = record_field_def.parent_def(ctx.db());
+    let parent_name = parent.name(ctx.db());
+    let target_module = parent.module(ctx.db());
+
+    let in_file_source = record_field_def.source(ctx.db());
+    let (offset, current_visibility, target) = match in_file_source.value {
+        hir::FieldSource::Named(it) => {
+            let s = it.syntax();
+            (vis_offset(s), it.visibility(), s.text_range())
+        }
+        hir::FieldSource::Pos(it) => {
+            let s = it.syntax();
+            (vis_offset(s), it.visibility(), s.text_range())
+        }
+    };
+
+    let missing_visibility =
+        if current_module.krate() == target_module.krate() { "pub(crate)" } else { "pub" };
+    let target_file = in_file_source.file_id.original_file(ctx.db());
+
+    let target_name = record_field_def.name(ctx.db());
+    let assist_label =
+        format!("Change visibility of {}.{} to {}", parent_name, target_name, missing_visibility);
+
+    acc.add(AssistId("fix_visibility", AssistKind::QuickFix), assist_label, target, |builder| {
+        builder.edit_file(target_file);
+        match ctx.config.snippet_cap {
+            Some(cap) => match current_visibility {
+                Some(current_visibility) => builder.replace_snippet(
+                    cap,
+                    current_visibility.syntax().text_range(),
+                    format!("$0{}", missing_visibility),
+                ),
+                None => builder.insert_snippet(cap, offset, format!("$0{} ", missing_visibility)),
+            },
+            None => match current_visibility {
+                Some(current_visibility) => {
+                    builder.replace(current_visibility.syntax().text_range(), missing_visibility)
+                }
+                None => builder.insert(offset, format!("{} ", missing_visibility)),
+            },
+        }
+    })
+}
+
+fn target_data_for_def(
+    db: &dyn HirDatabase,
+    def: hir::ModuleDef,
+) -> Option<(TextSize, Option<ast::Visibility>, TextRange, FileId, Option<hir::Name>)> {
+    fn offset_target_and_file_id<S, Ast>(
+        db: &dyn HirDatabase,
+        x: S,
+    ) -> (TextSize, Option<ast::Visibility>, TextRange, FileId)
+    where
+        S: HasSource<Ast = Ast>,
+        Ast: AstNode + ast::VisibilityOwner,
+    {
+        let source = x.source(db);
+        let in_file_syntax = source.syntax();
+        let file_id = in_file_syntax.file_id;
+        let syntax = in_file_syntax.value;
+        let current_visibility = source.value.visibility();
+        (
+            vis_offset(syntax),
+            current_visibility,
+            syntax.text_range(),
+            file_id.original_file(db.upcast()),
+        )
+    }
+
+    let target_name;
+    let (offset, current_visibility, target, target_file) = match def {
+        hir::ModuleDef::Function(f) => {
+            target_name = Some(f.name(db));
+            offset_target_and_file_id(db, f)
+        }
+        hir::ModuleDef::Adt(adt) => {
+            target_name = Some(adt.name(db));
+            match adt {
+                hir::Adt::Struct(s) => offset_target_and_file_id(db, s),
+                hir::Adt::Union(u) => offset_target_and_file_id(db, u),
+                hir::Adt::Enum(e) => offset_target_and_file_id(db, e),
+            }
+        }
+        hir::ModuleDef::Const(c) => {
+            target_name = c.name(db);
+            offset_target_and_file_id(db, c)
+        }
+        hir::ModuleDef::Static(s) => {
+            target_name = s.name(db);
+            offset_target_and_file_id(db, s)
+        }
+        hir::ModuleDef::Trait(t) => {
+            target_name = Some(t.name(db));
+            offset_target_and_file_id(db, t)
+        }
+        hir::ModuleDef::TypeAlias(t) => {
+            target_name = Some(t.name(db));
+            offset_target_and_file_id(db, t)
+        }
+        hir::ModuleDef::Module(m) => {
+            target_name = m.name(db);
+            let in_file_source = m.declaration_source(db)?;
+            let file_id = in_file_source.file_id.original_file(db.upcast());
+            let syntax = in_file_source.value.syntax();
+            (vis_offset(syntax), in_file_source.value.visibility(), syntax.text_range(), file_id)
+        }
+        // Enum variants can't be private, we can't modify builtin types
+        hir::ModuleDef::EnumVariant(_) | hir::ModuleDef::BuiltinType(_) => return None,
+    };
+
+    Some((offset, current_visibility, target, target_file, target_name))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn fix_visibility_of_fn() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { fn foo() {} }
+              fn main() { foo::foo<|>() } ",
+            r"mod foo { $0pub(crate) fn foo() {} }
+              fn main() { foo::foo() } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub fn foo() {} }
+              fn main() { foo::foo<|>() } ",
+        )
+    }
+
+    #[test]
+    fn fix_visibility_of_adt_in_submodule() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { struct Foo; }
+              fn main() { foo::Foo<|> } ",
+            r"mod foo { $0pub(crate) struct Foo; }
+              fn main() { foo::Foo } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub struct Foo; }
+              fn main() { foo::Foo<|> } ",
+        );
+        check_assist(
+            fix_visibility,
+            r"mod foo { enum Foo; }
+              fn main() { foo::Foo<|> } ",
+            r"mod foo { $0pub(crate) enum Foo; }
+              fn main() { foo::Foo } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub enum Foo; }
+              fn main() { foo::Foo<|> } ",
+        );
+        check_assist(
+            fix_visibility,
+            r"mod foo { union Foo; }
+              fn main() { foo::Foo<|> } ",
+            r"mod foo { $0pub(crate) union Foo; }
+              fn main() { foo::Foo } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub union Foo; }
+              fn main() { foo::Foo<|> } ",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_adt_in_other_file() {
+        check_assist(
+            fix_visibility,
+            r"
+//- /main.rs
+mod foo;
+fn main() { foo::Foo<|> }
+
+//- /foo.rs
+struct Foo;
+",
+            r"$0pub(crate) struct Foo;
+",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_struct_field() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { pub struct Foo { bar: (), } }
+              fn main() { foo::Foo { <|>bar: () }; } ",
+            r"mod foo { pub struct Foo { $0pub(crate) bar: (), } }
+              fn main() { foo::Foo { bar: () }; } ",
+        );
+        check_assist(
+            fix_visibility,
+            r"
+//- /lib.rs
+mod foo;
+fn main() { foo::Foo { <|>bar: () }; }
+//- /foo.rs
+pub struct Foo { bar: () }
+",
+            r"pub struct Foo { $0pub(crate) bar: () }
+",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub struct Foo { pub bar: (), } }
+              fn main() { foo::Foo { <|>bar: () }; } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"
+//- /lib.rs
+mod foo;
+fn main() { foo::Foo { <|>bar: () }; }
+//- /foo.rs
+pub struct Foo { pub bar: () }
+",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_enum_variant_field() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { pub enum Foo { Bar { bar: () } } }
+              fn main() { foo::Foo::Bar { <|>bar: () }; } ",
+            r"mod foo { pub enum Foo { Bar { $0pub(crate) bar: () } } }
+              fn main() { foo::Foo::Bar { bar: () }; } ",
+        );
+        check_assist(
+            fix_visibility,
+            r"
+//- /lib.rs
+mod foo;
+fn main() { foo::Foo::Bar { <|>bar: () }; }
+//- /foo.rs
+pub enum Foo { Bar { bar: () } }
+",
+            r"pub enum Foo { Bar { $0pub(crate) bar: () } }
+",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub struct Foo { pub bar: (), } }
+              fn main() { foo::Foo { <|>bar: () }; } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"
+//- /lib.rs
+mod foo;
+fn main() { foo::Foo { <|>bar: () }; }
+//- /foo.rs
+pub struct Foo { pub bar: () }
+",
+        );
+    }
+
+    #[test]
+    #[ignore]
+    // FIXME reenable this test when `Semantics::resolve_record_field` works with union fields
+    fn fix_visibility_of_union_field() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { pub union Foo { bar: (), } }
+              fn main() { foo::Foo { <|>bar: () }; } ",
+            r"mod foo { pub union Foo { $0pub(crate) bar: (), } }
+              fn main() { foo::Foo { bar: () }; } ",
+        );
+        check_assist(
+            fix_visibility,
+            r"
+//- /lib.rs
+mod foo;
+fn main() { foo::Foo { <|>bar: () }; }
+//- /foo.rs
+pub union Foo { bar: () }
+",
+            r"pub union Foo { $0pub(crate) bar: () }
+",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub union Foo { pub bar: (), } }
+              fn main() { foo::Foo { <|>bar: () }; } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"
+//- /lib.rs
+mod foo;
+fn main() { foo::Foo { <|>bar: () }; }
+//- /foo.rs
+pub union Foo { pub bar: () }
+",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_const() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { const FOO: () = (); }
+              fn main() { foo::FOO<|> } ",
+            r"mod foo { $0pub(crate) const FOO: () = (); }
+              fn main() { foo::FOO } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub const FOO: () = (); }
+              fn main() { foo::FOO<|> } ",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_static() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { static FOO: () = (); }
+              fn main() { foo::FOO<|> } ",
+            r"mod foo { $0pub(crate) static FOO: () = (); }
+              fn main() { foo::FOO } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub static FOO: () = (); }
+              fn main() { foo::FOO<|> } ",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_trait() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { trait Foo { fn foo(&self) {} } }
+              fn main() { let x: &dyn foo::<|>Foo; } ",
+            r"mod foo { $0pub(crate) trait Foo { fn foo(&self) {} } }
+              fn main() { let x: &dyn foo::Foo; } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub trait Foo { fn foo(&self) {} } }
+              fn main() { let x: &dyn foo::Foo<|>; } ",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_type_alias() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { type Foo = (); }
+              fn main() { let x: foo::Foo<|>; } ",
+            r"mod foo { $0pub(crate) type Foo = (); }
+              fn main() { let x: foo::Foo; } ",
+        );
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub type Foo = (); }
+              fn main() { let x: foo::Foo<|>; } ",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_module() {
+        check_assist(
+            fix_visibility,
+            r"mod foo { mod bar { fn bar() {} } }
+              fn main() { foo::bar<|>::bar(); } ",
+            r"mod foo { $0pub(crate) mod bar { fn bar() {} } }
+              fn main() { foo::bar::bar(); } ",
+        );
+
+        check_assist(
+            fix_visibility,
+            r"
+//- /main.rs
+mod foo;
+fn main() { foo::bar<|>::baz(); }
+
+//- /foo.rs
+mod bar {
+    pub fn baz() {}
+}
+",
+            r"$0pub(crate) mod bar {
+    pub fn baz() {}
+}
+",
+        );
+
+        check_assist_not_applicable(
+            fix_visibility,
+            r"mod foo { pub mod bar { pub fn bar() {} } }
+              fn main() { foo::bar<|>::bar(); } ",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_inline_module_in_other_file() {
+        check_assist(
+            fix_visibility,
+            r"
+//- /main.rs
+mod foo;
+fn main() { foo::bar<|>::baz(); }
+
+//- /foo.rs
+mod bar;
+//- /foo/bar.rs
+pub fn baz() {}
+",
+            r"$0pub(crate) mod bar;
+",
+        );
+    }
+
+    #[test]
+    fn fix_visibility_of_module_declaration_in_other_file() {
+        check_assist(
+            fix_visibility,
+            r"
+//- /main.rs
+mod foo;
+fn main() { foo::bar<|>>::baz(); }
+
+//- /foo.rs
+mod bar {
+    pub fn baz() {}
+}
+",
+            r"$0pub(crate) mod bar {
+    pub fn baz() {}
+}
+",
+        );
+    }
+
+    #[test]
+    fn adds_pub_when_target_is_in_another_crate() {
+        check_assist(
+            fix_visibility,
+            r"
+//- /main.rs crate:a deps:foo
+foo::Bar<|>
+//- /lib.rs crate:foo
+struct Bar;
+",
+            r"$0pub struct Bar;
+",
+        )
+    }
+
+    #[test]
+    fn replaces_pub_crate_with_pub() {
+        check_assist(
+            fix_visibility,
+            r"
+//- /main.rs crate:a deps:foo
+foo::Bar<|>
+//- /lib.rs crate:foo
+pub(crate) struct Bar;
+",
+            r"$0pub struct Bar;
+",
+        );
+        check_assist(
+            fix_visibility,
+            r"
+//- /main.rs crate:a deps:foo
+fn main() {
+    foo::Foo { <|>bar: () };
+}
+//- /lib.rs crate:foo
+pub struct Foo { pub(crate) bar: () }
+",
+            r"pub struct Foo { $0pub bar: () }
+",
+        );
+    }
+
+    #[test]
+    #[ignore]
+    // FIXME handle reexports properly
+    fn fix_visibility_of_reexport() {
+        check_assist(
+            fix_visibility,
+            r"
+            mod foo {
+                use bar::Baz;
+                mod bar { pub(super) struct Baz; }
+            }
+            foo::Baz<|>
+            ",
+            r"
+            mod foo {
+                $0pub(crate) use bar::Baz;
+                mod bar { pub(super) struct Baz; }
+            }
+            foo::Baz
+            ",
+        )
+    }
+}

crates/assists/src/handlers/flip_binexpr.rs

@@ -0,0 +1,142 @@
+use syntax::ast::{AstNode, BinExpr, BinOp};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: flip_binexpr
+//
+// Flips operands of a binary expression.
+//
+// ```
+// fn main() {
+//     let _ = 90 +<|> 2;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     let _ = 2 + 90;
+// }
+// ```
+pub(crate) fn flip_binexpr(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let expr = ctx.find_node_at_offset::<BinExpr>()?;
+    let lhs = expr.lhs()?.syntax().clone();
+    let rhs = expr.rhs()?.syntax().clone();
+    let op_range = expr.op_token()?.text_range();
+    // The assist should be applied only if the cursor is on the operator
+    let cursor_in_range = op_range.contains_range(ctx.frange.range);
+    if !cursor_in_range {
+        return None;
+    }
+    let action: FlipAction = expr.op_kind()?.into();
+    // The assist should not be applied for certain operators
+    if let FlipAction::DontFlip = action {
+        return None;
+    }
+
+    acc.add(
+        AssistId("flip_binexpr", AssistKind::RefactorRewrite),
+        "Flip binary expression",
+        op_range,
+        |edit| {
+            if let FlipAction::FlipAndReplaceOp(new_op) = action {
+                edit.replace(op_range, new_op);
+            }
+            edit.replace(lhs.text_range(), rhs.text());
+            edit.replace(rhs.text_range(), lhs.text());
+        },
+    )
+}
+
+enum FlipAction {
+    // Flip the expression
+    Flip,
+    // Flip the expression and replace the operator with this string
+    FlipAndReplaceOp(&'static str),
+    // Do not flip the expression
+    DontFlip,
+}
+
+impl From<BinOp> for FlipAction {
+    fn from(op_kind: BinOp) -> Self {
+        match op_kind {
+            kind if kind.is_assignment() => FlipAction::DontFlip,
+            BinOp::GreaterTest => FlipAction::FlipAndReplaceOp("<"),
+            BinOp::GreaterEqualTest => FlipAction::FlipAndReplaceOp("<="),
+            BinOp::LesserTest => FlipAction::FlipAndReplaceOp(">"),
+            BinOp::LesserEqualTest => FlipAction::FlipAndReplaceOp(">="),
+            _ => FlipAction::Flip,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    #[test]
+    fn flip_binexpr_target_is_the_op() {
+        check_assist_target(flip_binexpr, "fn f() { let res = 1 ==<|> 2; }", "==")
+    }
+
+    #[test]
+    fn flip_binexpr_not_applicable_for_assignment() {
+        check_assist_not_applicable(flip_binexpr, "fn f() { let mut _x = 1; _x +=<|> 2 }")
+    }
+
+    #[test]
+    fn flip_binexpr_works_for_eq() {
+        check_assist(
+            flip_binexpr,
+            "fn f() { let res = 1 ==<|> 2; }",
+            "fn f() { let res = 2 == 1; }",
+        )
+    }
+
+    #[test]
+    fn flip_binexpr_works_for_gt() {
+        check_assist(flip_binexpr, "fn f() { let res = 1 ><|> 2; }", "fn f() { let res = 2 < 1; }")
+    }
+
+    #[test]
+    fn flip_binexpr_works_for_lteq() {
+        check_assist(
+            flip_binexpr,
+            "fn f() { let res = 1 <=<|> 2; }",
+            "fn f() { let res = 2 >= 1; }",
+        )
+    }
+
+    #[test]
+    fn flip_binexpr_works_for_complex_expr() {
+        check_assist(
+            flip_binexpr,
+            "fn f() { let res = (1 + 1) ==<|> (2 + 2); }",
+            "fn f() { let res = (2 + 2) == (1 + 1); }",
+        )
+    }
+
+    #[test]
+    fn flip_binexpr_works_inside_match() {
+        check_assist(
+            flip_binexpr,
+            r#"
+            fn dyn_eq(&self, other: &dyn Diagnostic) -> bool {
+                match other.downcast_ref::<Self>() {
+                    None => false,
+                    Some(it) => it ==<|> self,
+                }
+            }
+            "#,
+            r#"
+            fn dyn_eq(&self, other: &dyn Diagnostic) -> bool {
+                match other.downcast_ref::<Self>() {
+                    None => false,
+                    Some(it) => self == it,
+                }
+            }
+            "#,
+        )
+    }
+}

crates/assists/src/handlers/flip_comma.rs

@@ -0,0 +1,84 @@
+use syntax::{algo::non_trivia_sibling, Direction, T};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: flip_comma
+//
+// Flips two comma-separated items.
+//
+// ```
+// fn main() {
+//     ((1, 2),<|> (3, 4));
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     ((3, 4), (1, 2));
+// }
+// ```
+pub(crate) fn flip_comma(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let comma = ctx.find_token_at_offset(T![,])?;
+    let prev = non_trivia_sibling(comma.clone().into(), Direction::Prev)?;
+    let next = non_trivia_sibling(comma.clone().into(), Direction::Next)?;
+
+    // Don't apply a "flip" in case of a last comma
+    // that typically comes before punctuation
+    if next.kind().is_punct() {
+        return None;
+    }
+
+    acc.add(
+        AssistId("flip_comma", AssistKind::RefactorRewrite),
+        "Flip comma",
+        comma.text_range(),
+        |edit| {
+            edit.replace(prev.text_range(), next.to_string());
+            edit.replace(next.text_range(), prev.to_string());
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_target};
+
+    #[test]
+    fn flip_comma_works_for_function_parameters() {
+        check_assist(
+            flip_comma,
+            "fn foo(x: i32,<|> y: Result<(), ()>) {}",
+            "fn foo(y: Result<(), ()>, x: i32) {}",
+        )
+    }
+
+    #[test]
+    fn flip_comma_target() {
+        check_assist_target(flip_comma, "fn foo(x: i32,<|> y: Result<(), ()>) {}", ",")
+    }
+
+    #[test]
+    #[should_panic]
+    fn flip_comma_before_punct() {
+        // See https://github.com/rust-analyzer/rust-analyzer/issues/1619
+        // "Flip comma" assist shouldn't be applicable to the last comma in enum or struct
+        // declaration body.
+        check_assist_target(
+            flip_comma,
+            "pub enum Test { \
+             A,<|> \
+             }",
+            ",",
+        );
+
+        check_assist_target(
+            flip_comma,
+            "pub struct Test { \
+             foo: usize,<|> \
+             }",
+            ",",
+        );
+    }
+}

crates/assists/src/handlers/flip_trait_bound.rs

@@ -0,0 +1,121 @@
+use syntax::{
+    algo::non_trivia_sibling,
+    ast::{self, AstNode},
+    Direction, T,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: flip_trait_bound
+//
+// Flips two trait bounds.
+//
+// ```
+// fn foo<T: Clone +<|> Copy>() { }
+// ```
+// ->
+// ```
+// fn foo<T: Copy + Clone>() { }
+// ```
+pub(crate) fn flip_trait_bound(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    // We want to replicate the behavior of `flip_binexpr` by only suggesting
+    // the assist when the cursor is on a `+`
+    let plus = ctx.find_token_at_offset(T![+])?;
+
+    // Make sure we're in a `TypeBoundList`
+    if ast::TypeBoundList::cast(plus.parent()).is_none() {
+        return None;
+    }
+
+    let (before, after) = (
+        non_trivia_sibling(plus.clone().into(), Direction::Prev)?,
+        non_trivia_sibling(plus.clone().into(), Direction::Next)?,
+    );
+
+    let target = plus.text_range();
+    acc.add(
+        AssistId("flip_trait_bound", AssistKind::RefactorRewrite),
+        "Flip trait bounds",
+        target,
+        |edit| {
+            edit.replace(before.text_range(), after.to_string());
+            edit.replace(after.text_range(), before.to_string());
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    #[test]
+    fn flip_trait_bound_assist_available() {
+        check_assist_target(flip_trait_bound, "struct S<T> where T: A <|>+ B + C { }", "+")
+    }
+
+    #[test]
+    fn flip_trait_bound_not_applicable_for_single_trait_bound() {
+        check_assist_not_applicable(flip_trait_bound, "struct S<T> where T: <|>A { }")
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_struct() {
+        check_assist(
+            flip_trait_bound,
+            "struct S<T> where T: A <|>+ B { }",
+            "struct S<T> where T: B + A { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_trait_impl() {
+        check_assist(
+            flip_trait_bound,
+            "impl X for S<T> where T: A +<|> B { }",
+            "impl X for S<T> where T: B + A { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_fn() {
+        check_assist(flip_trait_bound, "fn f<T: A <|>+ B>(t: T) { }", "fn f<T: B + A>(t: T) { }")
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_fn_where_clause() {
+        check_assist(
+            flip_trait_bound,
+            "fn f<T>(t: T) where T: A +<|> B { }",
+            "fn f<T>(t: T) where T: B + A { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_lifetime() {
+        check_assist(
+            flip_trait_bound,
+            "fn f<T>(t: T) where T: A <|>+ 'static { }",
+            "fn f<T>(t: T) where T: 'static + A { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_complex_bounds() {
+        check_assist(
+            flip_trait_bound,
+            "struct S<T> where T: A<T> <|>+ b_mod::B<T> + C<T> { }",
+            "struct S<T> where T: b_mod::B<T> + A<T> + C<T> { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_long_bounds() {
+        check_assist(
+            flip_trait_bound,
+            "struct S<T> where T: A + B + C + D + E + F +<|> G + H + I + J { }",
+            "struct S<T> where T: A + B + C + D + E + G + F + H + I + J { }",
+        )
+    }
+}

crates/assists/src/handlers/generate_derive.rs

@@ -0,0 +1,132 @@
+use syntax::{
+    ast::{self, AstNode, AttrsOwner},
+    SyntaxKind::{COMMENT, WHITESPACE},
+    TextSize,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: generate_derive
+//
+// Adds a new `#[derive()]` clause to a struct or enum.
+//
+// ```
+// struct Point {
+//     x: u32,
+//     y: u32,<|>
+// }
+// ```
+// ->
+// ```
+// #[derive($0)]
+// struct Point {
+//     x: u32,
+//     y: u32,
+// }
+// ```
+pub(crate) fn generate_derive(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let cap = ctx.config.snippet_cap?;
+    let nominal = ctx.find_node_at_offset::<ast::AdtDef>()?;
+    let node_start = derive_insertion_offset(&nominal)?;
+    let target = nominal.syntax().text_range();
+    acc.add(
+        AssistId("generate_derive", AssistKind::Generate),
+        "Add `#[derive]`",
+        target,
+        |builder| {
+            let derive_attr = nominal
+                .attrs()
+                .filter_map(|x| x.as_simple_call())
+                .filter(|(name, _arg)| name == "derive")
+                .map(|(_name, arg)| arg)
+                .next();
+            match derive_attr {
+                None => {
+                    builder.insert_snippet(cap, node_start, "#[derive($0)]\n");
+                }
+                Some(tt) => {
+                    // Just move the cursor.
+                    builder.insert_snippet(
+                        cap,
+                        tt.syntax().text_range().end() - TextSize::of(')'),
+                        "$0",
+                    )
+                }
+            };
+        },
+    )
+}
+
+// Insert `derive` after doc comments.
+fn derive_insertion_offset(nominal: &ast::AdtDef) -> Option<TextSize> {
+    let non_ws_child = nominal
+        .syntax()
+        .children_with_tokens()
+        .find(|it| it.kind() != COMMENT && it.kind() != WHITESPACE)?;
+    Some(non_ws_child.text_range().start())
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn add_derive_new() {
+        check_assist(
+            generate_derive,
+            "struct Foo { a: i32, <|>}",
+            "#[derive($0)]\nstruct Foo { a: i32, }",
+        );
+        check_assist(
+            generate_derive,
+            "struct Foo { <|> a: i32, }",
+            "#[derive($0)]\nstruct Foo {  a: i32, }",
+        );
+    }
+
+    #[test]
+    fn add_derive_existing() {
+        check_assist(
+            generate_derive,
+            "#[derive(Clone)]\nstruct Foo { a: i32<|>, }",
+            "#[derive(Clone$0)]\nstruct Foo { a: i32, }",
+        );
+    }
+
+    #[test]
+    fn add_derive_new_with_doc_comment() {
+        check_assist(
+            generate_derive,
+            "
+/// `Foo` is a pretty important struct.
+/// It does stuff.
+struct Foo { a: i32<|>, }
+            ",
+            "
+/// `Foo` is a pretty important struct.
+/// It does stuff.
+#[derive($0)]
+struct Foo { a: i32, }
+            ",
+        );
+    }
+
+    #[test]
+    fn add_derive_target() {
+        check_assist_target(
+            generate_derive,
+            "
+struct SomeThingIrrelevant;
+/// `Foo` is a pretty important struct.
+/// It does stuff.
+struct Foo { a: i32<|>, }
+struct EvenMoreIrrelevant;
+            ",
+            "/// `Foo` is a pretty important struct.
+/// It does stuff.
+struct Foo { a: i32, }",
+        );
+    }
+}

crates/assists/src/handlers/generate_from_impl_for_enum.rs

@@ -0,0 +1,200 @@
+use ide_db::RootDatabase;
+use syntax::ast::{self, AstNode, NameOwner};
+use test_utils::mark;
+
+use crate::{utils::FamousDefs, AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: generate_from_impl_for_enum
+//
+// Adds a From impl for an enum variant with one tuple field.
+//
+// ```
+// enum A { <|>One(u32) }
+// ```
+// ->
+// ```
+// enum A { One(u32) }
+//
+// impl From<u32> for A {
+//     fn from(v: u32) -> Self {
+//         A::One(v)
+//     }
+// }
+// ```
+pub(crate) fn generate_from_impl_for_enum(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let variant = ctx.find_node_at_offset::<ast::Variant>()?;
+    let variant_name = variant.name()?;
+    let enum_name = variant.parent_enum().name()?;
+    let field_list = match variant.kind() {
+        ast::StructKind::Tuple(field_list) => field_list,
+        _ => return None,
+    };
+    if field_list.fields().count() != 1 {
+        return None;
+    }
+    let field_type = field_list.fields().next()?.ty()?;
+    let path = match field_type {
+        ast::Type::PathType(it) => it,
+        _ => return None,
+    };
+
+    if existing_from_impl(&ctx.sema, &variant).is_some() {
+        mark::hit!(test_add_from_impl_already_exists);
+        return None;
+    }
+
+    let target = variant.syntax().text_range();
+    acc.add(
+        AssistId("generate_from_impl_for_enum", AssistKind::Generate),
+        "Generate `From` impl for this enum variant",
+        target,
+        |edit| {
+            let start_offset = variant.parent_enum().syntax().text_range().end();
+            let buf = format!(
+                r#"
+
+impl From<{0}> for {1} {{
+    fn from(v: {0}) -> Self {{
+        {1}::{2}(v)
+    }}
+}}"#,
+                path.syntax(),
+                enum_name,
+                variant_name
+            );
+            edit.insert(start_offset, buf);
+        },
+    )
+}
+
+fn existing_from_impl(
+    sema: &'_ hir::Semantics<'_, RootDatabase>,
+    variant: &ast::Variant,
+) -> Option<()> {
+    let variant = sema.to_def(variant)?;
+    let enum_ = variant.parent_enum(sema.db);
+    let krate = enum_.module(sema.db).krate();
+
+    let from_trait = FamousDefs(sema, krate).core_convert_From()?;
+
+    let enum_type = enum_.ty(sema.db);
+
+    let wrapped_type = variant.fields(sema.db).get(0)?.signature_ty(sema.db);
+
+    if enum_type.impls_trait(sema.db, from_trait, &[wrapped_type]) {
+        Some(())
+    } else {
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::mark;
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_generate_from_impl_for_enum() {
+        check_assist(
+            generate_from_impl_for_enum,
+            "enum A { <|>One(u32) }",
+            r#"enum A { One(u32) }
+
+impl From<u32> for A {
+    fn from(v: u32) -> Self {
+        A::One(v)
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_from_impl_for_enum_complicated_path() {
+        check_assist(
+            generate_from_impl_for_enum,
+            r#"enum A { <|>One(foo::bar::baz::Boo) }"#,
+            r#"enum A { One(foo::bar::baz::Boo) }
+
+impl From<foo::bar::baz::Boo> for A {
+    fn from(v: foo::bar::baz::Boo) -> Self {
+        A::One(v)
+    }
+}"#,
+        );
+    }
+
+    fn check_not_applicable(ra_fixture: &str) {
+        let fixture =
+            format!("//- /main.rs crate:main deps:core\n{}\n{}", ra_fixture, FamousDefs::FIXTURE);
+        check_assist_not_applicable(generate_from_impl_for_enum, &fixture)
+    }
+
+    #[test]
+    fn test_add_from_impl_no_element() {
+        check_not_applicable("enum A { <|>One }");
+    }
+
+    #[test]
+    fn test_add_from_impl_more_than_one_element_in_tuple() {
+        check_not_applicable("enum A { <|>One(u32, String) }");
+    }
+
+    #[test]
+    fn test_add_from_impl_struct_variant() {
+        check_not_applicable("enum A { <|>One { x: u32 } }");
+    }
+
+    #[test]
+    fn test_add_from_impl_already_exists() {
+        mark::check!(test_add_from_impl_already_exists);
+        check_not_applicable(
+            r#"
+enum A { <|>One(u32), }
+
+impl From<u32> for A {
+    fn from(v: u32) -> Self {
+        A::One(v)
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_add_from_impl_different_variant_impl_exists() {
+        check_assist(
+            generate_from_impl_for_enum,
+            r#"enum A { <|>One(u32), Two(String), }
+
+impl From<String> for A {
+    fn from(v: String) -> Self {
+        A::Two(v)
+    }
+}
+
+pub trait From<T> {
+    fn from(T) -> Self;
+}"#,
+            r#"enum A { One(u32), Two(String), }
+
+impl From<u32> for A {
+    fn from(v: u32) -> Self {
+        A::One(v)
+    }
+}
+
+impl From<String> for A {
+    fn from(v: String) -> Self {
+        A::Two(v)
+    }
+}
+
+pub trait From<T> {
+    fn from(T) -> Self;
+}"#,
+        );
+    }
+}

crates/assists/src/handlers/generate_impl.rs

@@ -0,0 +1,110 @@
+use itertools::Itertools;
+use stdx::format_to;
+use syntax::ast::{self, AstNode, GenericParamsOwner, NameOwner};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: generate_impl
+//
+// Adds a new inherent impl for a type.
+//
+// ```
+// struct Ctx<T: Clone> {
+//     data: T,<|>
+// }
+// ```
+// ->
+// ```
+// struct Ctx<T: Clone> {
+//     data: T,
+// }
+//
+// impl<T: Clone> Ctx<T> {
+//     $0
+// }
+// ```
+pub(crate) fn generate_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let nominal = ctx.find_node_at_offset::<ast::AdtDef>()?;
+    let name = nominal.name()?;
+    let target = nominal.syntax().text_range();
+    acc.add(
+        AssistId("generate_impl", AssistKind::Generate),
+        format!("Generate impl for `{}`", name),
+        target,
+        |edit| {
+            let type_params = nominal.generic_param_list();
+            let start_offset = nominal.syntax().text_range().end();
+            let mut buf = String::new();
+            buf.push_str("\n\nimpl");
+            if let Some(type_params) = &type_params {
+                format_to!(buf, "{}", type_params.syntax());
+            }
+            buf.push_str(" ");
+            buf.push_str(name.text().as_str());
+            if let Some(type_params) = type_params {
+                let lifetime_params = type_params
+                    .lifetime_params()
+                    .filter_map(|it| it.lifetime_token())
+                    .map(|it| it.text().clone());
+                let type_params = type_params
+                    .type_params()
+                    .filter_map(|it| it.name())
+                    .map(|it| it.text().clone());
+
+                let generic_params = lifetime_params.chain(type_params).format(", ");
+                format_to!(buf, "<{}>", generic_params)
+            }
+            match ctx.config.snippet_cap {
+                Some(cap) => {
+                    buf.push_str(" {\n    $0\n}");
+                    edit.insert_snippet(cap, start_offset, buf);
+                }
+                None => {
+                    buf.push_str(" {\n}");
+                    edit.insert(start_offset, buf);
+                }
+            }
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn test_add_impl() {
+        check_assist(
+            generate_impl,
+            "struct Foo {<|>}\n",
+            "struct Foo {}\n\nimpl Foo {\n    $0\n}\n",
+        );
+        check_assist(
+            generate_impl,
+            "struct Foo<T: Clone> {<|>}",
+            "struct Foo<T: Clone> {}\n\nimpl<T: Clone> Foo<T> {\n    $0\n}",
+        );
+        check_assist(
+            generate_impl,
+            "struct Foo<'a, T: Foo<'a>> {<|>}",
+            "struct Foo<'a, T: Foo<'a>> {}\n\nimpl<'a, T: Foo<'a>> Foo<'a, T> {\n    $0\n}",
+        );
+    }
+
+    #[test]
+    fn add_impl_target() {
+        check_assist_target(
+            generate_impl,
+            "
+struct SomeThingIrrelevant;
+/// Has a lifetime parameter
+struct Foo<'a, T: Foo<'a>> {<|>}
+struct EvenMoreIrrelevant;
+",
+            "/// Has a lifetime parameter
+struct Foo<'a, T: Foo<'a>> {}",
+        );
+    }
+}

crates/assists/src/handlers/generate_new.rs

@@ -0,0 +1,421 @@
+use hir::Adt;
+use itertools::Itertools;
+use stdx::format_to;
+use syntax::{
+    ast::{self, AstNode, GenericParamsOwner, NameOwner, StructKind, VisibilityOwner},
+    T,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: generate_new
+//
+// Adds a new inherent impl for a type.
+//
+// ```
+// struct Ctx<T: Clone> {
+//      data: T,<|>
+// }
+// ```
+// ->
+// ```
+// struct Ctx<T: Clone> {
+//      data: T,
+// }
+//
+// impl<T: Clone> Ctx<T> {
+//     fn $0new(data: T) -> Self { Self { data } }
+// }
+//
+// ```
+pub(crate) fn generate_new(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let strukt = ctx.find_node_at_offset::<ast::Struct>()?;
+
+    // We want to only apply this to non-union structs with named fields
+    let field_list = match strukt.kind() {
+        StructKind::Record(named) => named,
+        _ => return None,
+    };
+
+    // Return early if we've found an existing new fn
+    let impl_def = find_struct_impl(&ctx, &strukt)?;
+
+    let target = strukt.syntax().text_range();
+    acc.add(AssistId("generate_new", AssistKind::Generate), "Generate `new`", target, |builder| {
+        let mut buf = String::with_capacity(512);
+
+        if impl_def.is_some() {
+            buf.push('\n');
+        }
+
+        let vis = strukt.visibility().map_or(String::new(), |v| format!("{} ", v));
+
+        let params = field_list
+            .fields()
+            .filter_map(|f| Some(format!("{}: {}", f.name()?.syntax(), f.ty()?.syntax())))
+            .format(", ");
+        let fields = field_list.fields().filter_map(|f| f.name()).format(", ");
+
+        format_to!(buf, "    {}fn new({}) -> Self {{ Self {{ {} }} }}", vis, params, fields);
+
+        let start_offset = impl_def
+            .and_then(|impl_def| {
+                buf.push('\n');
+                let start = impl_def
+                    .syntax()
+                    .descendants_with_tokens()
+                    .find(|t| t.kind() == T!['{'])?
+                    .text_range()
+                    .end();
+
+                Some(start)
+            })
+            .unwrap_or_else(|| {
+                buf = generate_impl_text(&strukt, &buf);
+                strukt.syntax().text_range().end()
+            });
+
+        match ctx.config.snippet_cap {
+            None => builder.insert(start_offset, buf),
+            Some(cap) => {
+                buf = buf.replace("fn new", "fn $0new");
+                builder.insert_snippet(cap, start_offset, buf);
+            }
+        }
+    })
+}
+
+// Generates the surrounding `impl Type { <code> }` including type and lifetime
+// parameters
+fn generate_impl_text(strukt: &ast::Struct, code: &str) -> String {
+    let type_params = strukt.generic_param_list();
+    let mut buf = String::with_capacity(code.len());
+    buf.push_str("\n\nimpl");
+    if let Some(type_params) = &type_params {
+        format_to!(buf, "{}", type_params.syntax());
+    }
+    buf.push_str(" ");
+    buf.push_str(strukt.name().unwrap().text().as_str());
+    if let Some(type_params) = type_params {
+        let lifetime_params = type_params
+            .lifetime_params()
+            .filter_map(|it| it.lifetime_token())
+            .map(|it| it.text().clone());
+        let type_params =
+            type_params.type_params().filter_map(|it| it.name()).map(|it| it.text().clone());
+        format_to!(buf, "<{}>", lifetime_params.chain(type_params).format(", "))
+    }
+
+    format_to!(buf, " {{\n{}\n}}\n", code);
+
+    buf
+}
+
+// Uses a syntax-driven approach to find any impl blocks for the struct that
+// exist within the module/file
+//
+// Returns `None` if we've found an existing `new` fn
+//
+// FIXME: change the new fn checking to a more semantic approach when that's more
+// viable (e.g. we process proc macros, etc)
+fn find_struct_impl(ctx: &AssistContext, strukt: &ast::Struct) -> Option<Option<ast::Impl>> {
+    let db = ctx.db();
+    let module = strukt.syntax().ancestors().find(|node| {
+        ast::Module::can_cast(node.kind()) || ast::SourceFile::can_cast(node.kind())
+    })?;
+
+    let struct_def = ctx.sema.to_def(strukt)?;
+
+    let block = module.descendants().filter_map(ast::Impl::cast).find_map(|impl_blk| {
+        let blk = ctx.sema.to_def(&impl_blk)?;
+
+        // FIXME: handle e.g. `struct S<T>; impl<U> S<U> {}`
+        // (we currently use the wrong type parameter)
+        // also we wouldn't want to use e.g. `impl S<u32>`
+        let same_ty = match blk.target_ty(db).as_adt() {
+            Some(def) => def == Adt::Struct(struct_def),
+            None => false,
+        };
+        let not_trait_impl = blk.target_trait(db).is_none();
+
+        if !(same_ty && not_trait_impl) {
+            None
+        } else {
+            Some(impl_blk)
+        }
+    });
+
+    if let Some(ref impl_blk) = block {
+        if has_new_fn(impl_blk) {
+            return None;
+        }
+    }
+
+    Some(block)
+}
+
+fn has_new_fn(imp: &ast::Impl) -> bool {
+    if let Some(il) = imp.assoc_item_list() {
+        for item in il.assoc_items() {
+            if let ast::AssocItem::Fn(f) = item {
+                if let Some(name) = f.name() {
+                    if name.text().eq_ignore_ascii_case("new") {
+                        return true;
+                    }
+                }
+            }
+        }
+    }
+
+    false
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    #[rustfmt::skip]
+    fn test_generate_new() {
+        // Check output of generation
+        check_assist(
+            generate_new,
+"struct Foo {<|>}",
+"struct Foo {}
+
+impl Foo {
+    fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo<T: Clone> {<|>}",
+"struct Foo<T: Clone> {}
+
+impl<T: Clone> Foo<T> {
+    fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo<'a, T: Foo<'a>> {<|>}",
+"struct Foo<'a, T: Foo<'a>> {}
+
+impl<'a, T: Foo<'a>> Foo<'a, T> {
+    fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo { baz: String <|>}",
+"struct Foo { baz: String }
+
+impl Foo {
+    fn $0new(baz: String) -> Self { Self { baz } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo { baz: String, qux: Vec<i32> <|>}",
+"struct Foo { baz: String, qux: Vec<i32> }
+
+impl Foo {
+    fn $0new(baz: String, qux: Vec<i32>) -> Self { Self { baz, qux } }
+}
+",
+        );
+
+        // Check that visibility modifiers don't get brought in for fields
+        check_assist(
+            generate_new,
+"struct Foo { pub baz: String, pub qux: Vec<i32> <|>}",
+"struct Foo { pub baz: String, pub qux: Vec<i32> }
+
+impl Foo {
+    fn $0new(baz: String, qux: Vec<i32>) -> Self { Self { baz, qux } }
+}
+",
+        );
+
+        // Check that it reuses existing impls
+        check_assist(
+            generate_new,
+"struct Foo {<|>}
+
+impl Foo {}
+",
+"struct Foo {}
+
+impl Foo {
+    fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo {<|>}
+
+impl Foo {
+    fn qux(&self) {}
+}
+",
+"struct Foo {}
+
+impl Foo {
+    fn $0new() -> Self { Self {  } }
+
+    fn qux(&self) {}
+}
+",
+        );
+
+        check_assist(
+            generate_new,
+"struct Foo {<|>}
+
+impl Foo {
+    fn qux(&self) {}
+    fn baz() -> i32 {
+        5
+    }
+}
+",
+"struct Foo {}
+
+impl Foo {
+    fn $0new() -> Self { Self {  } }
+
+    fn qux(&self) {}
+    fn baz() -> i32 {
+        5
+    }
+}
+",
+        );
+
+        // Check visibility of new fn based on struct
+        check_assist(
+            generate_new,
+"pub struct Foo {<|>}",
+"pub struct Foo {}
+
+impl Foo {
+    pub fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"pub(crate) struct Foo {<|>}",
+"pub(crate) struct Foo {}
+
+impl Foo {
+    pub(crate) fn $0new() -> Self { Self {  } }
+}
+",
+        );
+    }
+
+    #[test]
+    fn generate_new_not_applicable_if_fn_exists() {
+        check_assist_not_applicable(
+            generate_new,
+            "
+struct Foo {<|>}
+
+impl Foo {
+    fn new() -> Self {
+        Self
+    }
+}",
+        );
+
+        check_assist_not_applicable(
+            generate_new,
+            "
+struct Foo {<|>}
+
+impl Foo {
+    fn New() -> Self {
+        Self
+    }
+}",
+        );
+    }
+
+    #[test]
+    fn generate_new_target() {
+        check_assist_target(
+            generate_new,
+            "
+struct SomeThingIrrelevant;
+/// Has a lifetime parameter
+struct Foo<'a, T: Foo<'a>> {<|>}
+struct EvenMoreIrrelevant;
+",
+            "/// Has a lifetime parameter
+struct Foo<'a, T: Foo<'a>> {}",
+        );
+    }
+
+    #[test]
+    fn test_unrelated_new() {
+        check_assist(
+            generate_new,
+            r##"
+pub struct AstId<N: AstNode> {
+    file_id: HirFileId,
+    file_ast_id: FileAstId<N>,
+}
+
+impl<N: AstNode> AstId<N> {
+    pub fn new(file_id: HirFileId, file_ast_id: FileAstId<N>) -> AstId<N> {
+        AstId { file_id, file_ast_id }
+    }
+}
+
+pub struct Source<T> {
+    pub file_id: HirFileId,<|>
+    pub ast: T,
+}
+
+impl<T> Source<T> {
+    pub fn map<F: FnOnce(T) -> U, U>(self, f: F) -> Source<U> {
+        Source { file_id: self.file_id, ast: f(self.ast) }
+    }
+}
+"##,
+            r##"
+pub struct AstId<N: AstNode> {
+    file_id: HirFileId,
+    file_ast_id: FileAstId<N>,
+}
+
+impl<N: AstNode> AstId<N> {
+    pub fn new(file_id: HirFileId, file_ast_id: FileAstId<N>) -> AstId<N> {
+        AstId { file_id, file_ast_id }
+    }
+}
+
+pub struct Source<T> {
+    pub file_id: HirFileId,
+    pub ast: T,
+}
+
+impl<T> Source<T> {
+    pub fn $0new(file_id: HirFileId, ast: T) -> Self { Self { file_id, ast } }
+
+    pub fn map<F: FnOnce(T) -> U, U>(self, f: F) -> Source<U> {
+        Source { file_id: self.file_id, ast: f(self.ast) }
+    }
+}
+"##,
+        );
+    }
+}

crates/assists/src/handlers/inline_local_variable.rs

@@ -0,0 +1,695 @@
+use ide_db::defs::Definition;
+use syntax::{
+    ast::{self, AstNode, AstToken},
+    TextRange,
+};
+use test_utils::mark;
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    AssistId, AssistKind,
+};
+
+// Assist: inline_local_variable
+//
+// Inlines local variable.
+//
+// ```
+// fn main() {
+//     let x<|> = 1 + 2;
+//     x * 4;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     (1 + 2) * 4;
+// }
+// ```
+pub(crate) fn inline_local_variable(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let let_stmt = ctx.find_node_at_offset::<ast::LetStmt>()?;
+    let bind_pat = match let_stmt.pat()? {
+        ast::Pat::IdentPat(pat) => pat,
+        _ => return None,
+    };
+    if bind_pat.mut_token().is_some() {
+        mark::hit!(test_not_inline_mut_variable);
+        return None;
+    }
+    if !bind_pat.syntax().text_range().contains_inclusive(ctx.offset()) {
+        mark::hit!(not_applicable_outside_of_bind_pat);
+        return None;
+    }
+    let initializer_expr = let_stmt.initializer()?;
+
+    let def = ctx.sema.to_def(&bind_pat)?;
+    let def = Definition::Local(def);
+    let refs = def.usages(&ctx.sema).all();
+    if refs.is_empty() {
+        mark::hit!(test_not_applicable_if_variable_unused);
+        return None;
+    };
+
+    let delete_range = if let Some(whitespace) = let_stmt
+        .syntax()
+        .next_sibling_or_token()
+        .and_then(|it| ast::Whitespace::cast(it.as_token()?.clone()))
+    {
+        TextRange::new(
+            let_stmt.syntax().text_range().start(),
+            whitespace.syntax().text_range().end(),
+        )
+    } else {
+        let_stmt.syntax().text_range()
+    };
+
+    let mut wrap_in_parens = vec![true; refs.len()];
+
+    for (i, desc) in refs.iter().enumerate() {
+        let usage_node = ctx
+            .covering_node_for_range(desc.file_range.range)
+            .ancestors()
+            .find_map(ast::PathExpr::cast)?;
+        let usage_parent_option = usage_node.syntax().parent().and_then(ast::Expr::cast);
+        let usage_parent = match usage_parent_option {
+            Some(u) => u,
+            None => {
+                wrap_in_parens[i] = false;
+                continue;
+            }
+        };
+
+        wrap_in_parens[i] = match (&initializer_expr, usage_parent) {
+            (ast::Expr::CallExpr(_), _)
+            | (ast::Expr::IndexExpr(_), _)
+            | (ast::Expr::MethodCallExpr(_), _)
+            | (ast::Expr::FieldExpr(_), _)
+            | (ast::Expr::TryExpr(_), _)
+            | (ast::Expr::RefExpr(_), _)
+            | (ast::Expr::Literal(_), _)
+            | (ast::Expr::TupleExpr(_), _)
+            | (ast::Expr::ArrayExpr(_), _)
+            | (ast::Expr::ParenExpr(_), _)
+            | (ast::Expr::PathExpr(_), _)
+            | (ast::Expr::BlockExpr(_), _)
+            | (ast::Expr::EffectExpr(_), _)
+            | (_, ast::Expr::CallExpr(_))
+            | (_, ast::Expr::TupleExpr(_))
+            | (_, ast::Expr::ArrayExpr(_))
+            | (_, ast::Expr::ParenExpr(_))
+            | (_, ast::Expr::ForExpr(_))
+            | (_, ast::Expr::WhileExpr(_))
+            | (_, ast::Expr::BreakExpr(_))
+            | (_, ast::Expr::ReturnExpr(_))
+            | (_, ast::Expr::MatchExpr(_)) => false,
+            _ => true,
+        };
+    }
+
+    let init_str = initializer_expr.syntax().text().to_string();
+    let init_in_paren = format!("({})", &init_str);
+
+    let target = bind_pat.syntax().text_range();
+    acc.add(
+        AssistId("inline_local_variable", AssistKind::RefactorInline),
+        "Inline variable",
+        target,
+        move |builder| {
+            builder.delete(delete_range);
+            for (desc, should_wrap) in refs.iter().zip(wrap_in_parens) {
+                let replacement =
+                    if should_wrap { init_in_paren.clone() } else { init_str.clone() };
+                builder.replace(desc.file_range.range, replacement)
+            }
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::mark;
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_inline_let_bind_literal_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn bar(a: usize) {}
+fn foo() {
+    let a<|> = 1;
+    a + 1;
+    if a > 10 {
+    }
+
+    while a > 10 {
+
+    }
+    let b = a * 10;
+    bar(a);
+}",
+            r"
+fn bar(a: usize) {}
+fn foo() {
+    1 + 1;
+    if 1 > 10 {
+    }
+
+    while 1 > 10 {
+
+    }
+    let b = 1 * 10;
+    bar(1);
+}",
+        );
+    }
+
+    #[test]
+    fn test_inline_let_bind_bin_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn bar(a: usize) {}
+fn foo() {
+    let a<|> = 1 + 1;
+    a + 1;
+    if a > 10 {
+    }
+
+    while a > 10 {
+
+    }
+    let b = a * 10;
+    bar(a);
+}",
+            r"
+fn bar(a: usize) {}
+fn foo() {
+    (1 + 1) + 1;
+    if (1 + 1) > 10 {
+    }
+
+    while (1 + 1) > 10 {
+
+    }
+    let b = (1 + 1) * 10;
+    bar(1 + 1);
+}",
+        );
+    }
+
+    #[test]
+    fn test_inline_let_bind_function_call_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn bar(a: usize) {}
+fn foo() {
+    let a<|> = bar(1);
+    a + 1;
+    if a > 10 {
+    }
+
+    while a > 10 {
+
+    }
+    let b = a * 10;
+    bar(a);
+}",
+            r"
+fn bar(a: usize) {}
+fn foo() {
+    bar(1) + 1;
+    if bar(1) > 10 {
+    }
+
+    while bar(1) > 10 {
+
+    }
+    let b = bar(1) * 10;
+    bar(bar(1));
+}",
+        );
+    }
+
+    #[test]
+    fn test_inline_let_bind_cast_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn bar(a: usize): usize { a }
+fn foo() {
+    let a<|> = bar(1) as u64;
+    a + 1;
+    if a > 10 {
+    }
+
+    while a > 10 {
+
+    }
+    let b = a * 10;
+    bar(a);
+}",
+            r"
+fn bar(a: usize): usize { a }
+fn foo() {
+    (bar(1) as u64) + 1;
+    if (bar(1) as u64) > 10 {
+    }
+
+    while (bar(1) as u64) > 10 {
+
+    }
+    let b = (bar(1) as u64) * 10;
+    bar(bar(1) as u64);
+}",
+        );
+    }
+
+    #[test]
+    fn test_inline_let_bind_block_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = { 10 + 1 };
+    a + 1;
+    if a > 10 {
+    }
+
+    while a > 10 {
+
+    }
+    let b = a * 10;
+    bar(a);
+}",
+            r"
+fn foo() {
+    { 10 + 1 } + 1;
+    if { 10 + 1 } > 10 {
+    }
+
+    while { 10 + 1 } > 10 {
+
+    }
+    let b = { 10 + 1 } * 10;
+    bar({ 10 + 1 });
+}",
+        );
+    }
+
+    #[test]
+    fn test_inline_let_bind_paren_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = ( 10 + 1 );
+    a + 1;
+    if a > 10 {
+    }
+
+    while a > 10 {
+
+    }
+    let b = a * 10;
+    bar(a);
+}",
+            r"
+fn foo() {
+    ( 10 + 1 ) + 1;
+    if ( 10 + 1 ) > 10 {
+    }
+
+    while ( 10 + 1 ) > 10 {
+
+    }
+    let b = ( 10 + 1 ) * 10;
+    bar(( 10 + 1 ));
+}",
+        );
+    }
+
+    #[test]
+    fn test_not_inline_mut_variable() {
+        mark::check!(test_not_inline_mut_variable);
+        check_assist_not_applicable(
+            inline_local_variable,
+            r"
+fn foo() {
+    let mut a<|> = 1 + 1;
+    a + 1;
+}",
+        );
+    }
+
+    #[test]
+    fn test_call_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = bar(10 + 1);
+    let b = a * 10;
+    let c = a as usize;
+}",
+            r"
+fn foo() {
+    let b = bar(10 + 1) * 10;
+    let c = bar(10 + 1) as usize;
+}",
+        );
+    }
+
+    #[test]
+    fn test_index_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let x = vec![1, 2, 3];
+    let a<|> = x[0];
+    let b = a * 10;
+    let c = a as usize;
+}",
+            r"
+fn foo() {
+    let x = vec![1, 2, 3];
+    let b = x[0] * 10;
+    let c = x[0] as usize;
+}",
+        );
+    }
+
+    #[test]
+    fn test_method_call_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let bar = vec![1];
+    let a<|> = bar.len();
+    let b = a * 10;
+    let c = a as usize;
+}",
+            r"
+fn foo() {
+    let bar = vec![1];
+    let b = bar.len() * 10;
+    let c = bar.len() as usize;
+}",
+        );
+    }
+
+    #[test]
+    fn test_field_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+struct Bar {
+    foo: usize
+}
+
+fn foo() {
+    let bar = Bar { foo: 1 };
+    let a<|> = bar.foo;
+    let b = a * 10;
+    let c = a as usize;
+}",
+            r"
+struct Bar {
+    foo: usize
+}
+
+fn foo() {
+    let bar = Bar { foo: 1 };
+    let b = bar.foo * 10;
+    let c = bar.foo as usize;
+}",
+        );
+    }
+
+    #[test]
+    fn test_try_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() -> Option<usize> {
+    let bar = Some(1);
+    let a<|> = bar?;
+    let b = a * 10;
+    let c = a as usize;
+    None
+}",
+            r"
+fn foo() -> Option<usize> {
+    let bar = Some(1);
+    let b = bar? * 10;
+    let c = bar? as usize;
+    None
+}",
+        );
+    }
+
+    #[test]
+    fn test_ref_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let bar = 10;
+    let a<|> = &bar;
+    let b = a * 10;
+}",
+            r"
+fn foo() {
+    let bar = 10;
+    let b = &bar * 10;
+}",
+        );
+    }
+
+    #[test]
+    fn test_tuple_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = (10, 20);
+    let b = a[0];
+}",
+            r"
+fn foo() {
+    let b = (10, 20)[0];
+}",
+        );
+    }
+
+    #[test]
+    fn test_array_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = [1, 2, 3];
+    let b = a.len();
+}",
+            r"
+fn foo() {
+    let b = [1, 2, 3].len();
+}",
+        );
+    }
+
+    #[test]
+    fn test_paren() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = (10 + 20);
+    let b = a * 10;
+    let c = a as usize;
+}",
+            r"
+fn foo() {
+    let b = (10 + 20) * 10;
+    let c = (10 + 20) as usize;
+}",
+        );
+    }
+
+    #[test]
+    fn test_path_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let d = 10;
+    let a<|> = d;
+    let b = a * 10;
+    let c = a as usize;
+}",
+            r"
+fn foo() {
+    let d = 10;
+    let b = d * 10;
+    let c = d as usize;
+}",
+        );
+    }
+
+    #[test]
+    fn test_block_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = { 10 };
+    let b = a * 10;
+    let c = a as usize;
+}",
+            r"
+fn foo() {
+    let b = { 10 } * 10;
+    let c = { 10 } as usize;
+}",
+        );
+    }
+
+    #[test]
+    fn test_used_in_different_expr1() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = 10 + 20;
+    let b = a * 10;
+    let c = (a, 20);
+    let d = [a, 10];
+    let e = (a);
+}",
+            r"
+fn foo() {
+    let b = (10 + 20) * 10;
+    let c = (10 + 20, 20);
+    let d = [10 + 20, 10];
+    let e = (10 + 20);
+}",
+        );
+    }
+
+    #[test]
+    fn test_used_in_for_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = vec![10, 20];
+    for i in a {}
+}",
+            r"
+fn foo() {
+    for i in vec![10, 20] {}
+}",
+        );
+    }
+
+    #[test]
+    fn test_used_in_while_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = 1 > 0;
+    while a {}
+}",
+            r"
+fn foo() {
+    while 1 > 0 {}
+}",
+        );
+    }
+
+    #[test]
+    fn test_used_in_break_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = 1 + 1;
+    loop {
+        break a;
+    }
+}",
+            r"
+fn foo() {
+    loop {
+        break 1 + 1;
+    }
+}",
+        );
+    }
+
+    #[test]
+    fn test_used_in_return_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = 1 > 0;
+    return a;
+}",
+            r"
+fn foo() {
+    return 1 > 0;
+}",
+        );
+    }
+
+    #[test]
+    fn test_used_in_match_expr() {
+        check_assist(
+            inline_local_variable,
+            r"
+fn foo() {
+    let a<|> = 1 > 0;
+    match a {}
+}",
+            r"
+fn foo() {
+    match 1 > 0 {}
+}",
+        );
+    }
+
+    #[test]
+    fn test_not_applicable_if_variable_unused() {
+        mark::check!(test_not_applicable_if_variable_unused);
+        check_assist_not_applicable(
+            inline_local_variable,
+            r"
+fn foo() {
+    let <|>a = 0;
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn not_applicable_outside_of_bind_pat() {
+        mark::check!(not_applicable_outside_of_bind_pat);
+        check_assist_not_applicable(
+            inline_local_variable,
+            r"
+fn main() {
+    let x = <|>1 + 2;
+    x * 4;
+}
+",
+        )
+    }
+}

crates/assists/src/handlers/introduce_named_lifetime.rs

@@ -0,0 +1,318 @@
+use rustc_hash::FxHashSet;
+use syntax::{
+    ast::{self, GenericParamsOwner, NameOwner},
+    AstNode, SyntaxKind, TextRange, TextSize,
+};
+
+use crate::{assist_context::AssistBuilder, AssistContext, AssistId, AssistKind, Assists};
+
+static ASSIST_NAME: &str = "introduce_named_lifetime";
+static ASSIST_LABEL: &str = "Introduce named lifetime";
+
+// Assist: introduce_named_lifetime
+//
+// Change an anonymous lifetime to a named lifetime.
+//
+// ```
+// impl Cursor<'_<|>> {
+//     fn node(self) -> &SyntaxNode {
+//         match self {
+//             Cursor::Replace(node) | Cursor::Before(node) => node,
+//         }
+//     }
+// }
+// ```
+// ->
+// ```
+// impl<'a> Cursor<'a> {
+//     fn node(self) -> &SyntaxNode {
+//         match self {
+//             Cursor::Replace(node) | Cursor::Before(node) => node,
+//         }
+//     }
+// }
+// ```
+// FIXME: How can we handle renaming any one of multiple anonymous lifetimes?
+// FIXME: should also add support for the case fun(f: &Foo) -> &<|>Foo
+pub(crate) fn introduce_named_lifetime(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let lifetime_token = ctx
+        .find_token_at_offset(SyntaxKind::LIFETIME)
+        .filter(|lifetime| lifetime.text() == "'_")?;
+    if let Some(fn_def) = lifetime_token.ancestors().find_map(ast::Fn::cast) {
+        generate_fn_def_assist(acc, &fn_def, lifetime_token.text_range())
+    } else if let Some(impl_def) = lifetime_token.ancestors().find_map(ast::Impl::cast) {
+        generate_impl_def_assist(acc, &impl_def, lifetime_token.text_range())
+    } else {
+        None
+    }
+}
+
+/// Generate the assist for the fn def case
+fn generate_fn_def_assist(
+    acc: &mut Assists,
+    fn_def: &ast::Fn,
+    lifetime_loc: TextRange,
+) -> Option<()> {
+    let param_list: ast::ParamList = fn_def.param_list()?;
+    let new_lifetime_param = generate_unique_lifetime_param_name(&fn_def.generic_param_list())?;
+    let end_of_fn_ident = fn_def.name()?.ident_token()?.text_range().end();
+    let self_param =
+        // use the self if it's a reference and has no explicit lifetime
+        param_list.self_param().filter(|p| p.lifetime_token().is_none() && p.amp_token().is_some());
+    // compute the location which implicitly has the same lifetime as the anonymous lifetime
+    let loc_needing_lifetime = if let Some(self_param) = self_param {
+        // if we have a self reference, use that
+        Some(self_param.self_token()?.text_range().start())
+    } else {
+        // otherwise, if there's a single reference parameter without a named liftime, use that
+        let fn_params_without_lifetime: Vec<_> = param_list
+            .params()
+            .filter_map(|param| match param.ty() {
+                Some(ast::Type::RefType(ascribed_type))
+                    if ascribed_type.lifetime_token() == None =>
+                {
+                    Some(ascribed_type.amp_token()?.text_range().end())
+                }
+                _ => None,
+            })
+            .collect();
+        match fn_params_without_lifetime.len() {
+            1 => Some(fn_params_without_lifetime.into_iter().nth(0)?),
+            0 => None,
+            // multiple unnnamed is invalid. assist is not applicable
+            _ => return None,
+        }
+    };
+    acc.add(AssistId(ASSIST_NAME, AssistKind::Refactor), ASSIST_LABEL, lifetime_loc, |builder| {
+        add_lifetime_param(fn_def, builder, end_of_fn_ident, new_lifetime_param);
+        builder.replace(lifetime_loc, format!("'{}", new_lifetime_param));
+        loc_needing_lifetime.map(|loc| builder.insert(loc, format!("'{} ", new_lifetime_param)));
+    })
+}
+
+/// Generate the assist for the impl def case
+fn generate_impl_def_assist(
+    acc: &mut Assists,
+    impl_def: &ast::Impl,
+    lifetime_loc: TextRange,
+) -> Option<()> {
+    let new_lifetime_param = generate_unique_lifetime_param_name(&impl_def.generic_param_list())?;
+    let end_of_impl_kw = impl_def.impl_token()?.text_range().end();
+    acc.add(AssistId(ASSIST_NAME, AssistKind::Refactor), ASSIST_LABEL, lifetime_loc, |builder| {
+        add_lifetime_param(impl_def, builder, end_of_impl_kw, new_lifetime_param);
+        builder.replace(lifetime_loc, format!("'{}", new_lifetime_param));
+    })
+}
+
+/// Given a type parameter list, generate a unique lifetime parameter name
+/// which is not in the list
+fn generate_unique_lifetime_param_name(
+    existing_type_param_list: &Option<ast::GenericParamList>,
+) -> Option<char> {
+    match existing_type_param_list {
+        Some(type_params) => {
+            let used_lifetime_params: FxHashSet<_> = type_params
+                .lifetime_params()
+                .map(|p| p.syntax().text().to_string()[1..].to_owned())
+                .collect();
+            (b'a'..=b'z').map(char::from).find(|c| !used_lifetime_params.contains(&c.to_string()))
+        }
+        None => Some('a'),
+    }
+}
+
+/// Add the lifetime param to `builder`. If there are type parameters in `type_params_owner`, add it to the end. Otherwise
+/// add new type params brackets with the lifetime parameter at `new_type_params_loc`.
+fn add_lifetime_param<TypeParamsOwner: ast::GenericParamsOwner>(
+    type_params_owner: &TypeParamsOwner,
+    builder: &mut AssistBuilder,
+    new_type_params_loc: TextSize,
+    new_lifetime_param: char,
+) {
+    match type_params_owner.generic_param_list() {
+        // add the new lifetime parameter to an existing type param list
+        Some(type_params) => {
+            builder.insert(
+                (u32::from(type_params.syntax().text_range().end()) - 1).into(),
+                format!(", '{}", new_lifetime_param),
+            );
+        }
+        // create a new type param list containing only the new lifetime parameter
+        None => {
+            builder.insert(new_type_params_loc, format!("<'{}>", new_lifetime_param));
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    #[test]
+    fn test_example_case() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"impl Cursor<'_<|>> {
+                fn node(self) -> &SyntaxNode {
+                    match self {
+                        Cursor::Replace(node) | Cursor::Before(node) => node,
+                    }
+                }
+            }"#,
+            r#"impl<'a> Cursor<'a> {
+                fn node(self) -> &SyntaxNode {
+                    match self {
+                        Cursor::Replace(node) | Cursor::Before(node) => node,
+                    }
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn test_example_case_simplified() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"impl Cursor<'_<|>> {"#,
+            r#"impl<'a> Cursor<'a> {"#,
+        );
+    }
+
+    #[test]
+    fn test_example_case_cursor_after_tick() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"impl Cursor<'<|>_> {"#,
+            r#"impl<'a> Cursor<'a> {"#,
+        );
+    }
+
+    #[test]
+    fn test_impl_with_other_type_param() {
+        check_assist(
+            introduce_named_lifetime,
+            "impl<I> fmt::Display for SepByBuilder<'_<|>, I>
+        where
+            I: Iterator,
+            I::Item: fmt::Display,
+        {",
+            "impl<I, 'a> fmt::Display for SepByBuilder<'a, I>
+        where
+            I: Iterator,
+            I::Item: fmt::Display,
+        {",
+        )
+    }
+
+    #[test]
+    fn test_example_case_cursor_before_tick() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"impl Cursor<<|>'_> {"#,
+            r#"impl<'a> Cursor<'a> {"#,
+        );
+    }
+
+    #[test]
+    fn test_not_applicable_cursor_position() {
+        check_assist_not_applicable(introduce_named_lifetime, r#"impl Cursor<'_><|> {"#);
+        check_assist_not_applicable(introduce_named_lifetime, r#"impl Cursor<|><'_> {"#);
+    }
+
+    #[test]
+    fn test_not_applicable_lifetime_already_name() {
+        check_assist_not_applicable(introduce_named_lifetime, r#"impl Cursor<'a<|>> {"#);
+        check_assist_not_applicable(introduce_named_lifetime, r#"fn my_fun<'a>() -> X<'a<|>>"#);
+    }
+
+    #[test]
+    fn test_with_type_parameter() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"impl<T> Cursor<T, '_<|>>"#,
+            r#"impl<T, 'a> Cursor<T, 'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_with_existing_lifetime_name_conflict() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"impl<'a, 'b> Cursor<'a, 'b, '_<|>>"#,
+            r#"impl<'a, 'b, 'c> Cursor<'a, 'b, 'c>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_return_value_anon_lifetime_param() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"fn my_fun() -> X<'_<|>>"#,
+            r#"fn my_fun<'a>() -> X<'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_return_value_anon_reference_lifetime() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"fn my_fun() -> &'_<|> X"#,
+            r#"fn my_fun<'a>() -> &'a X"#,
+        );
+    }
+
+    #[test]
+    fn test_function_param_anon_lifetime() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"fn my_fun(x: X<'_<|>>)"#,
+            r#"fn my_fun<'a>(x: X<'a>)"#,
+        );
+    }
+
+    #[test]
+    fn test_function_add_lifetime_to_params() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"fn my_fun(f: &Foo) -> X<'_<|>>"#,
+            r#"fn my_fun<'a>(f: &'a Foo) -> X<'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_add_lifetime_to_params_in_presence_of_other_lifetime() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"fn my_fun<'other>(f: &Foo, b: &'other Bar) -> X<'_<|>>"#,
+            r#"fn my_fun<'other, 'a>(f: &'a Foo, b: &'other Bar) -> X<'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_not_applicable_without_self_and_multiple_unnamed_param_lifetimes() {
+        // this is not permitted under lifetime elision rules
+        check_assist_not_applicable(
+            introduce_named_lifetime,
+            r#"fn my_fun(f: &Foo, b: &Bar) -> X<'_<|>>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_add_lifetime_to_self_ref_param() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"fn my_fun<'other>(&self, f: &Foo, b: &'other Bar) -> X<'_<|>>"#,
+            r#"fn my_fun<'other, 'a>(&'a self, f: &Foo, b: &'other Bar) -> X<'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_add_lifetime_to_param_with_non_ref_self() {
+        check_assist(
+            introduce_named_lifetime,
+            r#"fn my_fun<'other>(self, f: &Foo, b: &'other Bar) -> X<'_<|>>"#,
+            r#"fn my_fun<'other, 'a>(self, f: &'a Foo, b: &'other Bar) -> X<'a>"#,
+        );
+    }
+}

crates/assists/src/handlers/invert_if.rs

@@ -0,0 +1,109 @@
+use syntax::{
+    ast::{self, AstNode},
+    T,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    utils::invert_boolean_expression,
+    AssistId, AssistKind,
+};
+
+// Assist: invert_if
+//
+// Apply invert_if
+// This transforms if expressions of the form `if !x {A} else {B}` into `if x {B} else {A}`
+// This also works with `!=`. This assist can only be applied with the cursor
+// on `if`.
+//
+// ```
+// fn main() {
+//     if<|> !y { A } else { B }
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     if y { B } else { A }
+// }
+// ```
+
+pub(crate) fn invert_if(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let if_keyword = ctx.find_token_at_offset(T![if])?;
+    let expr = ast::IfExpr::cast(if_keyword.parent())?;
+    let if_range = if_keyword.text_range();
+    let cursor_in_range = if_range.contains_range(ctx.frange.range);
+    if !cursor_in_range {
+        return None;
+    }
+
+    // This assist should not apply for if-let.
+    if expr.condition()?.pat().is_some() {
+        return None;
+    }
+
+    let cond = expr.condition()?.expr()?;
+    let then_node = expr.then_branch()?.syntax().clone();
+    let else_block = match expr.else_branch()? {
+        ast::ElseBranch::Block(it) => it,
+        ast::ElseBranch::IfExpr(_) => return None,
+    };
+
+    let cond_range = cond.syntax().text_range();
+    let flip_cond = invert_boolean_expression(cond);
+    let else_node = else_block.syntax();
+    let else_range = else_node.text_range();
+    let then_range = then_node.text_range();
+    acc.add(AssistId("invert_if", AssistKind::RefactorRewrite), "Invert if", if_range, |edit| {
+        edit.replace(cond_range, flip_cond.syntax().text());
+        edit.replace(else_range, then_node.text());
+        edit.replace(then_range, else_node.text());
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    #[test]
+    fn invert_if_remove_inequality() {
+        check_assist(
+            invert_if,
+            "fn f() { i<|>f x != 3 { 1 } else { 3 + 2 } }",
+            "fn f() { if x == 3 { 3 + 2 } else { 1 } }",
+        )
+    }
+
+    #[test]
+    fn invert_if_remove_not() {
+        check_assist(
+            invert_if,
+            "fn f() { <|>if !cond { 3 * 2 } else { 1 } }",
+            "fn f() { if cond { 1 } else { 3 * 2 } }",
+        )
+    }
+
+    #[test]
+    fn invert_if_general_case() {
+        check_assist(
+            invert_if,
+            "fn f() { i<|>f cond { 3 * 2 } else { 1 } }",
+            "fn f() { if !cond { 1 } else { 3 * 2 } }",
+        )
+    }
+
+    #[test]
+    fn invert_if_doesnt_apply_with_cursor_not_on_if() {
+        check_assist_not_applicable(invert_if, "fn f() { if !<|>cond { 3 * 2 } else { 1 } }")
+    }
+
+    #[test]
+    fn invert_if_doesnt_apply_with_if_let() {
+        check_assist_not_applicable(
+            invert_if,
+            "fn f() { i<|>f let Some(_) = Some(1) { 1 } else { 0 } }",
+        )
+    }
+}

crates/assists/src/handlers/merge_imports.rs

@@ -0,0 +1,318 @@
+use std::iter::successors;
+
+use syntax::{
+    algo::{neighbor, skip_trivia_token, SyntaxRewriter},
+    ast::{self, edit::AstNodeEdit, make},
+    AstNode, Direction, InsertPosition, SyntaxElement, T,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    utils::next_prev,
+    AssistId, AssistKind,
+};
+
+// Assist: merge_imports
+//
+// Merges two imports with a common prefix.
+//
+// ```
+// use std::<|>fmt::Formatter;
+// use std::io;
+// ```
+// ->
+// ```
+// use std::{fmt::Formatter, io};
+// ```
+pub(crate) fn merge_imports(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let tree: ast::UseTree = ctx.find_node_at_offset()?;
+    let mut rewriter = SyntaxRewriter::default();
+    let mut offset = ctx.offset();
+
+    if let Some(use_item) = tree.syntax().parent().and_then(ast::Use::cast) {
+        let (merged, to_delete) = next_prev()
+            .filter_map(|dir| neighbor(&use_item, dir))
+            .filter_map(|it| Some((it.clone(), it.use_tree()?)))
+            .find_map(|(use_item, use_tree)| {
+                Some((try_merge_trees(&tree, &use_tree)?, use_item))
+            })?;
+
+        rewriter.replace_ast(&tree, &merged);
+        rewriter += to_delete.remove();
+
+        if to_delete.syntax().text_range().end() < offset {
+            offset -= to_delete.syntax().text_range().len();
+        }
+    } else {
+        let (merged, to_delete) = next_prev()
+            .filter_map(|dir| neighbor(&tree, dir))
+            .find_map(|use_tree| Some((try_merge_trees(&tree, &use_tree)?, use_tree.clone())))?;
+
+        rewriter.replace_ast(&tree, &merged);
+        rewriter += to_delete.remove();
+
+        if to_delete.syntax().text_range().end() < offset {
+            offset -= to_delete.syntax().text_range().len();
+        }
+    };
+
+    let target = tree.syntax().text_range();
+    acc.add(
+        AssistId("merge_imports", AssistKind::RefactorRewrite),
+        "Merge imports",
+        target,
+        |builder| {
+            builder.rewrite(rewriter);
+        },
+    )
+}
+
+fn try_merge_trees(old: &ast::UseTree, new: &ast::UseTree) -> Option<ast::UseTree> {
+    let lhs_path = old.path()?;
+    let rhs_path = new.path()?;
+
+    let (lhs_prefix, rhs_prefix) = common_prefix(&lhs_path, &rhs_path)?;
+
+    let lhs = old.split_prefix(&lhs_prefix);
+    let rhs = new.split_prefix(&rhs_prefix);
+
+    let should_insert_comma = lhs
+        .use_tree_list()?
+        .r_curly_token()
+        .and_then(|it| skip_trivia_token(it.prev_token()?, Direction::Prev))
+        .map(|it| it.kind() != T![,])
+        .unwrap_or(true);
+
+    let mut to_insert: Vec<SyntaxElement> = Vec::new();
+    if should_insert_comma {
+        to_insert.push(make::token(T![,]).into());
+        to_insert.push(make::tokens::single_space().into());
+    }
+    to_insert.extend(
+        rhs.use_tree_list()?
+            .syntax()
+            .children_with_tokens()
+            .filter(|it| it.kind() != T!['{'] && it.kind() != T!['}']),
+    );
+    let use_tree_list = lhs.use_tree_list()?;
+    let pos = InsertPosition::Before(use_tree_list.r_curly_token()?.into());
+    let use_tree_list = use_tree_list.insert_children(pos, to_insert);
+    Some(lhs.with_use_tree_list(use_tree_list))
+}
+
+fn common_prefix(lhs: &ast::Path, rhs: &ast::Path) -> Option<(ast::Path, ast::Path)> {
+    let mut res = None;
+    let mut lhs_curr = first_path(&lhs);
+    let mut rhs_curr = first_path(&rhs);
+    loop {
+        match (lhs_curr.segment(), rhs_curr.segment()) {
+            (Some(lhs), Some(rhs)) if lhs.syntax().text() == rhs.syntax().text() => (),
+            _ => break,
+        }
+        res = Some((lhs_curr.clone(), rhs_curr.clone()));
+
+        match (lhs_curr.parent_path(), rhs_curr.parent_path()) {
+            (Some(lhs), Some(rhs)) => {
+                lhs_curr = lhs;
+                rhs_curr = rhs;
+            }
+            _ => break,
+        }
+    }
+
+    res
+}
+
+fn first_path(path: &ast::Path) -> ast::Path {
+    successors(Some(path.clone()), |it| it.qualifier()).last().unwrap()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_merge_first() {
+        check_assist(
+            merge_imports,
+            r"
+use std::fmt<|>::Debug;
+use std::fmt::Display;
+",
+            r"
+use std::fmt::{Debug, Display};
+",
+        )
+    }
+
+    #[test]
+    fn test_merge_second() {
+        check_assist(
+            merge_imports,
+            r"
+use std::fmt::Debug;
+use std::fmt<|>::Display;
+",
+            r"
+use std::fmt::{Display, Debug};
+",
+        );
+    }
+
+    #[test]
+    fn merge_self1() {
+        check_assist(
+            merge_imports,
+            r"
+use std::fmt<|>;
+use std::fmt::Display;
+",
+            r"
+use std::fmt::{self, Display};
+",
+        );
+    }
+
+    #[test]
+    fn merge_self2() {
+        check_assist(
+            merge_imports,
+            r"
+use std::{fmt, <|>fmt::Display};
+",
+            r"
+use std::{fmt::{Display, self}};
+",
+        );
+    }
+
+    #[test]
+    fn test_merge_nested() {
+        check_assist(
+            merge_imports,
+            r"
+use std::{fmt<|>::Debug, fmt::Display};
+",
+            r"
+use std::{fmt::{Debug, Display}};
+",
+        );
+        check_assist(
+            merge_imports,
+            r"
+use std::{fmt::Debug, fmt<|>::Display};
+",
+            r"
+use std::{fmt::{Display, Debug}};
+",
+        );
+    }
+
+    #[test]
+    fn test_merge_single_wildcard_diff_prefixes() {
+        check_assist(
+            merge_imports,
+            r"
+use std<|>::cell::*;
+use std::str;
+",
+            r"
+use std::{cell::*, str};
+",
+        )
+    }
+
+    #[test]
+    fn test_merge_both_wildcard_diff_prefixes() {
+        check_assist(
+            merge_imports,
+            r"
+use std<|>::cell::*;
+use std::str::*;
+",
+            r"
+use std::{cell::*, str::*};
+",
+        )
+    }
+
+    #[test]
+    fn removes_just_enough_whitespace() {
+        check_assist(
+            merge_imports,
+            r"
+use foo<|>::bar;
+use foo::baz;
+
+/// Doc comment
+",
+            r"
+use foo::{bar, baz};
+
+/// Doc comment
+",
+        );
+    }
+
+    #[test]
+    fn works_with_trailing_comma() {
+        check_assist(
+            merge_imports,
+            r"
+use {
+    foo<|>::bar,
+    foo::baz,
+};
+",
+            r"
+use {
+    foo::{bar, baz},
+};
+",
+        );
+        check_assist(
+            merge_imports,
+            r"
+use {
+    foo::baz,
+    foo<|>::bar,
+};
+",
+            r"
+use {
+    foo::{bar, baz},
+};
+",
+        );
+    }
+
+    #[test]
+    fn test_double_comma() {
+        check_assist(
+            merge_imports,
+            r"
+use foo::bar::baz;
+use foo::<|>{
+    FooBar,
+};
+",
+            r"
+use foo::{
+    FooBar,
+bar::baz};
+",
+        )
+    }
+
+    #[test]
+    fn test_empty_use() {
+        check_assist_not_applicable(
+            merge_imports,
+            r"
+use std::<|>
+fn main() {}",
+        );
+    }
+}

crates/assists/src/handlers/merge_match_arms.rs

@@ -0,0 +1,248 @@
+use std::iter::successors;
+
+use syntax::{
+    algo::neighbor,
+    ast::{self, AstNode},
+    Direction,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists, TextRange};
+
+// Assist: merge_match_arms
+//
+// Merges identical match arms.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         <|>Action::Move(..) => foo(),
+//         Action::Stop => foo(),
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move(..) | Action::Stop => foo(),
+//     }
+// }
+// ```
+pub(crate) fn merge_match_arms(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let current_arm = ctx.find_node_at_offset::<ast::MatchArm>()?;
+    // Don't try to handle arms with guards for now - can add support for this later
+    if current_arm.guard().is_some() {
+        return None;
+    }
+    let current_expr = current_arm.expr()?;
+    let current_text_range = current_arm.syntax().text_range();
+
+    // We check if the following match arms match this one. We could, but don't,
+    // compare to the previous match arm as well.
+    let arms_to_merge = successors(Some(current_arm), |it| neighbor(it, Direction::Next))
+        .take_while(|arm| {
+            if arm.guard().is_some() {
+                return false;
+            }
+            match arm.expr() {
+                Some(expr) => expr.syntax().text() == current_expr.syntax().text(),
+                None => false,
+            }
+        })
+        .collect::<Vec<_>>();
+
+    if arms_to_merge.len() <= 1 {
+        return None;
+    }
+
+    acc.add(
+        AssistId("merge_match_arms", AssistKind::RefactorRewrite),
+        "Merge match arms",
+        current_text_range,
+        |edit| {
+            let pats = if arms_to_merge.iter().any(contains_placeholder) {
+                "_".into()
+            } else {
+                arms_to_merge
+                    .iter()
+                    .filter_map(ast::MatchArm::pat)
+                    .map(|x| x.syntax().to_string())
+                    .collect::<Vec<String>>()
+                    .join(" | ")
+            };
+
+            let arm = format!("{} => {}", pats, current_expr.syntax().text());
+
+            let start = arms_to_merge.first().unwrap().syntax().text_range().start();
+            let end = arms_to_merge.last().unwrap().syntax().text_range().end();
+
+            edit.replace(TextRange::new(start, end), arm);
+        },
+    )
+}
+
+fn contains_placeholder(a: &ast::MatchArm) -> bool {
+    matches!(a.pat(), Some(ast::Pat::WildcardPat(..)))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn merge_match_arms_single_patterns() {
+        check_assist(
+            merge_match_arms,
+            r#"
+            #[derive(Debug)]
+            enum X { A, B, C }
+
+            fn main() {
+                let x = X::A;
+                let y = match x {
+                    X::A => { 1i32<|> }
+                    X::B => { 1i32 }
+                    X::C => { 2i32 }
+                }
+            }
+            "#,
+            r#"
+            #[derive(Debug)]
+            enum X { A, B, C }
+
+            fn main() {
+                let x = X::A;
+                let y = match x {
+                    X::A | X::B => { 1i32 }
+                    X::C => { 2i32 }
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn merge_match_arms_multiple_patterns() {
+        check_assist(
+            merge_match_arms,
+            r#"
+            #[derive(Debug)]
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                let x = X::A;
+                let y = match x {
+                    X::A | X::B => {<|> 1i32 },
+                    X::C | X::D => { 1i32 },
+                    X::E => { 2i32 },
+                }
+            }
+            "#,
+            r#"
+            #[derive(Debug)]
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                let x = X::A;
+                let y = match x {
+                    X::A | X::B | X::C | X::D => { 1i32 },
+                    X::E => { 2i32 },
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn merge_match_arms_placeholder_pattern() {
+        check_assist(
+            merge_match_arms,
+            r#"
+            #[derive(Debug)]
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                let x = X::A;
+                let y = match x {
+                    X::A => { 1i32 },
+                    X::B => { 2i<|>32 },
+                    _ => { 2i32 }
+                }
+            }
+            "#,
+            r#"
+            #[derive(Debug)]
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                let x = X::A;
+                let y = match x {
+                    X::A => { 1i32 },
+                    _ => { 2i32 }
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn merges_all_subsequent_arms() {
+        check_assist(
+            merge_match_arms,
+            r#"
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                match X::A {
+                    X::A<|> => 92,
+                    X::B => 92,
+                    X::C => 92,
+                    X::D => 62,
+                    _ => panic!(),
+                }
+            }
+            "#,
+            r#"
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                match X::A {
+                    X::A | X::B | X::C => 92,
+                    X::D => 62,
+                    _ => panic!(),
+                }
+            }
+            "#,
+        )
+    }
+
+    #[test]
+    fn merge_match_arms_rejects_guards() {
+        check_assist_not_applicable(
+            merge_match_arms,
+            r#"
+            #[derive(Debug)]
+            enum X {
+                A(i32),
+                B,
+                C
+            }
+
+            fn main() {
+                let x = X::A;
+                let y = match x {
+                    X::A(a) if a > 5 => { <|>1i32 },
+                    X::B => { 1i32 },
+                    X::C => { 2i32 }
+                }
+            }
+            "#,
+        );
+    }
+}

crates/assists/src/handlers/move_bounds.rs

@@ -0,0 +1,152 @@
+use syntax::{
+    ast::{self, edit::AstNodeEdit, make, AstNode, NameOwner, TypeBoundsOwner},
+    match_ast,
+    SyntaxKind::*,
+    T,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: move_bounds_to_where_clause
+//
+// Moves inline type bounds to a where clause.
+//
+// ```
+// fn apply<T, U, <|>F: FnOnce(T) -> U>(f: F, x: T) -> U {
+//     f(x)
+// }
+// ```
+// ->
+// ```
+// fn apply<T, U, F>(f: F, x: T) -> U where F: FnOnce(T) -> U {
+//     f(x)
+// }
+// ```
+pub(crate) fn move_bounds_to_where_clause(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let type_param_list = ctx.find_node_at_offset::<ast::GenericParamList>()?;
+
+    let mut type_params = type_param_list.type_params();
+    if type_params.all(|p| p.type_bound_list().is_none()) {
+        return None;
+    }
+
+    let parent = type_param_list.syntax().parent()?;
+    if parent.children_with_tokens().any(|it| it.kind() == WHERE_CLAUSE) {
+        return None;
+    }
+
+    let anchor = match_ast! {
+        match parent {
+            ast::Fn(it) => it.body()?.syntax().clone().into(),
+            ast::Trait(it) => it.assoc_item_list()?.syntax().clone().into(),
+            ast::Impl(it) => it.assoc_item_list()?.syntax().clone().into(),
+            ast::Enum(it) => it.variant_list()?.syntax().clone().into(),
+            ast::Struct(it) => {
+                it.syntax().children_with_tokens()
+                    .find(|it| it.kind() == RECORD_FIELD_LIST || it.kind() == T![;])?
+            },
+            _ => return None
+        }
+    };
+
+    let target = type_param_list.syntax().text_range();
+    acc.add(
+        AssistId("move_bounds_to_where_clause", AssistKind::RefactorRewrite),
+        "Move to where clause",
+        target,
+        |edit| {
+            let new_params = type_param_list
+                .type_params()
+                .filter(|it| it.type_bound_list().is_some())
+                .map(|type_param| {
+                    let without_bounds = type_param.remove_bounds();
+                    (type_param, without_bounds)
+                });
+
+            let new_type_param_list = type_param_list.replace_descendants(new_params);
+            edit.replace_ast(type_param_list.clone(), new_type_param_list);
+
+            let where_clause = {
+                let predicates = type_param_list.type_params().filter_map(build_predicate);
+                make::where_clause(predicates)
+            };
+
+            let to_insert = match anchor.prev_sibling_or_token() {
+                Some(ref elem) if elem.kind() == WHITESPACE => {
+                    format!("{} ", where_clause.syntax())
+                }
+                _ => format!(" {}", where_clause.syntax()),
+            };
+            edit.insert(anchor.text_range().start(), to_insert);
+        },
+    )
+}
+
+fn build_predicate(param: ast::TypeParam) -> Option<ast::WherePred> {
+    let path = {
+        let name_ref = make::name_ref(&param.name()?.syntax().to_string());
+        let segment = make::path_segment(name_ref);
+        make::path_unqualified(segment)
+    };
+    let predicate = make::where_pred(path, param.type_bound_list()?.bounds());
+    Some(predicate)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::check_assist;
+
+    #[test]
+    fn move_bounds_to_where_clause_fn() {
+        check_assist(
+            move_bounds_to_where_clause,
+            r#"
+            fn foo<T: u32, <|>F: FnOnce(T) -> T>() {}
+            "#,
+            r#"
+            fn foo<T, F>() where T: u32, F: FnOnce(T) -> T {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_bounds_to_where_clause_impl() {
+        check_assist(
+            move_bounds_to_where_clause,
+            r#"
+            impl<U: u32, <|>T> A<U, T> {}
+            "#,
+            r#"
+            impl<U, T> A<U, T> where U: u32 {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_bounds_to_where_clause_struct() {
+        check_assist(
+            move_bounds_to_where_clause,
+            r#"
+            struct A<<|>T: Iterator<Item = u32>> {}
+            "#,
+            r#"
+            struct A<T> where T: Iterator<Item = u32> {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_bounds_to_where_clause_tuple_struct() {
+        check_assist(
+            move_bounds_to_where_clause,
+            r#"
+            struct Pair<<|>T: u32>(T, T);
+            "#,
+            r#"
+            struct Pair<T>(T, T) where T: u32;
+            "#,
+        );
+    }
+}

crates/assists/src/handlers/move_guard.rs

@@ -0,0 +1,293 @@
+use syntax::{
+    ast::{edit::AstNodeEdit, make, AstNode, IfExpr, MatchArm},
+    SyntaxKind::WHITESPACE,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: move_guard_to_arm_body
+//
+// Moves match guard into match arm body.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } <|>if distance > 10 => foo(),
+//         _ => (),
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } => if distance > 10 {
+//             foo()
+//         },
+//         _ => (),
+//     }
+// }
+// ```
+pub(crate) fn move_guard_to_arm_body(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let match_arm = ctx.find_node_at_offset::<MatchArm>()?;
+    let guard = match_arm.guard()?;
+    let space_before_guard = guard.syntax().prev_sibling_or_token();
+
+    let guard_condition = guard.expr()?;
+    let arm_expr = match_arm.expr()?;
+    let if_expr = make::expr_if(
+        make::condition(guard_condition, None),
+        make::block_expr(None, Some(arm_expr.clone())),
+    )
+    .indent(arm_expr.indent_level());
+
+    let target = guard.syntax().text_range();
+    acc.add(
+        AssistId("move_guard_to_arm_body", AssistKind::RefactorRewrite),
+        "Move guard to arm body",
+        target,
+        |edit| {
+            match space_before_guard {
+                Some(element) if element.kind() == WHITESPACE => {
+                    edit.delete(element.text_range());
+                }
+                _ => (),
+            };
+
+            edit.delete(guard.syntax().text_range());
+            edit.replace_ast(arm_expr, if_expr);
+        },
+    )
+}
+
+// Assist: move_arm_cond_to_match_guard
+//
+// Moves if expression from match arm body into a guard.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } => <|>if distance > 10 { foo() },
+//         _ => (),
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } if distance > 10 => foo(),
+//         _ => (),
+//     }
+// }
+// ```
+pub(crate) fn move_arm_cond_to_match_guard(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let match_arm: MatchArm = ctx.find_node_at_offset::<MatchArm>()?;
+    let match_pat = match_arm.pat()?;
+
+    let arm_body = match_arm.expr()?;
+    let if_expr: IfExpr = IfExpr::cast(arm_body.syntax().clone())?;
+    let cond = if_expr.condition()?;
+    let then_block = if_expr.then_branch()?;
+
+    // Not support if with else branch
+    if if_expr.else_branch().is_some() {
+        return None;
+    }
+    // Not support moving if let to arm guard
+    if cond.pat().is_some() {
+        return None;
+    }
+
+    let buf = format!(" if {}", cond.syntax().text());
+
+    let target = if_expr.syntax().text_range();
+    acc.add(
+        AssistId("move_arm_cond_to_match_guard", AssistKind::RefactorRewrite),
+        "Move condition to match guard",
+        target,
+        |edit| {
+            let then_only_expr = then_block.statements().next().is_none();
+
+            match &then_block.expr() {
+                Some(then_expr) if then_only_expr => {
+                    edit.replace(if_expr.syntax().text_range(), then_expr.syntax().text())
+                }
+                _ => edit.replace(if_expr.syntax().text_range(), then_block.syntax().text()),
+            }
+
+            edit.insert(match_pat.syntax().text_range().end(), buf);
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    #[test]
+    fn move_guard_to_arm_body_target() {
+        check_assist_target(
+            move_guard_to_arm_body,
+            r#"
+fn main() {
+    match 92 {
+        x <|>if x > 10 => false,
+        _ => true
+    }
+}
+"#,
+            r#"if x > 10"#,
+        );
+    }
+
+    #[test]
+    fn move_guard_to_arm_body_works() {
+        check_assist(
+            move_guard_to_arm_body,
+            r#"
+fn main() {
+    match 92 {
+        x <|>if x > 10 => false,
+        _ => true
+    }
+}
+"#,
+            r#"
+fn main() {
+    match 92 {
+        x => if x > 10 {
+            false
+        },
+        _ => true
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn move_guard_to_arm_body_works_complex_match() {
+        check_assist(
+            move_guard_to_arm_body,
+            r#"
+fn main() {
+    match 92 {
+        <|>x @ 4 | x @ 5    if x > 5 => true,
+        _ => false
+    }
+}
+"#,
+            r#"
+fn main() {
+    match 92 {
+        x @ 4 | x @ 5 => if x > 5 {
+            true
+        },
+        _ => false
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn move_arm_cond_to_match_guard_works() {
+        check_assist(
+            move_arm_cond_to_match_guard,
+            r#"
+fn main() {
+    match 92 {
+        x => if x > 10 { <|>false },
+        _ => true
+    }
+}
+"#,
+            r#"
+fn main() {
+    match 92 {
+        x if x > 10 => false,
+        _ => true
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn move_arm_cond_to_match_guard_if_let_not_works() {
+        check_assist_not_applicable(
+            move_arm_cond_to_match_guard,
+            r#"
+fn main() {
+    match 92 {
+        x => if let 62 = x { <|>false },
+        _ => true
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn move_arm_cond_to_match_guard_if_empty_body_works() {
+        check_assist(
+            move_arm_cond_to_match_guard,
+            r#"
+fn main() {
+    match 92 {
+        x => if x > 10 { <|> },
+        _ => true
+    }
+}
+"#,
+            r#"
+fn main() {
+    match 92 {
+        x if x > 10 => {  },
+        _ => true
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn move_arm_cond_to_match_guard_if_multiline_body_works() {
+        check_assist(
+            move_arm_cond_to_match_guard,
+            r#"
+fn main() {
+    match 92 {
+        x => if x > 10 {
+            92;<|>
+            false
+        },
+        _ => true
+    }
+}
+"#,
+            r#"
+fn main() {
+    match 92 {
+        x if x > 10 => {
+            92;
+            false
+        },
+        _ => true
+    }
+}
+"#,
+        );
+    }
+}

crates/assists/src/handlers/raw_string.rs

@@ -0,0 +1,504 @@
+use std::borrow::Cow;
+
+use syntax::{
+    ast::{self, HasQuotes, HasStringValue},
+    AstToken,
+    SyntaxKind::{RAW_STRING, STRING},
+    TextRange, TextSize,
+};
+use test_utils::mark;
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: make_raw_string
+//
+// Adds `r#` to a plain string literal.
+//
+// ```
+// fn main() {
+//     "Hello,<|> World!";
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     r#"Hello, World!"#;
+// }
+// ```
+pub(crate) fn make_raw_string(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let token = ctx.find_token_at_offset(STRING).and_then(ast::String::cast)?;
+    let value = token.value()?;
+    let target = token.syntax().text_range();
+    acc.add(
+        AssistId("make_raw_string", AssistKind::RefactorRewrite),
+        "Rewrite as raw string",
+        target,
+        |edit| {
+            let hashes = "#".repeat(required_hashes(&value).max(1));
+            if matches!(value, Cow::Borrowed(_)) {
+                // Avoid replacing the whole string to better position the cursor.
+                edit.insert(token.syntax().text_range().start(), format!("r{}", hashes));
+                edit.insert(token.syntax().text_range().end(), format!("{}", hashes));
+            } else {
+                edit.replace(
+                    token.syntax().text_range(),
+                    format!("r{}\"{}\"{}", hashes, value, hashes),
+                );
+            }
+        },
+    )
+}
+
+// Assist: make_usual_string
+//
+// Turns a raw string into a plain string.
+//
+// ```
+// fn main() {
+//     r#"Hello,<|> "World!""#;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     "Hello, \"World!\"";
+// }
+// ```
+pub(crate) fn make_usual_string(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let token = ctx.find_token_at_offset(RAW_STRING).and_then(ast::RawString::cast)?;
+    let value = token.value()?;
+    let target = token.syntax().text_range();
+    acc.add(
+        AssistId("make_usual_string", AssistKind::RefactorRewrite),
+        "Rewrite as regular string",
+        target,
+        |edit| {
+            // parse inside string to escape `"`
+            let escaped = value.escape_default().to_string();
+            if let Some(offsets) = token.quote_offsets() {
+                if token.text()[offsets.contents - token.syntax().text_range().start()] == escaped {
+                    edit.replace(offsets.quotes.0, "\"");
+                    edit.replace(offsets.quotes.1, "\"");
+                    return;
+                }
+            }
+
+            edit.replace(token.syntax().text_range(), format!("\"{}\"", escaped));
+        },
+    )
+}
+
+// Assist: add_hash
+//
+// Adds a hash to a raw string literal.
+//
+// ```
+// fn main() {
+//     r#"Hello,<|> World!"#;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     r##"Hello, World!"##;
+// }
+// ```
+pub(crate) fn add_hash(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let token = ctx.find_token_at_offset(RAW_STRING)?;
+    let target = token.text_range();
+    acc.add(AssistId("add_hash", AssistKind::Refactor), "Add #", target, |edit| {
+        edit.insert(token.text_range().start() + TextSize::of('r'), "#");
+        edit.insert(token.text_range().end(), "#");
+    })
+}
+
+// Assist: remove_hash
+//
+// Removes a hash from a raw string literal.
+//
+// ```
+// fn main() {
+//     r#"Hello,<|> World!"#;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     r"Hello, World!";
+// }
+// ```
+pub(crate) fn remove_hash(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let token = ctx.find_token_at_offset(RAW_STRING).and_then(ast::RawString::cast)?;
+
+    let text = token.text().as_str();
+    if !text.starts_with("r#") && text.ends_with('#') {
+        return None;
+    }
+
+    let existing_hashes = text.chars().skip(1).take_while(|&it| it == '#').count();
+
+    let text_range = token.syntax().text_range();
+    let internal_text = &text[token.text_range_between_quotes()? - text_range.start()];
+
+    if existing_hashes == required_hashes(internal_text) {
+        mark::hit!(cant_remove_required_hash);
+        return None;
+    }
+
+    acc.add(AssistId("remove_hash", AssistKind::RefactorRewrite), "Remove #", text_range, |edit| {
+        edit.delete(TextRange::at(text_range.start() + TextSize::of('r'), TextSize::of('#')));
+        edit.delete(TextRange::new(text_range.end() - TextSize::of('#'), text_range.end()));
+    })
+}
+
+fn required_hashes(s: &str) -> usize {
+    let mut res = 0usize;
+    for idx in s.match_indices('"').map(|(i, _)| i) {
+        let (_, sub) = s.split_at(idx + 1);
+        let n_hashes = sub.chars().take_while(|c| *c == '#').count();
+        res = res.max(n_hashes + 1)
+    }
+    res
+}
+
+#[test]
+fn test_required_hashes() {
+    assert_eq!(0, required_hashes("abc"));
+    assert_eq!(0, required_hashes("###"));
+    assert_eq!(1, required_hashes("\""));
+    assert_eq!(2, required_hashes("\"#abc"));
+    assert_eq!(0, required_hashes("#abc"));
+    assert_eq!(3, required_hashes("#ab\"##c"));
+    assert_eq!(5, required_hashes("#ab\"##\"####c"));
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::mark;
+
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn make_raw_string_target() {
+        check_assist_target(
+            make_raw_string,
+            r#"
+            fn f() {
+                let s = <|>"random\nstring";
+            }
+            "#,
+            r#""random\nstring""#,
+        );
+    }
+
+    #[test]
+    fn make_raw_string_works() {
+        check_assist(
+            make_raw_string,
+            r#"
+fn f() {
+    let s = <|>"random\nstring";
+}
+"#,
+            r##"
+fn f() {
+    let s = r#"random
+string"#;
+}
+"##,
+        )
+    }
+
+    #[test]
+    fn make_raw_string_works_inside_macros() {
+        check_assist(
+            make_raw_string,
+            r#"
+            fn f() {
+                format!(<|>"x = {}", 92)
+            }
+            "#,
+            r##"
+            fn f() {
+                format!(r#"x = {}"#, 92)
+            }
+            "##,
+        )
+    }
+
+    #[test]
+    fn make_raw_string_hashes_inside_works() {
+        check_assist(
+            make_raw_string,
+            r###"
+fn f() {
+    let s = <|>"#random##\nstring";
+}
+"###,
+            r####"
+fn f() {
+    let s = r#"#random##
+string"#;
+}
+"####,
+        )
+    }
+
+    #[test]
+    fn make_raw_string_closing_hashes_inside_works() {
+        check_assist(
+            make_raw_string,
+            r###"
+fn f() {
+    let s = <|>"#random\"##\nstring";
+}
+"###,
+            r####"
+fn f() {
+    let s = r###"#random"##
+string"###;
+}
+"####,
+        )
+    }
+
+    #[test]
+    fn make_raw_string_nothing_to_unescape_works() {
+        check_assist(
+            make_raw_string,
+            r#"
+            fn f() {
+                let s = <|>"random string";
+            }
+            "#,
+            r##"
+            fn f() {
+                let s = r#"random string"#;
+            }
+            "##,
+        )
+    }
+
+    #[test]
+    fn make_raw_string_not_works_on_partial_string() {
+        check_assist_not_applicable(
+            make_raw_string,
+            r#"
+            fn f() {
+                let s = "foo<|>
+            }
+            "#,
+        )
+    }
+
+    #[test]
+    fn make_usual_string_not_works_on_partial_string() {
+        check_assist_not_applicable(
+            make_usual_string,
+            r#"
+            fn main() {
+                let s = r#"bar<|>
+            }
+            "#,
+        )
+    }
+
+    #[test]
+    fn add_hash_target() {
+        check_assist_target(
+            add_hash,
+            r#"
+            fn f() {
+                let s = <|>r"random string";
+            }
+            "#,
+            r#"r"random string""#,
+        );
+    }
+
+    #[test]
+    fn add_hash_works() {
+        check_assist(
+            add_hash,
+            r#"
+            fn f() {
+                let s = <|>r"random string";
+            }
+            "#,
+            r##"
+            fn f() {
+                let s = r#"random string"#;
+            }
+            "##,
+        )
+    }
+
+    #[test]
+    fn add_more_hash_works() {
+        check_assist(
+            add_hash,
+            r##"
+            fn f() {
+                let s = <|>r#"random"string"#;
+            }
+            "##,
+            r###"
+            fn f() {
+                let s = r##"random"string"##;
+            }
+            "###,
+        )
+    }
+
+    #[test]
+    fn add_hash_not_works() {
+        check_assist_not_applicable(
+            add_hash,
+            r#"
+            fn f() {
+                let s = <|>"random string";
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn remove_hash_target() {
+        check_assist_target(
+            remove_hash,
+            r##"
+            fn f() {
+                let s = <|>r#"random string"#;
+            }
+            "##,
+            r##"r#"random string"#"##,
+        );
+    }
+
+    #[test]
+    fn remove_hash_works() {
+        check_assist(
+            remove_hash,
+            r##"fn f() { let s = <|>r#"random string"#; }"##,
+            r#"fn f() { let s = r"random string"; }"#,
+        )
+    }
+
+    #[test]
+    fn cant_remove_required_hash() {
+        mark::check!(cant_remove_required_hash);
+        check_assist_not_applicable(
+            remove_hash,
+            r##"
+            fn f() {
+                let s = <|>r#"random"str"ing"#;
+            }
+            "##,
+        )
+    }
+
+    #[test]
+    fn remove_more_hash_works() {
+        check_assist(
+            remove_hash,
+            r###"
+            fn f() {
+                let s = <|>r##"random string"##;
+            }
+            "###,
+            r##"
+            fn f() {
+                let s = r#"random string"#;
+            }
+            "##,
+        )
+    }
+
+    #[test]
+    fn remove_hash_doesnt_work() {
+        check_assist_not_applicable(remove_hash, r#"fn f() { let s = <|>"random string"; }"#);
+    }
+
+    #[test]
+    fn remove_hash_no_hash_doesnt_work() {
+        check_assist_not_applicable(remove_hash, r#"fn f() { let s = <|>r"random string"; }"#);
+    }
+
+    #[test]
+    fn make_usual_string_target() {
+        check_assist_target(
+            make_usual_string,
+            r##"
+            fn f() {
+                let s = <|>r#"random string"#;
+            }
+            "##,
+            r##"r#"random string"#"##,
+        );
+    }
+
+    #[test]
+    fn make_usual_string_works() {
+        check_assist(
+            make_usual_string,
+            r##"
+            fn f() {
+                let s = <|>r#"random string"#;
+            }
+            "##,
+            r#"
+            fn f() {
+                let s = "random string";
+            }
+            "#,
+        )
+    }
+
+    #[test]
+    fn make_usual_string_with_quote_works() {
+        check_assist(
+            make_usual_string,
+            r##"
+            fn f() {
+                let s = <|>r#"random"str"ing"#;
+            }
+            "##,
+            r#"
+            fn f() {
+                let s = "random\"str\"ing";
+            }
+            "#,
+        )
+    }
+
+    #[test]
+    fn make_usual_string_more_hash_works() {
+        check_assist(
+            make_usual_string,
+            r###"
+            fn f() {
+                let s = <|>r##"random string"##;
+            }
+            "###,
+            r##"
+            fn f() {
+                let s = "random string";
+            }
+            "##,
+        )
+    }
+
+    #[test]
+    fn make_usual_string_not_works() {
+        check_assist_not_applicable(
+            make_usual_string,
+            r#"
+            fn f() {
+                let s = <|>"random string";
+            }
+            "#,
+        );
+    }
+}

crates/assists/src/handlers/remove_dbg.rs

@@ -0,0 +1,206 @@
+use syntax::{
+    ast::{self, AstNode},
+    TextRange, TextSize, T,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: remove_dbg
+//
+// Removes `dbg!()` macro call.
+//
+// ```
+// fn main() {
+//     <|>dbg!(92);
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     92;
+// }
+// ```
+pub(crate) fn remove_dbg(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let macro_call = ctx.find_node_at_offset::<ast::MacroCall>()?;
+
+    if !is_valid_macrocall(&macro_call, "dbg")? {
+        return None;
+    }
+
+    let is_leaf = macro_call.syntax().next_sibling().is_none();
+
+    let macro_end = if macro_call.semicolon_token().is_some() {
+        macro_call.syntax().text_range().end() - TextSize::of(';')
+    } else {
+        macro_call.syntax().text_range().end()
+    };
+
+    // macro_range determines what will be deleted and replaced with macro_content
+    let macro_range = TextRange::new(macro_call.syntax().text_range().start(), macro_end);
+    let paste_instead_of_dbg = {
+        let text = macro_call.token_tree()?.syntax().text();
+
+        // leafiness determines if we should include the parenthesis or not
+        let slice_index: TextRange = if is_leaf {
+            // leaf means - we can extract the contents of the dbg! in text
+            TextRange::new(TextSize::of('('), text.len() - TextSize::of(')'))
+        } else {
+            // not leaf - means we should keep the parens
+            TextRange::up_to(text.len())
+        };
+        text.slice(slice_index).to_string()
+    };
+
+    let target = macro_call.syntax().text_range();
+    acc.add(AssistId("remove_dbg", AssistKind::Refactor), "Remove dbg!()", target, |builder| {
+        builder.replace(macro_range, paste_instead_of_dbg);
+    })
+}
+
+/// Verifies that the given macro_call actually matches the given name
+/// and contains proper ending tokens
+fn is_valid_macrocall(macro_call: &ast::MacroCall, macro_name: &str) -> Option<bool> {
+    let path = macro_call.path()?;
+    let name_ref = path.segment()?.name_ref()?;
+
+    // Make sure it is actually a dbg-macro call, dbg followed by !
+    let excl = path.syntax().next_sibling_or_token()?;
+
+    if name_ref.text() != macro_name || excl.kind() != T![!] {
+        return None;
+    }
+
+    let node = macro_call.token_tree()?.syntax().clone();
+    let first_child = node.first_child_or_token()?;
+    let last_child = node.last_child_or_token()?;
+
+    match (first_child.kind(), last_child.kind()) {
+        (T!['('], T![')']) | (T!['['], T![']']) | (T!['{'], T!['}']) => Some(true),
+        _ => Some(false),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn test_remove_dbg() {
+        check_assist(remove_dbg, "<|>dbg!(1 + 1)", "1 + 1");
+
+        check_assist(remove_dbg, "dbg!<|>((1 + 1))", "(1 + 1)");
+
+        check_assist(remove_dbg, "dbg!(1 <|>+ 1)", "1 + 1");
+
+        check_assist(remove_dbg, "let _ = <|>dbg!(1 + 1)", "let _ = 1 + 1");
+
+        check_assist(
+            remove_dbg,
+            "
+fn foo(n: usize) {
+    if let Some(_) = dbg!(n.<|>checked_sub(4)) {
+        // ...
+    }
+}
+",
+            "
+fn foo(n: usize) {
+    if let Some(_) = n.checked_sub(4) {
+        // ...
+    }
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_remove_dbg_with_brackets_and_braces() {
+        check_assist(remove_dbg, "dbg![<|>1 + 1]", "1 + 1");
+        check_assist(remove_dbg, "dbg!{<|>1 + 1}", "1 + 1");
+    }
+
+    #[test]
+    fn test_remove_dbg_not_applicable() {
+        check_assist_not_applicable(remove_dbg, "<|>vec![1, 2, 3]");
+        check_assist_not_applicable(remove_dbg, "<|>dbg(5, 6, 7)");
+        check_assist_not_applicable(remove_dbg, "<|>dbg!(5, 6, 7");
+    }
+
+    #[test]
+    fn test_remove_dbg_target() {
+        check_assist_target(
+            remove_dbg,
+            "
+fn foo(n: usize) {
+    if let Some(_) = dbg!(n.<|>checked_sub(4)) {
+        // ...
+    }
+}
+",
+            "dbg!(n.checked_sub(4))",
+        );
+    }
+
+    #[test]
+    fn test_remove_dbg_keep_semicolon() {
+        // https://github.com/rust-analyzer/rust-analyzer/issues/5129#issuecomment-651399779
+        // not quite though
+        // adding a comment at the end of the line makes
+        // the ast::MacroCall to include the semicolon at the end
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(1 * 20); // needless comment"#,
+            r#"let res = 1 * 20; // needless comment"#,
+        );
+    }
+
+    #[test]
+    fn test_remove_dbg_keep_expression() {
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(a + b).foo();"#,
+            r#"let res = (a + b).foo();"#,
+        );
+    }
+
+    #[test]
+    fn test_remove_dbg_from_inside_fn() {
+        check_assist_target(
+            remove_dbg,
+            r#"
+fn square(x: u32) -> u32 {
+    x * x
+}
+
+fn main() {
+    let x = square(dbg<|>!(5 + 10));
+    println!("{}", x);
+}"#,
+            "dbg!(5 + 10)",
+        );
+
+        check_assist(
+            remove_dbg,
+            r#"
+fn square(x: u32) -> u32 {
+    x * x
+}
+
+fn main() {
+    let x = square(dbg<|>!(5 + 10));
+    println!("{}", x);
+}"#,
+            r#"
+fn square(x: u32) -> u32 {
+    x * x
+}
+
+fn main() {
+    let x = square(5 + 10);
+    println!("{}", x);
+}"#,
+        );
+    }
+}

crates/assists/src/handlers/remove_mut.rs

@@ -0,0 +1,37 @@
+use syntax::{SyntaxKind, TextRange, T};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: remove_mut
+//
+// Removes the `mut` keyword.
+//
+// ```
+// impl Walrus {
+//     fn feed(&mut<|> self, amount: u32) {}
+// }
+// ```
+// ->
+// ```
+// impl Walrus {
+//     fn feed(&self, amount: u32) {}
+// }
+// ```
+pub(crate) fn remove_mut(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let mut_token = ctx.find_token_at_offset(T![mut])?;
+    let delete_from = mut_token.text_range().start();
+    let delete_to = match mut_token.next_token() {
+        Some(it) if it.kind() == SyntaxKind::WHITESPACE => it.text_range().end(),
+        _ => mut_token.text_range().end(),
+    };
+
+    let target = mut_token.text_range();
+    acc.add(
+        AssistId("remove_mut", AssistKind::Refactor),
+        "Remove `mut` keyword",
+        target,
+        |builder| {
+            builder.delete(TextRange::new(delete_from, delete_to));
+        },
+    )
+}

crates/assists/src/handlers/remove_unused_param.rs

@@ -0,0 +1,131 @@
+use ide_db::{defs::Definition, search::Reference};
+use syntax::{
+    algo::find_node_at_range,
+    ast::{self, ArgListOwner},
+    AstNode, SyntaxNode, TextRange, T,
+};
+use test_utils::mark;
+
+use crate::{
+    assist_context::AssistBuilder, utils::next_prev, AssistContext, AssistId, AssistKind, Assists,
+};
+
+// Assist: remove_unused_param
+//
+// Removes unused function parameter.
+//
+// ```
+// fn frobnicate(x: i32<|>) {}
+//
+// fn main() {
+//     frobnicate(92);
+// }
+// ```
+// ->
+// ```
+// fn frobnicate() {}
+//
+// fn main() {
+//     frobnicate();
+// }
+// ```
+pub(crate) fn remove_unused_param(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let param: ast::Param = ctx.find_node_at_offset()?;
+    let ident_pat = match param.pat()? {
+        ast::Pat::IdentPat(it) => it,
+        _ => return None,
+    };
+    let func = param.syntax().ancestors().find_map(ast::Fn::cast)?;
+    let param_position = func.param_list()?.params().position(|it| it == param)?;
+
+    let fn_def = {
+        let func = ctx.sema.to_def(&func)?;
+        Definition::ModuleDef(func.into())
+    };
+
+    let param_def = {
+        let local = ctx.sema.to_def(&ident_pat)?;
+        Definition::Local(local)
+    };
+    if param_def.usages(&ctx.sema).at_least_one() {
+        mark::hit!(keep_used);
+        return None;
+    }
+    acc.add(
+        AssistId("remove_unused_param", AssistKind::Refactor),
+        "Remove unused parameter",
+        param.syntax().text_range(),
+        |builder| {
+            builder.delete(range_with_coma(param.syntax()));
+            for usage in fn_def.usages(&ctx.sema).all() {
+                process_usage(ctx, builder, usage, param_position);
+            }
+        },
+    )
+}
+
+fn process_usage(
+    ctx: &AssistContext,
+    builder: &mut AssistBuilder,
+    usage: Reference,
+    arg_to_remove: usize,
+) -> Option<()> {
+    let source_file = ctx.sema.parse(usage.file_range.file_id);
+    let call_expr: ast::CallExpr =
+        find_node_at_range(source_file.syntax(), usage.file_range.range)?;
+    if call_expr.expr()?.syntax().text_range() != usage.file_range.range {
+        return None;
+    }
+    let arg = call_expr.arg_list()?.args().nth(arg_to_remove)?;
+
+    builder.edit_file(usage.file_range.file_id);
+    builder.delete(range_with_coma(arg.syntax()));
+
+    Some(())
+}
+
+fn range_with_coma(node: &SyntaxNode) -> TextRange {
+    let up_to = next_prev().find_map(|dir| {
+        node.siblings_with_tokens(dir)
+            .filter_map(|it| it.into_token())
+            .find(|it| it.kind() == T![,])
+    });
+    let up_to = up_to.map_or(node.text_range(), |it| it.text_range());
+    node.text_range().cover(up_to)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn remove_unused() {
+        check_assist(
+            remove_unused_param,
+            r#"
+fn a() { foo(9, 2) }
+fn foo(x: i32, <|>y: i32) { x; }
+fn b() { foo(9, 2,) }
+"#,
+            r#"
+fn a() { foo(9) }
+fn foo(x: i32) { x; }
+fn b() { foo(9, ) }
+"#,
+        );
+    }
+
+    #[test]
+    fn keep_used() {
+        mark::check!(keep_used);
+        check_assist_not_applicable(
+            remove_unused_param,
+            r#"
+fn foo(x: i32, <|>y: i32) { y; }
+fn main() { foo(9, 2) }
+"#,
+        );
+    }
+}

crates/assists/src/handlers/reorder_fields.rs

@@ -0,0 +1,220 @@
+use itertools::Itertools;
+use rustc_hash::FxHashMap;
+
+use hir::{Adt, ModuleDef, PathResolution, Semantics, Struct};
+use ide_db::RootDatabase;
+use syntax::{algo, ast, match_ast, AstNode, SyntaxKind, SyntaxKind::*, SyntaxNode};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: reorder_fields
+//
+// Reorder the fields of record literals and record patterns in the same order as in
+// the definition.
+//
+// ```
+// struct Foo {foo: i32, bar: i32};
+// const test: Foo = <|>Foo {bar: 0, foo: 1}
+// ```
+// ->
+// ```
+// struct Foo {foo: i32, bar: i32};
+// const test: Foo = Foo {foo: 1, bar: 0}
+// ```
+//
+pub(crate) fn reorder_fields(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    reorder::<ast::RecordExpr>(acc, ctx).or_else(|| reorder::<ast::RecordPat>(acc, ctx))
+}
+
+fn reorder<R: AstNode>(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let record = ctx.find_node_at_offset::<R>()?;
+    let path = record.syntax().children().find_map(ast::Path::cast)?;
+
+    let ranks = compute_fields_ranks(&path, &ctx)?;
+
+    let fields = get_fields(&record.syntax());
+    let sorted_fields = sorted_by_rank(&fields, |node| {
+        *ranks.get(&get_field_name(node)).unwrap_or(&usize::max_value())
+    });
+
+    if sorted_fields == fields {
+        return None;
+    }
+
+    let target = record.syntax().text_range();
+    acc.add(
+        AssistId("reorder_fields", AssistKind::RefactorRewrite),
+        "Reorder record fields",
+        target,
+        |edit| {
+            for (old, new) in fields.iter().zip(&sorted_fields) {
+                algo::diff(old, new).into_text_edit(edit.text_edit_builder());
+            }
+        },
+    )
+}
+
+fn get_fields_kind(node: &SyntaxNode) -> Vec<SyntaxKind> {
+    match node.kind() {
+        RECORD_EXPR => vec![RECORD_EXPR_FIELD],
+        RECORD_PAT => vec![RECORD_PAT_FIELD, IDENT_PAT],
+        _ => vec![],
+    }
+}
+
+fn get_field_name(node: &SyntaxNode) -> String {
+    let res = match_ast! {
+        match node {
+            ast::RecordExprField(field) => field.field_name().map(|it| it.to_string()),
+            ast::RecordPatField(field) => field.field_name().map(|it| it.to_string()),
+            _ => None,
+        }
+    };
+    res.unwrap_or_default()
+}
+
+fn get_fields(record: &SyntaxNode) -> Vec<SyntaxNode> {
+    let kinds = get_fields_kind(record);
+    record.children().flat_map(|n| n.children()).filter(|n| kinds.contains(&n.kind())).collect()
+}
+
+fn sorted_by_rank(
+    fields: &[SyntaxNode],
+    get_rank: impl Fn(&SyntaxNode) -> usize,
+) -> Vec<SyntaxNode> {
+    fields.iter().cloned().sorted_by_key(get_rank).collect()
+}
+
+fn struct_definition(path: &ast::Path, sema: &Semantics<RootDatabase>) -> Option<Struct> {
+    match sema.resolve_path(path) {
+        Some(PathResolution::Def(ModuleDef::Adt(Adt::Struct(s)))) => Some(s),
+        _ => None,
+    }
+}
+
+fn compute_fields_ranks(path: &ast::Path, ctx: &AssistContext) -> Option<FxHashMap<String, usize>> {
+    Some(
+        struct_definition(path, &ctx.sema)?
+            .fields(ctx.db())
+            .iter()
+            .enumerate()
+            .map(|(idx, field)| (field.name(ctx.db()).to_string(), idx))
+            .collect(),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn not_applicable_if_sorted() {
+        check_assist_not_applicable(
+            reorder_fields,
+            r#"
+        struct Foo {
+            foo: i32,
+            bar: i32,
+        }
+
+        const test: Foo = <|>Foo { foo: 0, bar: 0 };
+        "#,
+        )
+    }
+
+    #[test]
+    fn trivial_empty_fields() {
+        check_assist_not_applicable(
+            reorder_fields,
+            r#"
+        struct Foo {};
+        const test: Foo = <|>Foo {}
+        "#,
+        )
+    }
+
+    #[test]
+    fn reorder_struct_fields() {
+        check_assist(
+            reorder_fields,
+            r#"
+        struct Foo {foo: i32, bar: i32};
+        const test: Foo = <|>Foo {bar: 0, foo: 1}
+        "#,
+            r#"
+        struct Foo {foo: i32, bar: i32};
+        const test: Foo = Foo {foo: 1, bar: 0}
+        "#,
+        )
+    }
+
+    #[test]
+    fn reorder_struct_pattern() {
+        check_assist(
+            reorder_fields,
+            r#"
+        struct Foo { foo: i64, bar: i64, baz: i64 }
+
+        fn f(f: Foo) -> {
+            match f {
+                <|>Foo { baz: 0, ref mut bar, .. } => (),
+                _ => ()
+            }
+        }
+        "#,
+            r#"
+        struct Foo { foo: i64, bar: i64, baz: i64 }
+
+        fn f(f: Foo) -> {
+            match f {
+                Foo { ref mut bar, baz: 0, .. } => (),
+                _ => ()
+            }
+        }
+        "#,
+        )
+    }
+
+    #[test]
+    fn reorder_with_extra_field() {
+        check_assist(
+            reorder_fields,
+            r#"
+            struct Foo {
+                foo: String,
+                bar: String,
+            }
+
+            impl Foo {
+                fn new() -> Foo {
+                    let foo = String::new();
+                    <|>Foo {
+                        bar: foo.clone(),
+                        extra: "Extra field",
+                        foo,
+                    }
+                }
+            }
+            "#,
+            r#"
+            struct Foo {
+                foo: String,
+                bar: String,
+            }
+
+            impl Foo {
+                fn new() -> Foo {
+                    let foo = String::new();
+                    Foo {
+                        foo,
+                        bar: foo.clone(),
+                        extra: "Extra field",
+                    }
+                }
+            }
+            "#,
+        )
+    }
+}

crates/assists/src/handlers/replace_if_let_with_match.rs

@@ -0,0 +1,257 @@
+use syntax::{
+    ast::{
+        self,
+        edit::{AstNodeEdit, IndentLevel},
+        make,
+    },
+    AstNode,
+};
+
+use crate::{
+    utils::{unwrap_trivial_block, TryEnum},
+    AssistContext, AssistId, AssistKind, Assists,
+};
+
+// Assist: replace_if_let_with_match
+//
+// Replaces `if let` with an else branch with a `match` expression.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     <|>if let Action::Move { distance } = action {
+//         foo(distance)
+//     } else {
+//         bar()
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } => foo(distance),
+//         _ => bar(),
+//     }
+// }
+// ```
+pub(crate) fn replace_if_let_with_match(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
+    let cond = if_expr.condition()?;
+    let pat = cond.pat()?;
+    let expr = cond.expr()?;
+    let then_block = if_expr.then_branch()?;
+    let else_block = match if_expr.else_branch()? {
+        ast::ElseBranch::Block(it) => it,
+        ast::ElseBranch::IfExpr(_) => return None,
+    };
+
+    let target = if_expr.syntax().text_range();
+    acc.add(
+        AssistId("replace_if_let_with_match", AssistKind::RefactorRewrite),
+        "Replace with match",
+        target,
+        move |edit| {
+            let match_expr = {
+                let then_arm = {
+                    let then_block = then_block.reset_indent().indent(IndentLevel(1));
+                    let then_expr = unwrap_trivial_block(then_block);
+                    make::match_arm(vec![pat.clone()], then_expr)
+                };
+                let else_arm = {
+                    let pattern = ctx
+                        .sema
+                        .type_of_pat(&pat)
+                        .and_then(|ty| TryEnum::from_ty(&ctx.sema, &ty))
+                        .map(|it| it.sad_pattern())
+                        .unwrap_or_else(|| make::wildcard_pat().into());
+                    let else_expr = unwrap_trivial_block(else_block);
+                    make::match_arm(vec![pattern], else_expr)
+                };
+                let match_expr =
+                    make::expr_match(expr, make::match_arm_list(vec![then_arm, else_arm]));
+                match_expr.indent(IndentLevel::from_node(if_expr.syntax()))
+            };
+
+            edit.replace_ast::<ast::Expr>(if_expr.into(), match_expr);
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_target};
+
+    #[test]
+    fn test_replace_if_let_with_match_unwraps_simple_expressions() {
+        check_assist(
+            replace_if_let_with_match,
+            r#"
+impl VariantData {
+    pub fn is_struct(&self) -> bool {
+        if <|>let VariantData::Struct(..) = *self {
+            true
+        } else {
+            false
+        }
+    }
+}           "#,
+            r#"
+impl VariantData {
+    pub fn is_struct(&self) -> bool {
+        match *self {
+            VariantData::Struct(..) => true,
+            _ => false,
+        }
+    }
+}           "#,
+        )
+    }
+
+    #[test]
+    fn test_replace_if_let_with_match_doesnt_unwrap_multiline_expressions() {
+        check_assist(
+            replace_if_let_with_match,
+            r#"
+fn foo() {
+    if <|>let VariantData::Struct(..) = a {
+        bar(
+            123
+        )
+    } else {
+        false
+    }
+}           "#,
+            r#"
+fn foo() {
+    match a {
+        VariantData::Struct(..) => {
+            bar(
+                123
+            )
+        }
+        _ => false,
+    }
+}           "#,
+        )
+    }
+
+    #[test]
+    fn replace_if_let_with_match_target() {
+        check_assist_target(
+            replace_if_let_with_match,
+            r#"
+impl VariantData {
+    pub fn is_struct(&self) -> bool {
+        if <|>let VariantData::Struct(..) = *self {
+            true
+        } else {
+            false
+        }
+    }
+}           "#,
+            "if let VariantData::Struct(..) = *self {
+            true
+        } else {
+            false
+        }",
+        );
+    }
+
+    #[test]
+    fn special_case_option() {
+        check_assist(
+            replace_if_let_with_match,
+            r#"
+enum Option<T> { Some(T), None }
+use Option::*;
+
+fn foo(x: Option<i32>) {
+    <|>if let Some(x) = x {
+        println!("{}", x)
+    } else {
+        println!("none")
+    }
+}
+           "#,
+            r#"
+enum Option<T> { Some(T), None }
+use Option::*;
+
+fn foo(x: Option<i32>) {
+    match x {
+        Some(x) => println!("{}", x),
+        None => println!("none"),
+    }
+}
+           "#,
+        );
+    }
+
+    #[test]
+    fn special_case_result() {
+        check_assist(
+            replace_if_let_with_match,
+            r#"
+enum Result<T, E> { Ok(T), Err(E) }
+use Result::*;
+
+fn foo(x: Result<i32, ()>) {
+    <|>if let Ok(x) = x {
+        println!("{}", x)
+    } else {
+        println!("none")
+    }
+}
+           "#,
+            r#"
+enum Result<T, E> { Ok(T), Err(E) }
+use Result::*;
+
+fn foo(x: Result<i32, ()>) {
+    match x {
+        Ok(x) => println!("{}", x),
+        Err(_) => println!("none"),
+    }
+}
+           "#,
+        );
+    }
+
+    #[test]
+    fn nested_indent() {
+        check_assist(
+            replace_if_let_with_match,
+            r#"
+fn main() {
+    if true {
+        <|>if let Ok(rel_path) = path.strip_prefix(root_path) {
+            let rel_path = RelativePathBuf::from_path(rel_path).ok()?;
+            Some((*id, rel_path))
+        } else {
+            None
+        }
+    }
+}
+"#,
+            r#"
+fn main() {
+    if true {
+        match path.strip_prefix(root_path) {
+            Ok(rel_path) => {
+                let rel_path = RelativePathBuf::from_path(rel_path).ok()?;
+                Some((*id, rel_path))
+            }
+            _ => None,
+        }
+    }
+}
+"#,
+        )
+    }
+}

crates/assists/src/handlers/replace_let_with_if_let.rs

@@ -0,0 +1,100 @@
+use std::iter::once;
+
+use syntax::{
+    ast::{
+        self,
+        edit::{AstNodeEdit, IndentLevel},
+        make,
+    },
+    AstNode, T,
+};
+
+use crate::{utils::TryEnum, AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: replace_let_with_if_let
+//
+// Replaces `let` with an `if-let`.
+//
+// ```
+// # enum Option<T> { Some(T), None }
+//
+// fn main(action: Action) {
+//     <|>let x = compute();
+// }
+//
+// fn compute() -> Option<i32> { None }
+// ```
+// ->
+// ```
+// # enum Option<T> { Some(T), None }
+//
+// fn main(action: Action) {
+//     if let Some(x) = compute() {
+//     }
+// }
+//
+// fn compute() -> Option<i32> { None }
+// ```
+pub(crate) fn replace_let_with_if_let(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let let_kw = ctx.find_token_at_offset(T![let])?;
+    let let_stmt = let_kw.ancestors().find_map(ast::LetStmt::cast)?;
+    let init = let_stmt.initializer()?;
+    let original_pat = let_stmt.pat()?;
+    let ty = ctx.sema.type_of_expr(&init)?;
+    let happy_variant = TryEnum::from_ty(&ctx.sema, &ty).map(|it| it.happy_case());
+
+    let target = let_kw.text_range();
+    acc.add(
+        AssistId("replace_let_with_if_let", AssistKind::RefactorRewrite),
+        "Replace with if-let",
+        target,
+        |edit| {
+            let with_placeholder: ast::Pat = match happy_variant {
+                None => make::wildcard_pat().into(),
+                Some(var_name) => make::tuple_struct_pat(
+                    make::path_unqualified(make::path_segment(make::name_ref(var_name))),
+                    once(make::wildcard_pat().into()),
+                )
+                .into(),
+            };
+            let block =
+                make::block_expr(None, None).indent(IndentLevel::from_node(let_stmt.syntax()));
+            let if_ = make::expr_if(make::condition(init, Some(with_placeholder)), block);
+            let stmt = make::expr_stmt(if_);
+
+            let placeholder = stmt.syntax().descendants().find_map(ast::WildcardPat::cast).unwrap();
+            let stmt = stmt.replace_descendant(placeholder.into(), original_pat);
+
+            edit.replace_ast(ast::Stmt::from(let_stmt), ast::Stmt::from(stmt));
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_assist;
+
+    use super::*;
+
+    #[test]
+    fn replace_let_unknown_enum() {
+        check_assist(
+            replace_let_with_if_let,
+            r"
+enum E<T> { X(T), Y(T) }
+
+fn main() {
+    <|>let x = E::X(92);
+}
+            ",
+            r"
+enum E<T> { X(T), Y(T) }
+
+fn main() {
+    if let x = E::X(92) {
+    }
+}
+            ",
+        )
+    }
+}

crates/assists/src/handlers/replace_qualified_name_with_use.rs

@@ -0,0 +1,680 @@
+use syntax::{algo::SyntaxRewriter, ast, match_ast, AstNode, SyntaxNode, TextRange};
+use test_utils::mark;
+
+use crate::{
+    utils::{find_insert_use_container, insert_use_statement},
+    AssistContext, AssistId, AssistKind, Assists,
+};
+
+// Assist: replace_qualified_name_with_use
+//
+// Adds a use statement for a given fully-qualified name.
+//
+// ```
+// fn process(map: std::collections::<|>HashMap<String, String>) {}
+// ```
+// ->
+// ```
+// use std::collections::HashMap;
+//
+// fn process(map: HashMap<String, String>) {}
+// ```
+pub(crate) fn replace_qualified_name_with_use(
+    acc: &mut Assists,
+    ctx: &AssistContext,
+) -> Option<()> {
+    let path: ast::Path = ctx.find_node_at_offset()?;
+    // We don't want to mess with use statements
+    if path.syntax().ancestors().find_map(ast::Use::cast).is_some() {
+        return None;
+    }
+    if path.qualifier().is_none() {
+        mark::hit!(dont_import_trivial_paths);
+        return None;
+    }
+    let path_to_import = path.to_string().clone();
+    let path_to_import = match path.segment()?.generic_arg_list() {
+        Some(generic_args) => {
+            let generic_args_start =
+                generic_args.syntax().text_range().start() - path.syntax().text_range().start();
+            &path_to_import[TextRange::up_to(generic_args_start)]
+        }
+        None => path_to_import.as_str(),
+    };
+
+    let target = path.syntax().text_range();
+    acc.add(
+        AssistId("replace_qualified_name_with_use", AssistKind::RefactorRewrite),
+        "Replace qualified path with use",
+        target,
+        |builder| {
+            let container = match find_insert_use_container(path.syntax(), ctx) {
+                Some(c) => c,
+                None => return,
+            };
+            insert_use_statement(
+                path.syntax(),
+                &path_to_import.to_string(),
+                ctx,
+                builder.text_edit_builder(),
+            );
+
+            // Now that we've brought the name into scope, re-qualify all paths that could be
+            // affected (that is, all paths inside the node we added the `use` to).
+            let mut rewriter = SyntaxRewriter::default();
+            let syntax = container.either(|l| l.syntax().clone(), |r| r.syntax().clone());
+            shorten_paths(&mut rewriter, syntax, path);
+            builder.rewrite(rewriter);
+        },
+    )
+}
+
+/// Adds replacements to `re` that shorten `path` in all descendants of `node`.
+fn shorten_paths(rewriter: &mut SyntaxRewriter<'static>, node: SyntaxNode, path: ast::Path) {
+    for child in node.children() {
+        match_ast! {
+            match child {
+                // Don't modify `use` items, as this can break the `use` item when injecting a new
+                // import into the use tree.
+                ast::Use(_it) => continue,
+                // Don't descend into submodules, they don't have the same `use` items in scope.
+                ast::Module(_it) => continue,
+
+                ast::Path(p) => {
+                    match maybe_replace_path(rewriter, p.clone(), path.clone()) {
+                        Some(()) => {},
+                        None => shorten_paths(rewriter, p.syntax().clone(), path.clone()),
+                    }
+                },
+                _ => shorten_paths(rewriter, child, path.clone()),
+            }
+        }
+    }
+}
+
+fn maybe_replace_path(
+    rewriter: &mut SyntaxRewriter<'static>,
+    path: ast::Path,
+    target: ast::Path,
+) -> Option<()> {
+    if !path_eq(path.clone(), target) {
+        return None;
+    }
+
+    // Shorten `path`, leaving only its last segment.
+    if let Some(parent) = path.qualifier() {
+        rewriter.delete(parent.syntax());
+    }
+    if let Some(double_colon) = path.coloncolon_token() {
+        rewriter.delete(&double_colon);
+    }
+
+    Some(())
+}
+
+fn path_eq(lhs: ast::Path, rhs: ast::Path) -> bool {
+    let mut lhs_curr = lhs;
+    let mut rhs_curr = rhs;
+    loop {
+        match (lhs_curr.segment(), rhs_curr.segment()) {
+            (Some(lhs), Some(rhs)) if lhs.syntax().text() == rhs.syntax().text() => (),
+            _ => return false,
+        }
+
+        match (lhs_curr.qualifier(), rhs_curr.qualifier()) {
+            (Some(lhs), Some(rhs)) => {
+                lhs_curr = lhs;
+                rhs_curr = rhs;
+            }
+            (None, None) => return true,
+            _ => return false,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_replace_add_use_no_anchor() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+std::fmt::Debug<|>
+    ",
+            r"
+use std::fmt::Debug;
+
+Debug
+    ",
+        );
+    }
+    #[test]
+    fn test_replace_add_use_no_anchor_with_item_below() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+std::fmt::Debug<|>
+
+fn main() {
+}
+    ",
+            r"
+use std::fmt::Debug;
+
+Debug
+
+fn main() {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_replace_add_use_no_anchor_with_item_above() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+fn main() {
+}
+
+std::fmt::Debug<|>
+    ",
+            r"
+use std::fmt::Debug;
+
+fn main() {
+}
+
+Debug
+    ",
+        );
+    }
+
+    #[test]
+    fn test_replace_add_use_no_anchor_2seg() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+std::fmt<|>::Debug
+    ",
+            r"
+use std::fmt;
+
+fmt::Debug
+    ",
+        );
+    }
+
+    #[test]
+    fn test_replace_add_use() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use stdx;
+
+impl std::fmt::Debug<|> for Foo {
+}
+    ",
+            r"
+use stdx;
+use std::fmt::Debug;
+
+impl Debug for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_replace_file_use_other_anchor() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+impl std::fmt::Debug<|> for Foo {
+}
+    ",
+            r"
+use std::fmt::Debug;
+
+impl Debug for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_replace_add_use_other_anchor_indent() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+    impl std::fmt::Debug<|> for Foo {
+    }
+    ",
+            r"
+    use std::fmt::Debug;
+
+    impl Debug for Foo {
+    }
+    ",
+        );
+    }
+
+    #[test]
+    fn test_replace_split_different() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt;
+
+impl std::io<|> for Foo {
+}
+    ",
+            r"
+use std::{io, fmt};
+
+impl io for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_replace_split_self_for_use() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt;
+
+impl std::fmt::Debug<|> for Foo {
+}
+    ",
+            r"
+use std::fmt::{self, Debug, };
+
+impl Debug for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_replace_split_self_for_target() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt::Debug;
+
+impl std::fmt<|> for Foo {
+}
+    ",
+            r"
+use std::fmt::{self, Debug};
+
+impl fmt for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_replace_add_to_nested_self_nested() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt::{Debug, nested::{Display}};
+
+impl std::fmt::nested<|> for Foo {
+}
+",
+            r"
+use std::fmt::{Debug, nested::{Display, self}};
+
+impl nested for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_replace_add_to_nested_self_already_included() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt::{Debug, nested::{self, Display}};
+
+impl std::fmt::nested<|> for Foo {
+}
+",
+            r"
+use std::fmt::{Debug, nested::{self, Display}};
+
+impl nested for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_replace_add_to_nested_nested() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt::{Debug, nested::{Display}};
+
+impl std::fmt::nested::Debug<|> for Foo {
+}
+",
+            r"
+use std::fmt::{Debug, nested::{Display, Debug}};
+
+impl Debug for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_replace_split_common_target_longer() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt::Debug;
+
+impl std::fmt::nested::Display<|> for Foo {
+}
+",
+            r"
+use std::fmt::{nested::Display, Debug};
+
+impl Display for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_replace_split_common_use_longer() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt::nested::Debug;
+
+impl std::fmt::Display<|> for Foo {
+}
+",
+            r"
+use std::fmt::{Display, nested::Debug};
+
+impl Display for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_replace_use_nested_import() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use crate::{
+    ty::{Substs, Ty},
+    AssocItem,
+};
+
+fn foo() { crate::ty::lower<|>::trait_env() }
+",
+            r"
+use crate::{
+    ty::{Substs, Ty, lower},
+    AssocItem,
+};
+
+fn foo() { lower::trait_env() }
+",
+        );
+    }
+
+    #[test]
+    fn test_replace_alias() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt as foo;
+
+impl foo::Debug<|> for Foo {
+}
+",
+            r"
+use std::fmt as foo;
+
+impl Debug for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn dont_import_trivial_paths() {
+        mark::check!(dont_import_trivial_paths);
+        check_assist_not_applicable(
+            replace_qualified_name_with_use,
+            r"
+impl foo<|> for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_replace_not_applicable_in_use() {
+        check_assist_not_applicable(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt<|>;
+",
+        );
+    }
+
+    #[test]
+    fn test_replace_add_use_no_anchor_in_mod_mod() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+mod foo {
+    mod bar {
+        std::fmt::Debug<|>
+    }
+}
+    ",
+            r"
+mod foo {
+    mod bar {
+        use std::fmt::Debug;
+
+        Debug
+    }
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn inserts_imports_after_inner_attributes() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+#![allow(dead_code)]
+
+fn main() {
+    std::fmt::Debug<|>
+}
+    ",
+            r"
+#![allow(dead_code)]
+use std::fmt::Debug;
+
+fn main() {
+    Debug
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn replaces_all_affected_paths() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+fn main() {
+    std::fmt::Debug<|>;
+    let x: std::fmt::Debug = std::fmt::Debug;
+}
+    ",
+            r"
+use std::fmt::Debug;
+
+fn main() {
+    Debug;
+    let x: Debug = Debug;
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn replaces_all_affected_paths_mod() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+mod m {
+    fn f() {
+        std::fmt::Debug<|>;
+        let x: std::fmt::Debug = std::fmt::Debug;
+    }
+    fn g() {
+        std::fmt::Debug;
+    }
+}
+
+fn f() {
+    std::fmt::Debug;
+}
+    ",
+            r"
+mod m {
+    use std::fmt::Debug;
+
+    fn f() {
+        Debug;
+        let x: Debug = Debug;
+    }
+    fn g() {
+        Debug;
+    }
+}
+
+fn f() {
+    std::fmt::Debug;
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn does_not_replace_in_submodules() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+fn main() {
+    std::fmt::Debug<|>;
+}
+
+mod sub {
+    fn f() {
+        std::fmt::Debug;
+    }
+}
+    ",
+            r"
+use std::fmt::Debug;
+
+fn main() {
+    Debug;
+}
+
+mod sub {
+    fn f() {
+        std::fmt::Debug;
+    }
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn does_not_replace_in_use() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+use std::fmt::Display;
+
+fn main() {
+    std::fmt<|>;
+}
+    ",
+            r"
+use std::fmt::{self, Display};
+
+fn main() {
+    fmt;
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn does_not_replace_pub_use() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+pub use std::fmt;
+
+impl std::io<|> for Foo {
+}
+    ",
+            r"
+use std::io;
+
+pub use std::fmt;
+
+impl io for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn does_not_replace_pub_crate_use() {
+        check_assist(
+            replace_qualified_name_with_use,
+            r"
+pub(crate) use std::fmt;
+
+impl std::io<|> for Foo {
+}
+    ",
+            r"
+use std::io;
+
+pub(crate) use std::fmt;
+
+impl io for Foo {
+}
+    ",
+        );
+    }
+}

crates/assists/src/handlers/replace_unwrap_with_match.rs

@@ -0,0 +1,187 @@
+use std::iter;
+
+use syntax::{
+    ast::{
+        self,
+        edit::{AstNodeEdit, IndentLevel},
+        make,
+    },
+    AstNode,
+};
+
+use crate::{
+    utils::{render_snippet, Cursor, TryEnum},
+    AssistContext, AssistId, AssistKind, Assists,
+};
+
+// Assist: replace_unwrap_with_match
+//
+// Replaces `unwrap` a `match` expression. Works for Result and Option.
+//
+// ```
+// enum Result<T, E> { Ok(T), Err(E) }
+// fn main() {
+//     let x: Result<i32, i32> = Result::Ok(92);
+//     let y = x.<|>unwrap();
+// }
+// ```
+// ->
+// ```
+// enum Result<T, E> { Ok(T), Err(E) }
+// fn main() {
+//     let x: Result<i32, i32> = Result::Ok(92);
+//     let y = match x {
+//         Ok(a) => a,
+//         $0_ => unreachable!(),
+//     };
+// }
+// ```
+pub(crate) fn replace_unwrap_with_match(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let method_call: ast::MethodCallExpr = ctx.find_node_at_offset()?;
+    let name = method_call.name_ref()?;
+    if name.text() != "unwrap" {
+        return None;
+    }
+    let caller = method_call.receiver()?;
+    let ty = ctx.sema.type_of_expr(&caller)?;
+    let happy_variant = TryEnum::from_ty(&ctx.sema, &ty)?.happy_case();
+    let target = method_call.syntax().text_range();
+    acc.add(
+        AssistId("replace_unwrap_with_match", AssistKind::RefactorRewrite),
+        "Replace unwrap with match",
+        target,
+        |builder| {
+            let ok_path = make::path_unqualified(make::path_segment(make::name_ref(happy_variant)));
+            let it = make::ident_pat(make::name("a")).into();
+            let ok_tuple = make::tuple_struct_pat(ok_path, iter::once(it)).into();
+
+            let bind_path = make::path_unqualified(make::path_segment(make::name_ref("a")));
+            let ok_arm = make::match_arm(iter::once(ok_tuple), make::expr_path(bind_path));
+
+            let unreachable_call = make::expr_unreachable();
+            let err_arm =
+                make::match_arm(iter::once(make::wildcard_pat().into()), unreachable_call);
+
+            let match_arm_list = make::match_arm_list(vec![ok_arm, err_arm]);
+            let match_expr = make::expr_match(caller.clone(), match_arm_list)
+                .indent(IndentLevel::from_node(method_call.syntax()));
+
+            let range = method_call.syntax().text_range();
+            match ctx.config.snippet_cap {
+                Some(cap) => {
+                    let err_arm = match_expr
+                        .syntax()
+                        .descendants()
+                        .filter_map(ast::MatchArm::cast)
+                        .last()
+                        .unwrap();
+                    let snippet =
+                        render_snippet(cap, match_expr.syntax(), Cursor::Before(err_arm.syntax()));
+                    builder.replace_snippet(cap, range, snippet)
+                }
+                None => builder.replace(range, match_expr.to_string()),
+            }
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn test_replace_result_unwrap_with_match() {
+        check_assist(
+            replace_unwrap_with_match,
+            r"
+enum Result<T, E> { Ok(T), Err(E) }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = i(x).<|>unwrap();
+}
+            ",
+            r"
+enum Result<T, E> { Ok(T), Err(E) }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = match i(x) {
+        Ok(a) => a,
+        $0_ => unreachable!(),
+    };
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_replace_option_unwrap_with_match() {
+        check_assist(
+            replace_unwrap_with_match,
+            r"
+enum Option<T> { Some(T), None }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x = Option::Some(92);
+    let y = i(x).<|>unwrap();
+}
+            ",
+            r"
+enum Option<T> { Some(T), None }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x = Option::Some(92);
+    let y = match i(x) {
+        Some(a) => a,
+        $0_ => unreachable!(),
+    };
+}
+            ",
+        );
+    }
+
+    #[test]
+    fn test_replace_result_unwrap_with_match_chaining() {
+        check_assist(
+            replace_unwrap_with_match,
+            r"
+enum Result<T, E> { Ok(T), Err(E) }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = i(x).<|>unwrap().count_zeroes();
+}
+            ",
+            r"
+enum Result<T, E> { Ok(T), Err(E) }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = match i(x) {
+        Ok(a) => a,
+        $0_ => unreachable!(),
+    }.count_zeroes();
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn replace_unwrap_with_match_target() {
+        check_assist_target(
+            replace_unwrap_with_match,
+            r"
+enum Option<T> { Some(T), None }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x = Option::Some(92);
+    let y = i(x).<|>unwrap();
+}
+            ",
+            r"i(x).unwrap()",
+        );
+    }
+}

crates/assists/src/handlers/split_import.rs

@@ -0,0 +1,79 @@
+use std::iter::successors;
+
+use syntax::{ast, AstNode, T};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: split_import
+//
+// Wraps the tail of import into braces.
+//
+// ```
+// use std::<|>collections::HashMap;
+// ```
+// ->
+// ```
+// use std::{collections::HashMap};
+// ```
+pub(crate) fn split_import(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let colon_colon = ctx.find_token_at_offset(T![::])?;
+    let path = ast::Path::cast(colon_colon.parent())?.qualifier()?;
+    let top_path = successors(Some(path.clone()), |it| it.parent_path()).last()?;
+
+    let use_tree = top_path.syntax().ancestors().find_map(ast::UseTree::cast)?;
+
+    let new_tree = use_tree.split_prefix(&path);
+    if new_tree == use_tree {
+        return None;
+    }
+
+    let target = colon_colon.text_range();
+    acc.add(AssistId("split_import", AssistKind::RefactorRewrite), "Split import", target, |edit| {
+        edit.replace_ast(use_tree, new_tree);
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn test_split_import() {
+        check_assist(
+            split_import,
+            "use crate::<|>db::RootDatabase;",
+            "use crate::{db::RootDatabase};",
+        )
+    }
+
+    #[test]
+    fn split_import_works_with_trees() {
+        check_assist(
+            split_import,
+            "use crate:<|>:db::{RootDatabase, FileSymbol}",
+            "use crate::{db::{RootDatabase, FileSymbol}}",
+        )
+    }
+
+    #[test]
+    fn split_import_target() {
+        check_assist_target(split_import, "use crate::<|>db::{RootDatabase, FileSymbol}", "::");
+    }
+
+    #[test]
+    fn issue4044() {
+        check_assist_not_applicable(split_import, "use crate::<|>:::self;")
+    }
+
+    #[test]
+    fn test_empty_use() {
+        check_assist_not_applicable(
+            split_import,
+            r"
+use std::<|>
+fn main() {}",
+        );
+    }
+}

crates/assists/src/handlers/unwrap_block.rs

@@ -0,0 +1,517 @@
+use syntax::{
+    ast::{
+        self,
+        edit::{AstNodeEdit, IndentLevel},
+    },
+    AstNode, TextRange, T,
+};
+
+use crate::{utils::unwrap_trivial_block, AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: unwrap_block
+//
+// This assist removes if...else, for, while and loop control statements to just keep the body.
+//
+// ```
+// fn foo() {
+//     if true {<|>
+//         println!("foo");
+//     }
+// }
+// ```
+// ->
+// ```
+// fn foo() {
+//     println!("foo");
+// }
+// ```
+pub(crate) fn unwrap_block(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let assist_id = AssistId("unwrap_block", AssistKind::RefactorRewrite);
+    let assist_label = "Unwrap block";
+
+    let l_curly_token = ctx.find_token_at_offset(T!['{'])?;
+    let mut block = ast::BlockExpr::cast(l_curly_token.parent())?;
+    let mut parent = block.syntax().parent()?;
+    if ast::MatchArm::can_cast(parent.kind()) {
+        parent = parent.ancestors().find(|it| ast::MatchExpr::can_cast(it.kind()))?
+    }
+
+    let parent = ast::Expr::cast(parent)?;
+
+    match parent.clone() {
+        ast::Expr::ForExpr(_) | ast::Expr::WhileExpr(_) | ast::Expr::LoopExpr(_) => (),
+        ast::Expr::MatchExpr(_) => block = block.dedent(IndentLevel(1)),
+        ast::Expr::IfExpr(if_expr) => {
+            let then_branch = if_expr.then_branch()?;
+            if then_branch == block {
+                if let Some(ancestor) = if_expr.syntax().parent().and_then(ast::IfExpr::cast) {
+                    // For `else if` blocks
+                    let ancestor_then_branch = ancestor.then_branch()?;
+
+                    let target = then_branch.syntax().text_range();
+                    return acc.add(assist_id, assist_label, target, |edit| {
+                        let range_to_del_else_if = TextRange::new(
+                            ancestor_then_branch.syntax().text_range().end(),
+                            l_curly_token.text_range().start(),
+                        );
+                        let range_to_del_rest = TextRange::new(
+                            then_branch.syntax().text_range().end(),
+                            if_expr.syntax().text_range().end(),
+                        );
+
+                        edit.delete(range_to_del_rest);
+                        edit.delete(range_to_del_else_if);
+                        edit.replace(
+                            target,
+                            update_expr_string(then_branch.to_string(), &[' ', '{']),
+                        );
+                    });
+                }
+            } else {
+                let target = block.syntax().text_range();
+                return acc.add(assist_id, assist_label, target, |edit| {
+                    let range_to_del = TextRange::new(
+                        then_branch.syntax().text_range().end(),
+                        l_curly_token.text_range().start(),
+                    );
+
+                    edit.delete(range_to_del);
+                    edit.replace(target, update_expr_string(block.to_string(), &[' ', '{']));
+                });
+            }
+        }
+        _ => return None,
+    };
+
+    let unwrapped = unwrap_trivial_block(block);
+    let target = unwrapped.syntax().text_range();
+    acc.add(assist_id, assist_label, target, |builder| {
+        builder.replace(
+            parent.syntax().text_range(),
+            update_expr_string(unwrapped.to_string(), &[' ', '{', '\n']),
+        );
+    })
+}
+
+fn update_expr_string(expr_str: String, trim_start_pat: &[char]) -> String {
+    let expr_string = expr_str.trim_start_matches(trim_start_pat);
+    let mut expr_string_lines: Vec<&str> = expr_string.lines().collect();
+    expr_string_lines.pop(); // Delete last line
+
+    expr_string_lines
+        .into_iter()
+        .map(|line| line.replacen("    ", "", 1)) // Delete indentation
+        .collect::<Vec<String>>()
+        .join("\n")
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn simple_if() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                bar();
+                if true {<|>
+                    foo();
+
+                    //comment
+                    bar();
+                } else {
+                    println!("bar");
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                bar();
+                foo();
+
+                //comment
+                bar();
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_if_else() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                bar();
+                if true {
+                    foo();
+
+                    //comment
+                    bar();
+                } else {<|>
+                    println!("bar");
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                bar();
+                if true {
+                    foo();
+
+                    //comment
+                    bar();
+                }
+                println!("bar");
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_if_else_if() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                //bar();
+                if true {
+                    println!("true");
+
+                    //comment
+                    //bar();
+                } else if false {<|>
+                    println!("bar");
+                } else {
+                    println!("foo");
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                //bar();
+                if true {
+                    println!("true");
+
+                    //comment
+                    //bar();
+                }
+                println!("bar");
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_if_else_if_nested() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                //bar();
+                if true {
+                    println!("true");
+
+                    //comment
+                    //bar();
+                } else if false {
+                    println!("bar");
+                } else if true {<|>
+                    println!("foo");
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                //bar();
+                if true {
+                    println!("true");
+
+                    //comment
+                    //bar();
+                } else if false {
+                    println!("bar");
+                }
+                println!("foo");
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_if_else_if_nested_else() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                //bar();
+                if true {
+                    println!("true");
+
+                    //comment
+                    //bar();
+                } else if false {
+                    println!("bar");
+                } else if true {
+                    println!("foo");
+                } else {<|>
+                    println!("else");
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                //bar();
+                if true {
+                    println!("true");
+
+                    //comment
+                    //bar();
+                } else if false {
+                    println!("bar");
+                } else if true {
+                    println!("foo");
+                }
+                println!("else");
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_if_else_if_nested_middle() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                //bar();
+                if true {
+                    println!("true");
+
+                    //comment
+                    //bar();
+                } else if false {
+                    println!("bar");
+                } else if true {<|>
+                    println!("foo");
+                } else {
+                    println!("else");
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                //bar();
+                if true {
+                    println!("true");
+
+                    //comment
+                    //bar();
+                } else if false {
+                    println!("bar");
+                }
+                println!("foo");
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_if_bad_cursor_position() {
+        check_assist_not_applicable(
+            unwrap_block,
+            r#"
+            fn main() {
+                bar();<|>
+                if true {
+                    foo();
+
+                    //comment
+                    bar();
+                } else {
+                    println!("bar");
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_for() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                for i in 0..5 {<|>
+                    if true {
+                        foo();
+
+                        //comment
+                        bar();
+                    } else {
+                        println!("bar");
+                    }
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                if true {
+                    foo();
+
+                    //comment
+                    bar();
+                } else {
+                    println!("bar");
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_if_in_for() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                for i in 0..5 {
+                    if true {<|>
+                        foo();
+
+                        //comment
+                        bar();
+                    } else {
+                        println!("bar");
+                    }
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                for i in 0..5 {
+                    foo();
+
+                    //comment
+                    bar();
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_loop() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                loop {<|>
+                    if true {
+                        foo();
+
+                        //comment
+                        bar();
+                    } else {
+                        println!("bar");
+                    }
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                if true {
+                    foo();
+
+                    //comment
+                    bar();
+                } else {
+                    println!("bar");
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn simple_while() {
+        check_assist(
+            unwrap_block,
+            r#"
+            fn main() {
+                while true {<|>
+                    if true {
+                        foo();
+
+                        //comment
+                        bar();
+                    } else {
+                        println!("bar");
+                    }
+                }
+            }
+            "#,
+            r#"
+            fn main() {
+                if true {
+                    foo();
+
+                    //comment
+                    bar();
+                } else {
+                    println!("bar");
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn unwrap_match_arm() {
+        check_assist(
+            unwrap_block,
+            r#"
+fn main() {
+    match rel_path {
+        Ok(rel_path) => {<|>
+            let rel_path = RelativePathBuf::from_path(rel_path).ok()?;
+            Some((*id, rel_path))
+        }
+        Err(_) => None,
+    }
+}
+"#,
+            r#"
+fn main() {
+    let rel_path = RelativePathBuf::from_path(rel_path).ok()?;
+    Some((*id, rel_path))
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn simple_if_in_while_bad_cursor_position() {
+        check_assist_not_applicable(
+            unwrap_block,
+            r#"
+            fn main() {
+                while true {
+                    if true {
+                        foo();<|>
+
+                        //comment
+                        bar();
+                    } else {
+                        println!("bar");
+                    }
+                }
+            }
+            "#,
+        );
+    }
+}

crates/assists/src/lib.rs

@@ -0,0 +1,217 @@
+//! `assists` crate provides a bunch of code assists, also known as code
+//! actions (in LSP) or intentions (in IntelliJ).
+//!
+//! An assist is a micro-refactoring, which is automatically activated in
+//! certain context. For example, if the cursor is over `,`, a "swap `,`" assist
+//! becomes available.
+
+#[allow(unused)]
+macro_rules! eprintln {
+    ($($tt:tt)*) => { stdx::eprintln!($($tt)*) };
+}
+
+mod assist_config;
+mod assist_context;
+#[cfg(test)]
+mod tests;
+pub mod utils;
+pub mod ast_transform;
+
+use base_db::FileRange;
+use hir::Semantics;
+use ide_db::{label::Label, source_change::SourceChange, RootDatabase};
+use syntax::TextRange;
+
+pub(crate) use crate::assist_context::{AssistContext, Assists};
+
+pub use assist_config::AssistConfig;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AssistKind {
+    None,
+    QuickFix,
+    Generate,
+    Refactor,
+    RefactorExtract,
+    RefactorInline,
+    RefactorRewrite,
+}
+
+impl AssistKind {
+    pub fn contains(self, other: AssistKind) -> bool {
+        if self == other {
+            return true;
+        }
+
+        match self {
+            AssistKind::None | AssistKind::Generate => return true,
+            AssistKind::Refactor => match other {
+                AssistKind::RefactorExtract
+                | AssistKind::RefactorInline
+                | AssistKind::RefactorRewrite => return true,
+                _ => return false,
+            },
+            _ => return false,
+        }
+    }
+}
+
+/// Unique identifier of the assist, should not be shown to the user
+/// directly.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct AssistId(pub &'static str, pub AssistKind);
+
+#[derive(Clone, Debug)]
+pub struct GroupLabel(pub String);
+
+#[derive(Debug, Clone)]
+pub struct Assist {
+    pub id: AssistId,
+    /// Short description of the assist, as shown in the UI.
+    pub label: Label,
+    pub group: Option<GroupLabel>,
+    /// Target ranges are used to sort assists: the smaller the target range,
+    /// the more specific assist is, and so it should be sorted first.
+    pub target: TextRange,
+}
+
+#[derive(Debug, Clone)]
+pub struct ResolvedAssist {
+    pub assist: Assist,
+    pub source_change: SourceChange,
+}
+
+impl Assist {
+    /// Return all the assists applicable at the given position.
+    ///
+    /// Assists are returned in the "unresolved" state, that is only labels are
+    /// returned, without actual edits.
+    pub fn unresolved(db: &RootDatabase, config: &AssistConfig, range: FileRange) -> Vec<Assist> {
+        let sema = Semantics::new(db);
+        let ctx = AssistContext::new(sema, config, range);
+        let mut acc = Assists::new_unresolved(&ctx);
+        handlers::all().iter().for_each(|handler| {
+            handler(&mut acc, &ctx);
+        });
+        acc.finish_unresolved()
+    }
+
+    /// Return all the assists applicable at the given position.
+    ///
+    /// Assists are returned in the "resolved" state, that is with edit fully
+    /// computed.
+    pub fn resolved(
+        db: &RootDatabase,
+        config: &AssistConfig,
+        range: FileRange,
+    ) -> Vec<ResolvedAssist> {
+        let sema = Semantics::new(db);
+        let ctx = AssistContext::new(sema, config, range);
+        let mut acc = Assists::new_resolved(&ctx);
+        handlers::all().iter().for_each(|handler| {
+            handler(&mut acc, &ctx);
+        });
+        acc.finish_resolved()
+    }
+}
+
+mod handlers {
+    use crate::{AssistContext, Assists};
+
+    pub(crate) type Handler = fn(&mut Assists, &AssistContext) -> Option<()>;
+
+    mod add_custom_impl;
+    mod add_explicit_type;
+    mod add_missing_impl_members;
+    mod add_turbo_fish;
+    mod apply_demorgan;
+    mod auto_import;
+    mod change_return_type_to_result;
+    mod change_visibility;
+    mod early_return;
+    mod expand_glob_import;
+    mod extract_struct_from_enum_variant;
+    mod extract_variable;
+    mod fill_match_arms;
+    mod fix_visibility;
+    mod flip_binexpr;
+    mod flip_comma;
+    mod flip_trait_bound;
+    mod generate_derive;
+    mod generate_from_impl_for_enum;
+    mod generate_function;
+    mod generate_impl;
+    mod generate_new;
+    mod inline_local_variable;
+    mod introduce_named_lifetime;
+    mod invert_if;
+    mod merge_imports;
+    mod merge_match_arms;
+    mod move_bounds;
+    mod move_guard;
+    mod raw_string;
+    mod remove_dbg;
+    mod remove_mut;
+    mod remove_unused_param;
+    mod reorder_fields;
+    mod replace_if_let_with_match;
+    mod replace_let_with_if_let;
+    mod replace_qualified_name_with_use;
+    mod replace_unwrap_with_match;
+    mod split_import;
+    mod unwrap_block;
+
+    pub(crate) fn all() -> &'static [Handler] {
+        &[
+            // These are alphabetic for the foolish consistency
+            add_custom_impl::add_custom_impl,
+            add_explicit_type::add_explicit_type,
+            add_turbo_fish::add_turbo_fish,
+            apply_demorgan::apply_demorgan,
+            auto_import::auto_import,
+            change_return_type_to_result::change_return_type_to_result,
+            change_visibility::change_visibility,
+            early_return::convert_to_guarded_return,
+            expand_glob_import::expand_glob_import,
+            extract_struct_from_enum_variant::extract_struct_from_enum_variant,
+            extract_variable::extract_variable,
+            fill_match_arms::fill_match_arms,
+            fix_visibility::fix_visibility,
+            flip_binexpr::flip_binexpr,
+            flip_comma::flip_comma,
+            flip_trait_bound::flip_trait_bound,
+            generate_derive::generate_derive,
+            generate_from_impl_for_enum::generate_from_impl_for_enum,
+            generate_function::generate_function,
+            generate_impl::generate_impl,
+            generate_new::generate_new,
+            inline_local_variable::inline_local_variable,
+            introduce_named_lifetime::introduce_named_lifetime,
+            invert_if::invert_if,
+            merge_imports::merge_imports,
+            merge_match_arms::merge_match_arms,
+            move_bounds::move_bounds_to_where_clause,
+            move_guard::move_arm_cond_to_match_guard,
+            move_guard::move_guard_to_arm_body,
+            raw_string::add_hash,
+            raw_string::make_raw_string,
+            raw_string::make_usual_string,
+            raw_string::remove_hash,
+            remove_dbg::remove_dbg,
+            remove_mut::remove_mut,
+            remove_unused_param::remove_unused_param,
+            reorder_fields::reorder_fields,
+            replace_if_let_with_match::replace_if_let_with_match,
+            replace_let_with_if_let::replace_let_with_if_let,
+            replace_qualified_name_with_use::replace_qualified_name_with_use,
+            replace_unwrap_with_match::replace_unwrap_with_match,
+            split_import::split_import,
+            unwrap_block::unwrap_block,
+            // These are manually sorted for better priorities
+            add_missing_impl_members::add_missing_impl_members,
+            add_missing_impl_members::add_missing_default_members,
+            // Are you sure you want to add new assist here, and not to the
+            // sorted list above?
+        ]
+    }
+}

crates/assists/src/tests.rs

@@ -0,0 +1,179 @@
+mod generated;
+
+use base_db::{fixture::WithFixture, FileId, FileRange, SourceDatabaseExt};
+use hir::Semantics;
+use ide_db::RootDatabase;
+use syntax::TextRange;
+use test_utils::{assert_eq_text, extract_offset, extract_range};
+
+use crate::{handlers::Handler, Assist, AssistConfig, AssistContext, AssistKind, Assists};
+use stdx::trim_indent;
+
+pub(crate) fn with_single_file(text: &str) -> (RootDatabase, FileId) {
+    RootDatabase::with_single_file(text)
+}
+
+pub(crate) fn check_assist(assist: Handler, ra_fixture_before: &str, ra_fixture_after: &str) {
+    let ra_fixture_after = trim_indent(ra_fixture_after);
+    check(assist, ra_fixture_before, ExpectedResult::After(&ra_fixture_after));
+}
+
+// FIXME: instead of having a separate function here, maybe use
+// `extract_ranges` and mark the target as `<target> </target>` in the
+// fixture?
+pub(crate) fn check_assist_target(assist: Handler, ra_fixture: &str, target: &str) {
+    check(assist, ra_fixture, ExpectedResult::Target(target));
+}
+
+pub(crate) fn check_assist_not_applicable(assist: Handler, ra_fixture: &str) {
+    check(assist, ra_fixture, ExpectedResult::NotApplicable);
+}
+
+fn check_doc_test(assist_id: &str, before: &str, after: &str) {
+    let after = trim_indent(after);
+    let (db, file_id, selection) = RootDatabase::with_range_or_offset(&before);
+    let before = db.file_text(file_id).to_string();
+    let frange = FileRange { file_id, range: selection.into() };
+
+    let mut assist = Assist::resolved(&db, &AssistConfig::default(), frange)
+        .into_iter()
+        .find(|assist| assist.assist.id.0 == assist_id)
+        .unwrap_or_else(|| {
+            panic!(
+                "\n\nAssist is not applicable: {}\nAvailable assists: {}",
+                assist_id,
+                Assist::resolved(&db, &AssistConfig::default(), frange)
+                    .into_iter()
+                    .map(|assist| assist.assist.id.0)
+                    .collect::<Vec<_>>()
+                    .join(", ")
+            )
+        });
+
+    let actual = {
+        let change = assist.source_change.source_file_edits.pop().unwrap();
+        let mut actual = before;
+        change.edit.apply(&mut actual);
+        actual
+    };
+    assert_eq_text!(&after, &actual);
+}
+
+enum ExpectedResult<'a> {
+    NotApplicable,
+    After(&'a str),
+    Target(&'a str),
+}
+
+fn check(handler: Handler, before: &str, expected: ExpectedResult) {
+    let (db, file_with_caret_id, range_or_offset) = RootDatabase::with_range_or_offset(before);
+    let text_without_caret = db.file_text(file_with_caret_id).to_string();
+
+    let frange = FileRange { file_id: file_with_caret_id, range: range_or_offset.into() };
+
+    let sema = Semantics::new(&db);
+    let config = AssistConfig::default();
+    let ctx = AssistContext::new(sema, &config, frange);
+    let mut acc = Assists::new_resolved(&ctx);
+    handler(&mut acc, &ctx);
+    let mut res = acc.finish_resolved();
+    let assist = res.pop();
+    match (assist, expected) {
+        (Some(assist), ExpectedResult::After(after)) => {
+            let mut source_change = assist.source_change;
+            let change = source_change.source_file_edits.pop().unwrap();
+
+            let mut actual = db.file_text(change.file_id).as_ref().to_owned();
+            change.edit.apply(&mut actual);
+            assert_eq_text!(after, &actual);
+        }
+        (Some(assist), ExpectedResult::Target(target)) => {
+            let range = assist.assist.target;
+            assert_eq_text!(&text_without_caret[range], target);
+        }
+        (Some(_), ExpectedResult::NotApplicable) => panic!("assist should not be applicable!"),
+        (None, ExpectedResult::After(_)) | (None, ExpectedResult::Target(_)) => {
+            panic!("code action is not applicable")
+        }
+        (None, ExpectedResult::NotApplicable) => (),
+    };
+}
+
+#[test]
+fn assist_order_field_struct() {
+    let before = "struct Foo { <|>bar: u32 }";
+    let (before_cursor_pos, before) = extract_offset(before);
+    let (db, file_id) = with_single_file(&before);
+    let frange = FileRange { file_id, range: TextRange::empty(before_cursor_pos) };
+    let assists = Assist::resolved(&db, &AssistConfig::default(), frange);
+    let mut assists = assists.iter();
+
+    assert_eq!(
+        assists.next().expect("expected assist").assist.label,
+        "Change visibility to pub(crate)"
+    );
+    assert_eq!(assists.next().expect("expected assist").assist.label, "Add `#[derive]`");
+}
+
+#[test]
+fn assist_order_if_expr() {
+    let before = "
+    pub fn test_some_range(a: int) -> bool {
+        if let 2..6 = <|>5<|> {
+            true
+        } else {
+            false
+        }
+    }";
+    let (range, before) = extract_range(before);
+    let (db, file_id) = with_single_file(&before);
+    let frange = FileRange { file_id, range };
+    let assists = Assist::resolved(&db, &AssistConfig::default(), frange);
+    let mut assists = assists.iter();
+
+    assert_eq!(assists.next().expect("expected assist").assist.label, "Extract into variable");
+    assert_eq!(assists.next().expect("expected assist").assist.label, "Replace with match");
+}
+
+#[test]
+fn assist_filter_works() {
+    let before = "
+    pub fn test_some_range(a: int) -> bool {
+        if let 2..6 = <|>5<|> {
+            true
+        } else {
+            false
+        }
+    }";
+    let (range, before) = extract_range(before);
+    let (db, file_id) = with_single_file(&before);
+    let frange = FileRange { file_id, range };
+
+    {
+        let mut cfg = AssistConfig::default();
+        cfg.allowed = Some(vec![AssistKind::Refactor]);
+
+        let assists = Assist::resolved(&db, &cfg, frange);
+        let mut assists = assists.iter();
+
+        assert_eq!(assists.next().expect("expected assist").assist.label, "Extract into variable");
+        assert_eq!(assists.next().expect("expected assist").assist.label, "Replace with match");
+    }
+
+    {
+        let mut cfg = AssistConfig::default();
+        cfg.allowed = Some(vec![AssistKind::RefactorExtract]);
+        let assists = Assist::resolved(&db, &cfg, frange);
+        assert_eq!(assists.len(), 1);
+
+        let mut assists = assists.iter();
+        assert_eq!(assists.next().expect("expected assist").assist.label, "Extract into variable");
+    }
+
+    {
+        let mut cfg = AssistConfig::default();
+        cfg.allowed = Some(vec![AssistKind::QuickFix]);
+        let assists = Assist::resolved(&db, &cfg, frange);
+        assert!(assists.is_empty(), "All asserts but quickfixes should be filtered out");
+    }
+}

crates/assists/src/tests/generated.rs

@@ -0,0 +1,912 @@
+//! Generated file, do not edit by hand, see `xtask/src/codegen`
+
+use super::check_doc_test;
+
+#[test]
+fn doctest_add_custom_impl() {
+    check_doc_test(
+        "add_custom_impl",
+        r#####"
+#[derive(Deb<|>ug, Display)]
+struct S;
+"#####,
+        r#####"
+#[derive(Display)]
+struct S;
+
+impl Debug for S {
+    $0
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_add_explicit_type() {
+    check_doc_test(
+        "add_explicit_type",
+        r#####"
+fn main() {
+    let x<|> = 92;
+}
+"#####,
+        r#####"
+fn main() {
+    let x: i32 = 92;
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_add_hash() {
+    check_doc_test(
+        "add_hash",
+        r#####"
+fn main() {
+    r#"Hello,<|> World!"#;
+}
+"#####,
+        r#####"
+fn main() {
+    r##"Hello, World!"##;
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_add_impl_default_members() {
+    check_doc_test(
+        "add_impl_default_members",
+        r#####"
+trait Trait {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl Trait for () {
+    Type X = ();
+    fn foo(&self) {}<|>
+
+}
+"#####,
+        r#####"
+trait Trait {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl Trait for () {
+    Type X = ();
+    fn foo(&self) {}
+
+    $0fn bar(&self) {}
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_add_impl_missing_members() {
+    check_doc_test(
+        "add_impl_missing_members",
+        r#####"
+trait Trait<T> {
+    Type X;
+    fn foo(&self) -> T;
+    fn bar(&self) {}
+}
+
+impl Trait<u32> for () {<|>
+
+}
+"#####,
+        r#####"
+trait Trait<T> {
+    Type X;
+    fn foo(&self) -> T;
+    fn bar(&self) {}
+}
+
+impl Trait<u32> for () {
+    fn foo(&self) -> u32 {
+        ${0:todo!()}
+    }
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_add_turbo_fish() {
+    check_doc_test(
+        "add_turbo_fish",
+        r#####"
+fn make<T>() -> T { todo!() }
+fn main() {
+    let x = make<|>();
+}
+"#####,
+        r#####"
+fn make<T>() -> T { todo!() }
+fn main() {
+    let x = make::<${0:_}>();
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_apply_demorgan() {
+    check_doc_test(
+        "apply_demorgan",
+        r#####"
+fn main() {
+    if x != 4 ||<|> !y {}
+}
+"#####,
+        r#####"
+fn main() {
+    if !(x == 4 && y) {}
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_auto_import() {
+    check_doc_test(
+        "auto_import",
+        r#####"
+fn main() {
+    let map = HashMap<|>::new();
+}
+pub mod std { pub mod collections { pub struct HashMap { } } }
+"#####,
+        r#####"
+use std::collections::HashMap;
+
+fn main() {
+    let map = HashMap::new();
+}
+pub mod std { pub mod collections { pub struct HashMap { } } }
+"#####,
+    )
+}
+
+#[test]
+fn doctest_change_return_type_to_result() {
+    check_doc_test(
+        "change_return_type_to_result",
+        r#####"
+fn foo() -> i32<|> { 42i32 }
+"#####,
+        r#####"
+fn foo() -> Result<i32, ${0:_}> { Ok(42i32) }
+"#####,
+    )
+}
+
+#[test]
+fn doctest_change_visibility() {
+    check_doc_test(
+        "change_visibility",
+        r#####"
+<|>fn frobnicate() {}
+"#####,
+        r#####"
+pub(crate) fn frobnicate() {}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_convert_to_guarded_return() {
+    check_doc_test(
+        "convert_to_guarded_return",
+        r#####"
+fn main() {
+    <|>if cond {
+        foo();
+        bar();
+    }
+}
+"#####,
+        r#####"
+fn main() {
+    if !cond {
+        return;
+    }
+    foo();
+    bar();
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_expand_glob_import() {
+    check_doc_test(
+        "expand_glob_import",
+        r#####"
+mod foo {
+    pub struct Bar;
+    pub struct Baz;
+}
+
+use foo::*<|>;
+
+fn qux(bar: Bar, baz: Baz) {}
+"#####,
+        r#####"
+mod foo {
+    pub struct Bar;
+    pub struct Baz;
+}
+
+use foo::{Baz, Bar};
+
+fn qux(bar: Bar, baz: Baz) {}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_extract_struct_from_enum_variant() {
+    check_doc_test(
+        "extract_struct_from_enum_variant",
+        r#####"
+enum A { <|>One(u32, u32) }
+"#####,
+        r#####"
+struct One(pub u32, pub u32);
+
+enum A { One(One) }
+"#####,
+    )
+}
+
+#[test]
+fn doctest_extract_variable() {
+    check_doc_test(
+        "extract_variable",
+        r#####"
+fn main() {
+    <|>(1 + 2)<|> * 4;
+}
+"#####,
+        r#####"
+fn main() {
+    let $0var_name = (1 + 2);
+    var_name * 4;
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_fill_match_arms() {
+    check_doc_test(
+        "fill_match_arms",
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    match action {
+        <|>
+    }
+}
+"#####,
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    match action {
+        $0Action::Move { distance } => {}
+        Action::Stop => {}
+    }
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_fix_visibility() {
+    check_doc_test(
+        "fix_visibility",
+        r#####"
+mod m {
+    fn frobnicate() {}
+}
+fn main() {
+    m::frobnicate<|>() {}
+}
+"#####,
+        r#####"
+mod m {
+    $0pub(crate) fn frobnicate() {}
+}
+fn main() {
+    m::frobnicate() {}
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_flip_binexpr() {
+    check_doc_test(
+        "flip_binexpr",
+        r#####"
+fn main() {
+    let _ = 90 +<|> 2;
+}
+"#####,
+        r#####"
+fn main() {
+    let _ = 2 + 90;
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_flip_comma() {
+    check_doc_test(
+        "flip_comma",
+        r#####"
+fn main() {
+    ((1, 2),<|> (3, 4));
+}
+"#####,
+        r#####"
+fn main() {
+    ((3, 4), (1, 2));
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_flip_trait_bound() {
+    check_doc_test(
+        "flip_trait_bound",
+        r#####"
+fn foo<T: Clone +<|> Copy>() { }
+"#####,
+        r#####"
+fn foo<T: Copy + Clone>() { }
+"#####,
+    )
+}
+
+#[test]
+fn doctest_generate_derive() {
+    check_doc_test(
+        "generate_derive",
+        r#####"
+struct Point {
+    x: u32,
+    y: u32,<|>
+}
+"#####,
+        r#####"
+#[derive($0)]
+struct Point {
+    x: u32,
+    y: u32,
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_generate_from_impl_for_enum() {
+    check_doc_test(
+        "generate_from_impl_for_enum",
+        r#####"
+enum A { <|>One(u32) }
+"#####,
+        r#####"
+enum A { One(u32) }
+
+impl From<u32> for A {
+    fn from(v: u32) -> Self {
+        A::One(v)
+    }
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_generate_function() {
+    check_doc_test(
+        "generate_function",
+        r#####"
+struct Baz;
+fn baz() -> Baz { Baz }
+fn foo() {
+    bar<|>("", baz());
+}
+
+"#####,
+        r#####"
+struct Baz;
+fn baz() -> Baz { Baz }
+fn foo() {
+    bar("", baz());
+}
+
+fn bar(arg: &str, baz: Baz) {
+    ${0:todo!()}
+}
+
+"#####,
+    )
+}
+
+#[test]
+fn doctest_generate_impl() {
+    check_doc_test(
+        "generate_impl",
+        r#####"
+struct Ctx<T: Clone> {
+    data: T,<|>
+}
+"#####,
+        r#####"
+struct Ctx<T: Clone> {
+    data: T,
+}
+
+impl<T: Clone> Ctx<T> {
+    $0
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_generate_new() {
+    check_doc_test(
+        "generate_new",
+        r#####"
+struct Ctx<T: Clone> {
+     data: T,<|>
+}
+"#####,
+        r#####"
+struct Ctx<T: Clone> {
+     data: T,
+}
+
+impl<T: Clone> Ctx<T> {
+    fn $0new(data: T) -> Self { Self { data } }
+}
+
+"#####,
+    )
+}
+
+#[test]
+fn doctest_inline_local_variable() {
+    check_doc_test(
+        "inline_local_variable",
+        r#####"
+fn main() {
+    let x<|> = 1 + 2;
+    x * 4;
+}
+"#####,
+        r#####"
+fn main() {
+    (1 + 2) * 4;
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_introduce_named_lifetime() {
+    check_doc_test(
+        "introduce_named_lifetime",
+        r#####"
+impl Cursor<'_<|>> {
+    fn node(self) -> &SyntaxNode {
+        match self {
+            Cursor::Replace(node) | Cursor::Before(node) => node,
+        }
+    }
+}
+"#####,
+        r#####"
+impl<'a> Cursor<'a> {
+    fn node(self) -> &SyntaxNode {
+        match self {
+            Cursor::Replace(node) | Cursor::Before(node) => node,
+        }
+    }
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_invert_if() {
+    check_doc_test(
+        "invert_if",
+        r#####"
+fn main() {
+    if<|> !y { A } else { B }
+}
+"#####,
+        r#####"
+fn main() {
+    if y { B } else { A }
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_make_raw_string() {
+    check_doc_test(
+        "make_raw_string",
+        r#####"
+fn main() {
+    "Hello,<|> World!";
+}
+"#####,
+        r#####"
+fn main() {
+    r#"Hello, World!"#;
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_make_usual_string() {
+    check_doc_test(
+        "make_usual_string",
+        r#####"
+fn main() {
+    r#"Hello,<|> "World!""#;
+}
+"#####,
+        r#####"
+fn main() {
+    "Hello, \"World!\"";
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_merge_imports() {
+    check_doc_test(
+        "merge_imports",
+        r#####"
+use std::<|>fmt::Formatter;
+use std::io;
+"#####,
+        r#####"
+use std::{fmt::Formatter, io};
+"#####,
+    )
+}
+
+#[test]
+fn doctest_merge_match_arms() {
+    check_doc_test(
+        "merge_match_arms",
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    match action {
+        <|>Action::Move(..) => foo(),
+        Action::Stop => foo(),
+    }
+}
+"#####,
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    match action {
+        Action::Move(..) | Action::Stop => foo(),
+    }
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_move_arm_cond_to_match_guard() {
+    check_doc_test(
+        "move_arm_cond_to_match_guard",
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    match action {
+        Action::Move { distance } => <|>if distance > 10 { foo() },
+        _ => (),
+    }
+}
+"#####,
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    match action {
+        Action::Move { distance } if distance > 10 => foo(),
+        _ => (),
+    }
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_move_bounds_to_where_clause() {
+    check_doc_test(
+        "move_bounds_to_where_clause",
+        r#####"
+fn apply<T, U, <|>F: FnOnce(T) -> U>(f: F, x: T) -> U {
+    f(x)
+}
+"#####,
+        r#####"
+fn apply<T, U, F>(f: F, x: T) -> U where F: FnOnce(T) -> U {
+    f(x)
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_move_guard_to_arm_body() {
+    check_doc_test(
+        "move_guard_to_arm_body",
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    match action {
+        Action::Move { distance } <|>if distance > 10 => foo(),
+        _ => (),
+    }
+}
+"#####,
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    match action {
+        Action::Move { distance } => if distance > 10 {
+            foo()
+        },
+        _ => (),
+    }
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_remove_dbg() {
+    check_doc_test(
+        "remove_dbg",
+        r#####"
+fn main() {
+    <|>dbg!(92);
+}
+"#####,
+        r#####"
+fn main() {
+    92;
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_remove_hash() {
+    check_doc_test(
+        "remove_hash",
+        r#####"
+fn main() {
+    r#"Hello,<|> World!"#;
+}
+"#####,
+        r#####"
+fn main() {
+    r"Hello, World!";
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_remove_mut() {
+    check_doc_test(
+        "remove_mut",
+        r#####"
+impl Walrus {
+    fn feed(&mut<|> self, amount: u32) {}
+}
+"#####,
+        r#####"
+impl Walrus {
+    fn feed(&self, amount: u32) {}
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_remove_unused_param() {
+    check_doc_test(
+        "remove_unused_param",
+        r#####"
+fn frobnicate(x: i32<|>) {}
+
+fn main() {
+    frobnicate(92);
+}
+"#####,
+        r#####"
+fn frobnicate() {}
+
+fn main() {
+    frobnicate();
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_reorder_fields() {
+    check_doc_test(
+        "reorder_fields",
+        r#####"
+struct Foo {foo: i32, bar: i32};
+const test: Foo = <|>Foo {bar: 0, foo: 1}
+"#####,
+        r#####"
+struct Foo {foo: i32, bar: i32};
+const test: Foo = Foo {foo: 1, bar: 0}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_replace_if_let_with_match() {
+    check_doc_test(
+        "replace_if_let_with_match",
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    <|>if let Action::Move { distance } = action {
+        foo(distance)
+    } else {
+        bar()
+    }
+}
+"#####,
+        r#####"
+enum Action { Move { distance: u32 }, Stop }
+
+fn handle(action: Action) {
+    match action {
+        Action::Move { distance } => foo(distance),
+        _ => bar(),
+    }
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_replace_let_with_if_let() {
+    check_doc_test(
+        "replace_let_with_if_let",
+        r#####"
+enum Option<T> { Some(T), None }
+
+fn main(action: Action) {
+    <|>let x = compute();
+}
+
+fn compute() -> Option<i32> { None }
+"#####,
+        r#####"
+enum Option<T> { Some(T), None }
+
+fn main(action: Action) {
+    if let Some(x) = compute() {
+    }
+}
+
+fn compute() -> Option<i32> { None }
+"#####,
+    )
+}
+
+#[test]
+fn doctest_replace_qualified_name_with_use() {
+    check_doc_test(
+        "replace_qualified_name_with_use",
+        r#####"
+fn process(map: std::collections::<|>HashMap<String, String>) {}
+"#####,
+        r#####"
+use std::collections::HashMap;
+
+fn process(map: HashMap<String, String>) {}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_replace_unwrap_with_match() {
+    check_doc_test(
+        "replace_unwrap_with_match",
+        r#####"
+enum Result<T, E> { Ok(T), Err(E) }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = x.<|>unwrap();
+}
+"#####,
+        r#####"
+enum Result<T, E> { Ok(T), Err(E) }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = match x {
+        Ok(a) => a,
+        $0_ => unreachable!(),
+    };
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_split_import() {
+    check_doc_test(
+        "split_import",
+        r#####"
+use std::<|>collections::HashMap;
+"#####,
+        r#####"
+use std::{collections::HashMap};
+"#####,
+    )
+}
+
+#[test]
+fn doctest_unwrap_block() {
+    check_doc_test(
+        "unwrap_block",
+        r#####"
+fn foo() {
+    if true {<|>
+        println!("foo");
+    }
+}
+"#####,
+        r#####"
+fn foo() {
+    println!("foo");
+}
+"#####,
+    )
+}

crates/assists/src/utils.rs

@@ -0,0 +1,317 @@
+//! Assorted functions shared by several assists.
+pub(crate) mod insert_use;
+
+use std::{iter, ops};
+
+use hir::{Adt, Crate, Enum, ScopeDef, Semantics, Trait, Type};
+use ide_db::RootDatabase;
+use itertools::Itertools;
+use rustc_hash::FxHashSet;
+use syntax::{
+    ast::{self, make, NameOwner},
+    AstNode, Direction,
+    SyntaxKind::*,
+    SyntaxNode, TextSize, T,
+};
+
+use crate::assist_config::SnippetCap;
+
+pub(crate) use insert_use::{find_insert_use_container, insert_use_statement};
+
+pub(crate) fn unwrap_trivial_block(block: ast::BlockExpr) -> ast::Expr {
+    extract_trivial_expression(&block)
+        .filter(|expr| !expr.syntax().text().contains_char('\n'))
+        .unwrap_or_else(|| block.into())
+}
+
+pub fn extract_trivial_expression(block: &ast::BlockExpr) -> Option<ast::Expr> {
+    let has_anything_else = |thing: &SyntaxNode| -> bool {
+        let mut non_trivial_children =
+            block.syntax().children_with_tokens().filter(|it| match it.kind() {
+                WHITESPACE | T!['{'] | T!['}'] => false,
+                _ => it.as_node() != Some(thing),
+            });
+        non_trivial_children.next().is_some()
+    };
+
+    if let Some(expr) = block.expr() {
+        if has_anything_else(expr.syntax()) {
+            return None;
+        }
+        return Some(expr);
+    }
+    // Unwrap `{ continue; }`
+    let (stmt,) = block.statements().next_tuple()?;
+    if let ast::Stmt::ExprStmt(expr_stmt) = stmt {
+        if has_anything_else(expr_stmt.syntax()) {
+            return None;
+        }
+        let expr = expr_stmt.expr()?;
+        match expr.syntax().kind() {
+            CONTINUE_EXPR | BREAK_EXPR | RETURN_EXPR => return Some(expr),
+            _ => (),
+        }
+    }
+    None
+}
+
+#[derive(Clone, Copy, Debug)]
+pub(crate) enum Cursor<'a> {
+    Replace(&'a SyntaxNode),
+    Before(&'a SyntaxNode),
+}
+
+impl<'a> Cursor<'a> {
+    fn node(self) -> &'a SyntaxNode {
+        match self {
+            Cursor::Replace(node) | Cursor::Before(node) => node,
+        }
+    }
+}
+
+pub(crate) fn render_snippet(_cap: SnippetCap, node: &SyntaxNode, cursor: Cursor) -> String {
+    assert!(cursor.node().ancestors().any(|it| it == *node));
+    let range = cursor.node().text_range() - node.text_range().start();
+    let range: ops::Range<usize> = range.into();
+
+    let mut placeholder = cursor.node().to_string();
+    escape(&mut placeholder);
+    let tab_stop = match cursor {
+        Cursor::Replace(placeholder) => format!("${{0:{}}}", placeholder),
+        Cursor::Before(placeholder) => format!("$0{}", placeholder),
+    };
+
+    let mut buf = node.to_string();
+    buf.replace_range(range, &tab_stop);
+    return buf;
+
+    fn escape(buf: &mut String) {
+        stdx::replace(buf, '{', r"\{");
+        stdx::replace(buf, '}', r"\}");
+        stdx::replace(buf, '$', r"\$");
+    }
+}
+
+pub fn get_missing_assoc_items(
+    sema: &Semantics<RootDatabase>,
+    impl_def: &ast::Impl,
+) -> Vec<hir::AssocItem> {
+    // Names must be unique between constants and functions. However, type aliases
+    // may share the same name as a function or constant.
+    let mut impl_fns_consts = FxHashSet::default();
+    let mut impl_type = FxHashSet::default();
+
+    if let Some(item_list) = impl_def.assoc_item_list() {
+        for item in item_list.assoc_items() {
+            match item {
+                ast::AssocItem::Fn(f) => {
+                    if let Some(n) = f.name() {
+                        impl_fns_consts.insert(n.syntax().to_string());
+                    }
+                }
+
+                ast::AssocItem::TypeAlias(t) => {
+                    if let Some(n) = t.name() {
+                        impl_type.insert(n.syntax().to_string());
+                    }
+                }
+
+                ast::AssocItem::Const(c) => {
+                    if let Some(n) = c.name() {
+                        impl_fns_consts.insert(n.syntax().to_string());
+                    }
+                }
+                ast::AssocItem::MacroCall(_) => (),
+            }
+        }
+    }
+
+    resolve_target_trait(sema, impl_def).map_or(vec![], |target_trait| {
+        target_trait
+            .items(sema.db)
+            .iter()
+            .filter(|i| match i {
+                hir::AssocItem::Function(f) => {
+                    !impl_fns_consts.contains(&f.name(sema.db).to_string())
+                }
+                hir::AssocItem::TypeAlias(t) => !impl_type.contains(&t.name(sema.db).to_string()),
+                hir::AssocItem::Const(c) => c
+                    .name(sema.db)
+                    .map(|n| !impl_fns_consts.contains(&n.to_string()))
+                    .unwrap_or_default(),
+            })
+            .cloned()
+            .collect()
+    })
+}
+
+pub(crate) fn resolve_target_trait(
+    sema: &Semantics<RootDatabase>,
+    impl_def: &ast::Impl,
+) -> Option<hir::Trait> {
+    let ast_path =
+        impl_def.trait_().map(|it| it.syntax().clone()).and_then(ast::PathType::cast)?.path()?;
+
+    match sema.resolve_path(&ast_path) {
+        Some(hir::PathResolution::Def(hir::ModuleDef::Trait(def))) => Some(def),
+        _ => None,
+    }
+}
+
+pub(crate) fn vis_offset(node: &SyntaxNode) -> TextSize {
+    node.children_with_tokens()
+        .find(|it| !matches!(it.kind(), WHITESPACE | COMMENT | ATTR))
+        .map(|it| it.text_range().start())
+        .unwrap_or_else(|| node.text_range().start())
+}
+
+pub(crate) fn invert_boolean_expression(expr: ast::Expr) -> ast::Expr {
+    if let Some(expr) = invert_special_case(&expr) {
+        return expr;
+    }
+    make::expr_prefix(T![!], expr)
+}
+
+fn invert_special_case(expr: &ast::Expr) -> Option<ast::Expr> {
+    match expr {
+        ast::Expr::BinExpr(bin) => match bin.op_kind()? {
+            ast::BinOp::NegatedEqualityTest => bin.replace_op(T![==]).map(|it| it.into()),
+            ast::BinOp::EqualityTest => bin.replace_op(T![!=]).map(|it| it.into()),
+            _ => None,
+        },
+        ast::Expr::PrefixExpr(pe) if pe.op_kind()? == ast::PrefixOp::Not => pe.expr(),
+        // FIXME:
+        // ast::Expr::Literal(true | false )
+        _ => None,
+    }
+}
+
+#[derive(Clone, Copy)]
+pub enum TryEnum {
+    Result,
+    Option,
+}
+
+impl TryEnum {
+    const ALL: [TryEnum; 2] = [TryEnum::Option, TryEnum::Result];
+
+    pub fn from_ty(sema: &Semantics<RootDatabase>, ty: &Type) -> Option<TryEnum> {
+        let enum_ = match ty.as_adt() {
+            Some(Adt::Enum(it)) => it,
+            _ => return None,
+        };
+        TryEnum::ALL.iter().find_map(|&var| {
+            if &enum_.name(sema.db).to_string() == var.type_name() {
+                return Some(var);
+            }
+            None
+        })
+    }
+
+    pub(crate) fn happy_case(self) -> &'static str {
+        match self {
+            TryEnum::Result => "Ok",
+            TryEnum::Option => "Some",
+        }
+    }
+
+    pub(crate) fn sad_pattern(self) -> ast::Pat {
+        match self {
+            TryEnum::Result => make::tuple_struct_pat(
+                make::path_unqualified(make::path_segment(make::name_ref("Err"))),
+                iter::once(make::wildcard_pat().into()),
+            )
+            .into(),
+            TryEnum::Option => make::ident_pat(make::name("None")).into(),
+        }
+    }
+
+    fn type_name(self) -> &'static str {
+        match self {
+            TryEnum::Result => "Result",
+            TryEnum::Option => "Option",
+        }
+    }
+}
+
+/// Helps with finding well-know things inside the standard library. This is
+/// somewhat similar to the known paths infra inside hir, but it different; We
+/// want to make sure that IDE specific paths don't become interesting inside
+/// the compiler itself as well.
+pub(crate) struct FamousDefs<'a, 'b>(pub(crate) &'a Semantics<'b, RootDatabase>, pub(crate) Crate);
+
+#[allow(non_snake_case)]
+impl FamousDefs<'_, '_> {
+    #[cfg(test)]
+    pub(crate) const FIXTURE: &'static str = r#"//- /libcore.rs crate:core
+pub mod convert {
+    pub trait From<T> {
+        fn from(T) -> Self;
+    }
+}
+
+pub mod option {
+    pub enum Option<T> { None, Some(T)}
+}
+
+pub mod prelude {
+    pub use crate::{convert::From, option::Option::{self, *}};
+}
+#[prelude_import]
+pub use prelude::*;
+"#;
+
+    pub(crate) fn core_convert_From(&self) -> Option<Trait> {
+        self.find_trait("core:convert:From")
+    }
+
+    pub(crate) fn core_option_Option(&self) -> Option<Enum> {
+        self.find_enum("core:option:Option")
+    }
+
+    fn find_trait(&self, path: &str) -> Option<Trait> {
+        match self.find_def(path)? {
+            hir::ScopeDef::ModuleDef(hir::ModuleDef::Trait(it)) => Some(it),
+            _ => None,
+        }
+    }
+
+    fn find_enum(&self, path: &str) -> Option<Enum> {
+        match self.find_def(path)? {
+            hir::ScopeDef::ModuleDef(hir::ModuleDef::Adt(hir::Adt::Enum(it))) => Some(it),
+            _ => None,
+        }
+    }
+
+    fn find_def(&self, path: &str) -> Option<ScopeDef> {
+        let db = self.0.db;
+        let mut path = path.split(':');
+        let trait_ = path.next_back()?;
+        let std_crate = path.next()?;
+        let std_crate = self
+            .1
+            .dependencies(db)
+            .into_iter()
+            .find(|dep| &dep.name.to_string() == std_crate)?
+            .krate;
+
+        let mut module = std_crate.root_module(db);
+        for segment in path {
+            module = module.children(db).find_map(|child| {
+                let name = child.name(db)?;
+                if &name.to_string() == segment {
+                    Some(child)
+                } else {
+                    None
+                }
+            })?;
+        }
+        let def =
+            module.scope(db, None).into_iter().find(|(name, _def)| &name.to_string() == trait_)?.1;
+        Some(def)
+    }
+}
+
+pub(crate) fn next_prev() -> impl Iterator<Item = Direction> {
+    [Direction::Next, Direction::Prev].iter().copied()
+}

crates/assists/src/utils/insert_use.rs

@@ -0,0 +1,546 @@
+//! Handle syntactic aspects of inserting a new `use`.
+// FIXME: rewrite according to the plan, outlined in
+// https://github.com/rust-analyzer/rust-analyzer/issues/3301#issuecomment-592931553
+
+use std::iter::successors;
+
+use either::Either;
+use syntax::{
+    ast::{self, NameOwner, VisibilityOwner},
+    AstNode, AstToken, Direction, SmolStr,
+    SyntaxKind::{PATH, PATH_SEGMENT},
+    SyntaxNode, SyntaxToken, T,
+};
+use text_edit::TextEditBuilder;
+
+use crate::assist_context::AssistContext;
+
+/// Determines the containing syntax node in which to insert a `use` statement affecting `position`.
+pub(crate) fn find_insert_use_container(
+    position: &SyntaxNode,
+    ctx: &AssistContext,
+) -> Option<Either<ast::ItemList, ast::SourceFile>> {
+    ctx.sema.ancestors_with_macros(position.clone()).find_map(|n| {
+        if let Some(module) = ast::Module::cast(n.clone()) {
+            return module.item_list().map(|it| Either::Left(it));
+        }
+        Some(Either::Right(ast::SourceFile::cast(n)?))
+    })
+}
+
+/// Creates and inserts a use statement for the given path to import.
+/// The use statement is inserted in the scope most appropriate to the
+/// the cursor position given, additionally merged with the existing use imports.
+pub(crate) fn insert_use_statement(
+    // Ideally the position of the cursor, used to
+    position: &SyntaxNode,
+    path_to_import: &str,
+    ctx: &AssistContext,
+    builder: &mut TextEditBuilder,
+) {
+    let target = path_to_import.split("::").map(SmolStr::new).collect::<Vec<_>>();
+    let container = find_insert_use_container(position, ctx);
+
+    if let Some(container) = container {
+        let syntax = container.either(|l| l.syntax().clone(), |r| r.syntax().clone());
+        let action = best_action_for_target(syntax, position.clone(), &target);
+        make_assist(&action, &target, builder);
+    }
+}
+
+fn collect_path_segments_raw(
+    segments: &mut Vec<ast::PathSegment>,
+    mut path: ast::Path,
+) -> Option<usize> {
+    let oldlen = segments.len();
+    loop {
+        let mut children = path.syntax().children_with_tokens();
+        let (first, second, third) = (
+            children.next().map(|n| (n.clone(), n.kind())),
+            children.next().map(|n| (n.clone(), n.kind())),
+            children.next().map(|n| (n.clone(), n.kind())),
+        );
+        match (first, second, third) {
+            (Some((subpath, PATH)), Some((_, T![::])), Some((segment, PATH_SEGMENT))) => {
+                path = ast::Path::cast(subpath.as_node()?.clone())?;
+                segments.push(ast::PathSegment::cast(segment.as_node()?.clone())?);
+            }
+            (Some((segment, PATH_SEGMENT)), _, _) => {
+                segments.push(ast::PathSegment::cast(segment.as_node()?.clone())?);
+                break;
+            }
+            (_, _, _) => return None,
+        }
+    }
+    // We need to reverse only the new added segments
+    let only_new_segments = segments.split_at_mut(oldlen).1;
+    only_new_segments.reverse();
+    Some(segments.len() - oldlen)
+}
+
+fn fmt_segments_raw(segments: &[SmolStr], buf: &mut String) {
+    let mut iter = segments.iter();
+    if let Some(s) = iter.next() {
+        buf.push_str(s);
+    }
+    for s in iter {
+        buf.push_str("::");
+        buf.push_str(s);
+    }
+}
+
+/// Returns the number of common segments.
+fn compare_path_segments(left: &[SmolStr], right: &[ast::PathSegment]) -> usize {
+    left.iter().zip(right).take_while(|(l, r)| compare_path_segment(l, r)).count()
+}
+
+fn compare_path_segment(a: &SmolStr, b: &ast::PathSegment) -> bool {
+    if let Some(kb) = b.kind() {
+        match kb {
+            ast::PathSegmentKind::Name(nameref_b) => a == nameref_b.text(),
+            ast::PathSegmentKind::SelfKw => a == "self",
+            ast::PathSegmentKind::SuperKw => a == "super",
+            ast::PathSegmentKind::CrateKw => a == "crate",
+            ast::PathSegmentKind::Type { .. } => false, // not allowed in imports
+        }
+    } else {
+        false
+    }
+}
+
+fn compare_path_segment_with_name(a: &SmolStr, b: &ast::Name) -> bool {
+    a == b.text()
+}
+
+#[derive(Clone, Debug)]
+enum ImportAction {
+    Nothing,
+    // Add a brand new use statement.
+    AddNewUse {
+        anchor: Option<SyntaxNode>, // anchor node
+        add_after_anchor: bool,
+    },
+
+    // To split an existing use statement creating a nested import.
+    AddNestedImport {
+        // how may segments matched with the target path
+        common_segments: usize,
+        path_to_split: ast::Path,
+        // the first segment of path_to_split we want to add into the new nested list
+        first_segment_to_split: Option<ast::PathSegment>,
+        // Wether to add 'self' in addition to the target path
+        add_self: bool,
+    },
+    // To add the target path to an existing nested import tree list.
+    AddInTreeList {
+        common_segments: usize,
+        // The UseTreeList where to add the target path
+        tree_list: ast::UseTreeList,
+        add_self: bool,
+    },
+}
+
+impl ImportAction {
+    fn add_new_use(anchor: Option<SyntaxNode>, add_after_anchor: bool) -> Self {
+        ImportAction::AddNewUse { anchor, add_after_anchor }
+    }
+
+    fn add_nested_import(
+        common_segments: usize,
+        path_to_split: ast::Path,
+        first_segment_to_split: Option<ast::PathSegment>,
+        add_self: bool,
+    ) -> Self {
+        ImportAction::AddNestedImport {
+            common_segments,
+            path_to_split,
+            first_segment_to_split,
+            add_self,
+        }
+    }
+
+    fn add_in_tree_list(
+        common_segments: usize,
+        tree_list: ast::UseTreeList,
+        add_self: bool,
+    ) -> Self {
+        ImportAction::AddInTreeList { common_segments, tree_list, add_self }
+    }
+
+    fn better(left: ImportAction, right: ImportAction) -> ImportAction {
+        if left.is_better(&right) {
+            left
+        } else {
+            right
+        }
+    }
+
+    fn is_better(&self, other: &ImportAction) -> bool {
+        match (self, other) {
+            (ImportAction::Nothing, _) => true,
+            (ImportAction::AddInTreeList { .. }, ImportAction::Nothing) => false,
+            (
+                ImportAction::AddNestedImport { common_segments: n, .. },
+                ImportAction::AddInTreeList { common_segments: m, .. },
+            )
+            | (
+                ImportAction::AddInTreeList { common_segments: n, .. },
+                ImportAction::AddNestedImport { common_segments: m, .. },
+            )
+            | (
+                ImportAction::AddInTreeList { common_segments: n, .. },
+                ImportAction::AddInTreeList { common_segments: m, .. },
+            )
+            | (
+                ImportAction::AddNestedImport { common_segments: n, .. },
+                ImportAction::AddNestedImport { common_segments: m, .. },
+            ) => n > m,
+            (ImportAction::AddInTreeList { .. }, _) => true,
+            (ImportAction::AddNestedImport { .. }, ImportAction::Nothing) => false,
+            (ImportAction::AddNestedImport { .. }, _) => true,
+            (ImportAction::AddNewUse { .. }, _) => false,
+        }
+    }
+}
+
+// Find out the best ImportAction to import target path against current_use_tree.
+// If current_use_tree has a nested import the function gets called recursively on every UseTree inside a UseTreeList.
+fn walk_use_tree_for_best_action(
+    current_path_segments: &mut Vec<ast::PathSegment>, // buffer containing path segments
+    current_parent_use_tree_list: Option<ast::UseTreeList>, // will be Some value if we are in a nested import
+    current_use_tree: ast::UseTree, // the use tree we are currently examinating
+    target: &[SmolStr],             // the path we want to import
+) -> ImportAction {
+    // We save the number of segments in the buffer so we can restore the correct segments
+    // before returning. Recursive call will add segments so we need to delete them.
+    let prev_len = current_path_segments.len();
+
+    let tree_list = current_use_tree.use_tree_list();
+    let alias = current_use_tree.rename();
+
+    let path = match current_use_tree.path() {
+        Some(path) => path,
+        None => {
+            // If the use item don't have a path, it means it's broken (syntax error)
+            return ImportAction::add_new_use(
+                current_use_tree
+                    .syntax()
+                    .ancestors()
+                    .find_map(ast::Use::cast)
+                    .map(|it| it.syntax().clone()),
+                true,
+            );
+        }
+    };
+
+    // This can happen only if current_use_tree is a direct child of a UseItem
+    if let Some(name) = alias.and_then(|it| it.name()) {
+        if compare_path_segment_with_name(&target[0], &name) {
+            return ImportAction::Nothing;
+        }
+    }
+
+    collect_path_segments_raw(current_path_segments, path.clone());
+
+    // We compare only the new segments added in the line just above.
+    // The first prev_len segments were already compared in 'parent' recursive calls.
+    let left = target.split_at(prev_len).1;
+    let right = current_path_segments.split_at(prev_len).1;
+    let common = compare_path_segments(left, &right);
+    let mut action = match common {
+        0 => ImportAction::add_new_use(
+            // e.g: target is std::fmt and we can have
+            // use foo::bar
+            // We add a brand new use statement
+            current_use_tree
+                .syntax()
+                .ancestors()
+                .find_map(ast::Use::cast)
+                .map(|it| it.syntax().clone()),
+            true,
+        ),
+        common if common == left.len() && left.len() == right.len() => {
+            // e.g: target is std::fmt and we can have
+            // 1- use std::fmt;
+            // 2- use std::fmt::{ ... }
+            if let Some(list) = tree_list {
+                // In case 2 we need to add self to the nested list
+                // unless it's already there
+                let has_self = list.use_trees().map(|it| it.path()).any(|p| {
+                    p.and_then(|it| it.segment())
+                        .and_then(|it| it.kind())
+                        .filter(|k| *k == ast::PathSegmentKind::SelfKw)
+                        .is_some()
+                });
+
+                if has_self {
+                    ImportAction::Nothing
+                } else {
+                    ImportAction::add_in_tree_list(current_path_segments.len(), list, true)
+                }
+            } else {
+                // Case 1
+                ImportAction::Nothing
+            }
+        }
+        common if common != left.len() && left.len() == right.len() => {
+            // e.g: target is std::fmt and we have
+            // use std::io;
+            // We need to split.
+            let segments_to_split = current_path_segments.split_at(prev_len + common).1;
+            ImportAction::add_nested_import(
+                prev_len + common,
+                path,
+                Some(segments_to_split[0].clone()),
+                false,
+            )
+        }
+        common if common == right.len() && left.len() > right.len() => {
+            // e.g: target is std::fmt and we can have
+            // 1- use std;
+            // 2- use std::{ ... };
+
+            // fallback action
+            let mut better_action = ImportAction::add_new_use(
+                current_use_tree
+                    .syntax()
+                    .ancestors()
+                    .find_map(ast::Use::cast)
+                    .map(|it| it.syntax().clone()),
+                true,
+            );
+            if let Some(list) = tree_list {
+                // Case 2, check recursively if the path is already imported in the nested list
+                for u in list.use_trees() {
+                    let child_action = walk_use_tree_for_best_action(
+                        current_path_segments,
+                        Some(list.clone()),
+                        u,
+                        target,
+                    );
+                    if child_action.is_better(&better_action) {
+                        better_action = child_action;
+                        if let ImportAction::Nothing = better_action {
+                            return better_action;
+                        }
+                    }
+                }
+            } else {
+                // Case 1, split adding self
+                better_action = ImportAction::add_nested_import(prev_len + common, path, None, true)
+            }
+            better_action
+        }
+        common if common == left.len() && left.len() < right.len() => {
+            // e.g: target is std::fmt and we can have
+            // use std::fmt::Debug;
+            let segments_to_split = current_path_segments.split_at(prev_len + common).1;
+            ImportAction::add_nested_import(
+                prev_len + common,
+                path,
+                Some(segments_to_split[0].clone()),
+                true,
+            )
+        }
+        common if common < left.len() && common < right.len() => {
+            // e.g: target is std::fmt::nested::Debug
+            // use std::fmt::Display
+            let segments_to_split = current_path_segments.split_at(prev_len + common).1;
+            ImportAction::add_nested_import(
+                prev_len + common,
+                path,
+                Some(segments_to_split[0].clone()),
+                false,
+            )
+        }
+        _ => unreachable!(),
+    };
+
+    // If we are inside a UseTreeList adding a use statement become adding to the existing
+    // tree list.
+    action = match (current_parent_use_tree_list, action.clone()) {
+        (Some(use_tree_list), ImportAction::AddNewUse { .. }) => {
+            ImportAction::add_in_tree_list(prev_len, use_tree_list, false)
+        }
+        (_, _) => action,
+    };
+
+    // We remove the segments added
+    current_path_segments.truncate(prev_len);
+    action
+}
+
+fn best_action_for_target(
+    container: SyntaxNode,
+    anchor: SyntaxNode,
+    target: &[SmolStr],
+) -> ImportAction {
+    let mut storage = Vec::with_capacity(16); // this should be the only allocation
+    let best_action = container
+        .children()
+        .filter_map(ast::Use::cast)
+        .filter(|u| u.visibility().is_none())
+        .filter_map(|it| it.use_tree())
+        .map(|u| walk_use_tree_for_best_action(&mut storage, None, u, target))
+        .fold(None, |best, a| match best {
+            Some(best) => Some(ImportAction::better(best, a)),
+            None => Some(a),
+        });
+
+    match best_action {
+        Some(action) => action,
+        None => {
+            // We have no action and no UseItem was found in container so we find
+            // another item and we use it as anchor.
+            // If there are no items above, we choose the target path itself as anchor.
+            // todo: we should include even whitespace blocks as anchor candidates
+            let anchor = container.children().next().or_else(|| Some(anchor));
+
+            let add_after_anchor = anchor
+                .clone()
+                .and_then(ast::Attr::cast)
+                .map(|attr| attr.kind() == ast::AttrKind::Inner)
+                .unwrap_or(false);
+            ImportAction::add_new_use(anchor, add_after_anchor)
+        }
+    }
+}
+
+fn make_assist(action: &ImportAction, target: &[SmolStr], edit: &mut TextEditBuilder) {
+    match action {
+        ImportAction::AddNewUse { anchor, add_after_anchor } => {
+            make_assist_add_new_use(anchor, *add_after_anchor, target, edit)
+        }
+        ImportAction::AddInTreeList { common_segments, tree_list, add_self } => {
+            // We know that the fist n segments already exists in the use statement we want
+            // to modify, so we want to add only the last target.len() - n segments.
+            let segments_to_add = target.split_at(*common_segments).1;
+            make_assist_add_in_tree_list(tree_list, segments_to_add, *add_self, edit)
+        }
+        ImportAction::AddNestedImport {
+            common_segments,
+            path_to_split,
+            first_segment_to_split,
+            add_self,
+        } => {
+            let segments_to_add = target.split_at(*common_segments).1;
+            make_assist_add_nested_import(
+                path_to_split,
+                first_segment_to_split,
+                segments_to_add,
+                *add_self,
+                edit,
+            )
+        }
+        _ => {}
+    }
+}
+
+fn make_assist_add_new_use(
+    anchor: &Option<SyntaxNode>,
+    after: bool,
+    target: &[SmolStr],
+    edit: &mut TextEditBuilder,
+) {
+    if let Some(anchor) = anchor {
+        let indent = leading_indent(anchor);
+        let mut buf = String::new();
+        if after {
+            buf.push_str("\n");
+            if let Some(spaces) = &indent {
+                buf.push_str(spaces);
+            }
+        }
+        buf.push_str("use ");
+        fmt_segments_raw(target, &mut buf);
+        buf.push_str(";");
+        if !after {
+            buf.push_str("\n\n");
+            if let Some(spaces) = &indent {
+                buf.push_str(&spaces);
+            }
+        }
+        let position = if after { anchor.text_range().end() } else { anchor.text_range().start() };
+        edit.insert(position, buf);
+    }
+}
+
+fn make_assist_add_in_tree_list(
+    tree_list: &ast::UseTreeList,
+    target: &[SmolStr],
+    add_self: bool,
+    edit: &mut TextEditBuilder,
+) {
+    let last = tree_list.use_trees().last();
+    if let Some(last) = last {
+        let mut buf = String::new();
+        let comma = last.syntax().siblings(Direction::Next).find(|n| n.kind() == T![,]);
+        let offset = if let Some(comma) = comma {
+            comma.text_range().end()
+        } else {
+            buf.push_str(",");
+            last.syntax().text_range().end()
+        };
+        if add_self {
+            buf.push_str(" self")
+        } else {
+            buf.push_str(" ");
+        }
+        fmt_segments_raw(target, &mut buf);
+        edit.insert(offset, buf);
+    } else {
+    }
+}
+
+fn make_assist_add_nested_import(
+    path: &ast::Path,
+    first_segment_to_split: &Option<ast::PathSegment>,
+    target: &[SmolStr],
+    add_self: bool,
+    edit: &mut TextEditBuilder,
+) {
+    let use_tree = path.syntax().ancestors().find_map(ast::UseTree::cast);
+    if let Some(use_tree) = use_tree {
+        let (start, add_colon_colon) = if let Some(first_segment_to_split) = first_segment_to_split
+        {
+            (first_segment_to_split.syntax().text_range().start(), false)
+        } else {
+            (use_tree.syntax().text_range().end(), true)
+        };
+        let end = use_tree.syntax().text_range().end();
+
+        let mut buf = String::new();
+        if add_colon_colon {
+            buf.push_str("::");
+        }
+        buf.push_str("{");
+        if add_self {
+            buf.push_str("self, ");
+        }
+        fmt_segments_raw(target, &mut buf);
+        if !target.is_empty() {
+            buf.push_str(", ");
+        }
+        edit.insert(start, buf);
+        edit.insert(end, "}".to_string());
+    }
+}
+
+/// If the node is on the beginning of the line, calculate indent.
+fn leading_indent(node: &SyntaxNode) -> Option<SmolStr> {
+    for token in prev_tokens(node.first_token()?) {
+        if let Some(ws) = ast::Whitespace::cast(token.clone()) {
+            let ws_text = ws.text();
+            if let Some(pos) = ws_text.rfind('\n') {
+                return Some(ws_text[pos + 1..].into());
+            }
+        }
+        if token.text().contains('\n') {
+            break;
+        }
+    }
+    return None;
+    fn prev_tokens(token: SyntaxToken) -> impl Iterator<Item = SyntaxToken> {
+        successors(token.prev_token(), |token| token.prev_token())
+    }
+}

crates/base_db/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "base_db"
+version = "0.0.0"
+license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false
+
+[dependencies]
+salsa = "0.15.2"
+rustc-hash = "1.1.0"
+
+syntax = { path = "../syntax" }
+cfg = { path = "../cfg" }
+profile = { path = "../profile" }
+tt = { path = "../tt" }
+test_utils = { path = "../test_utils" }
+vfs = { path = "../vfs" }
+stdx = { path = "../stdx" }

crates/base_db/src/fixture.rs

@@ -0,0 +1,228 @@
+//! Fixtures are strings containing rust source code with optional metadata.
+//! A fixture without metadata is parsed into a single source file.
+//! Use this to test functionality local to one file.
+//!
+//! Simple Example:
+//! ```
+//! r#"
+//! fn main() {
+//!     println!("Hello World")
+//! }
+//! "#
+//! ```
+//!
+//! Metadata can be added to a fixture after a `//-` comment.
+//! The basic form is specifying filenames,
+//! which is also how to define multiple files in a single test fixture
+//!
+//! Example using two files in the same crate:
+//! ```
+//! "
+//! //- /main.rs
+//! mod foo;
+//! fn main() {
+//!     foo::bar();
+//! }
+//!
+//! //- /foo.rs
+//! pub fn bar() {}
+//! "
+//! ```
+//!
+//! Example using two crates with one file each, with one crate depending on the other:
+//! ```
+//! r#"
+//! //- /main.rs crate:a deps:b
+//! fn main() {
+//!     b::foo();
+//! }
+//! //- /lib.rs crate:b
+//! pub fn b() {
+//!     println!("Hello World")
+//! }
+//! "#
+//! ```
+//!
+//! Metadata allows specifying all settings and variables
+//! that are available in a real rust project:
+//! - crate names via `crate:cratename`
+//! - dependencies via `deps:dep1,dep2`
+//! - configuration settings via `cfg:dbg=false,opt_level=2`
+//! - environment variables via `env:PATH=/bin,RUST_LOG=debug`
+//!
+//! Example using all available metadata:
+//! ```
+//! "
+//! //- /lib.rs crate:foo deps:bar,baz cfg:foo=a,bar=b env:OUTDIR=path/to,OTHER=foo
+//! fn insert_source_code_here() {}
+//! "
+//! ```
+use std::{str::FromStr, sync::Arc};
+
+use cfg::CfgOptions;
+use rustc_hash::FxHashMap;
+use test_utils::{extract_range_or_offset, Fixture, RangeOrOffset, CURSOR_MARKER};
+use vfs::{file_set::FileSet, VfsPath};
+
+use crate::{
+    input::CrateName, CrateGraph, CrateId, Edition, Env, FileId, FilePosition, SourceDatabaseExt,
+    SourceRoot, SourceRootId,
+};
+
+pub const WORKSPACE: SourceRootId = SourceRootId(0);
+
+pub trait WithFixture: Default + SourceDatabaseExt + 'static {
+    fn with_single_file(text: &str) -> (Self, FileId) {
+        let mut db = Self::default();
+        let (_, files) = with_files(&mut db, text);
+        assert_eq!(files.len(), 1);
+        (db, files[0])
+    }
+
+    fn with_files(ra_fixture: &str) -> Self {
+        let mut db = Self::default();
+        let (pos, _) = with_files(&mut db, ra_fixture);
+        assert!(pos.is_none());
+        db
+    }
+
+    fn with_position(ra_fixture: &str) -> (Self, FilePosition) {
+        let (db, file_id, range_or_offset) = Self::with_range_or_offset(ra_fixture);
+        let offset = match range_or_offset {
+            RangeOrOffset::Range(_) => panic!(),
+            RangeOrOffset::Offset(it) => it,
+        };
+        (db, FilePosition { file_id, offset })
+    }
+
+    fn with_range_or_offset(ra_fixture: &str) -> (Self, FileId, RangeOrOffset) {
+        let mut db = Self::default();
+        let (pos, _) = with_files(&mut db, ra_fixture);
+        let (file_id, range_or_offset) = pos.unwrap();
+        (db, file_id, range_or_offset)
+    }
+
+    fn test_crate(&self) -> CrateId {
+        let crate_graph = self.crate_graph();
+        let mut it = crate_graph.iter();
+        let res = it.next().unwrap();
+        assert!(it.next().is_none());
+        res
+    }
+}
+
+impl<DB: SourceDatabaseExt + Default + 'static> WithFixture for DB {}
+
+fn with_files(
+    db: &mut dyn SourceDatabaseExt,
+    fixture: &str,
+) -> (Option<(FileId, RangeOrOffset)>, Vec<FileId>) {
+    let fixture = Fixture::parse(fixture);
+
+    let mut files = Vec::new();
+    let mut crate_graph = CrateGraph::default();
+    let mut crates = FxHashMap::default();
+    let mut crate_deps = Vec::new();
+    let mut default_crate_root: Option<FileId> = None;
+
+    let mut file_set = FileSet::default();
+    let source_root_id = WORKSPACE;
+    let source_root_prefix = "/".to_string();
+    let mut file_id = FileId(0);
+
+    let mut file_position = None;
+
+    for entry in fixture {
+        let text = if entry.text.contains(CURSOR_MARKER) {
+            let (range_or_offset, text) = extract_range_or_offset(&entry.text);
+            assert!(file_position.is_none());
+            file_position = Some((file_id, range_or_offset));
+            text.to_string()
+        } else {
+            entry.text.clone()
+        };
+
+        let meta = FileMeta::from(entry);
+        assert!(meta.path.starts_with(&source_root_prefix));
+
+        if let Some(krate) = meta.krate {
+            let crate_id = crate_graph.add_crate_root(
+                file_id,
+                meta.edition,
+                Some(krate.clone()),
+                meta.cfg,
+                meta.env,
+                Default::default(),
+            );
+            let crate_name = CrateName::new(&krate).unwrap();
+            let prev = crates.insert(crate_name.clone(), crate_id);
+            assert!(prev.is_none());
+            for dep in meta.deps {
+                let dep = CrateName::new(&dep).unwrap();
+                crate_deps.push((crate_name.clone(), dep))
+            }
+        } else if meta.path == "/main.rs" || meta.path == "/lib.rs" {
+            assert!(default_crate_root.is_none());
+            default_crate_root = Some(file_id);
+        }
+
+        db.set_file_text(file_id, Arc::new(text));
+        db.set_file_source_root(file_id, source_root_id);
+        let path = VfsPath::new_virtual_path(meta.path);
+        file_set.insert(file_id, path.into());
+        files.push(file_id);
+        file_id.0 += 1;
+    }
+
+    if crates.is_empty() {
+        let crate_root = default_crate_root.unwrap();
+        crate_graph.add_crate_root(
+            crate_root,
+            Edition::Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+    } else {
+        for (from, to) in crate_deps {
+            let from_id = crates[&from];
+            let to_id = crates[&to];
+            crate_graph.add_dep(from_id, CrateName::new(&to).unwrap(), to_id).unwrap();
+        }
+    }
+
+    db.set_source_root(source_root_id, Arc::new(SourceRoot::new_local(file_set)));
+    db.set_crate_graph(Arc::new(crate_graph));
+
+    (file_position, files)
+}
+
+struct FileMeta {
+    path: String,
+    krate: Option<String>,
+    deps: Vec<String>,
+    cfg: CfgOptions,
+    edition: Edition,
+    env: Env,
+}
+
+impl From<Fixture> for FileMeta {
+    fn from(f: Fixture) -> FileMeta {
+        let mut cfg = CfgOptions::default();
+        f.cfg_atoms.iter().for_each(|it| cfg.insert_atom(it.into()));
+        f.cfg_key_values.iter().for_each(|(k, v)| cfg.insert_key_value(k.into(), v.into()));
+
+        FileMeta {
+            path: f.path,
+            krate: f.krate,
+            deps: f.deps,
+            cfg,
+            edition: f
+                .edition
+                .as_ref()
+                .map_or(Edition::Edition2018, |v| Edition::from_str(&v).unwrap()),
+            env: f.env.into_iter().collect(),
+        }
+    }
+}

crates/base_db/src/input.rs

@@ -0,0 +1,453 @@
+//! This module specifies the input to rust-analyzer. In some sense, this is
+//! **the** most important module, because all other fancy stuff is strictly
+//! derived from this input.
+//!
+//! Note that neither this module, nor any other part of the analyzer's core do
+//! actual IO. See `vfs` and `project_model` in the `rust-analyzer` crate for how
+//! actual IO is done and lowered to input.
+
+use std::{fmt, iter::FromIterator, ops, str::FromStr, sync::Arc};
+
+use cfg::CfgOptions;
+use rustc_hash::{FxHashMap, FxHashSet};
+use syntax::SmolStr;
+use tt::TokenExpander;
+use vfs::file_set::FileSet;
+
+pub use vfs::FileId;
+
+/// Files are grouped into source roots. A source root is a directory on the
+/// file systems which is watched for changes. Typically it corresponds to a
+/// Rust crate. Source roots *might* be nested: in this case, a file belongs to
+/// the nearest enclosing source root. Paths to files are always relative to a
+/// source root, and the analyzer does not know the root path of the source root at
+/// all. So, a file from one source root can't refer to a file in another source
+/// root by path.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct SourceRootId(pub u32);
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct SourceRoot {
+    /// Sysroot or crates.io library.
+    ///
+    /// Libraries are considered mostly immutable, this assumption is used to
+    /// optimize salsa's query structure
+    pub is_library: bool,
+    pub(crate) file_set: FileSet,
+}
+
+impl SourceRoot {
+    pub fn new_local(file_set: FileSet) -> SourceRoot {
+        SourceRoot { is_library: false, file_set }
+    }
+    pub fn new_library(file_set: FileSet) -> SourceRoot {
+        SourceRoot { is_library: true, file_set }
+    }
+    pub fn iter(&self) -> impl Iterator<Item = FileId> + '_ {
+        self.file_set.iter()
+    }
+}
+
+/// `CrateGraph` is a bit of information which turns a set of text files into a
+/// number of Rust crates. Each crate is defined by the `FileId` of its root module,
+/// the set of cfg flags (not yet implemented) and the set of dependencies. Note
+/// that, due to cfg's, there might be several crates for a single `FileId`! As
+/// in the rust-lang proper, a crate does not have a name. Instead, names are
+/// specified on dependency edges. That is, a crate might be known under
+/// different names in different dependent crates.
+///
+/// Note that `CrateGraph` is build-system agnostic: it's a concept of the Rust
+/// language proper, not a concept of the build system. In practice, we get
+/// `CrateGraph` by lowering `cargo metadata` output.
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+pub struct CrateGraph {
+    arena: FxHashMap<CrateId, CrateData>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct CrateId(pub u32);
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct CrateName(SmolStr);
+
+impl CrateName {
+    /// Creates a crate name, checking for dashes in the string provided.
+    /// Dashes are not allowed in the crate names,
+    /// hence the input string is returned as `Err` for those cases.
+    pub fn new(name: &str) -> Result<CrateName, &str> {
+        if name.contains('-') {
+            Err(name)
+        } else {
+            Ok(Self(SmolStr::new(name)))
+        }
+    }
+
+    /// Creates a crate name, unconditionally replacing the dashes with underscores.
+    pub fn normalize_dashes(name: &str) -> CrateName {
+        Self(SmolStr::new(name.replace('-', "_")))
+    }
+}
+
+impl fmt::Display for CrateName {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl ops::Deref for CrateName {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        &*self.0
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct ProcMacroId(pub u32);
+
+#[derive(Debug, Clone)]
+pub struct ProcMacro {
+    pub name: SmolStr,
+    pub expander: Arc<dyn TokenExpander>,
+}
+
+impl Eq for ProcMacro {}
+impl PartialEq for ProcMacro {
+    fn eq(&self, other: &ProcMacro) -> bool {
+        self.name == other.name && Arc::ptr_eq(&self.expander, &other.expander)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CrateData {
+    pub root_file_id: FileId,
+    pub edition: Edition,
+    /// The name to display to the end user.
+    /// This actual crate name can be different in a particular dependent crate
+    /// or may even be missing for some cases, such as a dummy crate for the code snippet.
+    pub display_name: Option<String>,
+    pub cfg_options: CfgOptions,
+    pub env: Env,
+    pub dependencies: Vec<Dependency>,
+    pub proc_macro: Vec<ProcMacro>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum Edition {
+    Edition2018,
+    Edition2015,
+}
+
+#[derive(Default, Debug, Clone, PartialEq, Eq)]
+pub struct Env {
+    entries: FxHashMap<String, String>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Dependency {
+    pub crate_id: CrateId,
+    pub name: CrateName,
+}
+
+impl CrateGraph {
+    pub fn add_crate_root(
+        &mut self,
+        file_id: FileId,
+        edition: Edition,
+        display_name: Option<String>,
+        cfg_options: CfgOptions,
+        env: Env,
+        proc_macro: Vec<(SmolStr, Arc<dyn tt::TokenExpander>)>,
+    ) -> CrateId {
+        let proc_macro =
+            proc_macro.into_iter().map(|(name, it)| ProcMacro { name, expander: it }).collect();
+
+        let data = CrateData {
+            root_file_id: file_id,
+            edition,
+            display_name,
+            cfg_options,
+            env,
+            proc_macro,
+            dependencies: Vec::new(),
+        };
+        let crate_id = CrateId(self.arena.len() as u32);
+        let prev = self.arena.insert(crate_id, data);
+        assert!(prev.is_none());
+        crate_id
+    }
+
+    pub fn add_dep(
+        &mut self,
+        from: CrateId,
+        name: CrateName,
+        to: CrateId,
+    ) -> Result<(), CyclicDependenciesError> {
+        if self.dfs_find(from, to, &mut FxHashSet::default()) {
+            return Err(CyclicDependenciesError);
+        }
+        self.arena.get_mut(&from).unwrap().add_dep(name, to);
+        Ok(())
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.arena.is_empty()
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = CrateId> + '_ {
+        self.arena.keys().copied()
+    }
+
+    /// Returns an iterator over all transitive dependencies of the given crate.
+    pub fn transitive_deps(&self, of: CrateId) -> impl Iterator<Item = CrateId> + '_ {
+        let mut worklist = vec![of];
+        let mut deps = FxHashSet::default();
+
+        while let Some(krate) = worklist.pop() {
+            if !deps.insert(krate) {
+                continue;
+            }
+
+            worklist.extend(self[krate].dependencies.iter().map(|dep| dep.crate_id));
+        }
+
+        deps.remove(&of);
+        deps.into_iter()
+    }
+
+    // FIXME: this only finds one crate with the given root; we could have multiple
+    pub fn crate_id_for_crate_root(&self, file_id: FileId) -> Option<CrateId> {
+        let (&crate_id, _) =
+            self.arena.iter().find(|(_crate_id, data)| data.root_file_id == file_id)?;
+        Some(crate_id)
+    }
+
+    /// Extends this crate graph by adding a complete disjoint second crate
+    /// graph.
+    ///
+    /// The ids of the crates in the `other` graph are shifted by the return
+    /// amount.
+    pub fn extend(&mut self, other: CrateGraph) -> u32 {
+        let start = self.arena.len() as u32;
+        self.arena.extend(other.arena.into_iter().map(|(id, mut data)| {
+            let new_id = id.shift(start);
+            for dep in &mut data.dependencies {
+                dep.crate_id = dep.crate_id.shift(start);
+            }
+            (new_id, data)
+        }));
+        start
+    }
+
+    fn dfs_find(&self, target: CrateId, from: CrateId, visited: &mut FxHashSet<CrateId>) -> bool {
+        if !visited.insert(from) {
+            return false;
+        }
+
+        if target == from {
+            return true;
+        }
+
+        for dep in &self[from].dependencies {
+            let crate_id = dep.crate_id;
+            if self.dfs_find(target, crate_id, visited) {
+                return true;
+            }
+        }
+        false
+    }
+}
+
+impl ops::Index<CrateId> for CrateGraph {
+    type Output = CrateData;
+    fn index(&self, crate_id: CrateId) -> &CrateData {
+        &self.arena[&crate_id]
+    }
+}
+
+impl CrateId {
+    pub fn shift(self, amount: u32) -> CrateId {
+        CrateId(self.0 + amount)
+    }
+}
+
+impl CrateData {
+    fn add_dep(&mut self, name: CrateName, crate_id: CrateId) {
+        self.dependencies.push(Dependency { name, crate_id })
+    }
+}
+
+impl FromStr for Edition {
+    type Err = ParseEditionError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let res = match s {
+            "2015" => Edition::Edition2015,
+            "2018" => Edition::Edition2018,
+            _ => return Err(ParseEditionError { invalid_input: s.to_string() }),
+        };
+        Ok(res)
+    }
+}
+
+impl fmt::Display for Edition {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match self {
+            Edition::Edition2015 => "2015",
+            Edition::Edition2018 => "2018",
+        })
+    }
+}
+
+impl FromIterator<(String, String)> for Env {
+    fn from_iter<T: IntoIterator<Item = (String, String)>>(iter: T) -> Self {
+        Env { entries: FromIterator::from_iter(iter) }
+    }
+}
+
+impl Env {
+    pub fn set(&mut self, env: &str, value: String) {
+        self.entries.insert(env.to_owned(), value);
+    }
+
+    pub fn get(&self, env: &str) -> Option<String> {
+        self.entries.get(env).cloned()
+    }
+}
+
+#[derive(Debug)]
+pub struct ParseEditionError {
+    invalid_input: String,
+}
+
+impl fmt::Display for ParseEditionError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "invalid edition: {:?}", self.invalid_input)
+    }
+}
+
+impl std::error::Error for ParseEditionError {}
+
+#[derive(Debug)]
+pub struct CyclicDependenciesError;
+
+#[cfg(test)]
+mod tests {
+    use super::{CfgOptions, CrateGraph, CrateName, Dependency, Edition::Edition2018, Env, FileId};
+
+    #[test]
+    fn detect_cyclic_dependency_indirect() {
+        let mut graph = CrateGraph::default();
+        let crate1 = graph.add_crate_root(
+            FileId(1u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        let crate2 = graph.add_crate_root(
+            FileId(2u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        let crate3 = graph.add_crate_root(
+            FileId(3u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        assert!(graph.add_dep(crate1, CrateName::new("crate2").unwrap(), crate2).is_ok());
+        assert!(graph.add_dep(crate2, CrateName::new("crate3").unwrap(), crate3).is_ok());
+        assert!(graph.add_dep(crate3, CrateName::new("crate1").unwrap(), crate1).is_err());
+    }
+
+    #[test]
+    fn detect_cyclic_dependency_direct() {
+        let mut graph = CrateGraph::default();
+        let crate1 = graph.add_crate_root(
+            FileId(1u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        let crate2 = graph.add_crate_root(
+            FileId(2u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        assert!(graph.add_dep(crate1, CrateName::new("crate2").unwrap(), crate2).is_ok());
+        assert!(graph.add_dep(crate2, CrateName::new("crate2").unwrap(), crate2).is_err());
+    }
+
+    #[test]
+    fn it_works() {
+        let mut graph = CrateGraph::default();
+        let crate1 = graph.add_crate_root(
+            FileId(1u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        let crate2 = graph.add_crate_root(
+            FileId(2u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        let crate3 = graph.add_crate_root(
+            FileId(3u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        assert!(graph.add_dep(crate1, CrateName::new("crate2").unwrap(), crate2).is_ok());
+        assert!(graph.add_dep(crate2, CrateName::new("crate3").unwrap(), crate3).is_ok());
+    }
+
+    #[test]
+    fn dashes_are_normalized() {
+        let mut graph = CrateGraph::default();
+        let crate1 = graph.add_crate_root(
+            FileId(1u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        let crate2 = graph.add_crate_root(
+            FileId(2u32),
+            Edition2018,
+            None,
+            CfgOptions::default(),
+            Env::default(),
+            Default::default(),
+        );
+        assert!(graph
+            .add_dep(crate1, CrateName::normalize_dashes("crate-name-with-dashes"), crate2)
+            .is_ok());
+        assert_eq!(
+            graph[crate1].dependencies,
+            vec![Dependency {
+                crate_id: crate2,
+                name: CrateName::new("crate_name_with_dashes").unwrap()
+            }]
+        );
+    }
+}

crates/base_db/src/lib.rs

@@ -0,0 +1,167 @@
+//! base_db defines basic database traits. The concrete DB is defined by ide.
+mod cancellation;
+mod input;
+pub mod fixture;
+
+use std::{panic, sync::Arc};
+
+use rustc_hash::FxHashSet;
+use syntax::{ast, Parse, SourceFile, TextRange, TextSize};
+
+pub use crate::{
+    cancellation::Canceled,
+    input::{
+        CrateData, CrateGraph, CrateId, CrateName, Dependency, Edition, Env, FileId, ProcMacroId,
+        SourceRoot, SourceRootId,
+    },
+};
+pub use salsa;
+pub use vfs::{file_set::FileSet, VfsPath};
+
+#[macro_export]
+macro_rules! impl_intern_key {
+    ($name:ident) => {
+        impl $crate::salsa::InternKey for $name {
+            fn from_intern_id(v: $crate::salsa::InternId) -> Self {
+                $name(v)
+            }
+            fn as_intern_id(&self) -> $crate::salsa::InternId {
+                self.0
+            }
+        }
+    };
+}
+
+pub trait Upcast<T: ?Sized> {
+    fn upcast(&self) -> &T;
+}
+
+pub trait CheckCanceled {
+    /// Aborts current query if there are pending changes.
+    ///
+    /// rust-analyzer needs to be able to answer semantic questions about the
+    /// code while the code is being modified. A common problem is that a
+    /// long-running query is being calculated when a new change arrives.
+    ///
+    /// We can't just apply the change immediately: this will cause the pending
+    /// query to see inconsistent state (it will observe an absence of
+    /// repeatable read). So what we do is we **cancel** all pending queries
+    /// before applying the change.
+    ///
+    /// We implement cancellation by panicking with a special value and catching
+    /// it on the API boundary. Salsa explicitly supports this use-case.
+    fn check_canceled(&self);
+
+    fn catch_canceled<F, T>(&self, f: F) -> Result<T, Canceled>
+    where
+        Self: Sized + panic::RefUnwindSafe,
+        F: FnOnce(&Self) -> T + panic::UnwindSafe,
+    {
+        panic::catch_unwind(|| f(self)).map_err(|err| match err.downcast::<Canceled>() {
+            Ok(canceled) => *canceled,
+            Err(payload) => panic::resume_unwind(payload),
+        })
+    }
+}
+
+impl<T: salsa::Database> CheckCanceled for T {
+    fn check_canceled(&self) {
+        if self.salsa_runtime().is_current_revision_canceled() {
+            Canceled::throw()
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub struct FilePosition {
+    pub file_id: FileId,
+    pub offset: TextSize,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct FileRange {
+    pub file_id: FileId,
+    pub range: TextRange,
+}
+
+pub const DEFAULT_LRU_CAP: usize = 128;
+
+pub trait FileLoader {
+    /// Text of the file.
+    fn file_text(&self, file_id: FileId) -> Arc<String>;
+    /// Note that we intentionally accept a `&str` and not a `&Path` here. This
+    /// method exists to handle `#[path = "/some/path.rs"] mod foo;` and such,
+    /// so the input is guaranteed to be utf-8 string. One might be tempted to
+    /// introduce some kind of "utf-8 path with / separators", but that's a bad idea. Behold
+    /// `#[path = "C://no/way"]`
+    fn resolve_path(&self, anchor: FileId, path: &str) -> Option<FileId>;
+    fn relevant_crates(&self, file_id: FileId) -> Arc<FxHashSet<CrateId>>;
+}
+
+/// Database which stores all significant input facts: source code and project
+/// model. Everything else in rust-analyzer is derived from these queries.
+#[salsa::query_group(SourceDatabaseStorage)]
+pub trait SourceDatabase: CheckCanceled + FileLoader + std::fmt::Debug {
+    // Parses the file into the syntax tree.
+    #[salsa::invoke(parse_query)]
+    fn parse(&self, file_id: FileId) -> Parse<ast::SourceFile>;
+
+    /// The crate graph.
+    #[salsa::input]
+    fn crate_graph(&self) -> Arc<CrateGraph>;
+}
+
+fn parse_query(db: &dyn SourceDatabase, file_id: FileId) -> Parse<ast::SourceFile> {
+    let _p = profile::span("parse_query").detail(|| format!("{:?}", file_id));
+    let text = db.file_text(file_id);
+    SourceFile::parse(&*text)
+}
+
+/// We don't want to give HIR knowledge of source roots, hence we extract these
+/// methods into a separate DB.
+#[salsa::query_group(SourceDatabaseExtStorage)]
+pub trait SourceDatabaseExt: SourceDatabase {
+    #[salsa::input]
+    fn file_text(&self, file_id: FileId) -> Arc<String>;
+    /// Path to a file, relative to the root of its source root.
+    /// Source root of the file.
+    #[salsa::input]
+    fn file_source_root(&self, file_id: FileId) -> SourceRootId;
+    /// Contents of the source root.
+    #[salsa::input]
+    fn source_root(&self, id: SourceRootId) -> Arc<SourceRoot>;
+
+    fn source_root_crates(&self, id: SourceRootId) -> Arc<FxHashSet<CrateId>>;
+}
+
+fn source_root_crates(db: &dyn SourceDatabaseExt, id: SourceRootId) -> Arc<FxHashSet<CrateId>> {
+    let graph = db.crate_graph();
+    let res = graph
+        .iter()
+        .filter(|&krate| {
+            let root_file = graph[krate].root_file_id;
+            db.file_source_root(root_file) == id
+        })
+        .collect::<FxHashSet<_>>();
+    Arc::new(res)
+}
+
+/// Silly workaround for cyclic deps between the traits
+pub struct FileLoaderDelegate<T>(pub T);
+
+impl<T: SourceDatabaseExt> FileLoader for FileLoaderDelegate<&'_ T> {
+    fn file_text(&self, file_id: FileId) -> Arc<String> {
+        SourceDatabaseExt::file_text(self.0, file_id)
+    }
+    fn resolve_path(&self, anchor: FileId, path: &str) -> Option<FileId> {
+        // FIXME: this *somehow* should be platform agnostic...
+        let source_root = self.0.file_source_root(anchor);
+        let source_root = self.0.source_root(source_root);
+        source_root.file_set.resolve_path(anchor, path)
+    }
+
+    fn relevant_crates(&self, file_id: FileId) -> Arc<FxHashSet<CrateId>> {
+        let source_root = self.0.file_source_root(file_id);
+        self.0.source_root_crates(source_root)
+    }
+}

crates/cfg/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "cfg"
+version = "0.0.0"
+license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false
+
+[dependencies]
+rustc-hash = "1.1.0"
+
+tt = { path = "../tt" }
+
+[dev-dependencies]
+mbe = { path = "../mbe" }
+syntax = { path = "../syntax" }

crates/cfg/src/cfg_expr.rs

@@ -0,0 +1,133 @@
+//! The condition expression used in `#[cfg(..)]` attributes.
+//!
+//! See: https://doc.rust-lang.org/reference/conditional-compilation.html#conditional-compilation
+
+use std::slice::Iter as SliceIter;
+
+use tt::SmolStr;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum CfgExpr {
+    Invalid,
+    Atom(SmolStr),
+    KeyValue { key: SmolStr, value: SmolStr },
+    All(Vec<CfgExpr>),
+    Any(Vec<CfgExpr>),
+    Not(Box<CfgExpr>),
+}
+
+impl CfgExpr {
+    pub fn parse(tt: &tt::Subtree) -> CfgExpr {
+        next_cfg_expr(&mut tt.token_trees.iter()).unwrap_or(CfgExpr::Invalid)
+    }
+    /// Fold the cfg by querying all basic `Atom` and `KeyValue` predicates.
+    pub fn fold(&self, query: &dyn Fn(&SmolStr, Option<&SmolStr>) -> bool) -> Option<bool> {
+        match self {
+            CfgExpr::Invalid => None,
+            CfgExpr::Atom(name) => Some(query(name, None)),
+            CfgExpr::KeyValue { key, value } => Some(query(key, Some(value))),
+            CfgExpr::All(preds) => {
+                preds.iter().try_fold(true, |s, pred| Some(s && pred.fold(query)?))
+            }
+            CfgExpr::Any(preds) => {
+                preds.iter().try_fold(false, |s, pred| Some(s || pred.fold(query)?))
+            }
+            CfgExpr::Not(pred) => pred.fold(query).map(|s| !s),
+        }
+    }
+}
+
+fn next_cfg_expr(it: &mut SliceIter<tt::TokenTree>) -> Option<CfgExpr> {
+    let name = match it.next() {
+        None => return None,
+        Some(tt::TokenTree::Leaf(tt::Leaf::Ident(ident))) => ident.text.clone(),
+        Some(_) => return Some(CfgExpr::Invalid),
+    };
+
+    // Peek
+    let ret = match it.as_slice().first() {
+        Some(tt::TokenTree::Leaf(tt::Leaf::Punct(punct))) if punct.char == '=' => {
+            match it.as_slice().get(1) {
+                Some(tt::TokenTree::Leaf(tt::Leaf::Literal(literal))) => {
+                    it.next();
+                    it.next();
+                    // FIXME: escape? raw string?
+                    let value =
+                        SmolStr::new(literal.text.trim_start_matches('"').trim_end_matches('"'));
+                    CfgExpr::KeyValue { key: name, value }
+                }
+                _ => return Some(CfgExpr::Invalid),
+            }
+        }
+        Some(tt::TokenTree::Subtree(subtree)) => {
+            it.next();
+            let mut sub_it = subtree.token_trees.iter();
+            let mut subs = std::iter::from_fn(|| next_cfg_expr(&mut sub_it)).collect();
+            match name.as_str() {
+                "all" => CfgExpr::All(subs),
+                "any" => CfgExpr::Any(subs),
+                "not" => CfgExpr::Not(Box::new(subs.pop().unwrap_or(CfgExpr::Invalid))),
+                _ => CfgExpr::Invalid,
+            }
+        }
+        _ => CfgExpr::Atom(name),
+    };
+
+    // Eat comma separator
+    if let Some(tt::TokenTree::Leaf(tt::Leaf::Punct(punct))) = it.as_slice().first() {
+        if punct.char == ',' {
+            it.next();
+        }
+    }
+    Some(ret)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use mbe::ast_to_token_tree;
+    use syntax::ast::{self, AstNode};
+
+    fn assert_parse_result(input: &str, expected: CfgExpr) {
+        let (tt, _) = {
+            let source_file = ast::SourceFile::parse(input).ok().unwrap();
+            let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
+            ast_to_token_tree(&tt).unwrap()
+        };
+        let cfg = CfgExpr::parse(&tt);
+        assert_eq!(cfg, expected);
+    }
+
+    #[test]
+    fn test_cfg_expr_parser() {
+        assert_parse_result("#![cfg(foo)]", CfgExpr::Atom("foo".into()));
+        assert_parse_result("#![cfg(foo,)]", CfgExpr::Atom("foo".into()));
+        assert_parse_result(
+            "#![cfg(not(foo))]",
+            CfgExpr::Not(Box::new(CfgExpr::Atom("foo".into()))),
+        );
+        assert_parse_result("#![cfg(foo(bar))]", CfgExpr::Invalid);
+
+        // Only take the first
+        assert_parse_result(r#"#![cfg(foo, bar = "baz")]"#, CfgExpr::Atom("foo".into()));
+
+        assert_parse_result(
+            r#"#![cfg(all(foo, bar = "baz"))]"#,
+            CfgExpr::All(vec![
+                CfgExpr::Atom("foo".into()),
+                CfgExpr::KeyValue { key: "bar".into(), value: "baz".into() },
+            ]),
+        );
+
+        assert_parse_result(
+            r#"#![cfg(any(not(), all(), , bar = "baz",))]"#,
+            CfgExpr::Any(vec![
+                CfgExpr::Not(Box::new(CfgExpr::Invalid)),
+                CfgExpr::All(vec![]),
+                CfgExpr::Invalid,
+                CfgExpr::KeyValue { key: "bar".into(), value: "baz".into() },
+            ]),
+        );
+    }
+}

crates/cfg/src/lib.rs

@@ -0,0 +1,51 @@
+//! cfg defines conditional compiling options, `cfg` attibute parser and evaluator
+
+mod cfg_expr;
+
+use rustc_hash::FxHashSet;
+use tt::SmolStr;
+
+pub use cfg_expr::CfgExpr;
+
+/// Configuration options used for conditional compilition on items with `cfg` attributes.
+/// We have two kind of options in different namespaces: atomic options like `unix`, and
+/// key-value options like `target_arch="x86"`.
+///
+/// Note that for key-value options, one key can have multiple values (but not none).
+/// `feature` is an example. We have both `feature="foo"` and `feature="bar"` if features
+/// `foo` and `bar` are both enabled. And here, we store key-value options as a set of tuple
+/// of key and value in `key_values`.
+///
+/// See: https://doc.rust-lang.org/reference/conditional-compilation.html#set-configuration-options
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
+pub struct CfgOptions {
+    atoms: FxHashSet<SmolStr>,
+    key_values: FxHashSet<(SmolStr, SmolStr)>,
+}
+
+impl CfgOptions {
+    pub fn check(&self, cfg: &CfgExpr) -> Option<bool> {
+        cfg.fold(&|key, value| match value {
+            None => self.atoms.contains(key),
+            Some(value) => self.key_values.contains(&(key.clone(), value.clone())),
+        })
+    }
+
+    pub fn insert_atom(&mut self, key: SmolStr) {
+        self.atoms.insert(key);
+    }
+
+    pub fn insert_key_value(&mut self, key: SmolStr, value: SmolStr) {
+        self.key_values.insert((key, value));
+    }
+
+    pub fn append(&mut self, other: &CfgOptions) {
+        for atom in &other.atoms {
+            self.atoms.insert(atom.clone());
+        }
+
+        for (key, value) in &other.key_values {
+            self.key_values.insert((key.clone(), value.clone()));
+        }
+    }
+}

crates/expect/Cargo.toml

@@ -1,14 +0,0 @@
-[package]
-name = "expect"
-version = "0.1.0"
-authors = ["rust-analyzer developers"]
-edition = "2018"
-license = "MIT OR Apache-2.0"
-
-[lib]
-doctest = false
-
-[dependencies]
-once_cell = "1"
-difference = "2"
-stdx = { path = "../stdx" }

crates/expect/src/lib.rs

@@ -1,356 +0,0 @@
-//! Snapshot testing library, see
-//! https://github.com/rust-analyzer/rust-analyzer/pull/5101
-use std::{
-    collections::HashMap,
-    env, fmt, fs, mem,
-    ops::Range,
-    panic,
-    path::{Path, PathBuf},
-    sync::Mutex,
-};
-
-use difference::Changeset;
-use once_cell::sync::Lazy;
-use stdx::{lines_with_ends, trim_indent};
-
-const HELP: &str = "
-You can update all `expect![[]]` tests by running:
-
-    env UPDATE_EXPECT=1 cargo test
-
-To update a single test, place the cursor on `expect` token and use `run` feature of rust-analyzer.
-";
-
-fn update_expect() -> bool {
-    env::var("UPDATE_EXPECT").is_ok()
-}
-
-/// expect![[r#"inline snapshot"#]]
-#[macro_export]
-macro_rules! expect {
-    [[$data:literal]] => {$crate::Expect {
-        position: $crate::Position {
-            file: file!(),
-            line: line!(),
-            column: column!(),
-        },
-        data: $data,
-    }};
-    [[]] => { $crate::expect![[""]] };
-}
-
-/// expect_file!["/crates/foo/test_data/bar.html"]
-#[macro_export]
-macro_rules! expect_file {
-    [$path:expr] => {$crate::ExpectFile {
-        path: std::path::PathBuf::from($path)
-    }};
-}
-
-#[derive(Debug)]
-pub struct Expect {
-    pub position: Position,
-    pub data: &'static str,
-}
-
-#[derive(Debug)]
-pub struct ExpectFile {
-    pub path: PathBuf,
-}
-
-#[derive(Debug)]
-pub struct Position {
-    pub file: &'static str,
-    pub line: u32,
-    pub column: u32,
-}
-
-impl fmt::Display for Position {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}:{}:{}", self.file, self.line, self.column)
-    }
-}
-
-impl Expect {
-    pub fn assert_eq(&self, actual: &str) {
-        let trimmed = self.trimmed();
-        if &trimmed == actual {
-            return;
-        }
-        Runtime::fail_expect(self, &trimmed, actual);
-    }
-    pub fn assert_debug_eq(&self, actual: &impl fmt::Debug) {
-        let actual = format!("{:#?}\n", actual);
-        self.assert_eq(&actual)
-    }
-
-    fn trimmed(&self) -> String {
-        if !self.data.contains('\n') {
-            return self.data.to_string();
-        }
-        trim_indent(self.data)
-    }
-
-    fn locate(&self, file: &str) -> Location {
-        let mut target_line = None;
-        let mut line_start = 0;
-        for (i, line) in lines_with_ends(file).enumerate() {
-            if i == self.position.line as usize - 1 {
-                let pat = "expect![[";
-                let offset = line.find(pat).unwrap();
-                let literal_start = line_start + offset + pat.len();
-                let indent = line.chars().take_while(|&it| it == ' ').count();
-                target_line = Some((literal_start, indent));
-                break;
-            }
-            line_start += line.len();
-        }
-        let (literal_start, line_indent) = target_line.unwrap();
-        let literal_length =
-            file[literal_start..].find("]]").expect("Couldn't find matching `]]` for `expect![[`.");
-        let literal_range = literal_start..literal_start + literal_length;
-        Location { line_indent, literal_range }
-    }
-}
-
-impl ExpectFile {
-    pub fn assert_eq(&self, actual: &str) {
-        let expected = self.read();
-        if actual == expected {
-            return;
-        }
-        Runtime::fail_file(self, &expected, actual);
-    }
-    pub fn assert_debug_eq(&self, actual: &impl fmt::Debug) {
-        let actual = format!("{:#?}\n", actual);
-        self.assert_eq(&actual)
-    }
-    fn read(&self) -> String {
-        fs::read_to_string(self.abs_path()).unwrap_or_default().replace("\r\n", "\n")
-    }
-    fn write(&self, contents: &str) {
-        fs::write(self.abs_path(), contents).unwrap()
-    }
-    fn abs_path(&self) -> PathBuf {
-        WORKSPACE_ROOT.join(&self.path)
-    }
-}
-
-#[derive(Default)]
-struct Runtime {
-    help_printed: bool,
-    per_file: HashMap<&'static str, FileRuntime>,
-}
-static RT: Lazy<Mutex<Runtime>> = Lazy::new(Default::default);
-
-impl Runtime {
-    fn fail_expect(expect: &Expect, expected: &str, actual: &str) {
-        let mut rt = RT.lock().unwrap_or_else(|poisoned| poisoned.into_inner());
-        if update_expect() {
-            println!("\x1b[1m\x1b[92mupdating\x1b[0m: {}", expect.position);
-            rt.per_file
-                .entry(expect.position.file)
-                .or_insert_with(|| FileRuntime::new(expect))
-                .update(expect, actual);
-            return;
-        }
-        rt.panic(expect.position.to_string(), expected, actual);
-    }
-
-    fn fail_file(expect: &ExpectFile, expected: &str, actual: &str) {
-        let mut rt = RT.lock().unwrap_or_else(|poisoned| poisoned.into_inner());
-        if update_expect() {
-            println!("\x1b[1m\x1b[92mupdating\x1b[0m: {}", expect.path.display());
-            expect.write(actual);
-            return;
-        }
-        rt.panic(expect.path.display().to_string(), expected, actual);
-    }
-
-    fn panic(&mut self, position: String, expected: &str, actual: &str) {
-        let print_help = !mem::replace(&mut self.help_printed, true);
-        let help = if print_help { HELP } else { "" };
-
-        let diff = Changeset::new(actual, expected, "\n");
-
-        println!(
-            "\n
-\x1b[1m\x1b[91merror\x1b[97m: expect test failed\x1b[0m
-   \x1b[1m\x1b[34m-->\x1b[0m {}
-{}
-\x1b[1mExpect\x1b[0m:
-----
-{}
-----
-
-\x1b[1mActual\x1b[0m:
-----
-{}
-----
-
-\x1b[1mDiff\x1b[0m:
-----
-{}
-----
-",
-            position, help, expected, actual, diff
-        );
-        // Use resume_unwind instead of panic!() to prevent a backtrace, which is unnecessary noise.
-        panic::resume_unwind(Box::new(()));
-    }
-}
-
-struct FileRuntime {
-    path: PathBuf,
-    original_text: String,
-    patchwork: Patchwork,
-}
-
-impl FileRuntime {
-    fn new(expect: &Expect) -> FileRuntime {
-        let path = WORKSPACE_ROOT.join(expect.position.file);
-        let original_text = fs::read_to_string(&path).unwrap();
-        let patchwork = Patchwork::new(original_text.clone());
-        FileRuntime { path, original_text, patchwork }
-    }
-    fn update(&mut self, expect: &Expect, actual: &str) {
-        let loc = expect.locate(&self.original_text);
-        let patch = format_patch(loc.line_indent.clone(), actual);
-        self.patchwork.patch(loc.literal_range, &patch);
-        fs::write(&self.path, &self.patchwork.text).unwrap()
-    }
-}
-
-#[derive(Debug)]
-struct Location {
-    line_indent: usize,
-    literal_range: Range<usize>,
-}
-
-#[derive(Debug)]
-struct Patchwork {
-    text: String,
-    indels: Vec<(Range<usize>, usize)>,
-}
-
-impl Patchwork {
-    fn new(text: String) -> Patchwork {
-        Patchwork { text, indels: Vec::new() }
-    }
-    fn patch(&mut self, mut range: Range<usize>, patch: &str) {
-        self.indels.push((range.clone(), patch.len()));
-        self.indels.sort_by_key(|(delete, _insert)| delete.start);
-
-        let (delete, insert) = self
-            .indels
-            .iter()
-            .take_while(|(delete, _)| delete.start < range.start)
-            .map(|(delete, insert)| (delete.end - delete.start, insert))
-            .fold((0usize, 0usize), |(x1, y1), (x2, y2)| (x1 + x2, y1 + y2));
-
-        for pos in &mut [&mut range.start, &mut range.end] {
-            **pos -= delete;
-            **pos += insert;
-        }
-
-        self.text.replace_range(range, &patch);
-    }
-}
-
-fn format_patch(line_indent: usize, patch: &str) -> String {
-    let mut max_hashes = 0;
-    let mut cur_hashes = 0;
-    for byte in patch.bytes() {
-        if byte != b'#' {
-            cur_hashes = 0;
-            continue;
-        }
-        cur_hashes += 1;
-        max_hashes = max_hashes.max(cur_hashes);
-    }
-    let hashes = &"#".repeat(max_hashes + 1);
-    let indent = &" ".repeat(line_indent);
-    let is_multiline = patch.contains('\n');
-
-    let mut buf = String::new();
-    buf.push('r');
-    buf.push_str(hashes);
-    buf.push('"');
-    if is_multiline {
-        buf.push('\n');
-    }
-    let mut final_newline = false;
-    for line in lines_with_ends(patch) {
-        if is_multiline && !line.trim().is_empty() {
-            buf.push_str(indent);
-            buf.push_str("    ");
-        }
-        buf.push_str(line);
-        final_newline = line.ends_with('\n');
-    }
-    if final_newline {
-        buf.push_str(indent);
-    }
-    buf.push('"');
-    buf.push_str(hashes);
-    buf
-}
-
-static WORKSPACE_ROOT: Lazy<PathBuf> = Lazy::new(|| {
-    let my_manifest =
-        env::var("CARGO_MANIFEST_DIR").unwrap_or_else(|_| env!("CARGO_MANIFEST_DIR").to_owned());
-    // Heuristic, see https://github.com/rust-lang/cargo/issues/3946
-    Path::new(&my_manifest)
-        .ancestors()
-        .filter(|it| it.join("Cargo.toml").exists())
-        .last()
-        .unwrap()
-        .to_path_buf()
-});
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_format_patch() {
-        let patch = format_patch(0, "hello\nworld\n");
-        expect![[r##"
-            r#"
-                hello
-                world
-            "#"##]]
-        .assert_eq(&patch);
-
-        let patch = format_patch(4, "single line");
-        expect![[r##"r#"single line"#"##]].assert_eq(&patch);
-    }
-
-    #[test]
-    fn test_patchwork() {
-        let mut patchwork = Patchwork::new("one two three".to_string());
-        patchwork.patch(4..7, "zwei");
-        patchwork.patch(0..3, "один");
-        patchwork.patch(8..13, "3");
-        expect![[r#"
-            Patchwork {
-                text: "один zwei 3",
-                indels: [
-                    (
-                        0..3,
-                        8,
-                    ),
-                    (
-                        4..7,
-                        4,
-                    ),
-                    (
-                        8..13,
-                        1,
-                    ),
-                ],
-            }
-        "#]]
-        .assert_debug_eq(&patchwork);
-    }
-}

crates/flycheck/Cargo.toml

@@ -1,9 +1,9 @@
 [package]
-edition = "2018"
 name = "flycheck"
-version = "0.1.0"
-authors = ["rust-analyzer developers"]
+version = "0.0.0"
 license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
 
 [lib]
 doctest = false
@@ -14,4 +14,5 @@ log = "0.4.8"
 cargo_metadata = "0.11.1"
 serde_json = "1.0.48"
 jod-thread = "0.1.1"
-ra_toolchain = { path = "../ra_toolchain" }
+
+toolchain = { path = "../toolchain" }

crates/flycheck/src/lib.rs

@@ -1,4 +1,4 @@
-//! cargo_check provides the functionality needed to run `cargo check` or
+//! Flycheck provides the functionality needed to run `cargo check` or
 //! another compatible command (f.x. clippy) in a background thread and provide
 //! LSP diagnostics based on the output of the command.
 
@@ -147,6 +147,12 @@ impl FlycheckActor {
                     // avoid busy-waiting.
                     let cargo_handle = self.cargo_handle.take().unwrap();
                     let res = cargo_handle.join();
+                    if res.is_err() {
+                        log::error!(
+                            "Flycheck failed to run the following command: {:?}",
+                            self.check_command()
+                        )
+                    }
                     self.send(Message::Progress(Progress::DidFinish(res)));
                 }
                 Event::CheckEvent(Some(message)) => match message {
@@ -187,7 +193,7 @@ impl FlycheckActor {
                 extra_args,
                 features,
             } => {
-                let mut cmd = Command::new(ra_toolchain::cargo());
+                let mut cmd = Command::new(toolchain::cargo());
                 cmd.arg(command);
                 cmd.args(&["--workspace", "--message-format=json", "--manifest-path"])
                     .arg(self.workspace_root.join("Cargo.toml"));

crates/hir/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "hir"
+version = "0.0.0"
+license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false
+
+[dependencies]
+log = "0.4.8"
+rustc-hash = "1.1.0"
+either = "1.5.3"
+arrayvec = "0.5.1"
+itertools = "0.9.0"
+url = "2.1.1"
+
+stdx = { path = "../stdx" }
+syntax = { path = "../syntax" }
+base_db = { path = "../base_db" }
+profile = { path = "../profile" }
+hir_expand = { path = "../hir_expand" }
+hir_def = { path = "../hir_def" }
+hir_ty = { path = "../hir_ty" }
+tt = { path = "../tt" }

crates/hir/src/db.rs

@@ -0,0 +1,21 @@
+//! FIXME: write short doc here
+
+pub use hir_def::db::{
+    AttrsQuery, BodyQuery, BodyWithSourceMapQuery, ConstDataQuery, CrateDefMapQueryQuery,
+    CrateLangItemsQuery, DefDatabase, DefDatabaseStorage, DocumentationQuery, EnumDataQuery,
+    ExprScopesQuery, FunctionDataQuery, GenericParamsQuery, ImplDataQuery, ImportMapQuery,
+    InternConstQuery, InternDatabase, InternDatabaseStorage, InternEnumQuery, InternFunctionQuery,
+    InternImplQuery, InternStaticQuery, InternStructQuery, InternTraitQuery, InternTypeAliasQuery,
+    InternUnionQuery, ItemTreeQuery, LangItemQuery, ModuleLangItemsQuery, StaticDataQuery,
+    StructDataQuery, TraitDataQuery, TypeAliasDataQuery, UnionDataQuery,
+};
+pub use hir_expand::db::{
+    AstDatabase, AstDatabaseStorage, AstIdMapQuery, InternEagerExpansionQuery, InternMacroQuery,
+    MacroArgTextQuery, MacroDefQuery, MacroExpandQuery, ParseMacroQuery,
+};
+pub use hir_ty::db::*;
+
+#[test]
+fn hir_database_is_object_safe() {
+    fn _assert_object_safe(_: &dyn HirDatabase) {}
+}

crates/hir/src/diagnostics.rs

@@ -0,0 +1,6 @@
+//! FIXME: write short doc here
+pub use hir_def::diagnostics::UnresolvedModule;
+pub use hir_expand::diagnostics::{Diagnostic, DiagnosticSink, DiagnosticSinkBuilder};
+pub use hir_ty::diagnostics::{
+    MismatchedArgCount, MissingFields, MissingMatchArms, MissingOkInTailExpr, NoSuchField,
+};

crates/hir/src/from_id.rs

@@ -0,0 +1,247 @@
+//! Utility module for converting between hir_def ids and code_model wrappers.
+//!
+//! It's unclear if we need this long-term, but it's definitelly useful while we
+//! are splitting the hir.
+
+use hir_def::{
+    expr::PatId, AdtId, AssocItemId, AttrDefId, DefWithBodyId, EnumVariantId, FieldId,
+    GenericDefId, ModuleDefId, VariantId,
+};
+
+use crate::{
+    code_model::ItemInNs, Adt, AssocItem, AttrDef, DefWithBody, EnumVariant, Field, GenericDef,
+    Local, MacroDef, ModuleDef, VariantDef,
+};
+
+macro_rules! from_id {
+    ($(($id:path, $ty:path)),*) => {$(
+        impl From<$id> for $ty {
+            fn from(id: $id) -> $ty {
+                $ty { id }
+            }
+        }
+        impl From<$ty> for $id {
+            fn from(ty: $ty) -> $id {
+                ty.id
+            }
+        }
+    )*}
+}
+
+from_id![
+    (base_db::CrateId, crate::Crate),
+    (hir_def::ModuleId, crate::Module),
+    (hir_def::StructId, crate::Struct),
+    (hir_def::UnionId, crate::Union),
+    (hir_def::EnumId, crate::Enum),
+    (hir_def::TypeAliasId, crate::TypeAlias),
+    (hir_def::TraitId, crate::Trait),
+    (hir_def::StaticId, crate::Static),
+    (hir_def::ConstId, crate::Const),
+    (hir_def::FunctionId, crate::Function),
+    (hir_def::ImplId, crate::ImplDef),
+    (hir_def::TypeParamId, crate::TypeParam),
+    (hir_expand::MacroDefId, crate::MacroDef)
+];
+
+impl From<AdtId> for Adt {
+    fn from(id: AdtId) -> Self {
+        match id {
+            AdtId::StructId(it) => Adt::Struct(it.into()),
+            AdtId::UnionId(it) => Adt::Union(it.into()),
+            AdtId::EnumId(it) => Adt::Enum(it.into()),
+        }
+    }
+}
+
+impl From<Adt> for AdtId {
+    fn from(id: Adt) -> Self {
+        match id {
+            Adt::Struct(it) => AdtId::StructId(it.id),
+            Adt::Union(it) => AdtId::UnionId(it.id),
+            Adt::Enum(it) => AdtId::EnumId(it.id),
+        }
+    }
+}
+
+impl From<EnumVariantId> for EnumVariant {
+    fn from(id: EnumVariantId) -> Self {
+        EnumVariant { parent: id.parent.into(), id: id.local_id }
+    }
+}
+
+impl From<EnumVariant> for EnumVariantId {
+    fn from(def: EnumVariant) -> Self {
+        EnumVariantId { parent: def.parent.id, local_id: def.id }
+    }
+}
+
+impl From<ModuleDefId> for ModuleDef {
+    fn from(id: ModuleDefId) -> Self {
+        match id {
+            ModuleDefId::ModuleId(it) => ModuleDef::Module(it.into()),
+            ModuleDefId::FunctionId(it) => ModuleDef::Function(it.into()),
+            ModuleDefId::AdtId(it) => ModuleDef::Adt(it.into()),
+            ModuleDefId::EnumVariantId(it) => ModuleDef::EnumVariant(it.into()),
+            ModuleDefId::ConstId(it) => ModuleDef::Const(it.into()),
+            ModuleDefId::StaticId(it) => ModuleDef::Static(it.into()),
+            ModuleDefId::TraitId(it) => ModuleDef::Trait(it.into()),
+            ModuleDefId::TypeAliasId(it) => ModuleDef::TypeAlias(it.into()),
+            ModuleDefId::BuiltinType(it) => ModuleDef::BuiltinType(it),
+        }
+    }
+}
+
+impl From<ModuleDef> for ModuleDefId {
+    fn from(id: ModuleDef) -> Self {
+        match id {
+            ModuleDef::Module(it) => ModuleDefId::ModuleId(it.into()),
+            ModuleDef::Function(it) => ModuleDefId::FunctionId(it.into()),
+            ModuleDef::Adt(it) => ModuleDefId::AdtId(it.into()),
+            ModuleDef::EnumVariant(it) => ModuleDefId::EnumVariantId(it.into()),
+            ModuleDef::Const(it) => ModuleDefId::ConstId(it.into()),
+            ModuleDef::Static(it) => ModuleDefId::StaticId(it.into()),
+            ModuleDef::Trait(it) => ModuleDefId::TraitId(it.into()),
+            ModuleDef::TypeAlias(it) => ModuleDefId::TypeAliasId(it.into()),
+            ModuleDef::BuiltinType(it) => ModuleDefId::BuiltinType(it),
+        }
+    }
+}
+
+impl From<DefWithBody> for DefWithBodyId {
+    fn from(def: DefWithBody) -> Self {
+        match def {
+            DefWithBody::Function(it) => DefWithBodyId::FunctionId(it.id),
+            DefWithBody::Static(it) => DefWithBodyId::StaticId(it.id),
+            DefWithBody::Const(it) => DefWithBodyId::ConstId(it.id),
+        }
+    }
+}
+
+impl From<DefWithBodyId> for DefWithBody {
+    fn from(def: DefWithBodyId) -> Self {
+        match def {
+            DefWithBodyId::FunctionId(it) => DefWithBody::Function(it.into()),
+            DefWithBodyId::StaticId(it) => DefWithBody::Static(it.into()),
+            DefWithBodyId::ConstId(it) => DefWithBody::Const(it.into()),
+        }
+    }
+}
+
+impl From<AssocItemId> for AssocItem {
+    fn from(def: AssocItemId) -> Self {
+        match def {
+            AssocItemId::FunctionId(it) => AssocItem::Function(it.into()),
+            AssocItemId::TypeAliasId(it) => AssocItem::TypeAlias(it.into()),
+            AssocItemId::ConstId(it) => AssocItem::Const(it.into()),
+        }
+    }
+}
+
+impl From<GenericDef> for GenericDefId {
+    fn from(def: GenericDef) -> Self {
+        match def {
+            GenericDef::Function(it) => GenericDefId::FunctionId(it.id),
+            GenericDef::Adt(it) => GenericDefId::AdtId(it.into()),
+            GenericDef::Trait(it) => GenericDefId::TraitId(it.id),
+            GenericDef::TypeAlias(it) => GenericDefId::TypeAliasId(it.id),
+            GenericDef::ImplDef(it) => GenericDefId::ImplId(it.id),
+            GenericDef::EnumVariant(it) => {
+                GenericDefId::EnumVariantId(EnumVariantId { parent: it.parent.id, local_id: it.id })
+            }
+            GenericDef::Const(it) => GenericDefId::ConstId(it.id),
+        }
+    }
+}
+
+impl From<Adt> for GenericDefId {
+    fn from(id: Adt) -> Self {
+        match id {
+            Adt::Struct(it) => it.id.into(),
+            Adt::Union(it) => it.id.into(),
+            Adt::Enum(it) => it.id.into(),
+        }
+    }
+}
+
+impl From<VariantId> for VariantDef {
+    fn from(def: VariantId) -> Self {
+        match def {
+            VariantId::StructId(it) => VariantDef::Struct(it.into()),
+            VariantId::EnumVariantId(it) => VariantDef::EnumVariant(it.into()),
+            VariantId::UnionId(it) => VariantDef::Union(it.into()),
+        }
+    }
+}
+
+impl From<VariantDef> for VariantId {
+    fn from(def: VariantDef) -> Self {
+        match def {
+            VariantDef::Struct(it) => VariantId::StructId(it.id),
+            VariantDef::EnumVariant(it) => VariantId::EnumVariantId(it.into()),
+            VariantDef::Union(it) => VariantId::UnionId(it.id),
+        }
+    }
+}
+
+impl From<Field> for FieldId {
+    fn from(def: Field) -> Self {
+        FieldId { parent: def.parent.into(), local_id: def.id }
+    }
+}
+
+impl From<FieldId> for Field {
+    fn from(def: FieldId) -> Self {
+        Field { parent: def.parent.into(), id: def.local_id }
+    }
+}
+
+impl From<AttrDef> for AttrDefId {
+    fn from(def: AttrDef) -> Self {
+        match def {
+            AttrDef::Module(it) => AttrDefId::ModuleId(it.id),
+            AttrDef::Field(it) => AttrDefId::FieldId(it.into()),
+            AttrDef::Adt(it) => AttrDefId::AdtId(it.into()),
+            AttrDef::Function(it) => AttrDefId::FunctionId(it.id),
+            AttrDef::EnumVariant(it) => AttrDefId::EnumVariantId(it.into()),
+            AttrDef::Static(it) => AttrDefId::StaticId(it.id),
+            AttrDef::Const(it) => AttrDefId::ConstId(it.id),
+            AttrDef::Trait(it) => AttrDefId::TraitId(it.id),
+            AttrDef::TypeAlias(it) => AttrDefId::TypeAliasId(it.id),
+            AttrDef::MacroDef(it) => AttrDefId::MacroDefId(it.id),
+        }
+    }
+}
+
+impl From<AssocItem> for GenericDefId {
+    fn from(item: AssocItem) -> Self {
+        match item {
+            AssocItem::Function(f) => f.id.into(),
+            AssocItem::Const(c) => c.id.into(),
+            AssocItem::TypeAlias(t) => t.id.into(),
+        }
+    }
+}
+
+impl From<(DefWithBodyId, PatId)> for Local {
+    fn from((parent, pat_id): (DefWithBodyId, PatId)) -> Self {
+        Local { parent, pat_id }
+    }
+}
+
+impl From<MacroDef> for ItemInNs {
+    fn from(macro_def: MacroDef) -> Self {
+        ItemInNs::Macros(macro_def.into())
+    }
+}
+
+impl From<ModuleDef> for ItemInNs {
+    fn from(module_def: ModuleDef) -> Self {
+        match module_def {
+            ModuleDef::Static(_) | ModuleDef::Const(_) | ModuleDef::Function(_) => {
+                ItemInNs::Values(module_def.into())
+            }
+            _ => ItemInNs::Types(module_def.into()),
+        }
+    }
+}

crates/hir/src/has_source.rs

@@ -0,0 +1,135 @@
+//! Provides set of implementation for hir's objects that allows get back location in file.
+
+use either::Either;
+use hir_def::{
+    nameres::{ModuleOrigin, ModuleSource},
+    src::{HasChildSource, HasSource as _},
+    Lookup, VariantId,
+};
+use syntax::ast;
+
+use crate::{
+    db::HirDatabase, Const, Enum, EnumVariant, Field, FieldSource, Function, ImplDef, MacroDef,
+    Module, Static, Struct, Trait, TypeAlias, TypeParam, Union,
+};
+
+pub use hir_expand::InFile;
+
+pub trait HasSource {
+    type Ast;
+    fn source(self, db: &dyn HirDatabase) -> InFile<Self::Ast>;
+}
+
+/// NB: Module is !HasSource, because it has two source nodes at the same time:
+/// definition and declaration.
+impl Module {
+    /// Returns a node which defines this module. That is, a file or a `mod foo {}` with items.
+    pub fn definition_source(self, db: &dyn HirDatabase) -> InFile<ModuleSource> {
+        let def_map = db.crate_def_map(self.id.krate);
+        def_map[self.id.local_id].definition_source(db.upcast())
+    }
+
+    pub fn is_mod_rs(self, db: &dyn HirDatabase) -> bool {
+        let def_map = db.crate_def_map(self.id.krate);
+        match def_map[self.id.local_id].origin {
+            ModuleOrigin::File { is_mod_rs, .. } => is_mod_rs,
+            _ => false,
+        }
+    }
+
+    /// Returns a node which declares this module, either a `mod foo;` or a `mod foo {}`.
+    /// `None` for the crate root.
+    pub fn declaration_source(self, db: &dyn HirDatabase) -> Option<InFile<ast::Module>> {
+        let def_map = db.crate_def_map(self.id.krate);
+        def_map[self.id.local_id].declaration_source(db.upcast())
+    }
+}
+
+impl HasSource for Field {
+    type Ast = FieldSource;
+    fn source(self, db: &dyn HirDatabase) -> InFile<FieldSource> {
+        let var = VariantId::from(self.parent);
+        let src = var.child_source(db.upcast());
+        src.map(|it| match it[self.id].clone() {
+            Either::Left(it) => FieldSource::Pos(it),
+            Either::Right(it) => FieldSource::Named(it),
+        })
+    }
+}
+impl HasSource for Struct {
+    type Ast = ast::Struct;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Struct> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Union {
+    type Ast = ast::Union;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Union> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Enum {
+    type Ast = ast::Enum;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Enum> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for EnumVariant {
+    type Ast = ast::Variant;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Variant> {
+        self.parent.id.child_source(db.upcast()).map(|map| map[self.id].clone())
+    }
+}
+impl HasSource for Function {
+    type Ast = ast::Fn;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Fn> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Const {
+    type Ast = ast::Const;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Const> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Static {
+    type Ast = ast::Static;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Static> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Trait {
+    type Ast = ast::Trait;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Trait> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for TypeAlias {
+    type Ast = ast::TypeAlias;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::TypeAlias> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for MacroDef {
+    type Ast = ast::MacroCall;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::MacroCall> {
+        InFile {
+            file_id: self.id.ast_id.expect("MacroDef without ast_id").file_id,
+            value: self.id.ast_id.expect("MacroDef without ast_id").to_node(db.upcast()),
+        }
+    }
+}
+impl HasSource for ImplDef {
+    type Ast = ast::Impl;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Impl> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+
+impl HasSource for TypeParam {
+    type Ast = Either<ast::Trait, ast::TypeParam>;
+    fn source(self, db: &dyn HirDatabase) -> InFile<Self::Ast> {
+        let child_source = self.id.parent.child_source(db.upcast());
+        child_source.map(|it| it[self.id.local_id].clone())
+    }
+}

crates/hir/src/lib.rs

@@ -0,0 +1,69 @@
+//! HIR (previously known as descriptors) provides a high-level object oriented
+//! access to Rust code.
+//!
+//! The principal difference between HIR and syntax trees is that HIR is bound
+//! to a particular crate instance. That is, it has cfg flags and features
+//! applied. So, the relation between syntax and HIR is many-to-one.
+//!
+//! HIR is the public API of the all of the compiler logic above syntax trees.
+//! It is written in "OO" style. Each type is self contained (as in, it knows it's
+//! parents and full context). It should be "clean code".
+//!
+//! `hir_*` crates are the implementation of the compiler logic.
+//! They are written in "ECS" style, with relatively little abstractions.
+//! Many types are not self-contained, and explicitly use local indexes, arenas, etc.
+//!
+//! `hir` is what insulates the "we don't know how to actually write an incremental compiler"
+//! from the ide with completions, hovers, etc. It is a (soft, internal) boundary:
+//! https://www.tedinski.com/2018/02/06/system-boundaries.html.
+
+#![recursion_limit = "512"]
+
+mod semantics;
+pub mod db;
+mod source_analyzer;
+
+pub mod diagnostics;
+
+mod from_id;
+mod code_model;
+mod link_rewrite;
+
+mod has_source;
+
+pub use crate::{
+    code_model::{
+        Access, Adt, AsAssocItem, AssocItem, AssocItemContainer, AttrDef, Callable, CallableKind,
+        Const, Crate, CrateDependency, DefWithBody, Docs, Enum, EnumVariant, Field, FieldSource,
+        Function, GenericDef, HasAttrs, HasVisibility, ImplDef, Local, MacroDef, Module, ModuleDef,
+        ScopeDef, Static, Struct, Trait, Type, TypeAlias, TypeParam, Union, VariantDef, Visibility,
+    },
+    has_source::HasSource,
+    link_rewrite::resolve_doc_link,
+    semantics::{original_range, PathResolution, Semantics, SemanticsScope},
+};
+
+pub use hir_def::{
+    adt::StructKind,
+    attr::Attrs,
+    body::scope::ExprScopes,
+    builtin_type::BuiltinType,
+    docs::Documentation,
+    item_scope::ItemInNs,
+    nameres::ModuleSource,
+    path::ModPath,
+    type_ref::{Mutability, TypeRef},
+};
+pub use hir_expand::{
+    name::AsName, name::Name, HirFileId, InFile, MacroCallId, MacroCallLoc,
+    /* FIXME */ MacroDefId, MacroFile, Origin,
+};
+pub use hir_ty::display::HirDisplay;
+
+// These are negative re-exports: pub using these names is forbidden, they
+// should remain private to hir internals.
+#[allow(unused)]
+use {
+    hir_def::path::{Path, PathKind},
+    hir_expand::hygiene::Hygiene,
+};

crates/hir/src/link_rewrite.rs

@@ -0,0 +1,226 @@
+//! Resolves and rewrites links in markdown documentation for hovers/completion windows.
+
+use std::iter::once;
+
+use itertools::Itertools;
+use url::Url;
+
+use crate::{db::HirDatabase, Adt, AsName, Crate, Hygiene, ItemInNs, ModPath, ModuleDef};
+use hir_def::{db::DefDatabase, resolver::Resolver};
+use syntax::ast::Path;
+
+pub fn resolve_doc_link<T: Resolvable + Clone, D: DefDatabase + HirDatabase>(
+    db: &D,
+    definition: &T,
+    link_text: &str,
+    link_target: &str,
+) -> Option<(String, String)> {
+    try_resolve_intra(db, definition, link_text, &link_target).or_else(|| {
+        if let Some(definition) = definition.clone().try_into_module_def() {
+            try_resolve_path(db, &definition, &link_target)
+                .map(|target| (target, link_text.to_string()))
+        } else {
+            None
+        }
+    })
+}
+
+/// Try to resolve path to local documentation via intra-doc-links (i.e. `super::gateway::Shard`).
+///
+/// See [RFC1946](https://github.com/rust-lang/rfcs/blob/master/text/1946-intra-rustdoc-links.md).
+fn try_resolve_intra<T: Resolvable, D: DefDatabase + HirDatabase>(
+    db: &D,
+    definition: &T,
+    link_text: &str,
+    link_target: &str,
+) -> Option<(String, String)> {
+    // Set link_target for implied shortlinks
+    let link_target =
+        if link_target.is_empty() { link_text.trim_matches('`') } else { link_target };
+
+    // Namespace disambiguation
+    let namespace = Namespace::from_intra_spec(link_target);
+
+    // Strip prefixes/suffixes
+    let link_target = strip_prefixes_suffixes(link_target);
+
+    // Parse link as a module path
+    let path = Path::parse(link_target).ok()?;
+    let modpath = ModPath::from_src(path, &Hygiene::new_unhygienic()).unwrap();
+
+    // Resolve it relative to symbol's location (according to the RFC this should consider small scopes)
+    let resolver = definition.resolver(db)?;
+
+    let resolved = resolver.resolve_module_path_in_items(db, &modpath);
+    let (defid, namespace) = match namespace {
+        // FIXME: .or(resolved.macros)
+        None => resolved
+            .types
+            .map(|t| (t.0, Namespace::Types))
+            .or(resolved.values.map(|t| (t.0, Namespace::Values)))?,
+        Some(ns @ Namespace::Types) => (resolved.types?.0, ns),
+        Some(ns @ Namespace::Values) => (resolved.values?.0, ns),
+        // FIXME:
+        Some(Namespace::Macros) => None?,
+    };
+
+    // Get the filepath of the final symbol
+    let def: ModuleDef = defid.into();
+    let module = def.module(db)?;
+    let krate = module.krate();
+    let ns = match namespace {
+        Namespace::Types => ItemInNs::Types(defid),
+        Namespace::Values => ItemInNs::Values(defid),
+        // FIXME:
+        Namespace::Macros => None?,
+    };
+    let import_map = db.import_map(krate.into());
+    let path = import_map.path_of(ns)?;
+
+    Some((
+        get_doc_url(db, &krate)?
+            .join(&format!("{}/", krate.display_name(db)?))
+            .ok()?
+            .join(&path.segments.iter().map(|name| name.to_string()).join("/"))
+            .ok()?
+            .join(&get_symbol_filename(db, &def)?)
+            .ok()?
+            .into_string(),
+        strip_prefixes_suffixes(link_text).to_string(),
+    ))
+}
+
+/// Try to resolve path to local documentation via path-based links (i.e. `../gateway/struct.Shard.html`).
+fn try_resolve_path(db: &dyn HirDatabase, moddef: &ModuleDef, link_target: &str) -> Option<String> {
+    if !link_target.contains("#") && !link_target.contains(".html") {
+        return None;
+    }
+    let ns = ItemInNs::Types(moddef.clone().into());
+
+    let module = moddef.module(db)?;
+    let krate = module.krate();
+    let import_map = db.import_map(krate.into());
+    let base = once(format!("{}", krate.display_name(db)?))
+        .chain(import_map.path_of(ns)?.segments.iter().map(|name| format!("{}", name)))
+        .join("/");
+
+    get_doc_url(db, &krate)
+        .and_then(|url| url.join(&base).ok())
+        .and_then(|url| {
+            get_symbol_filename(db, moddef).as_deref().map(|f| url.join(f).ok()).flatten()
+        })
+        .and_then(|url| url.join(link_target).ok())
+        .map(|url| url.into_string())
+}
+
+// Strip prefixes, suffixes, and inline code marks from the given string.
+fn strip_prefixes_suffixes(mut s: &str) -> &str {
+    s = s.trim_matches('`');
+
+    [
+        (TYPES.0.iter(), TYPES.1.iter()),
+        (VALUES.0.iter(), VALUES.1.iter()),
+        (MACROS.0.iter(), MACROS.1.iter()),
+    ]
+    .iter()
+    .for_each(|(prefixes, suffixes)| {
+        prefixes.clone().for_each(|prefix| s = s.trim_start_matches(*prefix));
+        suffixes.clone().for_each(|suffix| s = s.trim_end_matches(*suffix));
+    });
+    let s = s.trim_start_matches("@").trim();
+    s
+}
+
+fn get_doc_url(db: &dyn HirDatabase, krate: &Crate) -> Option<Url> {
+    krate
+        .get_doc_url(db)
+        .or_else(||
+        // Fallback to docs.rs
+        // FIXME: Specify an exact version here. This may be difficult, as multiple versions of the same crate could exist.
+        Some(format!("https://docs.rs/{}/*/", krate.display_name(db)?)))
+        .and_then(|s| Url::parse(&s).ok())
+}
+
+/// Get the filename and extension generated for a symbol by rustdoc.
+///
+/// Example: `struct.Shard.html`
+fn get_symbol_filename(db: &dyn HirDatabase, definition: &ModuleDef) -> Option<String> {
+    Some(match definition {
+        ModuleDef::Adt(adt) => match adt {
+            Adt::Struct(s) => format!("struct.{}.html", s.name(db)),
+            Adt::Enum(e) => format!("enum.{}.html", e.name(db)),
+            Adt::Union(u) => format!("union.{}.html", u.name(db)),
+        },
+        ModuleDef::Module(_) => "index.html".to_string(),
+        ModuleDef::Trait(t) => format!("trait.{}.html", t.name(db)),
+        ModuleDef::TypeAlias(t) => format!("type.{}.html", t.name(db)),
+        ModuleDef::BuiltinType(t) => format!("primitive.{}.html", t.as_name()),
+        ModuleDef::Function(f) => format!("fn.{}.html", f.name(db)),
+        ModuleDef::EnumVariant(ev) => {
+            format!("enum.{}.html#variant.{}", ev.parent_enum(db).name(db), ev.name(db))
+        }
+        ModuleDef::Const(c) => format!("const.{}.html", c.name(db)?),
+        ModuleDef::Static(s) => format!("static.{}.html", s.name(db)?),
+    })
+}
+
+#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
+enum Namespace {
+    Types,
+    Values,
+    Macros,
+}
+
+static TYPES: ([&str; 7], [&str; 0]) =
+    (["type", "struct", "enum", "mod", "trait", "union", "module"], []);
+static VALUES: ([&str; 8], [&str; 1]) =
+    (["value", "function", "fn", "method", "const", "static", "mod", "module"], ["()"]);
+static MACROS: ([&str; 1], [&str; 1]) = (["macro"], ["!"]);
+
+impl Namespace {
+    /// Extract the specified namespace from an intra-doc-link if one exists.
+    ///
+    /// # Examples
+    ///
+    /// * `struct MyStruct` -> `Namespace::Types`
+    /// * `panic!` -> `Namespace::Macros`
+    /// * `fn@from_intra_spec` -> `Namespace::Values`
+    fn from_intra_spec(s: &str) -> Option<Self> {
+        [
+            (Namespace::Types, (TYPES.0.iter(), TYPES.1.iter())),
+            (Namespace::Values, (VALUES.0.iter(), VALUES.1.iter())),
+            (Namespace::Macros, (MACROS.0.iter(), MACROS.1.iter())),
+        ]
+        .iter()
+        .filter(|(_ns, (prefixes, suffixes))| {
+            prefixes
+                .clone()
+                .map(|prefix| {
+                    s.starts_with(*prefix)
+                        && s.chars()
+                            .nth(prefix.len() + 1)
+                            .map(|c| c == '@' || c == ' ')
+                            .unwrap_or(false)
+                })
+                .any(|cond| cond)
+                || suffixes
+                    .clone()
+                    .map(|suffix| {
+                        s.starts_with(*suffix)
+                            && s.chars()
+                                .nth(suffix.len() + 1)
+                                .map(|c| c == '@' || c == ' ')
+                                .unwrap_or(false)
+                    })
+                    .any(|cond| cond)
+        })
+        .map(|(ns, (_, _))| *ns)
+        .next()
+    }
+}
+
+/// Sealed trait used solely for the generic bound on [`resolve_doc_link`].
+pub trait Resolvable {
+    fn resolver<D: DefDatabase + HirDatabase>(&self, db: &D) -> Option<Resolver>;
+    fn try_into_module_def(self) -> Option<ModuleDef>;
+}

crates/hir/src/semantics.rs

@@ -0,0 +1,819 @@
+//! See `Semantics`.
+
+mod source_to_def;
+
+use std::{cell::RefCell, fmt, iter::successors};
+
+use base_db::{FileId, FileRange};
+use hir_def::{
+    resolver::{self, HasResolver, Resolver, TypeNs},
+    AsMacroCall, FunctionId, TraitId, VariantId,
+};
+use hir_expand::{hygiene::Hygiene, name::AsName, ExpansionInfo};
+use hir_ty::associated_type_shorthand_candidates;
+use itertools::Itertools;
+use rustc_hash::{FxHashMap, FxHashSet};
+use syntax::{
+    algo::{find_node_at_offset, skip_trivia_token},
+    ast, AstNode, Direction, SyntaxNode, SyntaxToken, TextRange, TextSize,
+};
+
+use crate::{
+    code_model::Access,
+    db::HirDatabase,
+    diagnostics::Diagnostic,
+    semantics::source_to_def::{ChildContainer, SourceToDefCache, SourceToDefCtx},
+    source_analyzer::{resolve_hir_path, SourceAnalyzer},
+    AssocItem, Callable, Crate, Field, Function, HirFileId, ImplDef, InFile, Local, MacroDef,
+    Module, ModuleDef, Name, Origin, Path, ScopeDef, Trait, Type, TypeAlias, TypeParam, VariantDef,
+};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum PathResolution {
+    /// An item
+    Def(ModuleDef),
+    /// A local binding (only value namespace)
+    Local(Local),
+    /// A generic parameter
+    TypeParam(TypeParam),
+    SelfType(ImplDef),
+    Macro(MacroDef),
+    AssocItem(AssocItem),
+}
+
+impl PathResolution {
+    fn in_type_ns(&self) -> Option<TypeNs> {
+        match self {
+            PathResolution::Def(ModuleDef::Adt(adt)) => Some(TypeNs::AdtId((*adt).into())),
+            PathResolution::Def(ModuleDef::BuiltinType(builtin)) => {
+                Some(TypeNs::BuiltinType(*builtin))
+            }
+            PathResolution::Def(ModuleDef::Const(_))
+            | PathResolution::Def(ModuleDef::EnumVariant(_))
+            | PathResolution::Def(ModuleDef::Function(_))
+            | PathResolution::Def(ModuleDef::Module(_))
+            | PathResolution::Def(ModuleDef::Static(_))
+            | PathResolution::Def(ModuleDef::Trait(_)) => None,
+            PathResolution::Def(ModuleDef::TypeAlias(alias)) => {
+                Some(TypeNs::TypeAliasId((*alias).into()))
+            }
+            PathResolution::Local(_) | PathResolution::Macro(_) => None,
+            PathResolution::TypeParam(param) => Some(TypeNs::GenericParam((*param).into())),
+            PathResolution::SelfType(impl_def) => Some(TypeNs::SelfType((*impl_def).into())),
+            PathResolution::AssocItem(AssocItem::Const(_))
+            | PathResolution::AssocItem(AssocItem::Function(_)) => None,
+            PathResolution::AssocItem(AssocItem::TypeAlias(alias)) => {
+                Some(TypeNs::TypeAliasId((*alias).into()))
+            }
+        }
+    }
+
+    /// Returns an iterator over associated types that may be specified after this path (using
+    /// `Ty::Assoc` syntax).
+    pub fn assoc_type_shorthand_candidates<R>(
+        &self,
+        db: &dyn HirDatabase,
+        mut cb: impl FnMut(TypeAlias) -> Option<R>,
+    ) -> Option<R> {
+        associated_type_shorthand_candidates(db, self.in_type_ns()?, |_, _, id| cb(id.into()))
+    }
+}
+
+/// Primary API to get semantic information, like types, from syntax trees.
+pub struct Semantics<'db, DB> {
+    pub db: &'db DB,
+    imp: SemanticsImpl<'db>,
+}
+
+pub struct SemanticsImpl<'db> {
+    pub db: &'db dyn HirDatabase,
+    s2d_cache: RefCell<SourceToDefCache>,
+    expansion_info_cache: RefCell<FxHashMap<HirFileId, Option<ExpansionInfo>>>,
+    cache: RefCell<FxHashMap<SyntaxNode, HirFileId>>,
+}
+
+impl<DB> fmt::Debug for Semantics<'_, DB> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Semantics {{ ... }}")
+    }
+}
+
+impl<'db, DB: HirDatabase> Semantics<'db, DB> {
+    pub fn new(db: &DB) -> Semantics<DB> {
+        let impl_ = SemanticsImpl::new(db);
+        Semantics { db, imp: impl_ }
+    }
+
+    pub fn parse(&self, file_id: FileId) -> ast::SourceFile {
+        self.imp.parse(file_id)
+    }
+
+    pub fn expand(&self, macro_call: &ast::MacroCall) -> Option<SyntaxNode> {
+        self.imp.expand(macro_call)
+    }
+    pub fn speculative_expand(
+        &self,
+        actual_macro_call: &ast::MacroCall,
+        hypothetical_args: &ast::TokenTree,
+        token_to_map: SyntaxToken,
+    ) -> Option<(SyntaxNode, SyntaxToken)> {
+        self.imp.speculative_expand(actual_macro_call, hypothetical_args, token_to_map)
+    }
+
+    pub fn descend_into_macros(&self, token: SyntaxToken) -> SyntaxToken {
+        self.imp.descend_into_macros(token)
+    }
+
+    pub fn descend_node_at_offset<N: ast::AstNode>(
+        &self,
+        node: &SyntaxNode,
+        offset: TextSize,
+    ) -> Option<N> {
+        self.imp.descend_node_at_offset(node, offset).find_map(N::cast)
+    }
+
+    pub fn original_range(&self, node: &SyntaxNode) -> FileRange {
+        self.imp.original_range(node)
+    }
+
+    pub fn diagnostics_display_range(&self, diagnostics: &dyn Diagnostic) -> FileRange {
+        self.imp.diagnostics_display_range(diagnostics)
+    }
+
+    pub fn ancestors_with_macros(&self, node: SyntaxNode) -> impl Iterator<Item = SyntaxNode> + '_ {
+        self.imp.ancestors_with_macros(node)
+    }
+
+    pub fn ancestors_at_offset_with_macros(
+        &self,
+        node: &SyntaxNode,
+        offset: TextSize,
+    ) -> impl Iterator<Item = SyntaxNode> + '_ {
+        self.imp.ancestors_at_offset_with_macros(node, offset)
+    }
+
+    /// Find a AstNode by offset inside SyntaxNode, if it is inside *Macrofile*,
+    /// search up until it is of the target AstNode type
+    pub fn find_node_at_offset_with_macros<N: AstNode>(
+        &self,
+        node: &SyntaxNode,
+        offset: TextSize,
+    ) -> Option<N> {
+        self.imp.ancestors_at_offset_with_macros(node, offset).find_map(N::cast)
+    }
+
+    /// Find a AstNode by offset inside SyntaxNode, if it is inside *MacroCall*,
+    /// descend it and find again
+    pub fn find_node_at_offset_with_descend<N: AstNode>(
+        &self,
+        node: &SyntaxNode,
+        offset: TextSize,
+    ) -> Option<N> {
+        if let Some(it) = find_node_at_offset(&node, offset) {
+            return Some(it);
+        }
+
+        self.imp.descend_node_at_offset(node, offset).find_map(N::cast)
+    }
+
+    pub fn type_of_expr(&self, expr: &ast::Expr) -> Option<Type> {
+        self.imp.type_of_expr(expr)
+    }
+
+    pub fn type_of_pat(&self, pat: &ast::Pat) -> Option<Type> {
+        self.imp.type_of_pat(pat)
+    }
+
+    pub fn type_of_self(&self, param: &ast::SelfParam) -> Option<Type> {
+        self.imp.type_of_self(param)
+    }
+
+    pub fn resolve_method_call(&self, call: &ast::MethodCallExpr) -> Option<Function> {
+        self.imp.resolve_method_call(call).map(Function::from)
+    }
+
+    pub fn resolve_method_call_as_callable(&self, call: &ast::MethodCallExpr) -> Option<Callable> {
+        self.imp.resolve_method_call_as_callable(call)
+    }
+
+    pub fn resolve_field(&self, field: &ast::FieldExpr) -> Option<Field> {
+        self.imp.resolve_field(field)
+    }
+
+    pub fn resolve_record_field(
+        &self,
+        field: &ast::RecordExprField,
+    ) -> Option<(Field, Option<Local>)> {
+        self.imp.resolve_record_field(field)
+    }
+
+    pub fn resolve_record_field_pat(&self, field: &ast::RecordPatField) -> Option<Field> {
+        self.imp.resolve_record_field_pat(field)
+    }
+
+    pub fn resolve_macro_call(&self, macro_call: &ast::MacroCall) -> Option<MacroDef> {
+        self.imp.resolve_macro_call(macro_call)
+    }
+
+    pub fn resolve_path(&self, path: &ast::Path) -> Option<PathResolution> {
+        self.imp.resolve_path(path)
+    }
+
+    pub fn resolve_extern_crate(&self, extern_crate: &ast::ExternCrate) -> Option<Crate> {
+        self.imp.resolve_extern_crate(extern_crate)
+    }
+
+    pub fn resolve_variant(&self, record_lit: ast::RecordExpr) -> Option<VariantDef> {
+        self.imp.resolve_variant(record_lit).map(VariantDef::from)
+    }
+
+    pub fn resolve_bind_pat_to_const(&self, pat: &ast::IdentPat) -> Option<ModuleDef> {
+        self.imp.resolve_bind_pat_to_const(pat)
+    }
+
+    // FIXME: use this instead?
+    // pub fn resolve_name_ref(&self, name_ref: &ast::NameRef) -> Option<???>;
+
+    pub fn record_literal_missing_fields(&self, literal: &ast::RecordExpr) -> Vec<(Field, Type)> {
+        self.imp.record_literal_missing_fields(literal)
+    }
+
+    pub fn record_pattern_missing_fields(&self, pattern: &ast::RecordPat) -> Vec<(Field, Type)> {
+        self.imp.record_pattern_missing_fields(pattern)
+    }
+
+    pub fn to_def<T: ToDef>(&self, src: &T) -> Option<T::Def> {
+        let src = self.imp.find_file(src.syntax().clone()).with_value(src).cloned();
+        T::to_def(&self.imp, src)
+    }
+
+    pub fn to_module_def(&self, file: FileId) -> Option<Module> {
+        self.imp.to_module_def(file)
+    }
+
+    pub fn scope(&self, node: &SyntaxNode) -> SemanticsScope<'db> {
+        self.imp.scope(node)
+    }
+
+    pub fn scope_at_offset(&self, node: &SyntaxNode, offset: TextSize) -> SemanticsScope<'db> {
+        self.imp.scope_at_offset(node, offset)
+    }
+
+    pub fn scope_for_def(&self, def: Trait) -> SemanticsScope<'db> {
+        self.imp.scope_for_def(def)
+    }
+
+    pub fn assert_contains_node(&self, node: &SyntaxNode) {
+        self.imp.assert_contains_node(node)
+    }
+
+    pub fn is_unsafe_method_call(&self, method_call_expr: &ast::MethodCallExpr) -> bool {
+        self.imp.is_unsafe_method_call(method_call_expr)
+    }
+
+    pub fn is_unsafe_ref_expr(&self, ref_expr: &ast::RefExpr) -> bool {
+        self.imp.is_unsafe_ref_expr(ref_expr)
+    }
+
+    pub fn is_unsafe_ident_pat(&self, ident_pat: &ast::IdentPat) -> bool {
+        self.imp.is_unsafe_ident_pat(ident_pat)
+    }
+}
+
+impl<'db> SemanticsImpl<'db> {
+    fn new(db: &'db dyn HirDatabase) -> Self {
+        SemanticsImpl {
+            db,
+            s2d_cache: Default::default(),
+            cache: Default::default(),
+            expansion_info_cache: Default::default(),
+        }
+    }
+
+    fn parse(&self, file_id: FileId) -> ast::SourceFile {
+        let tree = self.db.parse(file_id).tree();
+        self.cache(tree.syntax().clone(), file_id.into());
+        tree
+    }
+
+    fn expand(&self, macro_call: &ast::MacroCall) -> Option<SyntaxNode> {
+        let macro_call = self.find_file(macro_call.syntax().clone()).with_value(macro_call);
+        let sa = self.analyze2(macro_call.map(|it| it.syntax()), None);
+        let file_id = sa.expand(self.db, macro_call)?;
+        let node = self.db.parse_or_expand(file_id)?;
+        self.cache(node.clone(), file_id);
+        Some(node)
+    }
+
+    fn speculative_expand(
+        &self,
+        actual_macro_call: &ast::MacroCall,
+        hypothetical_args: &ast::TokenTree,
+        token_to_map: SyntaxToken,
+    ) -> Option<(SyntaxNode, SyntaxToken)> {
+        let macro_call =
+            self.find_file(actual_macro_call.syntax().clone()).with_value(actual_macro_call);
+        let sa = self.analyze2(macro_call.map(|it| it.syntax()), None);
+        let krate = sa.resolver.krate()?;
+        let macro_call_id = macro_call.as_call_id(self.db.upcast(), krate, |path| {
+            sa.resolver.resolve_path_as_macro(self.db.upcast(), &path)
+        })?;
+        hir_expand::db::expand_hypothetical(
+            self.db.upcast(),
+            macro_call_id,
+            hypothetical_args,
+            token_to_map,
+        )
+    }
+
+    fn descend_into_macros(&self, token: SyntaxToken) -> SyntaxToken {
+        let _p = profile::span("descend_into_macros");
+        let parent = token.parent();
+        let parent = self.find_file(parent);
+        let sa = self.analyze2(parent.as_ref(), None);
+
+        let token = successors(Some(parent.with_value(token)), |token| {
+            self.db.check_canceled();
+            let macro_call = token.value.ancestors().find_map(ast::MacroCall::cast)?;
+            let tt = macro_call.token_tree()?;
+            if !tt.syntax().text_range().contains_range(token.value.text_range()) {
+                return None;
+            }
+            let file_id = sa.expand(self.db, token.with_value(&macro_call))?;
+            let token = self
+                .expansion_info_cache
+                .borrow_mut()
+                .entry(file_id)
+                .or_insert_with(|| file_id.expansion_info(self.db.upcast()))
+                .as_ref()?
+                .map_token_down(token.as_ref())?;
+
+            self.cache(find_root(&token.value.parent()), token.file_id);
+
+            Some(token)
+        })
+        .last()
+        .unwrap();
+
+        token.value
+    }
+
+    fn descend_node_at_offset(
+        &self,
+        node: &SyntaxNode,
+        offset: TextSize,
+    ) -> impl Iterator<Item = SyntaxNode> + '_ {
+        // Handle macro token cases
+        node.token_at_offset(offset)
+            .map(|token| self.descend_into_macros(token))
+            .map(|it| self.ancestors_with_macros(it.parent()))
+            .flatten()
+    }
+
+    fn original_range(&self, node: &SyntaxNode) -> FileRange {
+        let node = self.find_file(node.clone());
+        original_range(self.db, node.as_ref())
+    }
+
+    fn diagnostics_display_range(&self, diagnostics: &dyn Diagnostic) -> FileRange {
+        let src = diagnostics.display_source();
+        let root = self.db.parse_or_expand(src.file_id).unwrap();
+        let node = src.value.to_node(&root);
+        self.cache(root, src.file_id);
+        original_range(self.db, src.with_value(&node))
+    }
+
+    fn ancestors_with_macros(&self, node: SyntaxNode) -> impl Iterator<Item = SyntaxNode> + '_ {
+        let node = self.find_file(node);
+        node.ancestors_with_macros(self.db.upcast()).map(|it| it.value)
+    }
+
+    fn ancestors_at_offset_with_macros(
+        &self,
+        node: &SyntaxNode,
+        offset: TextSize,
+    ) -> impl Iterator<Item = SyntaxNode> + '_ {
+        node.token_at_offset(offset)
+            .map(|token| self.ancestors_with_macros(token.parent()))
+            .kmerge_by(|node1, node2| node1.text_range().len() < node2.text_range().len())
+    }
+
+    fn type_of_expr(&self, expr: &ast::Expr) -> Option<Type> {
+        self.analyze(expr.syntax()).type_of_expr(self.db, &expr)
+    }
+
+    fn type_of_pat(&self, pat: &ast::Pat) -> Option<Type> {
+        self.analyze(pat.syntax()).type_of_pat(self.db, &pat)
+    }
+
+    fn type_of_self(&self, param: &ast::SelfParam) -> Option<Type> {
+        self.analyze(param.syntax()).type_of_self(self.db, &param)
+    }
+
+    fn resolve_method_call(&self, call: &ast::MethodCallExpr) -> Option<FunctionId> {
+        self.analyze(call.syntax()).resolve_method_call(self.db, call)
+    }
+
+    fn resolve_method_call_as_callable(&self, call: &ast::MethodCallExpr) -> Option<Callable> {
+        // FIXME: this erases Substs
+        let func = self.resolve_method_call(call)?;
+        let ty = self.db.value_ty(func.into());
+        let resolver = self.analyze(call.syntax()).resolver;
+        let ty = Type::new_with_resolver(self.db, &resolver, ty.value)?;
+        let mut res = ty.as_callable(self.db)?;
+        res.is_bound_method = true;
+        Some(res)
+    }
+
+    fn resolve_field(&self, field: &ast::FieldExpr) -> Option<Field> {
+        self.analyze(field.syntax()).resolve_field(self.db, field)
+    }
+
+    fn resolve_record_field(&self, field: &ast::RecordExprField) -> Option<(Field, Option<Local>)> {
+        self.analyze(field.syntax()).resolve_record_field(self.db, field)
+    }
+
+    fn resolve_record_field_pat(&self, field: &ast::RecordPatField) -> Option<Field> {
+        self.analyze(field.syntax()).resolve_record_field_pat(self.db, field)
+    }
+
+    fn resolve_macro_call(&self, macro_call: &ast::MacroCall) -> Option<MacroDef> {
+        let sa = self.analyze(macro_call.syntax());
+        let macro_call = self.find_file(macro_call.syntax().clone()).with_value(macro_call);
+        sa.resolve_macro_call(self.db, macro_call)
+    }
+
+    fn resolve_path(&self, path: &ast::Path) -> Option<PathResolution> {
+        self.analyze(path.syntax()).resolve_path(self.db, path)
+    }
+
+    fn resolve_extern_crate(&self, extern_crate: &ast::ExternCrate) -> Option<Crate> {
+        let krate = self.scope(extern_crate.syntax()).krate()?;
+        krate.dependencies(self.db).into_iter().find_map(|dep| {
+            if dep.name == extern_crate.name_ref()?.as_name() {
+                Some(dep.krate)
+            } else {
+                None
+            }
+        })
+    }
+
+    fn resolve_variant(&self, record_lit: ast::RecordExpr) -> Option<VariantId> {
+        self.analyze(record_lit.syntax()).resolve_variant(self.db, record_lit)
+    }
+
+    fn resolve_bind_pat_to_const(&self, pat: &ast::IdentPat) -> Option<ModuleDef> {
+        self.analyze(pat.syntax()).resolve_bind_pat_to_const(self.db, pat)
+    }
+
+    fn record_literal_missing_fields(&self, literal: &ast::RecordExpr) -> Vec<(Field, Type)> {
+        self.analyze(literal.syntax())
+            .record_literal_missing_fields(self.db, literal)
+            .unwrap_or_default()
+    }
+
+    fn record_pattern_missing_fields(&self, pattern: &ast::RecordPat) -> Vec<(Field, Type)> {
+        self.analyze(pattern.syntax())
+            .record_pattern_missing_fields(self.db, pattern)
+            .unwrap_or_default()
+    }
+
+    fn with_ctx<F: FnOnce(&mut SourceToDefCtx) -> T, T>(&self, f: F) -> T {
+        let mut cache = self.s2d_cache.borrow_mut();
+        let mut ctx = SourceToDefCtx { db: self.db, cache: &mut *cache };
+        f(&mut ctx)
+    }
+
+    fn to_module_def(&self, file: FileId) -> Option<Module> {
+        self.with_ctx(|ctx| ctx.file_to_def(file)).map(Module::from)
+    }
+
+    fn scope(&self, node: &SyntaxNode) -> SemanticsScope<'db> {
+        let node = self.find_file(node.clone());
+        let resolver = self.analyze2(node.as_ref(), None).resolver;
+        SemanticsScope { db: self.db, file_id: node.file_id, resolver }
+    }
+
+    fn scope_at_offset(&self, node: &SyntaxNode, offset: TextSize) -> SemanticsScope<'db> {
+        let node = self.find_file(node.clone());
+        let resolver = self.analyze2(node.as_ref(), Some(offset)).resolver;
+        SemanticsScope { db: self.db, file_id: node.file_id, resolver }
+    }
+
+    fn scope_for_def(&self, def: Trait) -> SemanticsScope<'db> {
+        let file_id = self.db.lookup_intern_trait(def.id).id.file_id;
+        let resolver = def.id.resolver(self.db.upcast());
+        SemanticsScope { db: self.db, file_id, resolver }
+    }
+
+    fn analyze(&self, node: &SyntaxNode) -> SourceAnalyzer {
+        let src = self.find_file(node.clone());
+        self.analyze2(src.as_ref(), None)
+    }
+
+    fn analyze2(&self, src: InFile<&SyntaxNode>, offset: Option<TextSize>) -> SourceAnalyzer {
+        let _p = profile::span("Semantics::analyze2");
+
+        let container = match self.with_ctx(|ctx| ctx.find_container(src)) {
+            Some(it) => it,
+            None => return SourceAnalyzer::new_for_resolver(Resolver::default(), src),
+        };
+
+        let resolver = match container {
+            ChildContainer::DefWithBodyId(def) => {
+                return SourceAnalyzer::new_for_body(self.db, def, src, offset)
+            }
+            ChildContainer::TraitId(it) => it.resolver(self.db.upcast()),
+            ChildContainer::ImplId(it) => it.resolver(self.db.upcast()),
+            ChildContainer::ModuleId(it) => it.resolver(self.db.upcast()),
+            ChildContainer::EnumId(it) => it.resolver(self.db.upcast()),
+            ChildContainer::VariantId(it) => it.resolver(self.db.upcast()),
+            ChildContainer::TypeAliasId(it) => it.resolver(self.db.upcast()),
+            ChildContainer::GenericDefId(it) => it.resolver(self.db.upcast()),
+        };
+        SourceAnalyzer::new_for_resolver(resolver, src)
+    }
+
+    fn cache(&self, root_node: SyntaxNode, file_id: HirFileId) {
+        assert!(root_node.parent().is_none());
+        let mut cache = self.cache.borrow_mut();
+        let prev = cache.insert(root_node, file_id);
+        assert!(prev == None || prev == Some(file_id))
+    }
+
+    fn assert_contains_node(&self, node: &SyntaxNode) {
+        self.find_file(node.clone());
+    }
+
+    fn lookup(&self, root_node: &SyntaxNode) -> Option<HirFileId> {
+        let cache = self.cache.borrow();
+        cache.get(root_node).copied()
+    }
+
+    fn find_file(&self, node: SyntaxNode) -> InFile<SyntaxNode> {
+        let root_node = find_root(&node);
+        let file_id = self.lookup(&root_node).unwrap_or_else(|| {
+            panic!(
+                "\n\nFailed to lookup {:?} in this Semantics.\n\
+                 Make sure to use only query nodes, derived from this instance of Semantics.\n\
+                 root node:   {:?}\n\
+                 known nodes: {}\n\n",
+                node,
+                root_node,
+                self.cache
+                    .borrow()
+                    .keys()
+                    .map(|it| format!("{:?}", it))
+                    .collect::<Vec<_>>()
+                    .join(", ")
+            )
+        });
+        InFile::new(file_id, node)
+    }
+
+    fn is_unsafe_method_call(&self, method_call_expr: &ast::MethodCallExpr) -> bool {
+        method_call_expr
+            .receiver()
+            .and_then(|expr| {
+                let field_expr = match expr {
+                    ast::Expr::FieldExpr(field_expr) => field_expr,
+                    _ => return None,
+                };
+                let ty = self.type_of_expr(&field_expr.expr()?)?;
+                if !ty.is_packed(self.db) {
+                    return None;
+                }
+
+                let func = self.resolve_method_call(&method_call_expr).map(Function::from)?;
+                let res = match func.self_param(self.db)?.access(self.db) {
+                    Access::Shared | Access::Exclusive => true,
+                    Access::Owned => false,
+                };
+                Some(res)
+            })
+            .unwrap_or(false)
+    }
+
+    fn is_unsafe_ref_expr(&self, ref_expr: &ast::RefExpr) -> bool {
+        ref_expr
+            .expr()
+            .and_then(|expr| {
+                let field_expr = match expr {
+                    ast::Expr::FieldExpr(field_expr) => field_expr,
+                    _ => return None,
+                };
+                let expr = field_expr.expr()?;
+                self.type_of_expr(&expr)
+            })
+            // Binding a reference to a packed type is possibly unsafe.
+            .map(|ty| ty.is_packed(self.db))
+            .unwrap_or(false)
+
+        // FIXME This needs layout computation to be correct. It will highlight
+        // more than it should with the current implementation.
+    }
+
+    fn is_unsafe_ident_pat(&self, ident_pat: &ast::IdentPat) -> bool {
+        if !ident_pat.ref_token().is_some() {
+            return false;
+        }
+
+        ident_pat
+            .syntax()
+            .parent()
+            .and_then(|parent| {
+                // `IdentPat` can live under `RecordPat` directly under `RecordPatField` or
+                // `RecordPatFieldList`. `RecordPatField` also lives under `RecordPatFieldList`,
+                // so this tries to lookup the `IdentPat` anywhere along that structure to the
+                // `RecordPat` so we can get the containing type.
+                let record_pat = ast::RecordPatField::cast(parent.clone())
+                    .and_then(|record_pat| record_pat.syntax().parent())
+                    .or_else(|| Some(parent.clone()))
+                    .and_then(|parent| {
+                        ast::RecordPatFieldList::cast(parent)?
+                            .syntax()
+                            .parent()
+                            .and_then(ast::RecordPat::cast)
+                    });
+
+                // If this doesn't match a `RecordPat`, fallback to a `LetStmt` to see if
+                // this is initialized from a `FieldExpr`.
+                if let Some(record_pat) = record_pat {
+                    self.type_of_pat(&ast::Pat::RecordPat(record_pat))
+                } else if let Some(let_stmt) = ast::LetStmt::cast(parent) {
+                    let field_expr = match let_stmt.initializer()? {
+                        ast::Expr::FieldExpr(field_expr) => field_expr,
+                        _ => return None,
+                    };
+
+                    self.type_of_expr(&field_expr.expr()?)
+                } else {
+                    None
+                }
+            })
+            // Binding a reference to a packed type is possibly unsafe.
+            .map(|ty| ty.is_packed(self.db))
+            .unwrap_or(false)
+    }
+}
+
+pub trait ToDef: AstNode + Clone {
+    type Def;
+
+    fn to_def(sema: &SemanticsImpl, src: InFile<Self>) -> Option<Self::Def>;
+}
+
+macro_rules! to_def_impls {
+    ($(($def:path, $ast:path, $meth:ident)),* ,) => {$(
+        impl ToDef for $ast {
+            type Def = $def;
+            fn to_def(sema: &SemanticsImpl, src: InFile<Self>) -> Option<Self::Def> {
+                sema.with_ctx(|ctx| ctx.$meth(src)).map(<$def>::from)
+            }
+        }
+    )*}
+}
+
+to_def_impls![
+    (crate::Module, ast::Module, module_to_def),
+    (crate::Struct, ast::Struct, struct_to_def),
+    (crate::Enum, ast::Enum, enum_to_def),
+    (crate::Union, ast::Union, union_to_def),
+    (crate::Trait, ast::Trait, trait_to_def),
+    (crate::ImplDef, ast::Impl, impl_to_def),
+    (crate::TypeAlias, ast::TypeAlias, type_alias_to_def),
+    (crate::Const, ast::Const, const_to_def),
+    (crate::Static, ast::Static, static_to_def),
+    (crate::Function, ast::Fn, fn_to_def),
+    (crate::Field, ast::RecordField, record_field_to_def),
+    (crate::Field, ast::TupleField, tuple_field_to_def),
+    (crate::EnumVariant, ast::Variant, enum_variant_to_def),
+    (crate::TypeParam, ast::TypeParam, type_param_to_def),
+    (crate::MacroDef, ast::MacroCall, macro_call_to_def), // this one is dubious, not all calls are macros
+    (crate::Local, ast::IdentPat, bind_pat_to_def),
+];
+
+fn find_root(node: &SyntaxNode) -> SyntaxNode {
+    node.ancestors().last().unwrap()
+}
+
+#[derive(Debug)]
+pub struct SemanticsScope<'a> {
+    pub db: &'a dyn HirDatabase,
+    file_id: HirFileId,
+    resolver: Resolver,
+}
+
+impl<'a> SemanticsScope<'a> {
+    pub fn module(&self) -> Option<Module> {
+        Some(Module { id: self.resolver.module()? })
+    }
+
+    pub fn krate(&self) -> Option<Crate> {
+        Some(Crate { id: self.resolver.krate()? })
+    }
+
+    /// Note: `FxHashSet<TraitId>` should be treated as an opaque type, passed into `Type
+    // FIXME: rename to visible_traits to not repeat scope?
+    pub fn traits_in_scope(&self) -> FxHashSet<TraitId> {
+        let resolver = &self.resolver;
+        resolver.traits_in_scope(self.db.upcast())
+    }
+
+    pub fn process_all_names(&self, f: &mut dyn FnMut(Name, ScopeDef)) {
+        let resolver = &self.resolver;
+
+        resolver.process_all_names(self.db.upcast(), &mut |name, def| {
+            let def = match def {
+                resolver::ScopeDef::PerNs(it) => {
+                    let items = ScopeDef::all_items(it);
+                    for item in items {
+                        f(name.clone(), item);
+                    }
+                    return;
+                }
+                resolver::ScopeDef::ImplSelfType(it) => ScopeDef::ImplSelfType(it.into()),
+                resolver::ScopeDef::AdtSelfType(it) => ScopeDef::AdtSelfType(it.into()),
+                resolver::ScopeDef::GenericParam(id) => ScopeDef::GenericParam(TypeParam { id }),
+                resolver::ScopeDef::Local(pat_id) => {
+                    let parent = resolver.body_owner().unwrap().into();
+                    ScopeDef::Local(Local { parent, pat_id })
+                }
+            };
+            f(name, def)
+        })
+    }
+
+    /// Resolve a path as-if it was written at the given scope. This is
+    /// necessary a heuristic, as it doesn't take hygiene into account.
+    pub fn speculative_resolve(&self, path: &ast::Path) -> Option<PathResolution> {
+        let hygiene = Hygiene::new(self.db.upcast(), self.file_id);
+        let path = Path::from_src(path.clone(), &hygiene)?;
+        resolve_hir_path(self.db, &self.resolver, &path)
+    }
+}
+
+// FIXME: Change `HasSource` trait to work with `Semantics` and remove this?
+pub fn original_range(db: &dyn HirDatabase, node: InFile<&SyntaxNode>) -> FileRange {
+    if let Some(range) = original_range_opt(db, node) {
+        let original_file = range.file_id.original_file(db.upcast());
+        if range.file_id == original_file.into() {
+            return FileRange { file_id: original_file, range: range.value };
+        }
+
+        log::error!("Fail to mapping up more for {:?}", range);
+        return FileRange { file_id: range.file_id.original_file(db.upcast()), range: range.value };
+    }
+
+    // Fall back to whole macro call
+    if let Some(expansion) = node.file_id.expansion_info(db.upcast()) {
+        if let Some(call_node) = expansion.call_node() {
+            return FileRange {
+                file_id: call_node.file_id.original_file(db.upcast()),
+                range: call_node.value.text_range(),
+            };
+        }
+    }
+
+    FileRange { file_id: node.file_id.original_file(db.upcast()), range: node.value.text_range() }
+}
+
+fn original_range_opt(
+    db: &dyn HirDatabase,
+    node: InFile<&SyntaxNode>,
+) -> Option<InFile<TextRange>> {
+    let expansion = node.file_id.expansion_info(db.upcast())?;
+
+    // the input node has only one token ?
+    let single = skip_trivia_token(node.value.first_token()?, Direction::Next)?
+        == skip_trivia_token(node.value.last_token()?, Direction::Prev)?;
+
+    Some(node.value.descendants().find_map(|it| {
+        let first = skip_trivia_token(it.first_token()?, Direction::Next)?;
+        let first = ascend_call_token(db, &expansion, node.with_value(first))?;
+
+        let last = skip_trivia_token(it.last_token()?, Direction::Prev)?;
+        let last = ascend_call_token(db, &expansion, node.with_value(last))?;
+
+        if (!single && first == last) || (first.file_id != last.file_id) {
+            return None;
+        }
+
+        Some(first.with_value(first.value.text_range().cover(last.value.text_range())))
+    })?)
+}
+
+fn ascend_call_token(
+    db: &dyn HirDatabase,
+    expansion: &ExpansionInfo,
+    token: InFile<SyntaxToken>,
+) -> Option<InFile<SyntaxToken>> {
+    let (mapped, origin) = expansion.map_token_up(token.as_ref())?;
+    if origin != Origin::Call {
+        return None;
+    }
+    if let Some(info) = mapped.file_id.expansion_info(db.upcast()) {
+        return ascend_call_token(db, &info, mapped);
+    }
+    Some(mapped)
+}

crates/hir/src/semantics/source_to_def.rs

@@ -0,0 +1,275 @@
+//! Maps *syntax* of various definitions to their semantic ids.
+
+use base_db::FileId;
+use hir_def::{
+    child_by_source::ChildBySource,
+    dyn_map::DynMap,
+    expr::PatId,
+    keys::{self, Key},
+    ConstId, DefWithBodyId, EnumId, EnumVariantId, FieldId, FunctionId, GenericDefId, ImplId,
+    ModuleId, StaticId, StructId, TraitId, TypeAliasId, TypeParamId, UnionId, VariantId,
+};
+use hir_expand::{name::AsName, AstId, MacroDefKind};
+use rustc_hash::FxHashMap;
+use stdx::impl_from;
+use syntax::{
+    ast::{self, NameOwner},
+    match_ast, AstNode, SyntaxNode,
+};
+
+use crate::{db::HirDatabase, InFile, MacroDefId};
+
+pub(super) type SourceToDefCache = FxHashMap<ChildContainer, DynMap>;
+
+pub(super) struct SourceToDefCtx<'a, 'b> {
+    pub(super) db: &'b dyn HirDatabase,
+    pub(super) cache: &'a mut SourceToDefCache,
+}
+
+impl SourceToDefCtx<'_, '_> {
+    pub(super) fn file_to_def(&mut self, file: FileId) -> Option<ModuleId> {
+        let _p = profile::span("SourceBinder::to_module_def");
+        let (krate, local_id) = self.db.relevant_crates(file).iter().find_map(|&crate_id| {
+            let crate_def_map = self.db.crate_def_map(crate_id);
+            let local_id = crate_def_map.modules_for_file(file).next()?;
+            Some((crate_id, local_id))
+        })?;
+        Some(ModuleId { krate, local_id })
+    }
+
+    pub(super) fn module_to_def(&mut self, src: InFile<ast::Module>) -> Option<ModuleId> {
+        let _p = profile::span("module_to_def");
+        let parent_declaration = src
+            .as_ref()
+            .map(|it| it.syntax())
+            .cloned()
+            .ancestors_with_macros(self.db.upcast())
+            .skip(1)
+            .find_map(|it| {
+                let m = ast::Module::cast(it.value.clone())?;
+                Some(it.with_value(m))
+            });
+
+        let parent_module = match parent_declaration {
+            Some(parent_declaration) => self.module_to_def(parent_declaration),
+            None => {
+                let file_id = src.file_id.original_file(self.db.upcast());
+                self.file_to_def(file_id)
+            }
+        }?;
+
+        let child_name = src.value.name()?.as_name();
+        let def_map = self.db.crate_def_map(parent_module.krate);
+        let child_id = *def_map[parent_module.local_id].children.get(&child_name)?;
+        Some(ModuleId { krate: parent_module.krate, local_id: child_id })
+    }
+
+    pub(super) fn trait_to_def(&mut self, src: InFile<ast::Trait>) -> Option<TraitId> {
+        self.to_def(src, keys::TRAIT)
+    }
+    pub(super) fn impl_to_def(&mut self, src: InFile<ast::Impl>) -> Option<ImplId> {
+        self.to_def(src, keys::IMPL)
+    }
+    pub(super) fn fn_to_def(&mut self, src: InFile<ast::Fn>) -> Option<FunctionId> {
+        self.to_def(src, keys::FUNCTION)
+    }
+    pub(super) fn struct_to_def(&mut self, src: InFile<ast::Struct>) -> Option<StructId> {
+        self.to_def(src, keys::STRUCT)
+    }
+    pub(super) fn enum_to_def(&mut self, src: InFile<ast::Enum>) -> Option<EnumId> {
+        self.to_def(src, keys::ENUM)
+    }
+    pub(super) fn union_to_def(&mut self, src: InFile<ast::Union>) -> Option<UnionId> {
+        self.to_def(src, keys::UNION)
+    }
+    pub(super) fn static_to_def(&mut self, src: InFile<ast::Static>) -> Option<StaticId> {
+        self.to_def(src, keys::STATIC)
+    }
+    pub(super) fn const_to_def(&mut self, src: InFile<ast::Const>) -> Option<ConstId> {
+        self.to_def(src, keys::CONST)
+    }
+    pub(super) fn type_alias_to_def(&mut self, src: InFile<ast::TypeAlias>) -> Option<TypeAliasId> {
+        self.to_def(src, keys::TYPE_ALIAS)
+    }
+    pub(super) fn record_field_to_def(&mut self, src: InFile<ast::RecordField>) -> Option<FieldId> {
+        self.to_def(src, keys::RECORD_FIELD)
+    }
+    pub(super) fn tuple_field_to_def(&mut self, src: InFile<ast::TupleField>) -> Option<FieldId> {
+        self.to_def(src, keys::TUPLE_FIELD)
+    }
+    pub(super) fn enum_variant_to_def(
+        &mut self,
+        src: InFile<ast::Variant>,
+    ) -> Option<EnumVariantId> {
+        self.to_def(src, keys::VARIANT)
+    }
+    pub(super) fn bind_pat_to_def(
+        &mut self,
+        src: InFile<ast::IdentPat>,
+    ) -> Option<(DefWithBodyId, PatId)> {
+        let container = self.find_pat_container(src.as_ref().map(|it| it.syntax()))?;
+        let (_body, source_map) = self.db.body_with_source_map(container);
+        let src = src.map(ast::Pat::from);
+        let pat_id = source_map.node_pat(src.as_ref())?;
+        Some((container, pat_id))
+    }
+
+    fn to_def<Ast: AstNode + 'static, ID: Copy + 'static>(
+        &mut self,
+        src: InFile<Ast>,
+        key: Key<Ast, ID>,
+    ) -> Option<ID> {
+        let container = self.find_container(src.as_ref().map(|it| it.syntax()))?;
+        let db = self.db;
+        let dyn_map =
+            &*self.cache.entry(container).or_insert_with(|| container.child_by_source(db));
+        dyn_map[key].get(&src).copied()
+    }
+
+    pub(super) fn type_param_to_def(&mut self, src: InFile<ast::TypeParam>) -> Option<TypeParamId> {
+        let container: ChildContainer =
+            self.find_type_param_container(src.as_ref().map(|it| it.syntax()))?.into();
+        let db = self.db;
+        let dyn_map =
+            &*self.cache.entry(container).or_insert_with(|| container.child_by_source(db));
+        dyn_map[keys::TYPE_PARAM].get(&src).copied()
+    }
+
+    // FIXME: use DynMap as well?
+    pub(super) fn macro_call_to_def(&mut self, src: InFile<ast::MacroCall>) -> Option<MacroDefId> {
+        let kind = MacroDefKind::Declarative;
+        let file_id = src.file_id.original_file(self.db.upcast());
+        let krate = self.file_to_def(file_id)?.krate;
+        let file_ast_id = self.db.ast_id_map(src.file_id).ast_id(&src.value);
+        let ast_id = Some(AstId::new(src.file_id, file_ast_id));
+        Some(MacroDefId { krate: Some(krate), ast_id, kind, local_inner: false })
+    }
+
+    pub(super) fn find_container(&mut self, src: InFile<&SyntaxNode>) -> Option<ChildContainer> {
+        for container in src.cloned().ancestors_with_macros(self.db.upcast()).skip(1) {
+            let res: ChildContainer = match_ast! {
+                match (container.value) {
+                    ast::Module(it) => {
+                        let def = self.module_to_def(container.with_value(it))?;
+                        def.into()
+                    },
+                    ast::Trait(it) => {
+                        let def = self.trait_to_def(container.with_value(it))?;
+                        def.into()
+                    },
+                    ast::Impl(it) => {
+                        let def = self.impl_to_def(container.with_value(it))?;
+                        def.into()
+                    },
+                    ast::Fn(it) => {
+                        let def = self.fn_to_def(container.with_value(it))?;
+                        DefWithBodyId::from(def).into()
+                    },
+                    ast::Struct(it) => {
+                        let def = self.struct_to_def(container.with_value(it))?;
+                        VariantId::from(def).into()
+                    },
+                    ast::Enum(it) => {
+                        let def = self.enum_to_def(container.with_value(it))?;
+                        def.into()
+                    },
+                    ast::Union(it) => {
+                        let def = self.union_to_def(container.with_value(it))?;
+                        VariantId::from(def).into()
+                    },
+                    ast::Static(it) => {
+                        let def = self.static_to_def(container.with_value(it))?;
+                        DefWithBodyId::from(def).into()
+                    },
+                    ast::Const(it) => {
+                        let def = self.const_to_def(container.with_value(it))?;
+                        DefWithBodyId::from(def).into()
+                    },
+                    ast::TypeAlias(it) => {
+                        let def = self.type_alias_to_def(container.with_value(it))?;
+                        def.into()
+                    },
+                    _ => continue,
+                }
+            };
+            return Some(res);
+        }
+
+        let def = self.file_to_def(src.file_id.original_file(self.db.upcast()))?;
+        Some(def.into())
+    }
+
+    fn find_type_param_container(&mut self, src: InFile<&SyntaxNode>) -> Option<GenericDefId> {
+        for container in src.cloned().ancestors_with_macros(self.db.upcast()).skip(1) {
+            let res: GenericDefId = match_ast! {
+                match (container.value) {
+                    ast::Fn(it) => self.fn_to_def(container.with_value(it))?.into(),
+                    ast::Struct(it) => self.struct_to_def(container.with_value(it))?.into(),
+                    ast::Enum(it) => self.enum_to_def(container.with_value(it))?.into(),
+                    ast::Trait(it) => self.trait_to_def(container.with_value(it))?.into(),
+                    ast::TypeAlias(it) => self.type_alias_to_def(container.with_value(it))?.into(),
+                    ast::Impl(it) => self.impl_to_def(container.with_value(it))?.into(),
+                    _ => continue,
+                }
+            };
+            return Some(res);
+        }
+        None
+    }
+
+    fn find_pat_container(&mut self, src: InFile<&SyntaxNode>) -> Option<DefWithBodyId> {
+        for container in src.cloned().ancestors_with_macros(self.db.upcast()).skip(1) {
+            let res: DefWithBodyId = match_ast! {
+                match (container.value) {
+                    ast::Const(it) => self.const_to_def(container.with_value(it))?.into(),
+                    ast::Static(it) => self.static_to_def(container.with_value(it))?.into(),
+                    ast::Fn(it) => self.fn_to_def(container.with_value(it))?.into(),
+                    _ => continue,
+                }
+            };
+            return Some(res);
+        }
+        None
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+pub(crate) enum ChildContainer {
+    DefWithBodyId(DefWithBodyId),
+    ModuleId(ModuleId),
+    TraitId(TraitId),
+    ImplId(ImplId),
+    EnumId(EnumId),
+    VariantId(VariantId),
+    TypeAliasId(TypeAliasId),
+    /// XXX: this might be the same def as, for example an `EnumId`. However,
+    /// here the children generic parameters, and not, eg enum variants.
+    GenericDefId(GenericDefId),
+}
+impl_from! {
+    DefWithBodyId,
+    ModuleId,
+    TraitId,
+    ImplId,
+    EnumId,
+    VariantId,
+    TypeAliasId,
+    GenericDefId
+    for ChildContainer
+}
+
+impl ChildContainer {
+    fn child_by_source(self, db: &dyn HirDatabase) -> DynMap {
+        let db = db.upcast();
+        match self {
+            ChildContainer::DefWithBodyId(it) => it.child_by_source(db),
+            ChildContainer::ModuleId(it) => it.child_by_source(db),
+            ChildContainer::TraitId(it) => it.child_by_source(db),
+            ChildContainer::ImplId(it) => it.child_by_source(db),
+            ChildContainer::EnumId(it) => it.child_by_source(db),
+            ChildContainer::VariantId(it) => it.child_by_source(db),
+            ChildContainer::TypeAliasId(_) => DynMap::default(),
+            ChildContainer::GenericDefId(it) => it.child_by_source(db),
+        }
+    }
+}

crates/hir/src/source_analyzer.rs

@@ -0,0 +1,534 @@
+//! Lookup hir elements using positions in the source code. This is a lossy
+//! transformation: in general, a single source might correspond to several
+//! modules, functions, etc, due to macros, cfgs and `#[path=]` attributes on
+//! modules.
+//!
+//! So, this modules should not be used during hir construction, it exists
+//! purely for "IDE needs".
+use std::{iter::once, sync::Arc};
+
+use hir_def::{
+    body::{
+        scope::{ExprScopes, ScopeId},
+        Body, BodySourceMap,
+    },
+    expr::{ExprId, Pat, PatId},
+    path::{ModPath, Path, PathKind},
+    resolver::{resolver_for_scope, Resolver, TypeNs, ValueNs},
+    AsMacroCall, DefWithBodyId, FieldId, FunctionId, LocalFieldId, VariantId,
+};
+use hir_expand::{hygiene::Hygiene, name::AsName, HirFileId, InFile};
+use hir_ty::{
+    diagnostics::{record_literal_missing_fields, record_pattern_missing_fields},
+    InferenceResult, Substs, Ty,
+};
+use syntax::{
+    ast::{self, AstNode},
+    SyntaxNode, TextRange, TextSize,
+};
+
+use crate::{
+    db::HirDatabase, semantics::PathResolution, Adt, Const, EnumVariant, Field, Function, Local,
+    MacroDef, ModuleDef, Static, Struct, Trait, Type, TypeAlias, TypeParam,
+};
+use base_db::CrateId;
+
+/// `SourceAnalyzer` is a convenience wrapper which exposes HIR API in terms of
+/// original source files. It should not be used inside the HIR itself.
+#[derive(Debug)]
+pub(crate) struct SourceAnalyzer {
+    file_id: HirFileId,
+    pub(crate) resolver: Resolver,
+    body: Option<Arc<Body>>,
+    body_source_map: Option<Arc<BodySourceMap>>,
+    infer: Option<Arc<InferenceResult>>,
+    scopes: Option<Arc<ExprScopes>>,
+}
+
+impl SourceAnalyzer {
+    pub(crate) fn new_for_body(
+        db: &dyn HirDatabase,
+        def: DefWithBodyId,
+        node: InFile<&SyntaxNode>,
+        offset: Option<TextSize>,
+    ) -> SourceAnalyzer {
+        let (body, source_map) = db.body_with_source_map(def);
+        let scopes = db.expr_scopes(def);
+        let scope = match offset {
+            None => scope_for(&scopes, &source_map, node),
+            Some(offset) => scope_for_offset(db, &scopes, &source_map, node.with_value(offset)),
+        };
+        let resolver = resolver_for_scope(db.upcast(), def, scope);
+        SourceAnalyzer {
+            resolver,
+            body: Some(body),
+            body_source_map: Some(source_map),
+            infer: Some(db.infer(def)),
+            scopes: Some(scopes),
+            file_id: node.file_id,
+        }
+    }
+
+    pub(crate) fn new_for_resolver(
+        resolver: Resolver,
+        node: InFile<&SyntaxNode>,
+    ) -> SourceAnalyzer {
+        SourceAnalyzer {
+            resolver,
+            body: None,
+            body_source_map: None,
+            infer: None,
+            scopes: None,
+            file_id: node.file_id,
+        }
+    }
+
+    fn expr_id(&self, db: &dyn HirDatabase, expr: &ast::Expr) -> Option<ExprId> {
+        let src = match expr {
+            ast::Expr::MacroCall(call) => {
+                self.expand_expr(db, InFile::new(self.file_id, call.clone()))?
+            }
+            _ => InFile::new(self.file_id, expr.clone()),
+        };
+        let sm = self.body_source_map.as_ref()?;
+        sm.node_expr(src.as_ref())
+    }
+
+    fn pat_id(&self, pat: &ast::Pat) -> Option<PatId> {
+        // FIXME: macros, see `expr_id`
+        let src = InFile { file_id: self.file_id, value: pat };
+        self.body_source_map.as_ref()?.node_pat(src)
+    }
+
+    fn expand_expr(
+        &self,
+        db: &dyn HirDatabase,
+        expr: InFile<ast::MacroCall>,
+    ) -> Option<InFile<ast::Expr>> {
+        let macro_file = self.body_source_map.as_ref()?.node_macro_file(expr.as_ref())?;
+        let expanded = db.parse_or_expand(macro_file)?;
+
+        let res = match ast::MacroCall::cast(expanded.clone()) {
+            Some(call) => self.expand_expr(db, InFile::new(macro_file, call))?,
+            _ => InFile::new(macro_file, ast::Expr::cast(expanded)?),
+        };
+        Some(res)
+    }
+
+    pub(crate) fn type_of_expr(&self, db: &dyn HirDatabase, expr: &ast::Expr) -> Option<Type> {
+        let expr_id = self.expr_id(db, expr)?;
+        let ty = self.infer.as_ref()?[expr_id].clone();
+        Type::new_with_resolver(db, &self.resolver, ty)
+    }
+
+    pub(crate) fn type_of_pat(&self, db: &dyn HirDatabase, pat: &ast::Pat) -> Option<Type> {
+        let pat_id = self.pat_id(pat)?;
+        let ty = self.infer.as_ref()?[pat_id].clone();
+        Type::new_with_resolver(db, &self.resolver, ty)
+    }
+
+    pub(crate) fn type_of_self(
+        &self,
+        db: &dyn HirDatabase,
+        param: &ast::SelfParam,
+    ) -> Option<Type> {
+        let src = InFile { file_id: self.file_id, value: param };
+        let pat_id = self.body_source_map.as_ref()?.node_self_param(src)?;
+        let ty = self.infer.as_ref()?[pat_id].clone();
+        Type::new_with_resolver(db, &self.resolver, ty)
+    }
+
+    pub(crate) fn resolve_method_call(
+        &self,
+        db: &dyn HirDatabase,
+        call: &ast::MethodCallExpr,
+    ) -> Option<FunctionId> {
+        let expr_id = self.expr_id(db, &call.clone().into())?;
+        self.infer.as_ref()?.method_resolution(expr_id)
+    }
+
+    pub(crate) fn resolve_field(
+        &self,
+        db: &dyn HirDatabase,
+        field: &ast::FieldExpr,
+    ) -> Option<Field> {
+        let expr_id = self.expr_id(db, &field.clone().into())?;
+        self.infer.as_ref()?.field_resolution(expr_id).map(|it| it.into())
+    }
+
+    pub(crate) fn resolve_record_field(
+        &self,
+        db: &dyn HirDatabase,
+        field: &ast::RecordExprField,
+    ) -> Option<(Field, Option<Local>)> {
+        let expr = field.expr()?;
+        let expr_id = self.expr_id(db, &expr)?;
+        let local = if field.name_ref().is_some() {
+            None
+        } else {
+            let local_name = field.field_name()?.as_name();
+            let path = ModPath::from_segments(PathKind::Plain, once(local_name));
+            match self.resolver.resolve_path_in_value_ns_fully(db.upcast(), &path) {
+                Some(ValueNs::LocalBinding(pat_id)) => {
+                    Some(Local { pat_id, parent: self.resolver.body_owner()? })
+                }
+                _ => None,
+            }
+        };
+        let struct_field = self.infer.as_ref()?.record_field_resolution(expr_id)?;
+        Some((struct_field.into(), local))
+    }
+
+    pub(crate) fn resolve_record_field_pat(
+        &self,
+        _db: &dyn HirDatabase,
+        field: &ast::RecordPatField,
+    ) -> Option<Field> {
+        let pat_id = self.pat_id(&field.pat()?)?;
+        let struct_field = self.infer.as_ref()?.record_field_pat_resolution(pat_id)?;
+        Some(struct_field.into())
+    }
+
+    pub(crate) fn resolve_macro_call(
+        &self,
+        db: &dyn HirDatabase,
+        macro_call: InFile<&ast::MacroCall>,
+    ) -> Option<MacroDef> {
+        let hygiene = Hygiene::new(db.upcast(), macro_call.file_id);
+        let path = macro_call.value.path().and_then(|ast| Path::from_src(ast, &hygiene))?;
+        self.resolver.resolve_path_as_macro(db.upcast(), path.mod_path()).map(|it| it.into())
+    }
+
+    pub(crate) fn resolve_bind_pat_to_const(
+        &self,
+        db: &dyn HirDatabase,
+        pat: &ast::IdentPat,
+    ) -> Option<ModuleDef> {
+        let pat_id = self.pat_id(&pat.clone().into())?;
+        let body = self.body.as_ref()?;
+        let path = match &body[pat_id] {
+            Pat::Path(path) => path,
+            _ => return None,
+        };
+        let res = resolve_hir_path(db, &self.resolver, &path)?;
+        match res {
+            PathResolution::Def(def) => Some(def),
+            _ => None,
+        }
+    }
+
+    pub(crate) fn resolve_path(
+        &self,
+        db: &dyn HirDatabase,
+        path: &ast::Path,
+    ) -> Option<PathResolution> {
+        if let Some(path_expr) = path.syntax().parent().and_then(ast::PathExpr::cast) {
+            let expr_id = self.expr_id(db, &path_expr.into())?;
+            if let Some(assoc) = self.infer.as_ref()?.assoc_resolutions_for_expr(expr_id) {
+                return Some(PathResolution::AssocItem(assoc.into()));
+            }
+            if let Some(VariantId::EnumVariantId(variant)) =
+                self.infer.as_ref()?.variant_resolution_for_expr(expr_id)
+            {
+                return Some(PathResolution::Def(ModuleDef::EnumVariant(variant.into())));
+            }
+        }
+
+        if let Some(path_pat) = path.syntax().parent().and_then(ast::PathPat::cast) {
+            let pat_id = self.pat_id(&path_pat.into())?;
+            if let Some(assoc) = self.infer.as_ref()?.assoc_resolutions_for_pat(pat_id) {
+                return Some(PathResolution::AssocItem(assoc.into()));
+            }
+            if let Some(VariantId::EnumVariantId(variant)) =
+                self.infer.as_ref()?.variant_resolution_for_pat(pat_id)
+            {
+                return Some(PathResolution::Def(ModuleDef::EnumVariant(variant.into())));
+            }
+        }
+
+        if let Some(rec_lit) = path.syntax().parent().and_then(ast::RecordExpr::cast) {
+            let expr_id = self.expr_id(db, &rec_lit.into())?;
+            if let Some(VariantId::EnumVariantId(variant)) =
+                self.infer.as_ref()?.variant_resolution_for_expr(expr_id)
+            {
+                return Some(PathResolution::Def(ModuleDef::EnumVariant(variant.into())));
+            }
+        }
+
+        if let Some(rec_pat) = path.syntax().parent().and_then(ast::RecordPat::cast) {
+            let pat_id = self.pat_id(&rec_pat.into())?;
+            if let Some(VariantId::EnumVariantId(variant)) =
+                self.infer.as_ref()?.variant_resolution_for_pat(pat_id)
+            {
+                return Some(PathResolution::Def(ModuleDef::EnumVariant(variant.into())));
+            }
+        }
+
+        // This must be a normal source file rather than macro file.
+        let hir_path = Path::from_src(path.clone(), &Hygiene::new(db.upcast(), self.file_id))?;
+
+        // Case where path is a qualifier of another path, e.g. foo::bar::Baz where we
+        // trying to resolve foo::bar.
+        if let Some(outer_path) = path.syntax().parent().and_then(ast::Path::cast) {
+            if let Some(qualifier) = outer_path.qualifier() {
+                if path == &qualifier {
+                    return resolve_hir_path_qualifier(db, &self.resolver, &hir_path);
+                }
+            }
+        }
+
+        resolve_hir_path(db, &self.resolver, &hir_path)
+    }
+
+    pub(crate) fn record_literal_missing_fields(
+        &self,
+        db: &dyn HirDatabase,
+        literal: &ast::RecordExpr,
+    ) -> Option<Vec<(Field, Type)>> {
+        let krate = self.resolver.krate()?;
+        let body = self.body.as_ref()?;
+        let infer = self.infer.as_ref()?;
+
+        let expr_id = self.expr_id(db, &literal.clone().into())?;
+        let substs = match &infer.type_of_expr[expr_id] {
+            Ty::Apply(a_ty) => &a_ty.parameters,
+            _ => return None,
+        };
+
+        let (variant, missing_fields, _exhaustive) =
+            record_literal_missing_fields(db, infer, expr_id, &body[expr_id])?;
+        let res = self.missing_fields(db, krate, substs, variant, missing_fields);
+        Some(res)
+    }
+
+    pub(crate) fn record_pattern_missing_fields(
+        &self,
+        db: &dyn HirDatabase,
+        pattern: &ast::RecordPat,
+    ) -> Option<Vec<(Field, Type)>> {
+        let krate = self.resolver.krate()?;
+        let body = self.body.as_ref()?;
+        let infer = self.infer.as_ref()?;
+
+        let pat_id = self.pat_id(&pattern.clone().into())?;
+        let substs = match &infer.type_of_pat[pat_id] {
+            Ty::Apply(a_ty) => &a_ty.parameters,
+            _ => return None,
+        };
+
+        let (variant, missing_fields, _exhaustive) =
+            record_pattern_missing_fields(db, infer, pat_id, &body[pat_id])?;
+        let res = self.missing_fields(db, krate, substs, variant, missing_fields);
+        Some(res)
+    }
+
+    fn missing_fields(
+        &self,
+        db: &dyn HirDatabase,
+        krate: CrateId,
+        substs: &Substs,
+        variant: VariantId,
+        missing_fields: Vec<LocalFieldId>,
+    ) -> Vec<(Field, Type)> {
+        let field_types = db.field_types(variant);
+
+        missing_fields
+            .into_iter()
+            .map(|local_id| {
+                let field = FieldId { parent: variant, local_id };
+                let ty = field_types[local_id].clone().subst(substs);
+                (field.into(), Type::new_with_resolver_inner(db, krate, &self.resolver, ty))
+            })
+            .collect()
+    }
+
+    pub(crate) fn expand(
+        &self,
+        db: &dyn HirDatabase,
+        macro_call: InFile<&ast::MacroCall>,
+    ) -> Option<HirFileId> {
+        let krate = self.resolver.krate()?;
+        let macro_call_id = macro_call.as_call_id(db.upcast(), krate, |path| {
+            self.resolver.resolve_path_as_macro(db.upcast(), &path)
+        })?;
+        Some(macro_call_id.as_file()).filter(|it| it.expansion_level(db.upcast()) < 64)
+    }
+
+    pub(crate) fn resolve_variant(
+        &self,
+        db: &dyn HirDatabase,
+        record_lit: ast::RecordExpr,
+    ) -> Option<VariantId> {
+        let infer = self.infer.as_ref()?;
+        let expr_id = self.expr_id(db, &record_lit.into())?;
+        infer.variant_resolution_for_expr(expr_id)
+    }
+}
+
+fn scope_for(
+    scopes: &ExprScopes,
+    source_map: &BodySourceMap,
+    node: InFile<&SyntaxNode>,
+) -> Option<ScopeId> {
+    node.value
+        .ancestors()
+        .filter_map(ast::Expr::cast)
+        .filter_map(|it| source_map.node_expr(InFile::new(node.file_id, &it)))
+        .find_map(|it| scopes.scope_for(it))
+}
+
+fn scope_for_offset(
+    db: &dyn HirDatabase,
+    scopes: &ExprScopes,
+    source_map: &BodySourceMap,
+    offset: InFile<TextSize>,
+) -> Option<ScopeId> {
+    scopes
+        .scope_by_expr()
+        .iter()
+        .filter_map(|(id, scope)| {
+            let source = source_map.expr_syntax(*id).ok()?;
+            // FIXME: correctly handle macro expansion
+            if source.file_id != offset.file_id {
+                return None;
+            }
+            let root = source.file_syntax(db.upcast());
+            let node = source.value.to_node(&root);
+            Some((node.syntax().text_range(), scope))
+        })
+        // find containing scope
+        .min_by_key(|(expr_range, _scope)| {
+            (
+                !(expr_range.start() <= offset.value && offset.value <= expr_range.end()),
+                expr_range.len(),
+            )
+        })
+        .map(|(expr_range, scope)| {
+            adjust(db, scopes, source_map, expr_range, offset).unwrap_or(*scope)
+        })
+}
+
+// XXX: during completion, cursor might be outside of any particular
+// expression. Try to figure out the correct scope...
+fn adjust(
+    db: &dyn HirDatabase,
+    scopes: &ExprScopes,
+    source_map: &BodySourceMap,
+    expr_range: TextRange,
+    offset: InFile<TextSize>,
+) -> Option<ScopeId> {
+    let child_scopes = scopes
+        .scope_by_expr()
+        .iter()
+        .filter_map(|(id, scope)| {
+            let source = source_map.expr_syntax(*id).ok()?;
+            // FIXME: correctly handle macro expansion
+            if source.file_id != offset.file_id {
+                return None;
+            }
+            let root = source.file_syntax(db.upcast());
+            let node = source.value.to_node(&root);
+            Some((node.syntax().text_range(), scope))
+        })
+        .filter(|&(range, _)| {
+            range.start() <= offset.value && expr_range.contains_range(range) && range != expr_range
+        });
+
+    child_scopes
+        .max_by(|&(r1, _), &(r2, _)| {
+            if r1.contains_range(r2) {
+                std::cmp::Ordering::Greater
+            } else if r2.contains_range(r1) {
+                std::cmp::Ordering::Less
+            } else {
+                r1.start().cmp(&r2.start())
+            }
+        })
+        .map(|(_ptr, scope)| *scope)
+}
+
+pub(crate) fn resolve_hir_path(
+    db: &dyn HirDatabase,
+    resolver: &Resolver,
+    path: &Path,
+) -> Option<PathResolution> {
+    let types =
+        resolver.resolve_path_in_type_ns_fully(db.upcast(), path.mod_path()).map(|ty| match ty {
+            TypeNs::SelfType(it) => PathResolution::SelfType(it.into()),
+            TypeNs::GenericParam(id) => PathResolution::TypeParam(TypeParam { id }),
+            TypeNs::AdtSelfType(it) | TypeNs::AdtId(it) => {
+                PathResolution::Def(Adt::from(it).into())
+            }
+            TypeNs::EnumVariantId(it) => PathResolution::Def(EnumVariant::from(it).into()),
+            TypeNs::TypeAliasId(it) => PathResolution::Def(TypeAlias::from(it).into()),
+            TypeNs::BuiltinType(it) => PathResolution::Def(it.into()),
+            TypeNs::TraitId(it) => PathResolution::Def(Trait::from(it).into()),
+        });
+
+    let body_owner = resolver.body_owner();
+    let values =
+        resolver.resolve_path_in_value_ns_fully(db.upcast(), path.mod_path()).and_then(|val| {
+            let res = match val {
+                ValueNs::LocalBinding(pat_id) => {
+                    let var = Local { parent: body_owner?.into(), pat_id };
+                    PathResolution::Local(var)
+                }
+                ValueNs::FunctionId(it) => PathResolution::Def(Function::from(it).into()),
+                ValueNs::ConstId(it) => PathResolution::Def(Const::from(it).into()),
+                ValueNs::StaticId(it) => PathResolution::Def(Static::from(it).into()),
+                ValueNs::StructId(it) => PathResolution::Def(Struct::from(it).into()),
+                ValueNs::EnumVariantId(it) => PathResolution::Def(EnumVariant::from(it).into()),
+                ValueNs::ImplSelf(impl_id) => PathResolution::SelfType(impl_id.into()),
+            };
+            Some(res)
+        });
+
+    let items = resolver
+        .resolve_module_path_in_items(db.upcast(), path.mod_path())
+        .take_types()
+        .map(|it| PathResolution::Def(it.into()));
+
+    types.or(values).or(items).or_else(|| {
+        resolver
+            .resolve_path_as_macro(db.upcast(), path.mod_path())
+            .map(|def| PathResolution::Macro(def.into()))
+    })
+}
+
+/// Resolves a path where we know it is a qualifier of another path.
+///
+/// For example, if we have:
+/// ```
+/// mod my {
+///     pub mod foo {
+///         struct Bar;
+///     }
+///
+///     pub fn foo() {}
+/// }
+/// ```
+/// then we know that `foo` in `my::foo::Bar` refers to the module, not the function.
+fn resolve_hir_path_qualifier(
+    db: &dyn HirDatabase,
+    resolver: &Resolver,
+    path: &Path,
+) -> Option<PathResolution> {
+    let items = resolver
+        .resolve_module_path_in_items(db.upcast(), path.mod_path())
+        .take_types()
+        .map(|it| PathResolution::Def(it.into()));
+
+    if items.is_some() {
+        return items;
+    }
+
+    resolver.resolve_path_in_type_ns_fully(db.upcast(), path.mod_path()).map(|ty| match ty {
+        TypeNs::SelfType(it) => PathResolution::SelfType(it.into()),
+        TypeNs::GenericParam(id) => PathResolution::TypeParam(TypeParam { id }),
+        TypeNs::AdtSelfType(it) | TypeNs::AdtId(it) => PathResolution::Def(Adt::from(it).into()),
+        TypeNs::EnumVariantId(it) => PathResolution::Def(EnumVariant::from(it).into()),
+        TypeNs::TypeAliasId(it) => PathResolution::Def(TypeAlias::from(it).into()),
+        TypeNs::BuiltinType(it) => PathResolution::Def(it.into()),
+        TypeNs::TraitId(it) => PathResolution::Def(Trait::from(it).into()),
+    })
+}

crates/hir_def/Cargo.toml

@@ -0,0 +1,35 @@
+[package]
+name = "hir_def"
+version = "0.0.0"
+license = "MIT OR Apache-2.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false
+
+[dependencies]
+log = "0.4.8"
+once_cell = "1.3.1"
+rustc-hash = "1.1.0"
+either = "1.5.3"
+anymap = "0.12.1"
+drop_bomb = "0.1.4"
+fst = { version = "0.4", default-features = false }
+itertools = "0.9.0"
+indexmap = "1.4.0"
+smallvec = "1.4.0"
+
+stdx = { path = "../stdx" }
+arena = { path = "../arena" }
+base_db = { path = "../base_db" }
+syntax = { path = "../syntax" }
+profile = { path = "../profile" }
+hir_expand = { path = "../hir_expand" }
+test_utils = { path = "../test_utils" }
+mbe = { path = "../mbe" }
+cfg = { path = "../cfg" }
+tt = { path = "../tt" }
+
+[dev-dependencies]
+expect-test = "0.1"

crates/hir_def/src/adt.rs

@@ -0,0 +1,329 @@
+//! Defines hir-level representation of structs, enums and unions
+
+use std::sync::Arc;
+
+use arena::{map::ArenaMap, Arena};
+use either::Either;
+use hir_expand::{
+    name::{AsName, Name},
+    InFile,
+};
+use syntax::ast::{self, NameOwner, VisibilityOwner};
+use tt::{Delimiter, DelimiterKind, Leaf, Subtree, TokenTree};
+
+use crate::{
+    body::{CfgExpander, LowerCtx},
+    db::DefDatabase,
+    item_tree::{AttrOwner, Field, Fields, ItemTree, ModItem},
+    src::HasChildSource,
+    src::HasSource,
+    trace::Trace,
+    type_ref::TypeRef,
+    visibility::RawVisibility,
+    EnumId, HasModule, LocalEnumVariantId, LocalFieldId, Lookup, ModuleId, StructId, UnionId,
+    VariantId,
+};
+use cfg::CfgOptions;
+
+/// Note that we use `StructData` for unions as well!
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct StructData {
+    pub name: Name,
+    pub variant_data: Arc<VariantData>,
+    pub repr: Option<ReprKind>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct EnumData {
+    pub name: Name,
+    pub variants: Arena<EnumVariantData>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct EnumVariantData {
+    pub name: Name,
+    pub variant_data: Arc<VariantData>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum VariantData {
+    Record(Arena<FieldData>),
+    Tuple(Arena<FieldData>),
+    Unit,
+}
+
+/// A single field of an enum variant or struct
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FieldData {
+    pub name: Name,
+    pub type_ref: TypeRef,
+    pub visibility: RawVisibility,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ReprKind {
+    Packed,
+    Other,
+}
+
+fn repr_from_value(item_tree: &ItemTree, of: AttrOwner) -> Option<ReprKind> {
+    item_tree.attrs(of).by_key("repr").tt_values().find_map(parse_repr_tt)
+}
+
+fn parse_repr_tt(tt: &Subtree) -> Option<ReprKind> {
+    match tt.delimiter {
+        Some(Delimiter { kind: DelimiterKind::Parenthesis, .. }) => {}
+        _ => return None,
+    }
+
+    let mut it = tt.token_trees.iter();
+    match it.next()? {
+        TokenTree::Leaf(Leaf::Ident(ident)) if ident.text == "packed" => Some(ReprKind::Packed),
+        _ => Some(ReprKind::Other),
+    }
+}
+
+impl StructData {
+    pub(crate) fn struct_data_query(db: &dyn DefDatabase, id: StructId) -> Arc<StructData> {
+        let loc = id.lookup(db);
+        let item_tree = db.item_tree(loc.id.file_id);
+        let repr = repr_from_value(&item_tree, ModItem::from(loc.id.value).into());
+        let cfg_options = db.crate_graph()[loc.container.module(db).krate].cfg_options.clone();
+
+        let strukt = &item_tree[loc.id.value];
+        let variant_data = lower_fields(&item_tree, &cfg_options, &strukt.fields);
+        Arc::new(StructData {
+            name: strukt.name.clone(),
+            variant_data: Arc::new(variant_data),
+            repr,
+        })
+    }
+    pub(crate) fn union_data_query(db: &dyn DefDatabase, id: UnionId) -> Arc<StructData> {
+        let loc = id.lookup(db);
+        let item_tree = db.item_tree(loc.id.file_id);
+        let repr = repr_from_value(&item_tree, ModItem::from(loc.id.value).into());
+        let cfg_options = db.crate_graph()[loc.container.module(db).krate].cfg_options.clone();
+
+        let union = &item_tree[loc.id.value];
+        let variant_data = lower_fields(&item_tree, &cfg_options, &union.fields);
+
+        Arc::new(StructData {
+            name: union.name.clone(),
+            variant_data: Arc::new(variant_data),
+            repr,
+        })
+    }
+}
+
+impl EnumData {
+    pub(crate) fn enum_data_query(db: &dyn DefDatabase, e: EnumId) -> Arc<EnumData> {
+        let loc = e.lookup(db);
+        let item_tree = db.item_tree(loc.id.file_id);
+        let cfg_options = db.crate_graph()[loc.container.module(db).krate].cfg_options.clone();
+
+        let enum_ = &item_tree[loc.id.value];
+        let mut variants = Arena::new();
+        for var_id in enum_.variants.clone() {
+            if item_tree.attrs(var_id.into()).is_cfg_enabled(&cfg_options) {
+                let var = &item_tree[var_id];
+                let var_data = lower_fields(&item_tree, &cfg_options, &var.fields);
+
+                variants.alloc(EnumVariantData {
+                    name: var.name.clone(),
+                    variant_data: Arc::new(var_data),
+                });
+            }
+        }
+
+        Arc::new(EnumData { name: enum_.name.clone(), variants })
+    }
+
+    pub fn variant(&self, name: &Name) -> Option<LocalEnumVariantId> {
+        let (id, _) = self.variants.iter().find(|(_id, data)| &data.name == name)?;
+        Some(id)
+    }
+}
+
+impl HasChildSource for EnumId {
+    type ChildId = LocalEnumVariantId;
+    type Value = ast::Variant;
+    fn child_source(&self, db: &dyn DefDatabase) -> InFile<ArenaMap<Self::ChildId, Self::Value>> {
+        let src = self.lookup(db).source(db);
+        let mut trace = Trace::new_for_map();
+        lower_enum(db, &mut trace, &src, self.lookup(db).container.module(db));
+        src.with_value(trace.into_map())
+    }
+}
+
+fn lower_enum(
+    db: &dyn DefDatabase,
+    trace: &mut Trace<EnumVariantData, ast::Variant>,
+    ast: &InFile<ast::Enum>,
+    module_id: ModuleId,
+) {
+    let expander = CfgExpander::new(db, ast.file_id, module_id.krate);
+    let variants = ast
+        .value
+        .variant_list()
+        .into_iter()
+        .flat_map(|it| it.variants())
+        .filter(|var| expander.is_cfg_enabled(var));
+    for var in variants {
+        trace.alloc(
+            || var.clone(),
+            || EnumVariantData {
+                name: var.name().map_or_else(Name::missing, |it| it.as_name()),
+                variant_data: Arc::new(VariantData::new(db, ast.with_value(var.kind()), module_id)),
+            },
+        );
+    }
+}
+
+impl VariantData {
+    fn new(db: &dyn DefDatabase, flavor: InFile<ast::StructKind>, module_id: ModuleId) -> Self {
+        let mut expander = CfgExpander::new(db, flavor.file_id, module_id.krate);
+        let mut trace = Trace::new_for_arena();
+        match lower_struct(db, &mut expander, &mut trace, &flavor) {
+            StructKind::Tuple => VariantData::Tuple(trace.into_arena()),
+            StructKind::Record => VariantData::Record(trace.into_arena()),
+            StructKind::Unit => VariantData::Unit,
+        }
+    }
+
+    pub fn fields(&self) -> &Arena<FieldData> {
+        const EMPTY: &Arena<FieldData> = &Arena::new();
+        match &self {
+            VariantData::Record(fields) | VariantData::Tuple(fields) => fields,
+            _ => EMPTY,
+        }
+    }
+
+    pub fn field(&self, name: &Name) -> Option<LocalFieldId> {
+        self.fields().iter().find_map(|(id, data)| if &data.name == name { Some(id) } else { None })
+    }
+
+    pub fn kind(&self) -> StructKind {
+        match self {
+            VariantData::Record(_) => StructKind::Record,
+            VariantData::Tuple(_) => StructKind::Tuple,
+            VariantData::Unit => StructKind::Unit,
+        }
+    }
+}
+
+impl HasChildSource for VariantId {
+    type ChildId = LocalFieldId;
+    type Value = Either<ast::TupleField, ast::RecordField>;
+
+    fn child_source(&self, db: &dyn DefDatabase) -> InFile<ArenaMap<Self::ChildId, Self::Value>> {
+        let (src, module_id) = match self {
+            VariantId::EnumVariantId(it) => {
+                // I don't really like the fact that we call into parent source
+                // here, this might add to more queries then necessary.
+                let src = it.parent.child_source(db);
+                (src.map(|map| map[it.local_id].kind()), it.parent.lookup(db).container.module(db))
+            }
+            VariantId::StructId(it) => {
+                (it.lookup(db).source(db).map(|it| it.kind()), it.lookup(db).container.module(db))
+            }
+            VariantId::UnionId(it) => (
+                it.lookup(db).source(db).map(|it| {
+                    it.record_field_list()
+                        .map(ast::StructKind::Record)
+                        .unwrap_or(ast::StructKind::Unit)
+                }),
+                it.lookup(db).container.module(db),
+            ),
+        };
+        let mut expander = CfgExpander::new(db, src.file_id, module_id.krate);
+        let mut trace = Trace::new_for_map();
+        lower_struct(db, &mut expander, &mut trace, &src);
+        src.with_value(trace.into_map())
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum StructKind {
+    Tuple,
+    Record,
+    Unit,
+}
+
+fn lower_struct(
+    db: &dyn DefDatabase,
+    expander: &mut CfgExpander,
+    trace: &mut Trace<FieldData, Either<ast::TupleField, ast::RecordField>>,
+    ast: &InFile<ast::StructKind>,
+) -> StructKind {
+    let ctx = LowerCtx::new(db, ast.file_id);
+
+    match &ast.value {
+        ast::StructKind::Tuple(fl) => {
+            for (i, fd) in fl.fields().enumerate() {
+                if !expander.is_cfg_enabled(&fd) {
+                    continue;
+                }
+
+                trace.alloc(
+                    || Either::Left(fd.clone()),
+                    || FieldData {
+                        name: Name::new_tuple_field(i),
+                        type_ref: TypeRef::from_ast_opt(&ctx, fd.ty()),
+                        visibility: RawVisibility::from_ast(db, ast.with_value(fd.visibility())),
+                    },
+                );
+            }
+            StructKind::Tuple
+        }
+        ast::StructKind::Record(fl) => {
+            for fd in fl.fields() {
+                if !expander.is_cfg_enabled(&fd) {
+                    continue;
+                }
+
+                trace.alloc(
+                    || Either::Right(fd.clone()),
+                    || FieldData {
+                        name: fd.name().map(|n| n.as_name()).unwrap_or_else(Name::missing),
+                        type_ref: TypeRef::from_ast_opt(&ctx, fd.ty()),
+                        visibility: RawVisibility::from_ast(db, ast.with_value(fd.visibility())),
+                    },
+                );
+            }
+            StructKind::Record
+        }
+        ast::StructKind::Unit => StructKind::Unit,
+    }
+}
+
+fn lower_fields(item_tree: &ItemTree, cfg_options: &CfgOptions, fields: &Fields) -> VariantData {
+    match fields {
+        Fields::Record(flds) => {
+            let mut arena = Arena::new();
+            for field_id in flds.clone() {
+                if item_tree.attrs(field_id.into()).is_cfg_enabled(cfg_options) {
+                    arena.alloc(lower_field(item_tree, &item_tree[field_id]));
+                }
+            }
+            VariantData::Record(arena)
+        }
+        Fields::Tuple(flds) => {
+            let mut arena = Arena::new();
+            for field_id in flds.clone() {
+                if item_tree.attrs(field_id.into()).is_cfg_enabled(cfg_options) {
+                    arena.alloc(lower_field(item_tree, &item_tree[field_id]));
+                }
+            }
+            VariantData::Tuple(arena)
+        }
+        Fields::Unit => VariantData::Unit,
+    }
+}
+
+fn lower_field(item_tree: &ItemTree, field: &Field) -> FieldData {
+    FieldData {
+        name: field.name.clone(),
+        type_ref: field.type_ref.clone(),
+        visibility: item_tree[field.visibility].clone(),
+    }
+}

crates/hir_def/src/attr.rs

@@ -0,0 +1,212 @@
+//! A higher level attributes based on TokenTree, with also some shortcuts.
+
+use std::{ops, sync::Arc};
+
+use cfg::{CfgExpr, CfgOptions};
+use either::Either;
+use hir_expand::{hygiene::Hygiene, AstId, InFile};
+use mbe::ast_to_token_tree;
+use syntax::{
+    ast::{self, AstNode, AttrsOwner},
+    SmolStr,
+};
+use tt::Subtree;
+
+use crate::{
+    db::DefDatabase,
+    item_tree::{ItemTreeId, ItemTreeNode},
+    nameres::ModuleSource,
+    path::ModPath,
+    src::HasChildSource,
+    AdtId, AttrDefId, Lookup,
+};
+
+#[derive(Default, Debug, Clone, PartialEq, Eq)]
+pub struct Attrs {
+    entries: Option<Arc<[Attr]>>,
+}
+
+impl ops::Deref for Attrs {
+    type Target = [Attr];
+
+    fn deref(&self) -> &[Attr] {
+        match &self.entries {
+            Some(it) => &*it,
+            None => &[],
+        }
+    }
+}
+
+impl Attrs {
+    pub const EMPTY: Attrs = Attrs { entries: None };
+
+    pub(crate) fn attrs_query(db: &dyn DefDatabase, def: AttrDefId) -> Attrs {
+        match def {
+            AttrDefId::ModuleId(module) => {
+                let def_map = db.crate_def_map(module.krate);
+                let mod_data = &def_map[module.local_id];
+                match mod_data.declaration_source(db) {
+                    Some(it) => {
+                        Attrs::from_attrs_owner(db, it.as_ref().map(|it| it as &dyn AttrsOwner))
+                    }
+                    None => Attrs::from_attrs_owner(
+                        db,
+                        mod_data.definition_source(db).as_ref().map(|src| match src {
+                            ModuleSource::SourceFile(file) => file as &dyn AttrsOwner,
+                            ModuleSource::Module(module) => module as &dyn AttrsOwner,
+                        }),
+                    ),
+                }
+            }
+            AttrDefId::FieldId(it) => {
+                let src = it.parent.child_source(db);
+                match &src.value[it.local_id] {
+                    Either::Left(_tuple) => Attrs::default(),
+                    Either::Right(record) => Attrs::from_attrs_owner(db, src.with_value(record)),
+                }
+            }
+            AttrDefId::EnumVariantId(var_id) => {
+                let src = var_id.parent.child_source(db);
+                let src = src.as_ref().map(|it| &it[var_id.local_id]);
+                Attrs::from_attrs_owner(db, src.map(|it| it as &dyn AttrsOwner))
+            }
+            AttrDefId::AdtId(it) => match it {
+                AdtId::StructId(it) => attrs_from_item_tree(it.lookup(db).id, db),
+                AdtId::EnumId(it) => attrs_from_item_tree(it.lookup(db).id, db),
+                AdtId::UnionId(it) => attrs_from_item_tree(it.lookup(db).id, db),
+            },
+            AttrDefId::TraitId(it) => attrs_from_item_tree(it.lookup(db).id, db),
+            AttrDefId::MacroDefId(it) => {
+                it.ast_id.map_or_else(Default::default, |ast_id| attrs_from_ast(ast_id, db))
+            }
+            AttrDefId::ImplId(it) => attrs_from_item_tree(it.lookup(db).id, db),
+            AttrDefId::ConstId(it) => attrs_from_item_tree(it.lookup(db).id, db),
+            AttrDefId::StaticId(it) => attrs_from_item_tree(it.lookup(db).id, db),
+            AttrDefId::FunctionId(it) => attrs_from_item_tree(it.lookup(db).id, db),
+            AttrDefId::TypeAliasId(it) => attrs_from_item_tree(it.lookup(db).id, db),
+        }
+    }
+
+    pub fn from_attrs_owner(db: &dyn DefDatabase, owner: InFile<&dyn AttrsOwner>) -> Attrs {
+        let hygiene = Hygiene::new(db.upcast(), owner.file_id);
+        Attrs::new(owner.value, &hygiene)
+    }
+
+    pub(crate) fn new(owner: &dyn AttrsOwner, hygiene: &Hygiene) -> Attrs {
+        let docs = ast::CommentIter::from_syntax_node(owner.syntax()).doc_comment_text().map(
+            |docs_text| Attr {
+                input: Some(AttrInput::Literal(SmolStr::new(docs_text))),
+                path: ModPath::from(hir_expand::name!(doc)),
+            },
+        );
+        let mut attrs = owner.attrs().peekable();
+        let entries = if attrs.peek().is_none() {
+            // Avoid heap allocation
+            None
+        } else {
+            Some(attrs.flat_map(|ast| Attr::from_src(ast, hygiene)).chain(docs).collect())
+        };
+        Attrs { entries }
+    }
+
+    pub fn merge(&self, other: Attrs) -> Attrs {
+        match (&self.entries, &other.entries) {
+            (None, None) => Attrs { entries: None },
+            (Some(entries), None) | (None, Some(entries)) => {
+                Attrs { entries: Some(entries.clone()) }
+            }
+            (Some(a), Some(b)) => {
+                Attrs { entries: Some(a.iter().chain(b.iter()).cloned().collect()) }
+            }
+        }
+    }
+
+    pub fn by_key(&self, key: &'static str) -> AttrQuery<'_> {
+        AttrQuery { attrs: self, key }
+    }
+
+    pub fn cfg(&self) -> impl Iterator<Item = CfgExpr> + '_ {
+        // FIXME: handle cfg_attr :-)
+        self.by_key("cfg").tt_values().map(CfgExpr::parse)
+    }
+    pub(crate) fn is_cfg_enabled(&self, cfg_options: &CfgOptions) -> bool {
+        self.cfg().all(|cfg| cfg_options.check(&cfg) != Some(false))
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Attr {
+    pub(crate) path: ModPath,
+    pub(crate) input: Option<AttrInput>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum AttrInput {
+    /// `#[attr = "string"]`
+    Literal(SmolStr),
+    /// `#[attr(subtree)]`
+    TokenTree(Subtree),
+}
+
+impl Attr {
+    fn from_src(ast: ast::Attr, hygiene: &Hygiene) -> Option<Attr> {
+        let path = ModPath::from_src(ast.path()?, hygiene)?;
+        let input = if let Some(lit) = ast.literal() {
+            // FIXME: escape? raw string?
+            let value = lit.syntax().first_token()?.text().trim_matches('"').into();
+            Some(AttrInput::Literal(value))
+        } else if let Some(tt) = ast.token_tree() {
+            Some(AttrInput::TokenTree(ast_to_token_tree(&tt)?.0))
+        } else {
+            None
+        };
+        Some(Attr { path, input })
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct AttrQuery<'a> {
+    attrs: &'a Attrs,
+    key: &'static str,
+}
+
+impl<'a> AttrQuery<'a> {
+    pub fn tt_values(self) -> impl Iterator<Item = &'a Subtree> {
+        self.attrs().filter_map(|attr| match attr.input.as_ref()? {
+            AttrInput::TokenTree(it) => Some(it),
+            _ => None,
+        })
+    }
+
+    pub fn string_value(self) -> Option<&'a SmolStr> {
+        self.attrs().find_map(|attr| match attr.input.as_ref()? {
+            AttrInput::Literal(it) => Some(it),
+            _ => None,
+        })
+    }
+
+    pub fn exists(self) -> bool {
+        self.attrs().next().is_some()
+    }
+
+    fn attrs(self) -> impl Iterator<Item = &'a Attr> {
+        let key = self.key;
+        self.attrs
+            .iter()
+            .filter(move |attr| attr.path.as_ident().map_or(false, |s| s.to_string() == key))
+    }
+}
+
+fn attrs_from_ast<N>(src: AstId<N>, db: &dyn DefDatabase) -> Attrs
+where
+    N: ast::AttrsOwner,
+{
+    let src = InFile::new(src.file_id, src.to_node(db.upcast()));
+    Attrs::from_attrs_owner(db, src.as_ref().map(|it| it as &dyn AttrsOwner))
+}
+
+fn attrs_from_item_tree<N: ItemTreeNode>(id: ItemTreeId<N>, db: &dyn DefDatabase) -> Attrs {
+    let tree = db.item_tree(id.file_id);
+    let mod_item = N::id_to_mod_item(id.value);
+    tree.attrs(mod_item.into()).clone()
+}

crates/hir_def/src/body.rs

@@ -0,0 +1,360 @@
+//! Defines `Body`: a lowered representation of bodies of functions, statics and
+//! consts.
+mod lower;
+pub mod scope;
+
+use std::{mem, ops::Index, sync::Arc};
+
+use arena::{map::ArenaMap, Arena};
+use base_db::CrateId;
+use cfg::CfgOptions;
+use drop_bomb::DropBomb;
+use either::Either;
+use hir_expand::{ast_id_map::AstIdMap, hygiene::Hygiene, AstId, HirFileId, InFile, MacroDefId};
+use rustc_hash::FxHashMap;
+use syntax::{ast, AstNode, AstPtr};
+use test_utils::mark;
+
+pub(crate) use lower::LowerCtx;
+
+use crate::{
+    attr::Attrs,
+    db::DefDatabase,
+    expr::{Expr, ExprId, Pat, PatId},
+    item_scope::BuiltinShadowMode,
+    item_scope::ItemScope,
+    nameres::CrateDefMap,
+    path::{ModPath, Path},
+    src::HasSource,
+    AsMacroCall, DefWithBodyId, HasModule, Lookup, ModuleId,
+};
+
+/// A subset of Expander that only deals with cfg attributes. We only need it to
+/// avoid cyclic queries in crate def map during enum processing.
+pub(crate) struct CfgExpander {
+    cfg_options: CfgOptions,
+    hygiene: Hygiene,
+}
+
+pub(crate) struct Expander {
+    cfg_expander: CfgExpander,
+    crate_def_map: Arc<CrateDefMap>,
+    current_file_id: HirFileId,
+    ast_id_map: Arc<AstIdMap>,
+    module: ModuleId,
+    recursion_limit: usize,
+}
+
+#[cfg(test)]
+const EXPANSION_RECURSION_LIMIT: usize = 32;
+
+#[cfg(not(test))]
+const EXPANSION_RECURSION_LIMIT: usize = 128;
+
+impl CfgExpander {
+    pub(crate) fn new(
+        db: &dyn DefDatabase,
+        current_file_id: HirFileId,
+        krate: CrateId,
+    ) -> CfgExpander {
+        let hygiene = Hygiene::new(db.upcast(), current_file_id);
+        let cfg_options = db.crate_graph()[krate].cfg_options.clone();
+        CfgExpander { cfg_options, hygiene }
+    }
+
+    pub(crate) fn parse_attrs(&self, owner: &dyn ast::AttrsOwner) -> Attrs {
+        Attrs::new(owner, &self.hygiene)
+    }
+
+    pub(crate) fn is_cfg_enabled(&self, owner: &dyn ast::AttrsOwner) -> bool {
+        let attrs = self.parse_attrs(owner);
+        attrs.is_cfg_enabled(&self.cfg_options)
+    }
+}
+
+impl Expander {
+    pub(crate) fn new(
+        db: &dyn DefDatabase,
+        current_file_id: HirFileId,
+        module: ModuleId,
+    ) -> Expander {
+        let cfg_expander = CfgExpander::new(db, current_file_id, module.krate);
+        let crate_def_map = db.crate_def_map(module.krate);
+        let ast_id_map = db.ast_id_map(current_file_id);
+        Expander {
+            cfg_expander,
+            crate_def_map,
+            current_file_id,
+            ast_id_map,
+            module,
+            recursion_limit: 0,
+        }
+    }
+
+    pub(crate) fn enter_expand<T: ast::AstNode>(
+        &mut self,
+        db: &dyn DefDatabase,
+        local_scope: Option<&ItemScope>,
+        macro_call: ast::MacroCall,
+    ) -> Option<(Mark, T)> {
+        self.recursion_limit += 1;
+        if self.recursion_limit > EXPANSION_RECURSION_LIMIT {
+            mark::hit!(your_stack_belongs_to_me);
+            return None;
+        }
+
+        let macro_call = InFile::new(self.current_file_id, &macro_call);
+
+        if let Some(call_id) = macro_call.as_call_id(db, self.crate_def_map.krate, |path| {
+            if let Some(local_scope) = local_scope {
+                if let Some(def) = path.as_ident().and_then(|n| local_scope.get_legacy_macro(n)) {
+                    return Some(def);
+                }
+            }
+            self.resolve_path_as_macro(db, &path)
+        }) {
+            let file_id = call_id.as_file();
+            if let Some(node) = db.parse_or_expand(file_id) {
+                if let Some(expr) = T::cast(node) {
+                    log::debug!("macro expansion {:#?}", expr.syntax());
+
+                    let mark = Mark {
+                        file_id: self.current_file_id,
+                        ast_id_map: mem::take(&mut self.ast_id_map),
+                        bomb: DropBomb::new("expansion mark dropped"),
+                    };
+                    self.cfg_expander.hygiene = Hygiene::new(db.upcast(), file_id);
+                    self.current_file_id = file_id;
+                    self.ast_id_map = db.ast_id_map(file_id);
+                    return Some((mark, expr));
+                }
+            }
+        }
+
+        // FIXME: Instead of just dropping the error from expansion
+        // report it
+        None
+    }
+
+    pub(crate) fn exit(&mut self, db: &dyn DefDatabase, mut mark: Mark) {
+        self.cfg_expander.hygiene = Hygiene::new(db.upcast(), mark.file_id);
+        self.current_file_id = mark.file_id;
+        self.ast_id_map = mem::take(&mut mark.ast_id_map);
+        self.recursion_limit -= 1;
+        mark.bomb.defuse();
+    }
+
+    pub(crate) fn to_source<T>(&self, value: T) -> InFile<T> {
+        InFile { file_id: self.current_file_id, value }
+    }
+
+    pub(crate) fn is_cfg_enabled(&self, owner: &dyn ast::AttrsOwner) -> bool {
+        self.cfg_expander.is_cfg_enabled(owner)
+    }
+
+    fn parse_path(&mut self, path: ast::Path) -> Option<Path> {
+        Path::from_src(path, &self.cfg_expander.hygiene)
+    }
+
+    fn resolve_path_as_macro(&self, db: &dyn DefDatabase, path: &ModPath) -> Option<MacroDefId> {
+        self.crate_def_map
+            .resolve_path(db, self.module.local_id, path, BuiltinShadowMode::Other)
+            .0
+            .take_macros()
+    }
+
+    fn ast_id<N: AstNode>(&self, item: &N) -> AstId<N> {
+        let file_local_id = self.ast_id_map.ast_id(item);
+        AstId::new(self.current_file_id, file_local_id)
+    }
+}
+
+pub(crate) struct Mark {
+    file_id: HirFileId,
+    ast_id_map: Arc<AstIdMap>,
+    bomb: DropBomb,
+}
+
+/// The body of an item (function, const etc.).
+#[derive(Debug, Eq, PartialEq)]
+pub struct Body {
+    pub exprs: Arena<Expr>,
+    pub pats: Arena<Pat>,
+    /// The patterns for the function's parameters. While the parameter types are
+    /// part of the function signature, the patterns are not (they don't change
+    /// the external type of the function).
+    ///
+    /// If this `Body` is for the body of a constant, this will just be
+    /// empty.
+    pub params: Vec<PatId>,
+    /// The `ExprId` of the actual body expression.
+    pub body_expr: ExprId,
+    pub item_scope: ItemScope,
+}
+
+pub type ExprPtr = AstPtr<ast::Expr>;
+pub type ExprSource = InFile<ExprPtr>;
+
+pub type PatPtr = Either<AstPtr<ast::Pat>, AstPtr<ast::SelfParam>>;
+pub type PatSource = InFile<PatPtr>;
+
+/// An item body together with the mapping from syntax nodes to HIR expression
+/// IDs. This is needed to go from e.g. a position in a file to the HIR
+/// expression containing it; but for type inference etc., we want to operate on
+/// a structure that is agnostic to the actual positions of expressions in the
+/// file, so that we don't recompute types whenever some whitespace is typed.
+///
+/// One complication here is that, due to macro expansion, a single `Body` might
+/// be spread across several files. So, for each ExprId and PatId, we record
+/// both the HirFileId and the position inside the file. However, we only store
+/// AST -> ExprId mapping for non-macro files, as it is not clear how to handle
+/// this properly for macros.
+#[derive(Default, Debug, Eq, PartialEq)]
+pub struct BodySourceMap {
+    expr_map: FxHashMap<ExprSource, ExprId>,
+    expr_map_back: ArenaMap<ExprId, Result<ExprSource, SyntheticSyntax>>,
+    pat_map: FxHashMap<PatSource, PatId>,
+    pat_map_back: ArenaMap<PatId, Result<PatSource, SyntheticSyntax>>,
+    field_map: FxHashMap<(ExprId, usize), InFile<AstPtr<ast::RecordExprField>>>,
+    expansions: FxHashMap<InFile<AstPtr<ast::MacroCall>>, HirFileId>,
+}
+
+#[derive(Default, Debug, Eq, PartialEq, Clone, Copy)]
+pub struct SyntheticSyntax;
+
+impl Body {
+    pub(crate) fn body_with_source_map_query(
+        db: &dyn DefDatabase,
+        def: DefWithBodyId,
+    ) -> (Arc<Body>, Arc<BodySourceMap>) {
+        let _p = profile::span("body_with_source_map_query");
+        let mut params = None;
+
+        let (file_id, module, body) = match def {
+            DefWithBodyId::FunctionId(f) => {
+                let f = f.lookup(db);
+                let src = f.source(db);
+                params = src.value.param_list();
+                (src.file_id, f.module(db), src.value.body().map(ast::Expr::from))
+            }
+            DefWithBodyId::ConstId(c) => {
+                let c = c.lookup(db);
+                let src = c.source(db);
+                (src.file_id, c.module(db), src.value.body())
+            }
+            DefWithBodyId::StaticId(s) => {
+                let s = s.lookup(db);
+                let src = s.source(db);
+                (src.file_id, s.module(db), src.value.body())
+            }
+        };
+        let expander = Expander::new(db, file_id, module);
+        let (body, source_map) = Body::new(db, def, expander, params, body);
+        (Arc::new(body), Arc::new(source_map))
+    }
+
+    pub(crate) fn body_query(db: &dyn DefDatabase, def: DefWithBodyId) -> Arc<Body> {
+        db.body_with_source_map(def).0
+    }
+
+    fn new(
+        db: &dyn DefDatabase,
+        def: DefWithBodyId,
+        expander: Expander,
+        params: Option<ast::ParamList>,
+        body: Option<ast::Expr>,
+    ) -> (Body, BodySourceMap) {
+        lower::lower(db, def, expander, params, body)
+    }
+}
+
+impl Index<ExprId> for Body {
+    type Output = Expr;
+
+    fn index(&self, expr: ExprId) -> &Expr {
+        &self.exprs[expr]
+    }
+}
+
+impl Index<PatId> for Body {
+    type Output = Pat;
+
+    fn index(&self, pat: PatId) -> &Pat {
+        &self.pats[pat]
+    }
+}
+
+impl BodySourceMap {
+    pub fn expr_syntax(&self, expr: ExprId) -> Result<ExprSource, SyntheticSyntax> {
+        self.expr_map_back[expr].clone()
+    }
+
+    pub fn node_expr(&self, node: InFile<&ast::Expr>) -> Option<ExprId> {
+        let src = node.map(|it| AstPtr::new(it));
+        self.expr_map.get(&src).cloned()
+    }
+
+    pub fn node_macro_file(&self, node: InFile<&ast::MacroCall>) -> Option<HirFileId> {
+        let src = node.map(|it| AstPtr::new(it));
+        self.expansions.get(&src).cloned()
+    }
+
+    pub fn pat_syntax(&self, pat: PatId) -> Result<PatSource, SyntheticSyntax> {
+        self.pat_map_back[pat].clone()
+    }
+
+    pub fn node_pat(&self, node: InFile<&ast::Pat>) -> Option<PatId> {
+        let src = node.map(|it| Either::Left(AstPtr::new(it)));
+        self.pat_map.get(&src).cloned()
+    }
+
+    pub fn node_self_param(&self, node: InFile<&ast::SelfParam>) -> Option<PatId> {
+        let src = node.map(|it| Either::Right(AstPtr::new(it)));
+        self.pat_map.get(&src).cloned()
+    }
+
+    pub fn field_syntax(&self, expr: ExprId, field: usize) -> InFile<AstPtr<ast::RecordExprField>> {
+        self.field_map[&(expr, field)].clone()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use base_db::{fixture::WithFixture, SourceDatabase};
+    use test_utils::mark;
+
+    use crate::ModuleDefId;
+
+    use super::*;
+
+    fn lower(ra_fixture: &str) -> Arc<Body> {
+        let (db, file_id) = crate::test_db::TestDB::with_single_file(ra_fixture);
+
+        let krate = db.crate_graph().iter().next().unwrap();
+        let def_map = db.crate_def_map(krate);
+        let module = def_map.modules_for_file(file_id).next().unwrap();
+        let module = &def_map[module];
+        let fn_def = match module.scope.declarations().next().unwrap() {
+            ModuleDefId::FunctionId(it) => it,
+            _ => panic!(),
+        };
+
+        db.body(fn_def.into())
+    }
+
+    #[test]
+    fn your_stack_belongs_to_me() {
+        mark::check!(your_stack_belongs_to_me);
+        lower(
+            "
+macro_rules! n_nuple {
+    ($e:tt) => ();
+    ($($rest:tt)*) => {{
+        (n_nuple!($($rest)*)None,)
+    }};
+}
+fn main() { n_nuple!(1,2,3); }
+",
+        );
+    }
+}

crates/hir_def/src/body/lower.rs

@@ -0,0 +1,931 @@
+//! Transforms `ast::Expr` into an equivalent `hir_def::expr::Expr`
+//! representation.
+
+use std::{any::type_name, sync::Arc};
+
+use arena::Arena;
+use either::Either;
+use hir_expand::{
+    hygiene::Hygiene,
+    name::{name, AsName, Name},
+    HirFileId, MacroDefId, MacroDefKind,
+};
+use rustc_hash::FxHashMap;
+use syntax::{
+    ast::{
+        self, ArgListOwner, ArrayExprKind, AstChildren, LiteralKind, LoopBodyOwner, NameOwner,
+        SlicePatComponents,
+    },
+    AstNode, AstPtr,
+};
+use test_utils::mark;
+
+use crate::{
+    adt::StructKind,
+    body::{Body, BodySourceMap, Expander, PatPtr, SyntheticSyntax},
+    builtin_type::{BuiltinFloat, BuiltinInt},
+    db::DefDatabase,
+    expr::{
+        dummy_expr_id, ArithOp, Array, BinaryOp, BindingAnnotation, CmpOp, Expr, ExprId, Literal,
+        LogicOp, MatchArm, Ordering, Pat, PatId, RecordFieldPat, RecordLitField, Statement,
+    },
+    item_scope::BuiltinShadowMode,
+    item_tree::{ItemTree, ItemTreeId, ItemTreeNode},
+    path::{GenericArgs, Path},
+    type_ref::{Mutability, Rawness, TypeRef},
+    AdtId, ConstLoc, ContainerId, DefWithBodyId, EnumLoc, FunctionLoc, Intern, ModuleDefId,
+    StaticLoc, StructLoc, TraitLoc, TypeAliasLoc, UnionLoc,
+};
+
+use super::{ExprSource, PatSource};
+
+pub(crate) struct LowerCtx {
+    hygiene: Hygiene,
+}
+
+impl LowerCtx {
+    pub fn new(db: &dyn DefDatabase, file_id: HirFileId) -> Self {
+        LowerCtx { hygiene: Hygiene::new(db.upcast(), file_id) }
+    }
+    pub fn with_hygiene(hygiene: &Hygiene) -> Self {
+        LowerCtx { hygiene: hygiene.clone() }
+    }
+
+    pub fn lower_path(&self, ast: ast::Path) -> Option<Path> {
+        Path::from_src(ast, &self.hygiene)
+    }
+}
+
+pub(super) fn lower(
+    db: &dyn DefDatabase,
+    def: DefWithBodyId,
+    expander: Expander,
+    params: Option<ast::ParamList>,
+    body: Option<ast::Expr>,
+) -> (Body, BodySourceMap) {
+    let item_tree = db.item_tree(expander.current_file_id);
+    ExprCollector {
+        db,
+        def,
+        source_map: BodySourceMap::default(),
+        body: Body {
+            exprs: Arena::default(),
+            pats: Arena::default(),
+            params: Vec::new(),
+            body_expr: dummy_expr_id(),
+            item_scope: Default::default(),
+        },
+        item_trees: {
+            let mut map = FxHashMap::default();
+            map.insert(expander.current_file_id, item_tree);
+            map
+        },
+        expander,
+    }
+    .collect(params, body)
+}
+
+struct ExprCollector<'a> {
+    db: &'a dyn DefDatabase,
+    def: DefWithBodyId,
+    expander: Expander,
+    body: Body,
+    source_map: BodySourceMap,
+
+    item_trees: FxHashMap<HirFileId, Arc<ItemTree>>,
+}
+
+impl ExprCollector<'_> {
+    fn collect(
+        mut self,
+        param_list: Option<ast::ParamList>,
+        body: Option<ast::Expr>,
+    ) -> (Body, BodySourceMap) {
+        if let Some(param_list) = param_list {
+            if let Some(self_param) = param_list.self_param() {
+                let ptr = AstPtr::new(&self_param);
+                let param_pat = self.alloc_pat(
+                    Pat::Bind {
+                        name: name![self],
+                        mode: BindingAnnotation::Unannotated,
+                        subpat: None,
+                    },
+                    Either::Right(ptr),
+                );
+                self.body.params.push(param_pat);
+            }
+
+            for param in param_list.params() {
+                let pat = match param.pat() {
+                    None => continue,
+                    Some(pat) => pat,
+                };
+                let param_pat = self.collect_pat(pat);
+                self.body.params.push(param_pat);
+            }
+        };
+
+        self.body.body_expr = self.collect_expr_opt(body);
+        (self.body, self.source_map)
+    }
+
+    fn ctx(&self) -> LowerCtx {
+        LowerCtx::new(self.db, self.expander.current_file_id)
+    }
+
+    fn alloc_expr(&mut self, expr: Expr, ptr: AstPtr<ast::Expr>) -> ExprId {
+        let src = self.expander.to_source(ptr);
+        let id = self.make_expr(expr, Ok(src.clone()));
+        self.source_map.expr_map.insert(src, id);
+        id
+    }
+    // desugared exprs don't have ptr, that's wrong and should be fixed
+    // somehow.
+    fn alloc_expr_desugared(&mut self, expr: Expr) -> ExprId {
+        self.make_expr(expr, Err(SyntheticSyntax))
+    }
+    fn empty_block(&mut self) -> ExprId {
+        self.alloc_expr_desugared(Expr::Block { statements: Vec::new(), tail: None, label: None })
+    }
+    fn missing_expr(&mut self) -> ExprId {
+        self.alloc_expr_desugared(Expr::Missing)
+    }
+    fn make_expr(&mut self, expr: Expr, src: Result<ExprSource, SyntheticSyntax>) -> ExprId {
+        let id = self.body.exprs.alloc(expr);
+        self.source_map.expr_map_back.insert(id, src);
+        id
+    }
+
+    fn alloc_pat(&mut self, pat: Pat, ptr: PatPtr) -> PatId {
+        let src = self.expander.to_source(ptr);
+        let id = self.make_pat(pat, Ok(src.clone()));
+        self.source_map.pat_map.insert(src, id);
+        id
+    }
+    fn missing_pat(&mut self) -> PatId {
+        self.make_pat(Pat::Missing, Err(SyntheticSyntax))
+    }
+    fn make_pat(&mut self, pat: Pat, src: Result<PatSource, SyntheticSyntax>) -> PatId {
+        let id = self.body.pats.alloc(pat);
+        self.source_map.pat_map_back.insert(id, src);
+        id
+    }
+
+    fn collect_expr(&mut self, expr: ast::Expr) -> ExprId {
+        let syntax_ptr = AstPtr::new(&expr);
+        if !self.expander.is_cfg_enabled(&expr) {
+            return self.missing_expr();
+        }
+
+        match expr {
+            ast::Expr::IfExpr(e) => {
+                let then_branch = self.collect_block_opt(e.then_branch());
+
+                let else_branch = e.else_branch().map(|b| match b {
+                    ast::ElseBranch::Block(it) => self.collect_block(it),
+                    ast::ElseBranch::IfExpr(elif) => {
+                        let expr: ast::Expr = ast::Expr::cast(elif.syntax().clone()).unwrap();
+                        self.collect_expr(expr)
+                    }
+                });
+
+                let condition = match e.condition() {
+                    None => self.missing_expr(),
+                    Some(condition) => match condition.pat() {
+                        None => self.collect_expr_opt(condition.expr()),
+                        // if let -- desugar to match
+                        Some(pat) => {
+                            let pat = self.collect_pat(pat);
+                            let match_expr = self.collect_expr_opt(condition.expr());
+                            let placeholder_pat = self.missing_pat();
+                            let arms = vec![
+                                MatchArm { pat, expr: then_branch, guard: None },
+                                MatchArm {
+                                    pat: placeholder_pat,
+                                    expr: else_branch.unwrap_or_else(|| self.empty_block()),
+                                    guard: None,
+                                },
+                            ];
+                            return self
+                                .alloc_expr(Expr::Match { expr: match_expr, arms }, syntax_ptr);
+                        }
+                    },
+                };
+
+                self.alloc_expr(Expr::If { condition, then_branch, else_branch }, syntax_ptr)
+            }
+            ast::Expr::EffectExpr(e) => match e.effect() {
+                ast::Effect::Try(_) => {
+                    let body = self.collect_block_opt(e.block_expr());
+                    self.alloc_expr(Expr::TryBlock { body }, syntax_ptr)
+                }
+                ast::Effect::Unsafe(_) => {
+                    let body = self.collect_block_opt(e.block_expr());
+                    self.alloc_expr(Expr::Unsafe { body }, syntax_ptr)
+                }
+                // FIXME: we need to record these effects somewhere...
+                ast::Effect::Label(label) => match e.block_expr() {
+                    Some(block) => {
+                        let res = self.collect_block(block);
+                        match &mut self.body.exprs[res] {
+                            Expr::Block { label: block_label, .. } => {
+                                *block_label =
+                                    label.lifetime_token().map(|t| Name::new_lifetime(&t))
+                            }
+                            _ => unreachable!(),
+                        }
+                        res
+                    }
+                    None => self.missing_expr(),
+                },
+                // FIXME: we need to record these effects somewhere...
+                ast::Effect::Async(_) => self.collect_block_opt(e.block_expr()),
+            },
+            ast::Expr::BlockExpr(e) => self.collect_block(e),
+            ast::Expr::LoopExpr(e) => {
+                let body = self.collect_block_opt(e.loop_body());
+                self.alloc_expr(
+                    Expr::Loop {
+                        body,
+                        label: e
+                            .label()
+                            .and_then(|l| l.lifetime_token())
+                            .map(|l| Name::new_lifetime(&l)),
+                    },
+                    syntax_ptr,
+                )
+            }
+            ast::Expr::WhileExpr(e) => {
+                let body = self.collect_block_opt(e.loop_body());
+
+                let condition = match e.condition() {
+                    None => self.missing_expr(),
+                    Some(condition) => match condition.pat() {
+                        None => self.collect_expr_opt(condition.expr()),
+                        // if let -- desugar to match
+                        Some(pat) => {
+                            mark::hit!(infer_resolve_while_let);
+                            let pat = self.collect_pat(pat);
+                            let match_expr = self.collect_expr_opt(condition.expr());
+                            let placeholder_pat = self.missing_pat();
+                            let break_ =
+                                self.alloc_expr_desugared(Expr::Break { expr: None, label: None });
+                            let arms = vec![
+                                MatchArm { pat, expr: body, guard: None },
+                                MatchArm { pat: placeholder_pat, expr: break_, guard: None },
+                            ];
+                            let match_expr =
+                                self.alloc_expr_desugared(Expr::Match { expr: match_expr, arms });
+                            return self.alloc_expr(
+                                Expr::Loop {
+                                    body: match_expr,
+                                    label: e
+                                        .label()
+                                        .and_then(|l| l.lifetime_token())
+                                        .map(|l| Name::new_lifetime(&l)),
+                                },
+                                syntax_ptr,
+                            );
+                        }
+                    },
+                };
+
+                self.alloc_expr(
+                    Expr::While {
+                        condition,
+                        body,
+                        label: e
+                            .label()
+                            .and_then(|l| l.lifetime_token())
+                            .map(|l| Name::new_lifetime(&l)),
+                    },
+                    syntax_ptr,
+                )
+            }
+            ast::Expr::ForExpr(e) => {
+                let iterable = self.collect_expr_opt(e.iterable());
+                let pat = self.collect_pat_opt(e.pat());
+                let body = self.collect_block_opt(e.loop_body());
+                self.alloc_expr(
+                    Expr::For {
+                        iterable,
+                        pat,
+                        body,
+                        label: e
+                            .label()
+                            .and_then(|l| l.lifetime_token())
+                            .map(|l| Name::new_lifetime(&l)),
+                    },
+                    syntax_ptr,
+                )
+            }
+            ast::Expr::CallExpr(e) => {
+                let callee = self.collect_expr_opt(e.expr());
+                let args = if let Some(arg_list) = e.arg_list() {
+                    arg_list.args().map(|e| self.collect_expr(e)).collect()
+                } else {
+                    Vec::new()
+                };
+                self.alloc_expr(Expr::Call { callee, args }, syntax_ptr)
+            }
+            ast::Expr::MethodCallExpr(e) => {
+                let receiver = self.collect_expr_opt(e.receiver());
+                let args = if let Some(arg_list) = e.arg_list() {
+                    arg_list.args().map(|e| self.collect_expr(e)).collect()
+                } else {
+                    Vec::new()
+                };
+                let method_name = e.name_ref().map(|nr| nr.as_name()).unwrap_or_else(Name::missing);
+                let generic_args =
+                    e.generic_arg_list().and_then(|it| GenericArgs::from_ast(&self.ctx(), it));
+                self.alloc_expr(
+                    Expr::MethodCall { receiver, method_name, args, generic_args },
+                    syntax_ptr,
+                )
+            }
+            ast::Expr::MatchExpr(e) => {
+                let expr = self.collect_expr_opt(e.expr());
+                let arms = if let Some(match_arm_list) = e.match_arm_list() {
+                    match_arm_list
+                        .arms()
+                        .map(|arm| MatchArm {
+                            pat: self.collect_pat_opt(arm.pat()),
+                            expr: self.collect_expr_opt(arm.expr()),
+                            guard: arm
+                                .guard()
+                                .and_then(|guard| guard.expr())
+                                .map(|e| self.collect_expr(e)),
+                        })
+                        .collect()
+                } else {
+                    Vec::new()
+                };
+                self.alloc_expr(Expr::Match { expr, arms }, syntax_ptr)
+            }
+            ast::Expr::PathExpr(e) => {
+                let path = e
+                    .path()
+                    .and_then(|path| self.expander.parse_path(path))
+                    .map(Expr::Path)
+                    .unwrap_or(Expr::Missing);
+                self.alloc_expr(path, syntax_ptr)
+            }
+            ast::Expr::ContinueExpr(e) => self.alloc_expr(
+                Expr::Continue { label: e.lifetime_token().map(|l| Name::new_lifetime(&l)) },
+                syntax_ptr,
+            ),
+            ast::Expr::BreakExpr(e) => {
+                let expr = e.expr().map(|e| self.collect_expr(e));
+                self.alloc_expr(
+                    Expr::Break { expr, label: e.lifetime_token().map(|l| Name::new_lifetime(&l)) },
+                    syntax_ptr,
+                )
+            }
+            ast::Expr::ParenExpr(e) => {
+                let inner = self.collect_expr_opt(e.expr());
+                // make the paren expr point to the inner expression as well
+                let src = self.expander.to_source(syntax_ptr);
+                self.source_map.expr_map.insert(src, inner);
+                inner
+            }
+            ast::Expr::ReturnExpr(e) => {
+                let expr = e.expr().map(|e| self.collect_expr(e));
+                self.alloc_expr(Expr::Return { expr }, syntax_ptr)
+            }
+            ast::Expr::RecordExpr(e) => {
+                let path = e.path().and_then(|path| self.expander.parse_path(path));
+                let mut field_ptrs = Vec::new();
+                let record_lit = if let Some(nfl) = e.record_expr_field_list() {
+                    let fields = nfl
+                        .fields()
+                        .inspect(|field| field_ptrs.push(AstPtr::new(field)))
+                        .filter_map(|field| {
+                            if !self.expander.is_cfg_enabled(&field) {
+                                return None;
+                            }
+                            let name = field.field_name()?.as_name();
+
+                            Some(RecordLitField {
+                                name,
+                                expr: match field.expr() {
+                                    Some(e) => self.collect_expr(e),
+                                    None => self.missing_expr(),
+                                },
+                            })
+                        })
+                        .collect();
+                    let spread = nfl.spread().map(|s| self.collect_expr(s));
+                    Expr::RecordLit { path, fields, spread }
+                } else {
+                    Expr::RecordLit { path, fields: Vec::new(), spread: None }
+                };
+
+                let res = self.alloc_expr(record_lit, syntax_ptr);
+                for (i, ptr) in field_ptrs.into_iter().enumerate() {
+                    let src = self.expander.to_source(ptr);
+                    self.source_map.field_map.insert((res, i), src);
+                }
+                res
+            }
+            ast::Expr::FieldExpr(e) => {
+                let expr = self.collect_expr_opt(e.expr());
+                let name = match e.field_access() {
+                    Some(kind) => kind.as_name(),
+                    _ => Name::missing(),
+                };
+                self.alloc_expr(Expr::Field { expr, name }, syntax_ptr)
+            }
+            ast::Expr::AwaitExpr(e) => {
+                let expr = self.collect_expr_opt(e.expr());
+                self.alloc_expr(Expr::Await { expr }, syntax_ptr)
+            }
+            ast::Expr::TryExpr(e) => {
+                let expr = self.collect_expr_opt(e.expr());
+                self.alloc_expr(Expr::Try { expr }, syntax_ptr)
+            }
+            ast::Expr::CastExpr(e) => {
+                let expr = self.collect_expr_opt(e.expr());
+                let type_ref = TypeRef::from_ast_opt(&self.ctx(), e.ty());
+                self.alloc_expr(Expr::Cast { expr, type_ref }, syntax_ptr)
+            }
+            ast::Expr::RefExpr(e) => {
+                let expr = self.collect_expr_opt(e.expr());
+                let raw_tok = e.raw_token().is_some();
+                let mutability = if raw_tok {
+                    if e.mut_token().is_some() {
+                        Mutability::Mut
+                    } else if e.const_token().is_some() {
+                        Mutability::Shared
+                    } else {
+                        unreachable!("parser only remaps to raw_token() if matching mutability token follows")
+                    }
+                } else {
+                    Mutability::from_mutable(e.mut_token().is_some())
+                };
+                let rawness = Rawness::from_raw(raw_tok);
+                self.alloc_expr(Expr::Ref { expr, rawness, mutability }, syntax_ptr)
+            }
+            ast::Expr::PrefixExpr(e) => {
+                let expr = self.collect_expr_opt(e.expr());
+                if let Some(op) = e.op_kind() {
+                    self.alloc_expr(Expr::UnaryOp { expr, op }, syntax_ptr)
+                } else {
+                    self.alloc_expr(Expr::Missing, syntax_ptr)
+                }
+            }
+            ast::Expr::ClosureExpr(e) => {
+                let mut args = Vec::new();
+                let mut arg_types = Vec::new();
+                if let Some(pl) = e.param_list() {
+                    for param in pl.params() {
+                        let pat = self.collect_pat_opt(param.pat());
+                        let type_ref = param.ty().map(|it| TypeRef::from_ast(&self.ctx(), it));
+                        args.push(pat);
+                        arg_types.push(type_ref);
+                    }
+                }
+                let ret_type =
+                    e.ret_type().and_then(|r| r.ty()).map(|it| TypeRef::from_ast(&self.ctx(), it));
+                let body = self.collect_expr_opt(e.body());
+                self.alloc_expr(Expr::Lambda { args, arg_types, ret_type, body }, syntax_ptr)
+            }
+            ast::Expr::BinExpr(e) => {
+                let lhs = self.collect_expr_opt(e.lhs());
+                let rhs = self.collect_expr_opt(e.rhs());
+                let op = e.op_kind().map(BinaryOp::from);
+                self.alloc_expr(Expr::BinaryOp { lhs, rhs, op }, syntax_ptr)
+            }
+            ast::Expr::TupleExpr(e) => {
+                let exprs = e.fields().map(|expr| self.collect_expr(expr)).collect();
+                self.alloc_expr(Expr::Tuple { exprs }, syntax_ptr)
+            }
+            ast::Expr::BoxExpr(e) => {
+                let expr = self.collect_expr_opt(e.expr());
+                self.alloc_expr(Expr::Box { expr }, syntax_ptr)
+            }
+
+            ast::Expr::ArrayExpr(e) => {
+                let kind = e.kind();
+
+                match kind {
+                    ArrayExprKind::ElementList(e) => {
+                        let exprs = e.map(|expr| self.collect_expr(expr)).collect();
+                        self.alloc_expr(Expr::Array(Array::ElementList(exprs)), syntax_ptr)
+                    }
+                    ArrayExprKind::Repeat { initializer, repeat } => {
+                        let initializer = self.collect_expr_opt(initializer);
+                        let repeat = self.collect_expr_opt(repeat);
+                        self.alloc_expr(
+                            Expr::Array(Array::Repeat { initializer, repeat }),
+                            syntax_ptr,
+                        )
+                    }
+                }
+            }
+
+            ast::Expr::Literal(e) => self.alloc_expr(Expr::Literal(e.kind().into()), syntax_ptr),
+            ast::Expr::IndexExpr(e) => {
+                let base = self.collect_expr_opt(e.base());
+                let index = self.collect_expr_opt(e.index());
+                self.alloc_expr(Expr::Index { base, index }, syntax_ptr)
+            }
+            ast::Expr::RangeExpr(e) => {
+                let lhs = e.start().map(|lhs| self.collect_expr(lhs));
+                let rhs = e.end().map(|rhs| self.collect_expr(rhs));
+                match e.op_kind() {
+                    Some(range_type) => {
+                        self.alloc_expr(Expr::Range { lhs, rhs, range_type }, syntax_ptr)
+                    }
+                    None => self.alloc_expr(Expr::Missing, syntax_ptr),
+                }
+            }
+            ast::Expr::MacroCall(e) => {
+                if let Some(name) = e.is_macro_rules().map(|it| it.as_name()) {
+                    let mac = MacroDefId {
+                        krate: Some(self.expander.module.krate),
+                        ast_id: Some(self.expander.ast_id(&e)),
+                        kind: MacroDefKind::Declarative,
+                        local_inner: false,
+                    };
+                    self.body.item_scope.define_legacy_macro(name, mac);
+
+                    // FIXME: do we still need to allocate this as missing ?
+                    self.alloc_expr(Expr::Missing, syntax_ptr)
+                } else {
+                    let macro_call = self.expander.to_source(AstPtr::new(&e));
+                    match self.expander.enter_expand(self.db, Some(&self.body.item_scope), e) {
+                        Some((mark, expansion)) => {
+                            self.source_map
+                                .expansions
+                                .insert(macro_call, self.expander.current_file_id);
+
+                            let item_tree = self.db.item_tree(self.expander.current_file_id);
+                            self.item_trees.insert(self.expander.current_file_id, item_tree);
+                            let id = self.collect_expr(expansion);
+                            self.expander.exit(self.db, mark);
+                            id
+                        }
+                        None => self.alloc_expr(Expr::Missing, syntax_ptr),
+                    }
+                }
+            }
+        }
+    }
+
+    fn find_inner_item<N: ItemTreeNode>(&self, ast: &N::Source) -> Option<ItemTreeId<N>> {
+        let id = self.expander.ast_id(ast);
+        let tree = &self.item_trees[&id.file_id];
+
+        // FIXME: This probably breaks with `use` items, since they produce multiple item tree nodes
+
+        // Root file (non-macro).
+        let item_tree_id = tree
+            .all_inner_items()
+            .chain(tree.top_level_items().iter().copied())
+            .filter_map(|mod_item| mod_item.downcast::<N>())
+            .find(|tree_id| tree[*tree_id].ast_id().upcast() == id.value.upcast())
+            .or_else(|| {
+                log::debug!(
+                    "couldn't find inner {} item for {:?} (AST: `{}` - {:?})",
+                    type_name::<N>(),
+                    id,
+                    ast.syntax(),
+                    ast.syntax(),
+                );
+                None
+            })?;
+
+        Some(ItemTreeId::new(id.file_id, item_tree_id))
+    }
+
+    fn collect_expr_opt(&mut self, expr: Option<ast::Expr>) -> ExprId {
+        if let Some(expr) = expr {
+            self.collect_expr(expr)
+        } else {
+            self.missing_expr()
+        }
+    }
+
+    fn collect_block(&mut self, block: ast::BlockExpr) -> ExprId {
+        let syntax_node_ptr = AstPtr::new(&block.clone().into());
+        self.collect_block_items(&block);
+        let statements = block
+            .statements()
+            .filter_map(|s| {
+                let stmt = match s {
+                    ast::Stmt::LetStmt(stmt) => {
+                        let pat = self.collect_pat_opt(stmt.pat());
+                        let type_ref = stmt.ty().map(|it| TypeRef::from_ast(&self.ctx(), it));
+                        let initializer = stmt.initializer().map(|e| self.collect_expr(e));
+                        Statement::Let { pat, type_ref, initializer }
+                    }
+                    ast::Stmt::ExprStmt(stmt) => {
+                        Statement::Expr(self.collect_expr_opt(stmt.expr()))
+                    }
+                    ast::Stmt::Item(_) => return None,
+                };
+                Some(stmt)
+            })
+            .collect();
+        let tail = block.expr().map(|e| self.collect_expr(e));
+        self.alloc_expr(Expr::Block { statements, tail, label: None }, syntax_node_ptr)
+    }
+
+    fn collect_block_items(&mut self, block: &ast::BlockExpr) {
+        let container = ContainerId::DefWithBodyId(self.def);
+
+        let items = block
+            .statements()
+            .filter_map(|stmt| match stmt {
+                ast::Stmt::Item(it) => Some(it),
+                ast::Stmt::LetStmt(_) | ast::Stmt::ExprStmt(_) => None,
+            })
+            .filter_map(|item| {
+                let (def, name): (ModuleDefId, Option<ast::Name>) = match item {
+                    ast::Item::Fn(def) => {
+                        let id = self.find_inner_item(&def)?;
+                        (
+                            FunctionLoc { container: container.into(), id }.intern(self.db).into(),
+                            def.name(),
+                        )
+                    }
+                    ast::Item::TypeAlias(def) => {
+                        let id = self.find_inner_item(&def)?;
+                        (
+                            TypeAliasLoc { container: container.into(), id }.intern(self.db).into(),
+                            def.name(),
+                        )
+                    }
+                    ast::Item::Const(def) => {
+                        let id = self.find_inner_item(&def)?;
+                        (
+                            ConstLoc { container: container.into(), id }.intern(self.db).into(),
+                            def.name(),
+                        )
+                    }
+                    ast::Item::Static(def) => {
+                        let id = self.find_inner_item(&def)?;
+                        (StaticLoc { container, id }.intern(self.db).into(), def.name())
+                    }
+                    ast::Item::Struct(def) => {
+                        let id = self.find_inner_item(&def)?;
+                        (StructLoc { container, id }.intern(self.db).into(), def.name())
+                    }
+                    ast::Item::Enum(def) => {
+                        let id = self.find_inner_item(&def)?;
+                        (EnumLoc { container, id }.intern(self.db).into(), def.name())
+                    }
+                    ast::Item::Union(def) => {
+                        let id = self.find_inner_item(&def)?;
+                        (UnionLoc { container, id }.intern(self.db).into(), def.name())
+                    }
+                    ast::Item::Trait(def) => {
+                        let id = self.find_inner_item(&def)?;
+                        (TraitLoc { container, id }.intern(self.db).into(), def.name())
+                    }
+                    ast::Item::ExternBlock(_) => return None, // FIXME: collect from extern blocks
+                    ast::Item::Impl(_)
+                    | ast::Item::Use(_)
+                    | ast::Item::ExternCrate(_)
+                    | ast::Item::Module(_)
+                    | ast::Item::MacroCall(_) => return None,
+                };
+
+                Some((def, name))
+            })
+            .collect::<Vec<_>>();
+
+        for (def, name) in items {
+            self.body.item_scope.define_def(def);
+            if let Some(name) = name {
+                let vis = crate::visibility::Visibility::Public; // FIXME determine correctly
+                let has_constructor = match def {
+                    ModuleDefId::AdtId(AdtId::StructId(s)) => {
+                        self.db.struct_data(s).variant_data.kind() != StructKind::Record
+                    }
+                    _ => true,
+                };
+                self.body.item_scope.push_res(
+                    name.as_name(),
+                    crate::per_ns::PerNs::from_def(def, vis, has_constructor),
+                );
+            }
+        }
+    }
+
+    fn collect_block_opt(&mut self, expr: Option<ast::BlockExpr>) -> ExprId {
+        if let Some(block) = expr {
+            self.collect_block(block)
+        } else {
+            self.missing_expr()
+        }
+    }
+
+    fn collect_pat(&mut self, pat: ast::Pat) -> PatId {
+        let pattern = match &pat {
+            ast::Pat::IdentPat(bp) => {
+                let name = bp.name().map(|nr| nr.as_name()).unwrap_or_else(Name::missing);
+                let annotation =
+                    BindingAnnotation::new(bp.mut_token().is_some(), bp.ref_token().is_some());
+                let subpat = bp.pat().map(|subpat| self.collect_pat(subpat));
+                if annotation == BindingAnnotation::Unannotated && subpat.is_none() {
+                    // This could also be a single-segment path pattern. To
+                    // decide that, we need to try resolving the name.
+                    let (resolved, _) = self.expander.crate_def_map.resolve_path(
+                        self.db,
+                        self.expander.module.local_id,
+                        &name.clone().into(),
+                        BuiltinShadowMode::Other,
+                    );
+                    match resolved.take_values() {
+                        Some(ModuleDefId::ConstId(_)) => Pat::Path(name.into()),
+                        Some(ModuleDefId::EnumVariantId(_)) => {
+                            // this is only really valid for unit variants, but
+                            // shadowing other enum variants with a pattern is
+                            // an error anyway
+                            Pat::Path(name.into())
+                        }
+                        Some(ModuleDefId::AdtId(AdtId::StructId(s)))
+                            if self.db.struct_data(s).variant_data.kind() != StructKind::Record =>
+                        {
+                            // Funnily enough, record structs *can* be shadowed
+                            // by pattern bindings (but unit or tuple structs
+                            // can't).
+                            Pat::Path(name.into())
+                        }
+                        // shadowing statics is an error as well, so we just ignore that case here
+                        _ => Pat::Bind { name, mode: annotation, subpat },
+                    }
+                } else {
+                    Pat::Bind { name, mode: annotation, subpat }
+                }
+            }
+            ast::Pat::TupleStructPat(p) => {
+                let path = p.path().and_then(|path| self.expander.parse_path(path));
+                let (args, ellipsis) = self.collect_tuple_pat(p.fields());
+                Pat::TupleStruct { path, args, ellipsis }
+            }
+            ast::Pat::RefPat(p) => {
+                let pat = self.collect_pat_opt(p.pat());
+                let mutability = Mutability::from_mutable(p.mut_token().is_some());
+                Pat::Ref { pat, mutability }
+            }
+            ast::Pat::PathPat(p) => {
+                let path = p.path().and_then(|path| self.expander.parse_path(path));
+                path.map(Pat::Path).unwrap_or(Pat::Missing)
+            }
+            ast::Pat::OrPat(p) => {
+                let pats = p.pats().map(|p| self.collect_pat(p)).collect();
+                Pat::Or(pats)
+            }
+            ast::Pat::ParenPat(p) => return self.collect_pat_opt(p.pat()),
+            ast::Pat::TuplePat(p) => {
+                let (args, ellipsis) = self.collect_tuple_pat(p.fields());
+                Pat::Tuple { args, ellipsis }
+            }
+            ast::Pat::WildcardPat(_) => Pat::Wild,
+            ast::Pat::RecordPat(p) => {
+                let path = p.path().and_then(|path| self.expander.parse_path(path));
+                let args: Vec<_> = p
+                    .record_pat_field_list()
+                    .expect("every struct should have a field list")
+                    .fields()
+                    .filter_map(|f| {
+                        let ast_pat = f.pat()?;
+                        let pat = self.collect_pat(ast_pat);
+                        let name = f.field_name()?.as_name();
+                        Some(RecordFieldPat { name, pat })
+                    })
+                    .collect();
+
+                let ellipsis = p
+                    .record_pat_field_list()
+                    .expect("every struct should have a field list")
+                    .dotdot_token()
+                    .is_some();
+
+                Pat::Record { path, args, ellipsis }
+            }
+            ast::Pat::SlicePat(p) => {
+                let SlicePatComponents { prefix, slice, suffix } = p.components();
+
+                // FIXME properly handle `RestPat`
+                Pat::Slice {
+                    prefix: prefix.into_iter().map(|p| self.collect_pat(p)).collect(),
+                    slice: slice.map(|p| self.collect_pat(p)),
+                    suffix: suffix.into_iter().map(|p| self.collect_pat(p)).collect(),
+                }
+            }
+            ast::Pat::LiteralPat(lit) => {
+                if let Some(ast_lit) = lit.literal() {
+                    let expr = Expr::Literal(ast_lit.kind().into());
+                    let expr_ptr = AstPtr::new(&ast::Expr::Literal(ast_lit));
+                    let expr_id = self.alloc_expr(expr, expr_ptr);
+                    Pat::Lit(expr_id)
+                } else {
+                    Pat::Missing
+                }
+            }
+            ast::Pat::RestPat(_) => {
+                // `RestPat` requires special handling and should not be mapped
+                // to a Pat. Here we are using `Pat::Missing` as a fallback for
+                // when `RestPat` is mapped to `Pat`, which can easily happen
+                // when the source code being analyzed has a malformed pattern
+                // which includes `..` in a place where it isn't valid.
+
+                Pat::Missing
+            }
+            // FIXME: implement
+            ast::Pat::BoxPat(_) | ast::Pat::RangePat(_) | ast::Pat::MacroPat(_) => Pat::Missing,
+        };
+        let ptr = AstPtr::new(&pat);
+        self.alloc_pat(pattern, Either::Left(ptr))
+    }
+
+    fn collect_pat_opt(&mut self, pat: Option<ast::Pat>) -> PatId {
+        if let Some(pat) = pat {
+            self.collect_pat(pat)
+        } else {
+            self.missing_pat()
+        }
+    }
+
+    fn collect_tuple_pat(&mut self, args: AstChildren<ast::Pat>) -> (Vec<PatId>, Option<usize>) {
+        // Find the location of the `..`, if there is one. Note that we do not
+        // consider the possiblity of there being multiple `..` here.
+        let ellipsis = args.clone().position(|p| matches!(p, ast::Pat::RestPat(_)));
+        // We want to skip the `..` pattern here, since we account for it above.
+        let args = args
+            .filter(|p| !matches!(p, ast::Pat::RestPat(_)))
+            .map(|p| self.collect_pat(p))
+            .collect();
+
+        (args, ellipsis)
+    }
+}
+
+impl From<ast::BinOp> for BinaryOp {
+    fn from(ast_op: ast::BinOp) -> Self {
+        match ast_op {
+            ast::BinOp::BooleanOr => BinaryOp::LogicOp(LogicOp::Or),
+            ast::BinOp::BooleanAnd => BinaryOp::LogicOp(LogicOp::And),
+            ast::BinOp::EqualityTest => BinaryOp::CmpOp(CmpOp::Eq { negated: false }),
+            ast::BinOp::NegatedEqualityTest => BinaryOp::CmpOp(CmpOp::Eq { negated: true }),
+            ast::BinOp::LesserEqualTest => {
+                BinaryOp::CmpOp(CmpOp::Ord { ordering: Ordering::Less, strict: false })
+            }
+            ast::BinOp::GreaterEqualTest => {
+                BinaryOp::CmpOp(CmpOp::Ord { ordering: Ordering::Greater, strict: false })
+            }
+            ast::BinOp::LesserTest => {
+                BinaryOp::CmpOp(CmpOp::Ord { ordering: Ordering::Less, strict: true })
+            }
+            ast::BinOp::GreaterTest => {
+                BinaryOp::CmpOp(CmpOp::Ord { ordering: Ordering::Greater, strict: true })
+            }
+            ast::BinOp::Addition => BinaryOp::ArithOp(ArithOp::Add),
+            ast::BinOp::Multiplication => BinaryOp::ArithOp(ArithOp::Mul),
+            ast::BinOp::Subtraction => BinaryOp::ArithOp(ArithOp::Sub),
+            ast::BinOp::Division => BinaryOp::ArithOp(ArithOp::Div),
+            ast::BinOp::Remainder => BinaryOp::ArithOp(ArithOp::Rem),
+            ast::BinOp::LeftShift => BinaryOp::ArithOp(ArithOp::Shl),
+            ast::BinOp::RightShift => BinaryOp::ArithOp(ArithOp::Shr),
+            ast::BinOp::BitwiseXor => BinaryOp::ArithOp(ArithOp::BitXor),
+            ast::BinOp::BitwiseOr => BinaryOp::ArithOp(ArithOp::BitOr),
+            ast::BinOp::BitwiseAnd => BinaryOp::ArithOp(ArithOp::BitAnd),
+            ast::BinOp::Assignment => BinaryOp::Assignment { op: None },
+            ast::BinOp::AddAssign => BinaryOp::Assignment { op: Some(ArithOp::Add) },
+            ast::BinOp::DivAssign => BinaryOp::Assignment { op: Some(ArithOp::Div) },
+            ast::BinOp::MulAssign => BinaryOp::Assignment { op: Some(ArithOp::Mul) },
+            ast::BinOp::RemAssign => BinaryOp::Assignment { op: Some(ArithOp::Rem) },
+            ast::BinOp::ShlAssign => BinaryOp::Assignment { op: Some(ArithOp::Shl) },
+            ast::BinOp::ShrAssign => BinaryOp::Assignment { op: Some(ArithOp::Shr) },
+            ast::BinOp::SubAssign => BinaryOp::Assignment { op: Some(ArithOp::Sub) },
+            ast::BinOp::BitOrAssign => BinaryOp::Assignment { op: Some(ArithOp::BitOr) },
+            ast::BinOp::BitAndAssign => BinaryOp::Assignment { op: Some(ArithOp::BitAnd) },
+            ast::BinOp::BitXorAssign => BinaryOp::Assignment { op: Some(ArithOp::BitXor) },
+        }
+    }
+}
+
+impl From<ast::LiteralKind> for Literal {
+    fn from(ast_lit_kind: ast::LiteralKind) -> Self {
+        match ast_lit_kind {
+            LiteralKind::IntNumber { suffix } => {
+                let known_name = suffix.and_then(|it| BuiltinInt::from_suffix(&it));
+
+                Literal::Int(Default::default(), known_name)
+            }
+            LiteralKind::FloatNumber { suffix } => {
+                let known_name = suffix.and_then(|it| BuiltinFloat::from_suffix(&it));
+
+                Literal::Float(Default::default(), known_name)
+            }
+            LiteralKind::ByteString => Literal::ByteString(Default::default()),
+            LiteralKind::String => Literal::String(Default::default()),
+            LiteralKind::Byte => Literal::Int(Default::default(), Some(BuiltinInt::U8)),
+            LiteralKind::Bool(val) => Literal::Bool(val),
+            LiteralKind::Char => Literal::Char(Default::default()),
+        }
+    }
+}

crates/hir_def/src/body/scope.rs

@@ -0,0 +1,456 @@
+//! Name resolution for expressions.
+use std::sync::Arc;
+
+use arena::{Arena, Idx};
+use hir_expand::name::Name;
+use rustc_hash::FxHashMap;
+
+use crate::{
+    body::Body,
+    db::DefDatabase,
+    expr::{Expr, ExprId, Pat, PatId, Statement},
+    DefWithBodyId,
+};
+
+pub type ScopeId = Idx<ScopeData>;
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct ExprScopes {
+    scopes: Arena<ScopeData>,
+    scope_by_expr: FxHashMap<ExprId, ScopeId>,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct ScopeEntry {
+    name: Name,
+    pat: PatId,
+}
+
+impl ScopeEntry {
+    pub fn name(&self) -> &Name {
+        &self.name
+    }
+
+    pub fn pat(&self) -> PatId {
+        self.pat
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct ScopeData {
+    parent: Option<ScopeId>,
+    entries: Vec<ScopeEntry>,
+}
+
+impl ExprScopes {
+    pub(crate) fn expr_scopes_query(db: &dyn DefDatabase, def: DefWithBodyId) -> Arc<ExprScopes> {
+        let body = db.body(def);
+        Arc::new(ExprScopes::new(&*body))
+    }
+
+    fn new(body: &Body) -> ExprScopes {
+        let mut scopes =
+            ExprScopes { scopes: Arena::default(), scope_by_expr: FxHashMap::default() };
+        let root = scopes.root_scope();
+        scopes.add_params_bindings(body, root, &body.params);
+        compute_expr_scopes(body.body_expr, body, &mut scopes, root);
+        scopes
+    }
+
+    pub fn entries(&self, scope: ScopeId) -> &[ScopeEntry] {
+        &self.scopes[scope].entries
+    }
+
+    pub fn scope_chain(&self, scope: Option<ScopeId>) -> impl Iterator<Item = ScopeId> + '_ {
+        std::iter::successors(scope, move |&scope| self.scopes[scope].parent)
+    }
+
+    pub fn resolve_name_in_scope(&self, scope: ScopeId, name: &Name) -> Option<&ScopeEntry> {
+        self.scope_chain(Some(scope))
+            .find_map(|scope| self.entries(scope).iter().find(|it| it.name == *name))
+    }
+
+    pub fn scope_for(&self, expr: ExprId) -> Option<ScopeId> {
+        self.scope_by_expr.get(&expr).copied()
+    }
+
+    pub fn scope_by_expr(&self) -> &FxHashMap<ExprId, ScopeId> {
+        &self.scope_by_expr
+    }
+
+    fn root_scope(&mut self) -> ScopeId {
+        self.scopes.alloc(ScopeData { parent: None, entries: vec![] })
+    }
+
+    fn new_scope(&mut self, parent: ScopeId) -> ScopeId {
+        self.scopes.alloc(ScopeData { parent: Some(parent), entries: vec![] })
+    }
+
+    fn add_bindings(&mut self, body: &Body, scope: ScopeId, pat: PatId) {
+        let pattern = &body[pat];
+        if let Pat::Bind { name, .. } = pattern {
+            let entry = ScopeEntry { name: name.clone(), pat };
+            self.scopes[scope].entries.push(entry);
+        }
+
+        pattern.walk_child_pats(|pat| self.add_bindings(body, scope, pat));
+    }
+
+    fn add_params_bindings(&mut self, body: &Body, scope: ScopeId, params: &[PatId]) {
+        params.iter().for_each(|pat| self.add_bindings(body, scope, *pat));
+    }
+
+    fn set_scope(&mut self, node: ExprId, scope: ScopeId) {
+        self.scope_by_expr.insert(node, scope);
+    }
+}
+
+fn compute_block_scopes(
+    statements: &[Statement],
+    tail: Option<ExprId>,
+    body: &Body,
+    scopes: &mut ExprScopes,
+    mut scope: ScopeId,
+) {
+    for stmt in statements {
+        match stmt {
+            Statement::Let { pat, initializer, .. } => {
+                if let Some(expr) = initializer {
+                    scopes.set_scope(*expr, scope);
+                    compute_expr_scopes(*expr, body, scopes, scope);
+                }
+                scope = scopes.new_scope(scope);
+                scopes.add_bindings(body, scope, *pat);
+            }
+            Statement::Expr(expr) => {
+                scopes.set_scope(*expr, scope);
+                compute_expr_scopes(*expr, body, scopes, scope);
+            }
+        }
+    }
+    if let Some(expr) = tail {
+        compute_expr_scopes(expr, body, scopes, scope);
+    }
+}
+
+fn compute_expr_scopes(expr: ExprId, body: &Body, scopes: &mut ExprScopes, scope: ScopeId) {
+    scopes.set_scope(expr, scope);
+    match &body[expr] {
+        Expr::Block { statements, tail, .. } => {
+            compute_block_scopes(&statements, *tail, body, scopes, scope);
+        }
+        Expr::For { iterable, pat, body: body_expr, .. } => {
+            compute_expr_scopes(*iterable, body, scopes, scope);
+            let scope = scopes.new_scope(scope);
+            scopes.add_bindings(body, scope, *pat);
+            compute_expr_scopes(*body_expr, body, scopes, scope);
+        }
+        Expr::Lambda { args, body: body_expr, .. } => {
+            let scope = scopes.new_scope(scope);
+            scopes.add_params_bindings(body, scope, &args);
+            compute_expr_scopes(*body_expr, body, scopes, scope);
+        }
+        Expr::Match { expr, arms } => {
+            compute_expr_scopes(*expr, body, scopes, scope);
+            for arm in arms {
+                let scope = scopes.new_scope(scope);
+                scopes.add_bindings(body, scope, arm.pat);
+                if let Some(guard) = arm.guard {
+                    scopes.set_scope(guard, scope);
+                    compute_expr_scopes(guard, body, scopes, scope);
+                }
+                scopes.set_scope(arm.expr, scope);
+                compute_expr_scopes(arm.expr, body, scopes, scope);
+            }
+        }
+        e => e.walk_child_exprs(|e| compute_expr_scopes(e, body, scopes, scope)),
+    };
+}
+
+#[cfg(test)]
+mod tests {
+    use base_db::{fixture::WithFixture, FileId, SourceDatabase};
+    use hir_expand::{name::AsName, InFile};
+    use syntax::{algo::find_node_at_offset, ast, AstNode};
+    use test_utils::{assert_eq_text, extract_offset, mark};
+
+    use crate::{db::DefDatabase, test_db::TestDB, FunctionId, ModuleDefId};
+
+    fn find_function(db: &TestDB, file_id: FileId) -> FunctionId {
+        let krate = db.test_crate();
+        let crate_def_map = db.crate_def_map(krate);
+
+        let module = crate_def_map.modules_for_file(file_id).next().unwrap();
+        let (_, def) = crate_def_map[module].scope.entries().next().unwrap();
+        match def.take_values().unwrap() {
+            ModuleDefId::FunctionId(it) => it,
+            _ => panic!(),
+        }
+    }
+
+    fn do_check(ra_fixture: &str, expected: &[&str]) {
+        let (offset, code) = extract_offset(ra_fixture);
+        let code = {
+            let mut buf = String::new();
+            let off: usize = offset.into();
+            buf.push_str(&code[..off]);
+            buf.push_str("<|>marker");
+            buf.push_str(&code[off..]);
+            buf
+        };
+
+        let (db, position) = TestDB::with_position(&code);
+        let file_id = position.file_id;
+        let offset = position.offset;
+
+        let file_syntax = db.parse(file_id).syntax_node();
+        let marker: ast::PathExpr = find_node_at_offset(&file_syntax, offset).unwrap();
+        let function = find_function(&db, file_id);
+
+        let scopes = db.expr_scopes(function.into());
+        let (_body, source_map) = db.body_with_source_map(function.into());
+
+        let expr_id = source_map
+            .node_expr(InFile { file_id: file_id.into(), value: &marker.into() })
+            .unwrap();
+        let scope = scopes.scope_for(expr_id);
+
+        let actual = scopes
+            .scope_chain(scope)
+            .flat_map(|scope| scopes.entries(scope))
+            .map(|it| it.name().to_string())
+            .collect::<Vec<_>>()
+            .join("\n");
+        let expected = expected.join("\n");
+        assert_eq_text!(&expected, &actual);
+    }
+
+    #[test]
+    fn test_lambda_scope() {
+        do_check(
+            r"
+            fn quux(foo: i32) {
+                let f = |bar, baz: i32| {
+                    <|>
+                };
+            }",
+            &["bar", "baz", "foo"],
+        );
+    }
+
+    #[test]
+    fn test_call_scope() {
+        do_check(
+            r"
+            fn quux() {
+                f(|x| <|> );
+            }",
+            &["x"],
+        );
+    }
+
+    #[test]
+    fn test_method_call_scope() {
+        do_check(
+            r"
+            fn quux() {
+                z.f(|x| <|> );
+            }",
+            &["x"],
+        );
+    }
+
+    #[test]
+    fn test_loop_scope() {
+        do_check(
+            r"
+            fn quux() {
+                loop {
+                    let x = ();
+                    <|>
+                };
+            }",
+            &["x"],
+        );
+    }
+
+    #[test]
+    fn test_match() {
+        do_check(
+            r"
+            fn quux() {
+                match () {
+                    Some(x) => {
+                        <|>
+                    }
+                };
+            }",
+            &["x"],
+        );
+    }
+
+    #[test]
+    fn test_shadow_variable() {
+        do_check(
+            r"
+            fn foo(x: String) {
+                let x : &str = &x<|>;
+            }",
+            &["x"],
+        );
+    }
+
+    #[test]
+    fn test_bindings_after_at() {
+        do_check(
+            r"
+fn foo() {
+    match Some(()) {
+        opt @ Some(unit) => {
+            <|>
+        }
+        _ => {}
+    }
+}
+",
+            &["opt", "unit"],
+        );
+    }
+
+    #[test]
+    fn macro_inner_item() {
+        do_check(
+            r"
+            macro_rules! mac {
+                () => {{
+                    fn inner() {}
+                    inner();
+                }};
+            }
+
+            fn foo() {
+                mac!();
+                <|>
+            }
+        ",
+            &[],
+        );
+    }
+
+    #[test]
+    fn broken_inner_item() {
+        do_check(
+            r"
+            fn foo() {
+                trait {}
+                <|>
+            }
+        ",
+            &[],
+        );
+    }
+
+    fn do_check_local_name(ra_fixture: &str, expected_offset: u32) {
+        let (db, position) = TestDB::with_position(ra_fixture);
+        let file_id = position.file_id;
+        let offset = position.offset;
+
+        let file = db.parse(file_id).ok().unwrap();
+        let expected_name = find_node_at_offset::<ast::Name>(file.syntax(), expected_offset.into())
+            .expect("failed to find a name at the target offset");
+        let name_ref: ast::NameRef = find_node_at_offset(file.syntax(), offset).unwrap();
+
+        let function = find_function(&db, file_id);
+
+        let scopes = db.expr_scopes(function.into());
+        let (_body, source_map) = db.body_with_source_map(function.into());
+
+        let expr_scope = {
+            let expr_ast = name_ref.syntax().ancestors().find_map(ast::Expr::cast).unwrap();
+            let expr_id =
+                source_map.node_expr(InFile { file_id: file_id.into(), value: &expr_ast }).unwrap();
+            scopes.scope_for(expr_id).unwrap()
+        };
+
+        let resolved = scopes.resolve_name_in_scope(expr_scope, &name_ref.as_name()).unwrap();
+        let pat_src = source_map.pat_syntax(resolved.pat()).unwrap();
+
+        let local_name = pat_src.value.either(
+            |it| it.syntax_node_ptr().to_node(file.syntax()),
+            |it| it.syntax_node_ptr().to_node(file.syntax()),
+        );
+        assert_eq!(local_name.text_range(), expected_name.syntax().text_range());
+    }
+
+    #[test]
+    fn test_resolve_local_name() {
+        do_check_local_name(
+            r#"
+fn foo(x: i32, y: u32) {
+    {
+        let z = x * 2;
+    }
+    {
+        let t = x<|> * 3;
+    }
+}
+"#,
+            7,
+        );
+    }
+
+    #[test]
+    fn test_resolve_local_name_declaration() {
+        do_check_local_name(
+            r#"
+fn foo(x: String) {
+    let x : &str = &x<|>;
+}
+"#,
+            7,
+        );
+    }
+
+    #[test]
+    fn test_resolve_local_name_shadow() {
+        do_check_local_name(
+            r"
+fn foo(x: String) {
+    let x : &str = &x;
+    x<|>
+}
+",
+            28,
+        );
+    }
+
+    #[test]
+    fn ref_patterns_contribute_bindings() {
+        do_check_local_name(
+            r"
+fn foo() {
+    if let Some(&from) = bar() {
+        from<|>;
+    }
+}
+",
+            28,
+        );
+    }
+
+    #[test]
+    fn while_let_desugaring() {
+        mark::check!(infer_resolve_while_let);
+        do_check_local_name(
+            r#"
+fn test() {
+    let foo: Option<f32> = None;
+    while let Option::Some(spam) = foo {
+        spam<|>
+    }
+}
+"#,
+            75,
+        );
+    }
+}

crates/hir_def/src/data.rs

@@ -0,0 +1,278 @@
+//! Contains basic data about various HIR declarations.
+
+use std::sync::Arc;
+
+use hir_expand::{name::Name, InFile};
+use syntax::ast;
+
+use crate::{
+    attr::Attrs,
+    body::Expander,
+    db::DefDatabase,
+    item_tree::{AssocItem, ItemTreeId, ModItem},
+    type_ref::{TypeBound, TypeRef},
+    visibility::RawVisibility,
+    AssocContainerId, AssocItemId, ConstId, ConstLoc, FunctionId, FunctionLoc, HasModule, ImplId,
+    Intern, Lookup, ModuleId, StaticId, TraitId, TypeAliasId, TypeAliasLoc,
+};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FunctionData {
+    pub name: Name,
+    pub params: Vec<TypeRef>,
+    pub ret_type: TypeRef,
+    pub attrs: Attrs,
+    /// True if the first param is `self`. This is relevant to decide whether this
+    /// can be called as a method.
+    pub has_self_param: bool,
+    pub is_unsafe: bool,
+    pub is_varargs: bool,
+    pub visibility: RawVisibility,
+}
+
+impl FunctionData {
+    pub(crate) fn fn_data_query(db: &dyn DefDatabase, func: FunctionId) -> Arc<FunctionData> {
+        let loc = func.lookup(db);
+        let item_tree = db.item_tree(loc.id.file_id);
+        let func = &item_tree[loc.id.value];
+
+        Arc::new(FunctionData {
+            name: func.name.clone(),
+            params: func.params.to_vec(),
+            ret_type: func.ret_type.clone(),
+            attrs: item_tree.attrs(ModItem::from(loc.id.value).into()).clone(),
+            has_self_param: func.has_self_param,
+            is_unsafe: func.is_unsafe,
+            is_varargs: func.is_varargs,
+            visibility: item_tree[func.visibility].clone(),
+        })
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct TypeAliasData {
+    pub name: Name,
+    pub type_ref: Option<TypeRef>,
+    pub visibility: RawVisibility,
+    /// Bounds restricting the type alias itself (eg. `type Ty: Bound;` in a trait or impl).
+    pub bounds: Vec<TypeBound>,
+}
+
+impl TypeAliasData {
+    pub(crate) fn type_alias_data_query(
+        db: &dyn DefDatabase,
+        typ: TypeAliasId,
+    ) -> Arc<TypeAliasData> {
+        let loc = typ.lookup(db);
+        let item_tree = db.item_tree(loc.id.file_id);
+        let typ = &item_tree[loc.id.value];
+
+        Arc::new(TypeAliasData {
+            name: typ.name.clone(),
+            type_ref: typ.type_ref.clone(),
+            visibility: item_tree[typ.visibility].clone(),
+            bounds: typ.bounds.to_vec(),
+        })
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct TraitData {
+    pub name: Name,
+    pub items: Vec<(Name, AssocItemId)>,
+    pub auto: bool,
+}
+
+impl TraitData {
+    pub(crate) fn trait_data_query(db: &dyn DefDatabase, tr: TraitId) -> Arc<TraitData> {
+        let tr_loc = tr.lookup(db);
+        let item_tree = db.item_tree(tr_loc.id.file_id);
+        let tr_def = &item_tree[tr_loc.id.value];
+        let name = tr_def.name.clone();
+        let auto = tr_def.auto;
+        let module_id = tr_loc.container.module(db);
+        let container = AssocContainerId::TraitId(tr);
+        let mut expander = Expander::new(db, tr_loc.id.file_id, module_id);
+
+        let items = collect_items(
+            db,
+            module_id,
+            &mut expander,
+            tr_def.items.iter().copied(),
+            tr_loc.id.file_id,
+            container,
+            100,
+        );
+
+        Arc::new(TraitData { name, items, auto })
+    }
+
+    pub fn associated_types(&self) -> impl Iterator<Item = TypeAliasId> + '_ {
+        self.items.iter().filter_map(|(_name, item)| match item {
+            AssocItemId::TypeAliasId(t) => Some(*t),
+            _ => None,
+        })
+    }
+
+    pub fn associated_type_by_name(&self, name: &Name) -> Option<TypeAliasId> {
+        self.items.iter().find_map(|(item_name, item)| match item {
+            AssocItemId::TypeAliasId(t) if item_name == name => Some(*t),
+            _ => None,
+        })
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ImplData {
+    pub target_trait: Option<TypeRef>,
+    pub target_type: TypeRef,
+    pub items: Vec<AssocItemId>,
+    pub is_negative: bool,
+}
+
+impl ImplData {
+    pub(crate) fn impl_data_query(db: &dyn DefDatabase, id: ImplId) -> Arc<ImplData> {
+        let _p = profile::span("impl_data_query");
+        let impl_loc = id.lookup(db);
+
+        let item_tree = db.item_tree(impl_loc.id.file_id);
+        let impl_def = &item_tree[impl_loc.id.value];
+        let target_trait = impl_def.target_trait.clone();
+        let target_type = impl_def.target_type.clone();
+        let is_negative = impl_def.is_negative;
+        let module_id = impl_loc.container.module(db);
+        let container = AssocContainerId::ImplId(id);
+        let mut expander = Expander::new(db, impl_loc.id.file_id, module_id);
+
+        let items = collect_items(
+            db,
+            module_id,
+            &mut expander,
+            impl_def.items.iter().copied(),
+            impl_loc.id.file_id,
+            container,
+            100,
+        );
+        let items = items.into_iter().map(|(_, item)| item).collect();
+
+        Arc::new(ImplData { target_trait, target_type, items, is_negative })
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ConstData {
+    /// const _: () = ();
+    pub name: Option<Name>,
+    pub type_ref: TypeRef,
+    pub visibility: RawVisibility,
+}
+
+impl ConstData {
+    pub(crate) fn const_data_query(db: &dyn DefDatabase, konst: ConstId) -> Arc<ConstData> {
+        let loc = konst.lookup(db);
+        let item_tree = db.item_tree(loc.id.file_id);
+        let konst = &item_tree[loc.id.value];
+
+        Arc::new(ConstData {
+            name: konst.name.clone(),
+            type_ref: konst.type_ref.clone(),
+            visibility: item_tree[konst.visibility].clone(),
+        })
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct StaticData {
+    pub name: Option<Name>,
+    pub type_ref: TypeRef,
+    pub visibility: RawVisibility,
+    pub mutable: bool,
+}
+
+impl StaticData {
+    pub(crate) fn static_data_query(db: &dyn DefDatabase, konst: StaticId) -> Arc<StaticData> {
+        let node = konst.lookup(db);
+        let item_tree = db.item_tree(node.id.file_id);
+        let statik = &item_tree[node.id.value];
+
+        Arc::new(StaticData {
+            name: Some(statik.name.clone()),
+            type_ref: statik.type_ref.clone(),
+            visibility: item_tree[statik.visibility].clone(),
+            mutable: statik.mutable,
+        })
+    }
+}
+
+fn collect_items(
+    db: &dyn DefDatabase,
+    module: ModuleId,
+    expander: &mut Expander,
+    assoc_items: impl Iterator<Item = AssocItem>,
+    file_id: crate::HirFileId,
+    container: AssocContainerId,
+    limit: usize,
+) -> Vec<(Name, AssocItemId)> {
+    if limit == 0 {
+        return Vec::new();
+    }
+
+    let item_tree = db.item_tree(file_id);
+    let cfg_options = db.crate_graph()[module.krate].cfg_options.clone();
+
+    let mut items = Vec::new();
+    for item in assoc_items {
+        match item {
+            AssocItem::Function(id) => {
+                let item = &item_tree[id];
+                let attrs = item_tree.attrs(ModItem::from(id).into());
+                if !attrs.is_cfg_enabled(&cfg_options) {
+                    continue;
+                }
+                let def = FunctionLoc { container, id: ItemTreeId::new(file_id, id) }.intern(db);
+                items.push((item.name.clone(), def.into()));
+            }
+            // FIXME: cfg?
+            AssocItem::Const(id) => {
+                let item = &item_tree[id];
+                let name = match item.name.clone() {
+                    Some(name) => name,
+                    None => continue,
+                };
+                let def = ConstLoc { container, id: ItemTreeId::new(file_id, id) }.intern(db);
+                items.push((name, def.into()));
+            }
+            AssocItem::TypeAlias(id) => {
+                let item = &item_tree[id];
+                let def = TypeAliasLoc { container, id: ItemTreeId::new(file_id, id) }.intern(db);
+                items.push((item.name.clone(), def.into()));
+            }
+            AssocItem::MacroCall(call) => {
+                let call = &item_tree[call];
+                let ast_id_map = db.ast_id_map(file_id);
+                let root = db.parse_or_expand(file_id).unwrap();
+                let call = ast_id_map.get(call.ast_id).to_node(&root);
+
+                if let Some((mark, mac)) = expander.enter_expand(db, None, call) {
+                    let src: InFile<ast::MacroItems> = expander.to_source(mac);
+                    let item_tree = db.item_tree(src.file_id);
+                    let iter =
+                        item_tree.top_level_items().iter().filter_map(ModItem::as_assoc_item);
+                    items.extend(collect_items(
+                        db,
+                        module,
+                        expander,
+                        iter,
+                        src.file_id,
+                        container,
+                        limit - 1,
+                    ));
+
+                    expander.exit(db, mark);
+                }
+            }
+        }
+    }
+
+    items
+}

crates/hir_def/src/db.rs

@@ -0,0 +1,120 @@
+//! Defines database & queries for name resolution.
+use std::sync::Arc;
+
+use base_db::{salsa, CrateId, SourceDatabase, Upcast};
+use hir_expand::{db::AstDatabase, HirFileId};
+use syntax::SmolStr;
+
+use crate::{
+    adt::{EnumData, StructData},
+    attr::Attrs,
+    body::{scope::ExprScopes, Body, BodySourceMap},
+    data::{ConstData, FunctionData, ImplData, StaticData, TraitData, TypeAliasData},
+    docs::Documentation,
+    generics::GenericParams,
+    import_map::ImportMap,
+    item_tree::ItemTree,
+    lang_item::{LangItemTarget, LangItems},
+    nameres::CrateDefMap,
+    AttrDefId, ConstId, ConstLoc, DefWithBodyId, EnumId, EnumLoc, FunctionId, FunctionLoc,
+    GenericDefId, ImplId, ImplLoc, ModuleId, StaticId, StaticLoc, StructId, StructLoc, TraitId,
+    TraitLoc, TypeAliasId, TypeAliasLoc, UnionId, UnionLoc,
+};
+
+#[salsa::query_group(InternDatabaseStorage)]
+pub trait InternDatabase: SourceDatabase {
+    #[salsa::interned]
+    fn intern_function(&self, loc: FunctionLoc) -> FunctionId;
+    #[salsa::interned]
+    fn intern_struct(&self, loc: StructLoc) -> StructId;
+    #[salsa::interned]
+    fn intern_union(&self, loc: UnionLoc) -> UnionId;
+    #[salsa::interned]
+    fn intern_enum(&self, loc: EnumLoc) -> EnumId;
+    #[salsa::interned]
+    fn intern_const(&self, loc: ConstLoc) -> ConstId;
+    #[salsa::interned]
+    fn intern_static(&self, loc: StaticLoc) -> StaticId;
+    #[salsa::interned]
+    fn intern_trait(&self, loc: TraitLoc) -> TraitId;
+    #[salsa::interned]
+    fn intern_type_alias(&self, loc: TypeAliasLoc) -> TypeAliasId;
+    #[salsa::interned]
+    fn intern_impl(&self, loc: ImplLoc) -> ImplId;
+}
+
+#[salsa::query_group(DefDatabaseStorage)]
+pub trait DefDatabase: InternDatabase + AstDatabase + Upcast<dyn AstDatabase> {
+    #[salsa::invoke(ItemTree::item_tree_query)]
+    fn item_tree(&self, file_id: HirFileId) -> Arc<ItemTree>;
+
+    #[salsa::invoke(crate_def_map_wait)]
+    #[salsa::transparent]
+    fn crate_def_map(&self, krate: CrateId) -> Arc<CrateDefMap>;
+
+    #[salsa::invoke(CrateDefMap::crate_def_map_query)]
+    fn crate_def_map_query(&self, krate: CrateId) -> Arc<CrateDefMap>;
+
+    #[salsa::invoke(StructData::struct_data_query)]
+    fn struct_data(&self, id: StructId) -> Arc<StructData>;
+    #[salsa::invoke(StructData::union_data_query)]
+    fn union_data(&self, id: UnionId) -> Arc<StructData>;
+
+    #[salsa::invoke(EnumData::enum_data_query)]
+    fn enum_data(&self, e: EnumId) -> Arc<EnumData>;
+
+    #[salsa::invoke(ImplData::impl_data_query)]
+    fn impl_data(&self, e: ImplId) -> Arc<ImplData>;
+
+    #[salsa::invoke(TraitData::trait_data_query)]
+    fn trait_data(&self, e: TraitId) -> Arc<TraitData>;
+
+    #[salsa::invoke(TypeAliasData::type_alias_data_query)]
+    fn type_alias_data(&self, e: TypeAliasId) -> Arc<TypeAliasData>;
+
+    #[salsa::invoke(FunctionData::fn_data_query)]
+    fn function_data(&self, func: FunctionId) -> Arc<FunctionData>;
+
+    #[salsa::invoke(ConstData::const_data_query)]
+    fn const_data(&self, konst: ConstId) -> Arc<ConstData>;
+
+    #[salsa::invoke(StaticData::static_data_query)]
+    fn static_data(&self, konst: StaticId) -> Arc<StaticData>;
+
+    #[salsa::invoke(Body::body_with_source_map_query)]
+    fn body_with_source_map(&self, def: DefWithBodyId) -> (Arc<Body>, Arc<BodySourceMap>);
+
+    #[salsa::invoke(Body::body_query)]
+    fn body(&self, def: DefWithBodyId) -> Arc<Body>;
+
+    #[salsa::invoke(ExprScopes::expr_scopes_query)]
+    fn expr_scopes(&self, def: DefWithBodyId) -> Arc<ExprScopes>;
+
+    #[salsa::invoke(GenericParams::generic_params_query)]
+    fn generic_params(&self, def: GenericDefId) -> Arc<GenericParams>;
+
+    #[salsa::invoke(Attrs::attrs_query)]
+    fn attrs(&self, def: AttrDefId) -> Attrs;
+
+    #[salsa::invoke(LangItems::module_lang_items_query)]
+    fn module_lang_items(&self, module: ModuleId) -> Option<Arc<LangItems>>;
+
+    #[salsa::invoke(LangItems::crate_lang_items_query)]
+    fn crate_lang_items(&self, krate: CrateId) -> Arc<LangItems>;
+
+    #[salsa::invoke(LangItems::lang_item_query)]
+    fn lang_item(&self, start_crate: CrateId, item: SmolStr) -> Option<LangItemTarget>;
+
+    // FIXME(https://github.com/rust-analyzer/rust-analyzer/issues/2148#issuecomment-550519102)
+    // Remove this query completely, in favor of `Attrs::docs` method
+    #[salsa::invoke(Documentation::documentation_query)]
+    fn documentation(&self, def: AttrDefId) -> Option<Documentation>;
+
+    #[salsa::invoke(ImportMap::import_map_query)]
+    fn import_map(&self, krate: CrateId) -> Arc<ImportMap>;
+}
+
+fn crate_def_map_wait(db: &impl DefDatabase, krate: CrateId) -> Arc<CrateDefMap> {
+    let _p = profile::span("crate_def_map:wait");
+    db.crate_def_map_query(krate)
+}

crates/hir_def/src/diagnostics.rs

@@ -0,0 +1,30 @@
+//! Diagnostics produced by `hir_def`.
+
+use std::any::Any;
+
+use hir_expand::diagnostics::{Diagnostic, DiagnosticCode};
+use syntax::{ast, AstPtr, SyntaxNodePtr};
+
+use hir_expand::{HirFileId, InFile};
+
+#[derive(Debug)]
+pub struct UnresolvedModule {
+    pub file: HirFileId,
+    pub decl: AstPtr<ast::Module>,
+    pub candidate: String,
+}
+
+impl Diagnostic for UnresolvedModule {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("unresolved-module")
+    }
+    fn message(&self) -> String {
+        "unresolved module".to_string()
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file, self.decl.clone().into())
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}

crates/hir_def/src/docs.rs

@@ -0,0 +1,121 @@
+//! Defines hir documentation.
+//!
+//! This really shouldn't exist, instead, we should deshugar doc comments into attributes, see
+//! https://github.com/rust-analyzer/rust-analyzer/issues/2148#issuecomment-550519102
+
+use std::sync::Arc;
+
+use either::Either;
+use syntax::ast;
+
+use crate::{
+    db::DefDatabase,
+    src::{HasChildSource, HasSource},
+    AdtId, AttrDefId, Lookup,
+};
+
+/// Holds documentation
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Documentation(Arc<str>);
+
+impl Into<String> for Documentation {
+    fn into(self) -> String {
+        self.as_str().to_owned()
+    }
+}
+
+impl Documentation {
+    fn new(s: &str) -> Documentation {
+        Documentation(s.into())
+    }
+
+    pub fn from_ast<N>(node: &N) -> Option<Documentation>
+    where
+        N: ast::DocCommentsOwner + ast::AttrsOwner,
+    {
+        docs_from_ast(node)
+    }
+
+    pub fn as_str(&self) -> &str {
+        &*self.0
+    }
+
+    pub(crate) fn documentation_query(
+        db: &dyn DefDatabase,
+        def: AttrDefId,
+    ) -> Option<Documentation> {
+        match def {
+            AttrDefId::ModuleId(module) => {
+                let def_map = db.crate_def_map(module.krate);
+                let src = def_map[module.local_id].declaration_source(db)?;
+                docs_from_ast(&src.value)
+            }
+            AttrDefId::FieldId(it) => {
+                let src = it.parent.child_source(db);
+                match &src.value[it.local_id] {
+                    Either::Left(_tuple) => None,
+                    Either::Right(record) => docs_from_ast(record),
+                }
+            }
+            AttrDefId::AdtId(it) => match it {
+                AdtId::StructId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+                AdtId::EnumId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+                AdtId::UnionId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+            },
+            AttrDefId::EnumVariantId(it) => {
+                let src = it.parent.child_source(db);
+                docs_from_ast(&src.value[it.local_id])
+            }
+            AttrDefId::TraitId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+            AttrDefId::MacroDefId(it) => docs_from_ast(&it.ast_id?.to_node(db.upcast())),
+            AttrDefId::ConstId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+            AttrDefId::StaticId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+            AttrDefId::FunctionId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+            AttrDefId::TypeAliasId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+            AttrDefId::ImplId(_) => None,
+        }
+    }
+}
+
+pub(crate) fn docs_from_ast<N>(node: &N) -> Option<Documentation>
+where
+    N: ast::DocCommentsOwner + ast::AttrsOwner,
+{
+    let doc_comment_text = node.doc_comment_text();
+    let doc_attr_text = expand_doc_attrs(node);
+    let docs = merge_doc_comments_and_attrs(doc_comment_text, doc_attr_text);
+    docs.map(|it| Documentation::new(&it))
+}
+
+fn merge_doc_comments_and_attrs(
+    doc_comment_text: Option<String>,
+    doc_attr_text: Option<String>,
+) -> Option<String> {
+    match (doc_comment_text, doc_attr_text) {
+        (Some(mut comment_text), Some(attr_text)) => {
+            comment_text.push_str("\n\n");
+            comment_text.push_str(&attr_text);
+            Some(comment_text)
+        }
+        (Some(comment_text), None) => Some(comment_text),
+        (None, Some(attr_text)) => Some(attr_text),
+        (None, None) => None,
+    }
+}
+
+fn expand_doc_attrs(owner: &dyn ast::AttrsOwner) -> Option<String> {
+    let mut docs = String::new();
+    for attr in owner.attrs() {
+        if let Some(("doc", value)) =
+            attr.as_simple_key_value().as_ref().map(|(k, v)| (k.as_str(), v.as_str()))
+        {
+            docs.push_str(value);
+            docs.push_str("\n\n");
+        }
+    }
+    if docs.is_empty() {
+        None
+    } else {
+        Some(docs.trim_end_matches("\n\n").to_owned())
+    }
+}

crates/hir_def/src/expr.rs

@@ -0,0 +1,420 @@
+//! This module describes hir-level representation of expressions.
+//!
+//! This representaion is:
+//!
+//! 1. Identity-based. Each expression has an `id`, so we can distinguish
+//!    between different `1` in `1 + 1`.
+//! 2. Independent of syntax. Though syntactic provenance information can be
+//!    attached separately via id-based side map.
+//! 3. Unresolved. Paths are stored as sequences of names, and not as defs the
+//!    names refer to.
+//! 4. Desugared. There's no `if let`.
+//!
+//! See also a neighboring `body` module.
+
+use arena::{Idx, RawId};
+use hir_expand::name::Name;
+use syntax::ast::RangeOp;
+
+use crate::{
+    builtin_type::{BuiltinFloat, BuiltinInt},
+    path::{GenericArgs, Path},
+    type_ref::{Mutability, Rawness, TypeRef},
+};
+
+pub type ExprId = Idx<Expr>;
+pub(crate) fn dummy_expr_id() -> ExprId {
+    ExprId::from_raw(RawId::from(!0))
+}
+
+pub type PatId = Idx<Pat>;
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum Literal {
+    String(String),
+    ByteString(Vec<u8>),
+    Char(char),
+    Bool(bool),
+    Int(u64, Option<BuiltinInt>),
+    Float(u64, Option<BuiltinFloat>), // FIXME: f64 is not Eq
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum Expr {
+    /// This is produced if the syntax tree does not have a required expression piece.
+    Missing,
+    Path(Path),
+    If {
+        condition: ExprId,
+        then_branch: ExprId,
+        else_branch: Option<ExprId>,
+    },
+    Block {
+        statements: Vec<Statement>,
+        tail: Option<ExprId>,
+        label: Option<Name>,
+    },
+    Loop {
+        body: ExprId,
+        label: Option<Name>,
+    },
+    While {
+        condition: ExprId,
+        body: ExprId,
+        label: Option<Name>,
+    },
+    For {
+        iterable: ExprId,
+        pat: PatId,
+        body: ExprId,
+        label: Option<Name>,
+    },
+    Call {
+        callee: ExprId,
+        args: Vec<ExprId>,
+    },
+    MethodCall {
+        receiver: ExprId,
+        method_name: Name,
+        args: Vec<ExprId>,
+        generic_args: Option<GenericArgs>,
+    },
+    Match {
+        expr: ExprId,
+        arms: Vec<MatchArm>,
+    },
+    Continue {
+        label: Option<Name>,
+    },
+    Break {
+        expr: Option<ExprId>,
+        label: Option<Name>,
+    },
+    Return {
+        expr: Option<ExprId>,
+    },
+    RecordLit {
+        path: Option<Path>,
+        fields: Vec<RecordLitField>,
+        spread: Option<ExprId>,
+    },
+    Field {
+        expr: ExprId,
+        name: Name,
+    },
+    Await {
+        expr: ExprId,
+    },
+    Try {
+        expr: ExprId,
+    },
+    TryBlock {
+        body: ExprId,
+    },
+    Cast {
+        expr: ExprId,
+        type_ref: TypeRef,
+    },
+    Ref {
+        expr: ExprId,
+        rawness: Rawness,
+        mutability: Mutability,
+    },
+    Box {
+        expr: ExprId,
+    },
+    UnaryOp {
+        expr: ExprId,
+        op: UnaryOp,
+    },
+    BinaryOp {
+        lhs: ExprId,
+        rhs: ExprId,
+        op: Option<BinaryOp>,
+    },
+    Range {
+        lhs: Option<ExprId>,
+        rhs: Option<ExprId>,
+        range_type: RangeOp,
+    },
+    Index {
+        base: ExprId,
+        index: ExprId,
+    },
+    Lambda {
+        args: Vec<PatId>,
+        arg_types: Vec<Option<TypeRef>>,
+        ret_type: Option<TypeRef>,
+        body: ExprId,
+    },
+    Tuple {
+        exprs: Vec<ExprId>,
+    },
+    Unsafe {
+        body: ExprId,
+    },
+    Array(Array),
+    Literal(Literal),
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum BinaryOp {
+    LogicOp(LogicOp),
+    ArithOp(ArithOp),
+    CmpOp(CmpOp),
+    Assignment { op: Option<ArithOp> },
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum LogicOp {
+    And,
+    Or,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum CmpOp {
+    Eq { negated: bool },
+    Ord { ordering: Ordering, strict: bool },
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum Ordering {
+    Less,
+    Greater,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum ArithOp {
+    Add,
+    Mul,
+    Sub,
+    Div,
+    Rem,
+    Shl,
+    Shr,
+    BitXor,
+    BitOr,
+    BitAnd,
+}
+
+pub use syntax::ast::PrefixOp as UnaryOp;
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum Array {
+    ElementList(Vec<ExprId>),
+    Repeat { initializer: ExprId, repeat: ExprId },
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct MatchArm {
+    pub pat: PatId,
+    pub guard: Option<ExprId>,
+    pub expr: ExprId,
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct RecordLitField {
+    pub name: Name,
+    pub expr: ExprId,
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum Statement {
+    Let { pat: PatId, type_ref: Option<TypeRef>, initializer: Option<ExprId> },
+    Expr(ExprId),
+}
+
+impl Expr {
+    pub fn walk_child_exprs(&self, mut f: impl FnMut(ExprId)) {
+        match self {
+            Expr::Missing => {}
+            Expr::Path(_) => {}
+            Expr::If { condition, then_branch, else_branch } => {
+                f(*condition);
+                f(*then_branch);
+                if let Some(else_branch) = else_branch {
+                    f(*else_branch);
+                }
+            }
+            Expr::Block { statements, tail, .. } => {
+                for stmt in statements {
+                    match stmt {
+                        Statement::Let { initializer, .. } => {
+                            if let Some(expr) = initializer {
+                                f(*expr);
+                            }
+                        }
+                        Statement::Expr(e) => f(*e),
+                    }
+                }
+                if let Some(expr) = tail {
+                    f(*expr);
+                }
+            }
+            Expr::TryBlock { body } | Expr::Unsafe { body } => f(*body),
+            Expr::Loop { body, .. } => f(*body),
+            Expr::While { condition, body, .. } => {
+                f(*condition);
+                f(*body);
+            }
+            Expr::For { iterable, body, .. } => {
+                f(*iterable);
+                f(*body);
+            }
+            Expr::Call { callee, args } => {
+                f(*callee);
+                for arg in args {
+                    f(*arg);
+                }
+            }
+            Expr::MethodCall { receiver, args, .. } => {
+                f(*receiver);
+                for arg in args {
+                    f(*arg);
+                }
+            }
+            Expr::Match { expr, arms } => {
+                f(*expr);
+                for arm in arms {
+                    f(arm.expr);
+                }
+            }
+            Expr::Continue { .. } => {}
+            Expr::Break { expr, .. } | Expr::Return { expr } => {
+                if let Some(expr) = expr {
+                    f(*expr);
+                }
+            }
+            Expr::RecordLit { fields, spread, .. } => {
+                for field in fields {
+                    f(field.expr);
+                }
+                if let Some(expr) = spread {
+                    f(*expr);
+                }
+            }
+            Expr::Lambda { body, .. } => {
+                f(*body);
+            }
+            Expr::BinaryOp { lhs, rhs, .. } => {
+                f(*lhs);
+                f(*rhs);
+            }
+            Expr::Range { lhs, rhs, .. } => {
+                if let Some(lhs) = rhs {
+                    f(*lhs);
+                }
+                if let Some(rhs) = lhs {
+                    f(*rhs);
+                }
+            }
+            Expr::Index { base, index } => {
+                f(*base);
+                f(*index);
+            }
+            Expr::Field { expr, .. }
+            | Expr::Await { expr }
+            | Expr::Try { expr }
+            | Expr::Cast { expr, .. }
+            | Expr::Ref { expr, .. }
+            | Expr::UnaryOp { expr, .. }
+            | Expr::Box { expr } => {
+                f(*expr);
+            }
+            Expr::Tuple { exprs } => {
+                for expr in exprs {
+                    f(*expr);
+                }
+            }
+            Expr::Array(a) => match a {
+                Array::ElementList(exprs) => {
+                    for expr in exprs {
+                        f(*expr);
+                    }
+                }
+                Array::Repeat { initializer, repeat } => {
+                    f(*initializer);
+                    f(*repeat)
+                }
+            },
+            Expr::Literal(_) => {}
+        }
+    }
+}
+
+/// Explicit binding annotations given in the HIR for a binding. Note
+/// that this is not the final binding *mode* that we infer after type
+/// inference.
+#[derive(Clone, PartialEq, Eq, Debug, Copy)]
+pub enum BindingAnnotation {
+    /// No binding annotation given: this means that the final binding mode
+    /// will depend on whether we have skipped through a `&` reference
+    /// when matching. For example, the `x` in `Some(x)` will have binding
+    /// mode `None`; if you do `let Some(x) = &Some(22)`, it will
+    /// ultimately be inferred to be by-reference.
+    Unannotated,
+
+    /// Annotated with `mut x` -- could be either ref or not, similar to `None`.
+    Mutable,
+
+    /// Annotated as `ref`, like `ref x`
+    Ref,
+
+    /// Annotated as `ref mut x`.
+    RefMut,
+}
+
+impl BindingAnnotation {
+    pub fn new(is_mutable: bool, is_ref: bool) -> Self {
+        match (is_mutable, is_ref) {
+            (true, true) => BindingAnnotation::RefMut,
+            (false, true) => BindingAnnotation::Ref,
+            (true, false) => BindingAnnotation::Mutable,
+            (false, false) => BindingAnnotation::Unannotated,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct RecordFieldPat {
+    pub name: Name,
+    pub pat: PatId,
+}
+
+/// Close relative to rustc's hir::PatKind
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum Pat {
+    Missing,
+    Wild,
+    Tuple { args: Vec<PatId>, ellipsis: Option<usize> },
+    Or(Vec<PatId>),
+    Record { path: Option<Path>, args: Vec<RecordFieldPat>, ellipsis: bool },
+    Range { start: ExprId, end: ExprId },
+    Slice { prefix: Vec<PatId>, slice: Option<PatId>, suffix: Vec<PatId> },
+    Path(Path),
+    Lit(ExprId),
+    Bind { mode: BindingAnnotation, name: Name, subpat: Option<PatId> },
+    TupleStruct { path: Option<Path>, args: Vec<PatId>, ellipsis: Option<usize> },
+    Ref { pat: PatId, mutability: Mutability },
+}
+
+impl Pat {
+    pub fn walk_child_pats(&self, mut f: impl FnMut(PatId)) {
+        match self {
+            Pat::Range { .. } | Pat::Lit(..) | Pat::Path(..) | Pat::Wild | Pat::Missing => {}
+            Pat::Bind { subpat, .. } => {
+                subpat.iter().copied().for_each(f);
+            }
+            Pat::Or(args) | Pat::Tuple { args, .. } | Pat::TupleStruct { args, .. } => {
+                args.iter().copied().for_each(f);
+            }
+            Pat::Ref { pat, .. } => f(*pat),
+            Pat::Slice { prefix, slice, suffix } => {
+                let total_iter = prefix.iter().chain(slice.iter()).chain(suffix.iter());
+                total_iter.copied().for_each(f);
+            }
+            Pat::Record { args, .. } => {
+                args.iter().map(|f| f.pat).for_each(f);
+            }
+        }
+    }
+}

crates/hir_def/src/find_path.rs

@@ -0,0 +1,687 @@
+//! An algorithm to find a path to refer to a certain item.
+
+use hir_expand::name::{known, AsName, Name};
+use rustc_hash::FxHashSet;
+use test_utils::mark;
+
+use crate::{
+    db::DefDatabase,
+    item_scope::ItemInNs,
+    path::{ModPath, PathKind},
+    visibility::Visibility,
+    ModuleDefId, ModuleId,
+};
+
+// FIXME: handle local items
+
+/// Find a path that can be used to refer to a certain item. This can depend on
+/// *from where* you're referring to the item, hence the `from` parameter.
+pub fn find_path(db: &dyn DefDatabase, item: ItemInNs, from: ModuleId) -> Option<ModPath> {
+    let _p = profile::span("find_path");
+    find_path_inner(db, item, from, MAX_PATH_LEN)
+}
+
+const MAX_PATH_LEN: usize = 15;
+
+impl ModPath {
+    fn starts_with_std(&self) -> bool {
+        self.segments.first() == Some(&known::std)
+    }
+
+    // When std library is present, paths starting with `std::`
+    // should be preferred over paths starting with `core::` and `alloc::`
+    fn can_start_with_std(&self) -> bool {
+        let first_segment = self.segments.first();
+        first_segment == Some(&known::alloc) || first_segment == Some(&known::core)
+    }
+}
+
+fn find_path_inner(
+    db: &dyn DefDatabase,
+    item: ItemInNs,
+    from: ModuleId,
+    max_len: usize,
+) -> Option<ModPath> {
+    if max_len == 0 {
+        return None;
+    }
+
+    // Base cases:
+
+    // - if the item is already in scope, return the name under which it is
+    let def_map = db.crate_def_map(from.krate);
+    let from_scope: &crate::item_scope::ItemScope = &def_map.modules[from.local_id].scope;
+    if let Some((name, _)) = from_scope.name_of(item) {
+        return Some(ModPath::from_segments(PathKind::Plain, vec![name.clone()]));
+    }
+
+    // - if the item is the crate root, return `crate`
+    if item
+        == ItemInNs::Types(ModuleDefId::ModuleId(ModuleId {
+            krate: from.krate,
+            local_id: def_map.root,
+        }))
+    {
+        return Some(ModPath::from_segments(PathKind::Crate, Vec::new()));
+    }
+
+    // - if the item is the module we're in, use `self`
+    if item == ItemInNs::Types(from.into()) {
+        return Some(ModPath::from_segments(PathKind::Super(0), Vec::new()));
+    }
+
+    // - if the item is the parent module, use `super` (this is not used recursively, since `super::super` is ugly)
+    if let Some(parent_id) = def_map.modules[from.local_id].parent {
+        if item
+            == ItemInNs::Types(ModuleDefId::ModuleId(ModuleId {
+                krate: from.krate,
+                local_id: parent_id,
+            }))
+        {
+            return Some(ModPath::from_segments(PathKind::Super(1), Vec::new()));
+        }
+    }
+
+    // - if the item is the crate root of a dependency crate, return the name from the extern prelude
+    for (name, def_id) in &def_map.extern_prelude {
+        if item == ItemInNs::Types(*def_id) {
+            return Some(ModPath::from_segments(PathKind::Plain, vec![name.clone()]));
+        }
+    }
+
+    // - if the item is in the prelude, return the name from there
+    if let Some(prelude_module) = def_map.prelude {
+        let prelude_def_map = db.crate_def_map(prelude_module.krate);
+        let prelude_scope: &crate::item_scope::ItemScope =
+            &prelude_def_map.modules[prelude_module.local_id].scope;
+        if let Some((name, vis)) = prelude_scope.name_of(item) {
+            if vis.is_visible_from(db, from) {
+                return Some(ModPath::from_segments(PathKind::Plain, vec![name.clone()]));
+            }
+        }
+    }
+
+    // - if the item is a builtin, it's in scope
+    if let ItemInNs::Types(ModuleDefId::BuiltinType(builtin)) = item {
+        return Some(ModPath::from_segments(PathKind::Plain, vec![builtin.as_name()]));
+    }
+
+    // Recursive case:
+    // - if the item is an enum variant, refer to it via the enum
+    if let Some(ModuleDefId::EnumVariantId(variant)) = item.as_module_def_id() {
+        if let Some(mut path) = find_path(db, ItemInNs::Types(variant.parent.into()), from) {
+            let data = db.enum_data(variant.parent);
+            path.segments.push(data.variants[variant.local_id].name.clone());
+            return Some(path);
+        }
+        // If this doesn't work, it seems we have no way of referring to the
+        // enum; that's very weird, but there might still be a reexport of the
+        // variant somewhere
+    }
+
+    // - otherwise, look for modules containing (reexporting) it and import it from one of those
+
+    let crate_root = ModuleId { local_id: def_map.root, krate: from.krate };
+    let crate_attrs = db.attrs(crate_root.into());
+    let prefer_no_std = crate_attrs.by_key("no_std").exists();
+    let mut best_path = None;
+    let mut best_path_len = max_len;
+
+    if item.krate(db) == Some(from.krate) {
+        // Item was defined in the same crate that wants to import it. It cannot be found in any
+        // dependency in this case.
+
+        let local_imports = find_local_import_locations(db, item, from);
+        for (module_id, name) in local_imports {
+            if let Some(mut path) = find_path_inner(
+                db,
+                ItemInNs::Types(ModuleDefId::ModuleId(module_id)),
+                from,
+                best_path_len - 1,
+            ) {
+                path.segments.push(name);
+
+                let new_path = if let Some(best_path) = best_path {
+                    select_best_path(best_path, path, prefer_no_std)
+                } else {
+                    path
+                };
+                best_path_len = new_path.len();
+                best_path = Some(new_path);
+            }
+        }
+    } else {
+        // Item was defined in some upstream crate. This means that it must be exported from one,
+        // too (unless we can't name it at all). It could *also* be (re)exported by the same crate
+        // that wants to import it here, but we always prefer to use the external path here.
+
+        let crate_graph = db.crate_graph();
+        let extern_paths = crate_graph[from.krate].dependencies.iter().filter_map(|dep| {
+            let import_map = db.import_map(dep.crate_id);
+            import_map.import_info_for(item).and_then(|info| {
+                // Determine best path for containing module and append last segment from `info`.
+                let mut path = find_path_inner(
+                    db,
+                    ItemInNs::Types(ModuleDefId::ModuleId(info.container)),
+                    from,
+                    best_path_len - 1,
+                )?;
+                path.segments.push(info.path.segments.last().unwrap().clone());
+                Some(path)
+            })
+        });
+
+        for path in extern_paths {
+            let new_path = if let Some(best_path) = best_path {
+                select_best_path(best_path, path, prefer_no_std)
+            } else {
+                path
+            };
+            best_path = Some(new_path);
+        }
+    }
+
+    best_path
+}
+
+fn select_best_path(old_path: ModPath, new_path: ModPath, prefer_no_std: bool) -> ModPath {
+    if old_path.starts_with_std() && new_path.can_start_with_std() {
+        if prefer_no_std {
+            mark::hit!(prefer_no_std_paths);
+            new_path
+        } else {
+            mark::hit!(prefer_std_paths);
+            old_path
+        }
+    } else if new_path.starts_with_std() && old_path.can_start_with_std() {
+        if prefer_no_std {
+            mark::hit!(prefer_no_std_paths);
+            old_path
+        } else {
+            mark::hit!(prefer_std_paths);
+            new_path
+        }
+    } else if new_path.len() < old_path.len() {
+        new_path
+    } else {
+        old_path
+    }
+}
+
+/// Finds locations in `from.krate` from which `item` can be imported by `from`.
+fn find_local_import_locations(
+    db: &dyn DefDatabase,
+    item: ItemInNs,
+    from: ModuleId,
+) -> Vec<(ModuleId, Name)> {
+    let _p = profile::span("find_local_import_locations");
+
+    // `from` can import anything below `from` with visibility of at least `from`, and anything
+    // above `from` with any visibility. That means we do not need to descend into private siblings
+    // of `from` (and similar).
+
+    let def_map = db.crate_def_map(from.krate);
+
+    // Compute the initial worklist. We start with all direct child modules of `from` as well as all
+    // of its (recursive) parent modules.
+    let data = &def_map.modules[from.local_id];
+    let mut worklist = data
+        .children
+        .values()
+        .map(|child| ModuleId { krate: from.krate, local_id: *child })
+        .collect::<Vec<_>>();
+    let mut parent = data.parent;
+    while let Some(p) = parent {
+        worklist.push(ModuleId { krate: from.krate, local_id: p });
+        parent = def_map.modules[p].parent;
+    }
+
+    let mut seen: FxHashSet<_> = FxHashSet::default();
+
+    let mut locations = Vec::new();
+    while let Some(module) = worklist.pop() {
+        if !seen.insert(module) {
+            continue; // already processed this module
+        }
+
+        let ext_def_map;
+        let data = if module.krate == from.krate {
+            &def_map[module.local_id]
+        } else {
+            // The crate might reexport a module defined in another crate.
+            ext_def_map = db.crate_def_map(module.krate);
+            &ext_def_map[module.local_id]
+        };
+
+        if let Some((name, vis)) = data.scope.name_of(item) {
+            if vis.is_visible_from(db, from) {
+                let is_private = if let Visibility::Module(private_to) = vis {
+                    private_to.local_id == module.local_id
+                } else {
+                    false
+                };
+                let is_original_def = if let Some(module_def_id) = item.as_module_def_id() {
+                    data.scope.declarations().any(|it| it == module_def_id)
+                } else {
+                    false
+                };
+
+                // Ignore private imports. these could be used if we are
+                // in a submodule of this module, but that's usually not
+                // what the user wants; and if this module can import
+                // the item and we're a submodule of it, so can we.
+                // Also this keeps the cached data smaller.
+                if !is_private || is_original_def {
+                    locations.push((module, name.clone()));
+                }
+            }
+        }
+
+        // Descend into all modules visible from `from`.
+        for (_, per_ns) in data.scope.entries() {
+            if let Some((ModuleDefId::ModuleId(module), vis)) = per_ns.take_types_vis() {
+                if vis.is_visible_from(db, from) {
+                    worklist.push(module);
+                }
+            }
+        }
+    }
+
+    locations
+}
+
+#[cfg(test)]
+mod tests {
+    use base_db::fixture::WithFixture;
+    use hir_expand::hygiene::Hygiene;
+    use syntax::ast::AstNode;
+    use test_utils::mark;
+
+    use crate::test_db::TestDB;
+
+    use super::*;
+
+    /// `code` needs to contain a cursor marker; checks that `find_path` for the
+    /// item the `path` refers to returns that same path when called from the
+    /// module the cursor is in.
+    fn check_found_path(ra_fixture: &str, path: &str) {
+        let (db, pos) = TestDB::with_position(ra_fixture);
+        let module = db.module_for_file(pos.file_id);
+        let parsed_path_file = syntax::SourceFile::parse(&format!("use {};", path));
+        let ast_path =
+            parsed_path_file.syntax_node().descendants().find_map(syntax::ast::Path::cast).unwrap();
+        let mod_path = ModPath::from_src(ast_path, &Hygiene::new_unhygienic()).unwrap();
+
+        let crate_def_map = db.crate_def_map(module.krate);
+        let resolved = crate_def_map
+            .resolve_path(
+                &db,
+                module.local_id,
+                &mod_path,
+                crate::item_scope::BuiltinShadowMode::Module,
+            )
+            .0
+            .take_types()
+            .unwrap();
+
+        let found_path = find_path(&db, ItemInNs::Types(resolved), module);
+
+        assert_eq!(found_path, Some(mod_path));
+    }
+
+    #[test]
+    fn same_module() {
+        let code = r#"
+            //- /main.rs
+            struct S;
+            <|>
+        "#;
+        check_found_path(code, "S");
+    }
+
+    #[test]
+    fn enum_variant() {
+        let code = r#"
+            //- /main.rs
+            enum E { A }
+            <|>
+        "#;
+        check_found_path(code, "E::A");
+    }
+
+    #[test]
+    fn sub_module() {
+        let code = r#"
+            //- /main.rs
+            mod foo {
+                pub struct S;
+            }
+            <|>
+        "#;
+        check_found_path(code, "foo::S");
+    }
+
+    #[test]
+    fn super_module() {
+        let code = r#"
+            //- /main.rs
+            mod foo;
+            //- /foo.rs
+            mod bar;
+            struct S;
+            //- /foo/bar.rs
+            <|>
+        "#;
+        check_found_path(code, "super::S");
+    }
+
+    #[test]
+    fn self_module() {
+        let code = r#"
+            //- /main.rs
+            mod foo;
+            //- /foo.rs
+            <|>
+        "#;
+        check_found_path(code, "self");
+    }
+
+    #[test]
+    fn crate_root() {
+        let code = r#"
+            //- /main.rs
+            mod foo;
+            //- /foo.rs
+            <|>
+        "#;
+        check_found_path(code, "crate");
+    }
+
+    #[test]
+    fn same_crate() {
+        let code = r#"
+            //- /main.rs
+            mod foo;
+            struct S;
+            //- /foo.rs
+            <|>
+        "#;
+        check_found_path(code, "crate::S");
+    }
+
+    #[test]
+    fn different_crate() {
+        let code = r#"
+            //- /main.rs crate:main deps:std
+            <|>
+            //- /std.rs crate:std
+            pub struct S;
+        "#;
+        check_found_path(code, "std::S");
+    }
+
+    #[test]
+    fn different_crate_renamed() {
+        let code = r#"
+            //- /main.rs crate:main deps:std
+            extern crate std as std_renamed;
+            <|>
+            //- /std.rs crate:std
+            pub struct S;
+        "#;
+        check_found_path(code, "std_renamed::S");
+    }
+
+    #[test]
+    fn partially_imported() {
+        // Tests that short paths are used even for external items, when parts of the path are
+        // already in scope.
+        check_found_path(
+            r#"
+            //- /main.rs crate:main deps:syntax
+
+            use syntax::ast;
+            <|>
+
+            //- /lib.rs crate:syntax
+            pub mod ast {
+                pub enum ModuleItem {
+                    A, B, C,
+                }
+            }
+        "#,
+            "ast::ModuleItem",
+        );
+
+        check_found_path(
+            r#"
+            //- /main.rs crate:main deps:syntax
+
+            <|>
+
+            //- /lib.rs crate:syntax
+            pub mod ast {
+                pub enum ModuleItem {
+                    A, B, C,
+                }
+            }
+        "#,
+            "syntax::ast::ModuleItem",
+        );
+    }
+
+    #[test]
+    fn same_crate_reexport() {
+        let code = r#"
+            //- /main.rs
+            mod bar {
+                mod foo { pub(super) struct S; }
+                pub(crate) use foo::*;
+            }
+            <|>
+        "#;
+        check_found_path(code, "bar::S");
+    }
+
+    #[test]
+    fn same_crate_reexport_rename() {
+        let code = r#"
+            //- /main.rs
+            mod bar {
+                mod foo { pub(super) struct S; }
+                pub(crate) use foo::S as U;
+            }
+            <|>
+        "#;
+        check_found_path(code, "bar::U");
+    }
+
+    #[test]
+    fn different_crate_reexport() {
+        let code = r#"
+            //- /main.rs crate:main deps:std
+            <|>
+            //- /std.rs crate:std deps:core
+            pub use core::S;
+            //- /core.rs crate:core
+            pub struct S;
+        "#;
+        check_found_path(code, "std::S");
+    }
+
+    #[test]
+    fn prelude() {
+        let code = r#"
+            //- /main.rs crate:main deps:std
+            <|>
+            //- /std.rs crate:std
+            pub mod prelude { pub struct S; }
+            #[prelude_import]
+            pub use prelude::*;
+        "#;
+        check_found_path(code, "S");
+    }
+
+    #[test]
+    fn enum_variant_from_prelude() {
+        let code = r#"
+            //- /main.rs crate:main deps:std
+            <|>
+            //- /std.rs crate:std
+            pub mod prelude {
+                pub enum Option<T> { Some(T), None }
+                pub use Option::*;
+            }
+            #[prelude_import]
+            pub use prelude::*;
+        "#;
+        check_found_path(code, "None");
+        check_found_path(code, "Some");
+    }
+
+    #[test]
+    fn shortest_path() {
+        let code = r#"
+            //- /main.rs
+            pub mod foo;
+            pub mod baz;
+            struct S;
+            <|>
+            //- /foo.rs
+            pub mod bar { pub struct S; }
+            //- /baz.rs
+            pub use crate::foo::bar::S;
+        "#;
+        check_found_path(code, "baz::S");
+    }
+
+    #[test]
+    fn discount_private_imports() {
+        let code = r#"
+            //- /main.rs
+            mod foo;
+            pub mod bar { pub struct S; }
+            use bar::S;
+            //- /foo.rs
+            <|>
+        "#;
+        // crate::S would be shorter, but using private imports seems wrong
+        check_found_path(code, "crate::bar::S");
+    }
+
+    #[test]
+    fn import_cycle() {
+        let code = r#"
+            //- /main.rs
+            pub mod foo;
+            pub mod bar;
+            pub mod baz;
+            //- /bar.rs
+            <|>
+            //- /foo.rs
+            pub use super::baz;
+            pub struct S;
+            //- /baz.rs
+            pub use super::foo;
+        "#;
+        check_found_path(code, "crate::foo::S");
+    }
+
+    #[test]
+    fn prefer_std_paths_over_alloc() {
+        mark::check!(prefer_std_paths);
+        let code = r#"
+        //- /main.rs crate:main deps:alloc,std
+        <|>
+
+        //- /std.rs crate:std deps:alloc
+        pub mod sync {
+            pub use alloc::sync::Arc;
+        }
+
+        //- /zzz.rs crate:alloc
+        pub mod sync {
+            pub struct Arc;
+        }
+        "#;
+        check_found_path(code, "std::sync::Arc");
+    }
+
+    #[test]
+    fn prefer_core_paths_over_std() {
+        mark::check!(prefer_no_std_paths);
+        let code = r#"
+        //- /main.rs crate:main deps:core,std
+        #![no_std]
+
+        <|>
+
+        //- /std.rs crate:std deps:core
+
+        pub mod fmt {
+            pub use core::fmt::Error;
+        }
+
+        //- /zzz.rs crate:core
+
+        pub mod fmt {
+            pub struct Error;
+        }
+        "#;
+        check_found_path(code, "core::fmt::Error");
+    }
+
+    #[test]
+    fn prefer_alloc_paths_over_std() {
+        let code = r#"
+        //- /main.rs crate:main deps:alloc,std
+        #![no_std]
+
+        <|>
+
+        //- /std.rs crate:std deps:alloc
+
+        pub mod sync {
+            pub use alloc::sync::Arc;
+        }
+
+        //- /zzz.rs crate:alloc
+
+        pub mod sync {
+            pub struct Arc;
+        }
+        "#;
+        check_found_path(code, "alloc::sync::Arc");
+    }
+
+    #[test]
+    fn prefer_shorter_paths_if_not_alloc() {
+        let code = r#"
+        //- /main.rs crate:main deps:megaalloc,std
+        <|>
+
+        //- /std.rs crate:std deps:megaalloc
+        pub mod sync {
+            pub use megaalloc::sync::Arc;
+        }
+
+        //- /zzz.rs crate:megaalloc
+        pub struct Arc;
+        "#;
+        check_found_path(code, "megaalloc::Arc");
+    }
+
+    #[test]
+    fn builtins_are_in_scope() {
+        let code = r#"
+        //- /main.rs
+        <|>
+
+        pub mod primitive {
+            pub use u8;
+        }
+        "#;
+        check_found_path(code, "u8");
+        check_found_path(code, "u16");
+    }
+}

crates/hir_def/src/generics.rs

@@ -0,0 +1,339 @@
+//! Many kinds of items or constructs can have generic parameters: functions,
+//! structs, impls, traits, etc. This module provides a common HIR for these
+//! generic parameters. See also the `Generics` type and the `generics_of` query
+//! in rustc.
+use std::sync::Arc;
+
+use arena::{map::ArenaMap, Arena};
+use base_db::FileId;
+use either::Either;
+use hir_expand::{
+    name::{name, AsName, Name},
+    InFile,
+};
+use syntax::ast::{self, GenericParamsOwner, NameOwner, TypeBoundsOwner};
+
+use crate::{
+    body::LowerCtx,
+    child_by_source::ChildBySource,
+    db::DefDatabase,
+    dyn_map::DynMap,
+    keys,
+    src::HasChildSource,
+    src::HasSource,
+    type_ref::{TypeBound, TypeRef},
+    AdtId, GenericDefId, LocalTypeParamId, Lookup, TypeParamId,
+};
+
+/// Data about a generic parameter (to a function, struct, impl, ...).
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct TypeParamData {
+    pub name: Option<Name>,
+    pub default: Option<TypeRef>,
+    pub provenance: TypeParamProvenance,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum TypeParamProvenance {
+    TypeParamList,
+    TraitSelf,
+    ArgumentImplTrait,
+}
+
+/// Data about the generic parameters of a function, struct, impl, etc.
+#[derive(Clone, PartialEq, Eq, Debug, Default)]
+pub struct GenericParams {
+    pub types: Arena<TypeParamData>,
+    // lifetimes: Arena<LocalLifetimeParamId, LifetimeParamData>,
+    pub where_predicates: Vec<WherePredicate>,
+}
+
+/// A single predicate from a where clause, i.e. `where Type: Trait`. Combined
+/// where clauses like `where T: Foo + Bar` are turned into multiple of these.
+/// It might still result in multiple actual predicates though, because of
+/// associated type bindings like `Iterator<Item = u32>`.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct WherePredicate {
+    pub target: WherePredicateTarget,
+    pub bound: TypeBound,
+}
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub enum WherePredicateTarget {
+    TypeRef(TypeRef),
+    /// For desugared where predicates that can directly refer to a type param.
+    TypeParam(LocalTypeParamId),
+}
+
+type SourceMap = ArenaMap<LocalTypeParamId, Either<ast::Trait, ast::TypeParam>>;
+
+impl GenericParams {
+    pub(crate) fn generic_params_query(
+        db: &dyn DefDatabase,
+        def: GenericDefId,
+    ) -> Arc<GenericParams> {
+        let _p = profile::span("generic_params_query");
+
+        let generics = match def {
+            GenericDefId::FunctionId(id) => {
+                let id = id.lookup(db).id;
+                let tree = db.item_tree(id.file_id);
+                let item = &tree[id.value];
+                tree[item.generic_params].clone()
+            }
+            GenericDefId::AdtId(AdtId::StructId(id)) => {
+                let id = id.lookup(db).id;
+                let tree = db.item_tree(id.file_id);
+                let item = &tree[id.value];
+                tree[item.generic_params].clone()
+            }
+            GenericDefId::AdtId(AdtId::EnumId(id)) => {
+                let id = id.lookup(db).id;
+                let tree = db.item_tree(id.file_id);
+                let item = &tree[id.value];
+                tree[item.generic_params].clone()
+            }
+            GenericDefId::AdtId(AdtId::UnionId(id)) => {
+                let id = id.lookup(db).id;
+                let tree = db.item_tree(id.file_id);
+                let item = &tree[id.value];
+                tree[item.generic_params].clone()
+            }
+            GenericDefId::TraitId(id) => {
+                let id = id.lookup(db).id;
+                let tree = db.item_tree(id.file_id);
+                let item = &tree[id.value];
+                tree[item.generic_params].clone()
+            }
+            GenericDefId::TypeAliasId(id) => {
+                let id = id.lookup(db).id;
+                let tree = db.item_tree(id.file_id);
+                let item = &tree[id.value];
+                tree[item.generic_params].clone()
+            }
+            GenericDefId::ImplId(id) => {
+                let id = id.lookup(db).id;
+                let tree = db.item_tree(id.file_id);
+                let item = &tree[id.value];
+                tree[item.generic_params].clone()
+            }
+            GenericDefId::EnumVariantId(_) | GenericDefId::ConstId(_) => GenericParams::default(),
+        };
+        Arc::new(generics)
+    }
+
+    fn new(db: &dyn DefDatabase, def: GenericDefId) -> (GenericParams, InFile<SourceMap>) {
+        let mut generics = GenericParams { types: Arena::default(), where_predicates: Vec::new() };
+        let mut sm = ArenaMap::default();
+
+        // FIXME: add `: Sized` bound for everything except for `Self` in traits
+        let file_id = match def {
+            GenericDefId::FunctionId(it) => {
+                let src = it.lookup(db).source(db);
+                let lower_ctx = LowerCtx::new(db, src.file_id);
+                generics.fill(&lower_ctx, &mut sm, &src.value);
+                // lower `impl Trait` in arguments
+                let data = db.function_data(it);
+                for param in &data.params {
+                    generics.fill_implicit_impl_trait_args(param);
+                }
+                src.file_id
+            }
+            GenericDefId::AdtId(AdtId::StructId(it)) => {
+                let src = it.lookup(db).source(db);
+                let lower_ctx = LowerCtx::new(db, src.file_id);
+                generics.fill(&lower_ctx, &mut sm, &src.value);
+                src.file_id
+            }
+            GenericDefId::AdtId(AdtId::UnionId(it)) => {
+                let src = it.lookup(db).source(db);
+                let lower_ctx = LowerCtx::new(db, src.file_id);
+                generics.fill(&lower_ctx, &mut sm, &src.value);
+                src.file_id
+            }
+            GenericDefId::AdtId(AdtId::EnumId(it)) => {
+                let src = it.lookup(db).source(db);
+                let lower_ctx = LowerCtx::new(db, src.file_id);
+                generics.fill(&lower_ctx, &mut sm, &src.value);
+                src.file_id
+            }
+            GenericDefId::TraitId(it) => {
+                let src = it.lookup(db).source(db);
+                let lower_ctx = LowerCtx::new(db, src.file_id);
+
+                // traits get the Self type as an implicit first type parameter
+                let self_param_id = generics.types.alloc(TypeParamData {
+                    name: Some(name![Self]),
+                    default: None,
+                    provenance: TypeParamProvenance::TraitSelf,
+                });
+                sm.insert(self_param_id, Either::Left(src.value.clone()));
+                // add super traits as bounds on Self
+                // i.e., trait Foo: Bar is equivalent to trait Foo where Self: Bar
+                let self_param = TypeRef::Path(name![Self].into());
+                generics.fill_bounds(&lower_ctx, &src.value, self_param);
+
+                generics.fill(&lower_ctx, &mut sm, &src.value);
+                src.file_id
+            }
+            GenericDefId::TypeAliasId(it) => {
+                let src = it.lookup(db).source(db);
+                let lower_ctx = LowerCtx::new(db, src.file_id);
+
+                generics.fill(&lower_ctx, &mut sm, &src.value);
+                src.file_id
+            }
+            // Note that we don't add `Self` here: in `impl`s, `Self` is not a
+            // type-parameter, but rather is a type-alias for impl's target
+            // type, so this is handled by the resolver.
+            GenericDefId::ImplId(it) => {
+                let src = it.lookup(db).source(db);
+                let lower_ctx = LowerCtx::new(db, src.file_id);
+
+                generics.fill(&lower_ctx, &mut sm, &src.value);
+                src.file_id
+            }
+            // We won't be using this ID anyway
+            GenericDefId::EnumVariantId(_) | GenericDefId::ConstId(_) => FileId(!0).into(),
+        };
+
+        (generics, InFile::new(file_id, sm))
+    }
+
+    pub(crate) fn fill(
+        &mut self,
+        lower_ctx: &LowerCtx,
+        sm: &mut SourceMap,
+        node: &dyn GenericParamsOwner,
+    ) {
+        if let Some(params) = node.generic_param_list() {
+            self.fill_params(lower_ctx, sm, params)
+        }
+        if let Some(where_clause) = node.where_clause() {
+            self.fill_where_predicates(lower_ctx, where_clause);
+        }
+    }
+
+    pub(crate) fn fill_bounds(
+        &mut self,
+        lower_ctx: &LowerCtx,
+        node: &dyn ast::TypeBoundsOwner,
+        type_ref: TypeRef,
+    ) {
+        for bound in
+            node.type_bound_list().iter().flat_map(|type_bound_list| type_bound_list.bounds())
+        {
+            self.add_where_predicate_from_bound(lower_ctx, bound, type_ref.clone());
+        }
+    }
+
+    fn fill_params(
+        &mut self,
+        lower_ctx: &LowerCtx,
+        sm: &mut SourceMap,
+        params: ast::GenericParamList,
+    ) {
+        for type_param in params.type_params() {
+            let name = type_param.name().map_or_else(Name::missing, |it| it.as_name());
+            // FIXME: Use `Path::from_src`
+            let default = type_param.default_type().map(|it| TypeRef::from_ast(lower_ctx, it));
+            let param = TypeParamData {
+                name: Some(name.clone()),
+                default,
+                provenance: TypeParamProvenance::TypeParamList,
+            };
+            let param_id = self.types.alloc(param);
+            sm.insert(param_id, Either::Right(type_param.clone()));
+
+            let type_ref = TypeRef::Path(name.into());
+            self.fill_bounds(&lower_ctx, &type_param, type_ref);
+        }
+    }
+
+    fn fill_where_predicates(&mut self, lower_ctx: &LowerCtx, where_clause: ast::WhereClause) {
+        for pred in where_clause.predicates() {
+            let type_ref = match pred.ty() {
+                Some(type_ref) => type_ref,
+                None => continue,
+            };
+            let type_ref = TypeRef::from_ast(lower_ctx, type_ref);
+            for bound in pred.type_bound_list().iter().flat_map(|l| l.bounds()) {
+                self.add_where_predicate_from_bound(lower_ctx, bound, type_ref.clone());
+            }
+        }
+    }
+
+    fn add_where_predicate_from_bound(
+        &mut self,
+        lower_ctx: &LowerCtx,
+        bound: ast::TypeBound,
+        type_ref: TypeRef,
+    ) {
+        if bound.question_mark_token().is_some() {
+            // FIXME: remove this bound
+            return;
+        }
+        let bound = TypeBound::from_ast(lower_ctx, bound);
+        self.where_predicates
+            .push(WherePredicate { target: WherePredicateTarget::TypeRef(type_ref), bound });
+    }
+
+    pub(crate) fn fill_implicit_impl_trait_args(&mut self, type_ref: &TypeRef) {
+        type_ref.walk(&mut |type_ref| {
+            if let TypeRef::ImplTrait(bounds) = type_ref {
+                let param = TypeParamData {
+                    name: None,
+                    default: None,
+                    provenance: TypeParamProvenance::ArgumentImplTrait,
+                };
+                let param_id = self.types.alloc(param);
+                for bound in bounds {
+                    self.where_predicates.push(WherePredicate {
+                        target: WherePredicateTarget::TypeParam(param_id),
+                        bound: bound.clone(),
+                    });
+                }
+            }
+        });
+    }
+
+    pub fn find_by_name(&self, name: &Name) -> Option<LocalTypeParamId> {
+        self.types
+            .iter()
+            .find_map(|(id, p)| if p.name.as_ref() == Some(name) { Some(id) } else { None })
+    }
+
+    pub fn find_trait_self_param(&self) -> Option<LocalTypeParamId> {
+        self.types.iter().find_map(|(id, p)| {
+            if p.provenance == TypeParamProvenance::TraitSelf {
+                Some(id)
+            } else {
+                None
+            }
+        })
+    }
+}
+
+impl HasChildSource for GenericDefId {
+    type ChildId = LocalTypeParamId;
+    type Value = Either<ast::Trait, ast::TypeParam>;
+    fn child_source(&self, db: &dyn DefDatabase) -> InFile<SourceMap> {
+        let (_, sm) = GenericParams::new(db, *self);
+        sm
+    }
+}
+
+impl ChildBySource for GenericDefId {
+    fn child_by_source(&self, db: &dyn DefDatabase) -> DynMap {
+        let mut res = DynMap::default();
+        let arena_map = self.child_source(db);
+        let arena_map = arena_map.as_ref();
+        for (local_id, src) in arena_map.value.iter() {
+            let id = TypeParamId { parent: *self, local_id };
+            if let Either::Right(type_param) = src {
+                res[keys::TYPE_PARAM].insert(arena_map.with_value(type_param.clone()), id)
+            }
+        }
+        res
+    }
+}

crates/hir_def/src/import_map.rs

@@ -0,0 +1,745 @@
+//! A map of all publicly exported items in a crate.
+
+use std::{cmp::Ordering, fmt, hash::BuildHasherDefault, sync::Arc};
+
+use base_db::CrateId;
+use fst::{self, Streamer};
+use indexmap::{map::Entry, IndexMap};
+use rustc_hash::{FxHashMap, FxHasher};
+use smallvec::SmallVec;
+use syntax::SmolStr;
+
+use crate::{
+    db::DefDatabase,
+    item_scope::ItemInNs,
+    path::{ModPath, PathKind},
+    visibility::Visibility,
+    AssocItemId, ModuleDefId, ModuleId, TraitId,
+};
+
+type FxIndexMap<K, V> = IndexMap<K, V, BuildHasherDefault<FxHasher>>;
+
+/// Item import details stored in the `ImportMap`.
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct ImportInfo {
+    /// A path that can be used to import the item, relative to the crate's root.
+    pub path: ModPath,
+    /// The module containing this item.
+    pub container: ModuleId,
+}
+
+/// A map from publicly exported items to the path needed to import/name them from a downstream
+/// crate.
+///
+/// Reexports of items are taken into account, ie. if something is exported under multiple
+/// names, the one with the shortest import path will be used.
+///
+/// Note that all paths are relative to the containing crate's root, so the crate name still needs
+/// to be prepended to the `ModPath` before the path is valid.
+#[derive(Default)]
+pub struct ImportMap {
+    map: FxIndexMap<ItemInNs, ImportInfo>,
+
+    /// List of keys stored in `map`, sorted lexicographically by their `ModPath`. Indexed by the
+    /// values returned by running `fst`.
+    ///
+    /// Since a path can refer to multiple items due to namespacing, we store all items with the
+    /// same path right after each other. This allows us to find all items after the FST gives us
+    /// the index of the first one.
+    importables: Vec<ItemInNs>,
+    fst: fst::Map<Vec<u8>>,
+
+    /// Maps names of associated items to the item's ID. Only includes items whose defining trait is
+    /// exported.
+    assoc_map: FxHashMap<SmolStr, SmallVec<[AssocItemId; 1]>>,
+}
+
+impl ImportMap {
+    pub fn import_map_query(db: &dyn DefDatabase, krate: CrateId) -> Arc<Self> {
+        let _p = profile::span("import_map_query");
+        let def_map = db.crate_def_map(krate);
+        let mut import_map = Self::default();
+
+        // We look only into modules that are public(ly reexported), starting with the crate root.
+        let empty = ModPath { kind: PathKind::Plain, segments: vec![] };
+        let root = ModuleId { krate, local_id: def_map.root };
+        let mut worklist = vec![(root, empty)];
+        while let Some((module, mod_path)) = worklist.pop() {
+            let ext_def_map;
+            let mod_data = if module.krate == krate {
+                &def_map[module.local_id]
+            } else {
+                // The crate might reexport a module defined in another crate.
+                ext_def_map = db.crate_def_map(module.krate);
+                &ext_def_map[module.local_id]
+            };
+
+            let visible_items = mod_data.scope.entries().filter_map(|(name, per_ns)| {
+                let per_ns = per_ns.filter_visibility(|vis| vis == Visibility::Public);
+                if per_ns.is_none() {
+                    None
+                } else {
+                    Some((name, per_ns))
+                }
+            });
+
+            for (name, per_ns) in visible_items {
+                let mk_path = || {
+                    let mut path = mod_path.clone();
+                    path.segments.push(name.clone());
+                    path
+                };
+
+                for item in per_ns.iter_items() {
+                    let path = mk_path();
+                    match import_map.map.entry(item) {
+                        Entry::Vacant(entry) => {
+                            entry.insert(ImportInfo { path, container: module });
+                        }
+                        Entry::Occupied(mut entry) => {
+                            // If the new path is shorter, prefer that one.
+                            if path.len() < entry.get().path.len() {
+                                *entry.get_mut() = ImportInfo { path, container: module };
+                            } else {
+                                continue;
+                            }
+                        }
+                    }
+
+                    // If we've just added a path to a module, descend into it. We might traverse
+                    // modules multiple times, but only if the new path to it is shorter than the
+                    // first (else we `continue` above).
+                    if let Some(ModuleDefId::ModuleId(mod_id)) = item.as_module_def_id() {
+                        worklist.push((mod_id, mk_path()));
+                    }
+
+                    // If we've added a path to a trait, add the trait's methods to the method map.
+                    if let Some(ModuleDefId::TraitId(tr)) = item.as_module_def_id() {
+                        import_map.collect_trait_methods(db, tr);
+                    }
+                }
+            }
+        }
+
+        let mut importables = import_map.map.iter().collect::<Vec<_>>();
+
+        importables.sort_by(cmp);
+
+        // Build the FST, taking care not to insert duplicate values.
+
+        let mut builder = fst::MapBuilder::memory();
+        let mut last_batch_start = 0;
+
+        for idx in 0..importables.len() {
+            if let Some(next_item) = importables.get(idx + 1) {
+                if cmp(&importables[last_batch_start], next_item) == Ordering::Equal {
+                    continue;
+                }
+            }
+
+            let start = last_batch_start;
+            last_batch_start = idx + 1;
+
+            let key = fst_path(&importables[start].1.path);
+
+            builder.insert(key, start as u64).unwrap();
+        }
+
+        import_map.fst = fst::Map::new(builder.into_inner().unwrap()).unwrap();
+        import_map.importables = importables.iter().map(|(item, _)| **item).collect();
+
+        Arc::new(import_map)
+    }
+
+    /// Returns the `ModPath` needed to import/mention `item`, relative to this crate's root.
+    pub fn path_of(&self, item: ItemInNs) -> Option<&ModPath> {
+        Some(&self.map.get(&item)?.path)
+    }
+
+    pub fn import_info_for(&self, item: ItemInNs) -> Option<&ImportInfo> {
+        self.map.get(&item)
+    }
+
+    fn collect_trait_methods(&mut self, db: &dyn DefDatabase, tr: TraitId) {
+        let data = db.trait_data(tr);
+        for (name, item) in data.items.iter() {
+            self.assoc_map.entry(name.to_string().into()).or_default().push(*item);
+        }
+    }
+}
+
+impl PartialEq for ImportMap {
+    fn eq(&self, other: &Self) -> bool {
+        // `fst` and `importables` are built from `map`, so we don't need to compare them.
+        self.map == other.map
+    }
+}
+
+impl Eq for ImportMap {}
+
+impl fmt::Debug for ImportMap {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut importable_paths: Vec<_> = self
+            .map
+            .iter()
+            .map(|(item, info)| {
+                let ns = match item {
+                    ItemInNs::Types(_) => "t",
+                    ItemInNs::Values(_) => "v",
+                    ItemInNs::Macros(_) => "m",
+                };
+                format!("- {} ({})", info.path, ns)
+            })
+            .collect();
+
+        importable_paths.sort();
+        f.write_str(&importable_paths.join("\n"))
+    }
+}
+
+fn fst_path(path: &ModPath) -> String {
+    let mut s = path.to_string();
+    s.make_ascii_lowercase();
+    s
+}
+
+fn cmp((_, lhs): &(&ItemInNs, &ImportInfo), (_, rhs): &(&ItemInNs, &ImportInfo)) -> Ordering {
+    let lhs_str = fst_path(&lhs.path);
+    let rhs_str = fst_path(&rhs.path);
+    lhs_str.cmp(&rhs_str)
+}
+
+#[derive(Debug)]
+pub struct Query {
+    query: String,
+    lowercased: String,
+    anchor_end: bool,
+    case_sensitive: bool,
+    limit: usize,
+}
+
+impl Query {
+    pub fn new(query: &str) -> Self {
+        Self {
+            lowercased: query.to_lowercase(),
+            query: query.to_string(),
+            anchor_end: false,
+            case_sensitive: false,
+            limit: usize::max_value(),
+        }
+    }
+
+    /// Only returns items whose paths end with the (case-insensitive) query string as their last
+    /// segment.
+    pub fn anchor_end(self) -> Self {
+        Self { anchor_end: true, ..self }
+    }
+
+    /// Limits the returned number of items to `limit`.
+    pub fn limit(self, limit: usize) -> Self {
+        Self { limit, ..self }
+    }
+
+    /// Respect casing of the query string when matching.
+    pub fn case_sensitive(self) -> Self {
+        Self { case_sensitive: true, ..self }
+    }
+}
+
+/// Searches dependencies of `krate` for an importable path matching `query`.
+///
+/// This returns a list of items that could be imported from dependencies of `krate`.
+pub fn search_dependencies<'a>(
+    db: &'a dyn DefDatabase,
+    krate: CrateId,
+    query: Query,
+) -> Vec<ItemInNs> {
+    let _p = profile::span("search_dependencies").detail(|| format!("{:?}", query));
+
+    let graph = db.crate_graph();
+    let import_maps: Vec<_> =
+        graph[krate].dependencies.iter().map(|dep| db.import_map(dep.crate_id)).collect();
+
+    let automaton = fst::automaton::Subsequence::new(&query.lowercased);
+
+    let mut op = fst::map::OpBuilder::new();
+    for map in &import_maps {
+        op = op.add(map.fst.search(&automaton));
+    }
+
+    let mut stream = op.union();
+    let mut res = Vec::new();
+    while let Some((_, indexed_values)) = stream.next() {
+        for indexed_value in indexed_values {
+            let import_map = &import_maps[indexed_value.index];
+            let importables = &import_map.importables[indexed_value.value as usize..];
+
+            // Path shared by the importable items in this group.
+            let path = &import_map.map[&importables[0]].path;
+
+            if query.anchor_end {
+                // Last segment must match query.
+                let last = path.segments.last().unwrap().to_string();
+                if last.to_lowercase() != query.lowercased {
+                    continue;
+                }
+            }
+
+            // Add the items from this `ModPath` group. Those are all subsequent items in
+            // `importables` whose paths match `path`.
+            let iter = importables.iter().copied().take_while(|item| {
+                let item_path = &import_map.map[item].path;
+                fst_path(item_path) == fst_path(path)
+            });
+
+            if query.case_sensitive {
+                // FIXME: This does not do a subsequence match.
+                res.extend(iter.filter(|item| {
+                    let item_path = &import_map.map[item].path;
+                    item_path.to_string().contains(&query.query)
+                }));
+            } else {
+                res.extend(iter);
+            }
+
+            if res.len() >= query.limit {
+                res.truncate(query.limit);
+                return res;
+            }
+        }
+    }
+
+    // Add all exported associated items whose names match the query (exactly).
+    for map in &import_maps {
+        if let Some(v) = map.assoc_map.get(&*query.query) {
+            res.extend(v.iter().map(|&assoc| {
+                ItemInNs::Types(match assoc {
+                    AssocItemId::FunctionId(it) => it.into(),
+                    AssocItemId::ConstId(it) => it.into(),
+                    AssocItemId::TypeAliasId(it) => it.into(),
+                })
+            }));
+        }
+    }
+
+    res
+}
+
+#[cfg(test)]
+mod tests {
+    use base_db::{fixture::WithFixture, SourceDatabase, Upcast};
+    use expect_test::{expect, Expect};
+
+    use crate::{test_db::TestDB, AssocContainerId, Lookup};
+
+    use super::*;
+
+    fn check_search(ra_fixture: &str, krate_name: &str, query: Query, expect: Expect) {
+        let db = TestDB::with_files(ra_fixture);
+        let crate_graph = db.crate_graph();
+        let krate = crate_graph
+            .iter()
+            .find(|krate| {
+                crate_graph[*krate].display_name.as_ref().map(|n| n.to_string())
+                    == Some(krate_name.to_string())
+            })
+            .unwrap();
+
+        let actual = search_dependencies(db.upcast(), krate, query)
+            .into_iter()
+            .filter_map(|item| {
+                let mark = match item {
+                    ItemInNs::Types(_) => "t",
+                    ItemInNs::Values(_) => "v",
+                    ItemInNs::Macros(_) => "m",
+                };
+                let item = assoc_to_trait(&db, item);
+                item.krate(db.upcast()).map(|krate| {
+                    let map = db.import_map(krate);
+                    let path = map.path_of(item).unwrap();
+                    format!(
+                        "{}::{} ({})\n",
+                        crate_graph[krate].display_name.as_ref().unwrap(),
+                        path,
+                        mark
+                    )
+                })
+            })
+            .collect::<String>();
+        expect.assert_eq(&actual)
+    }
+
+    fn assoc_to_trait(db: &dyn DefDatabase, item: ItemInNs) -> ItemInNs {
+        let assoc: AssocItemId = match item {
+            ItemInNs::Types(it) | ItemInNs::Values(it) => match it {
+                ModuleDefId::TypeAliasId(it) => it.into(),
+                ModuleDefId::FunctionId(it) => it.into(),
+                ModuleDefId::ConstId(it) => it.into(),
+                _ => return item,
+            },
+            _ => return item,
+        };
+
+        let container = match assoc {
+            AssocItemId::FunctionId(it) => it.lookup(db).container,
+            AssocItemId::ConstId(it) => it.lookup(db).container,
+            AssocItemId::TypeAliasId(it) => it.lookup(db).container,
+        };
+
+        match container {
+            AssocContainerId::TraitId(it) => ItemInNs::Types(it.into()),
+            _ => item,
+        }
+    }
+
+    fn check(ra_fixture: &str, expect: Expect) {
+        let db = TestDB::with_files(ra_fixture);
+        let crate_graph = db.crate_graph();
+
+        let actual = crate_graph
+            .iter()
+            .filter_map(|krate| {
+                let cdata = &crate_graph[krate];
+                let name = cdata.display_name.as_ref()?;
+
+                let map = db.import_map(krate);
+
+                Some(format!("{}:\n{:?}\n", name, map))
+            })
+            .collect::<String>();
+
+        expect.assert_eq(&actual)
+    }
+
+    #[test]
+    fn smoke() {
+        check(
+            r"
+            //- /main.rs crate:main deps:lib
+
+            mod private {
+                pub use lib::Pub;
+                pub struct InPrivateModule;
+            }
+
+            pub mod publ1 {
+                use lib::Pub;
+            }
+
+            pub mod real_pub {
+                pub use lib::Pub;
+            }
+            pub mod real_pu2 { // same path length as above
+                pub use lib::Pub;
+            }
+
+            //- /lib.rs crate:lib
+            pub struct Pub {}
+            pub struct Pub2; // t + v
+            struct Priv;
+        ",
+            expect![[r#"
+                main:
+                - publ1 (t)
+                - real_pu2 (t)
+                - real_pub (t)
+                - real_pub::Pub (t)
+                lib:
+                - Pub (t)
+                - Pub2 (t)
+                - Pub2 (v)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn prefers_shortest_path() {
+        check(
+            r"
+            //- /main.rs crate:main
+
+            pub mod sub {
+                pub mod subsub {
+                    pub struct Def {}
+                }
+
+                pub use super::sub::subsub::Def;
+            }
+        ",
+            expect![[r#"
+                main:
+                - sub (t)
+                - sub::Def (t)
+                - sub::subsub (t)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn type_reexport_cross_crate() {
+        // Reexports need to be visible from a crate, even if the original crate exports the item
+        // at a shorter path.
+        check(
+            r"
+            //- /main.rs crate:main deps:lib
+            pub mod m {
+                pub use lib::S;
+            }
+            //- /lib.rs crate:lib
+            pub struct S;
+        ",
+            expect![[r#"
+                main:
+                - m (t)
+                - m::S (t)
+                - m::S (v)
+                lib:
+                - S (t)
+                - S (v)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn macro_reexport() {
+        check(
+            r"
+            //- /main.rs crate:main deps:lib
+            pub mod m {
+                pub use lib::pub_macro;
+            }
+            //- /lib.rs crate:lib
+            #[macro_export]
+            macro_rules! pub_macro {
+                () => {};
+            }
+        ",
+            expect![[r#"
+                main:
+                - m (t)
+                - m::pub_macro (m)
+                lib:
+                - pub_macro (m)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn module_reexport() {
+        // Reexporting modules from a dependency adds all contents to the import map.
+        check(
+            r"
+            //- /main.rs crate:main deps:lib
+            pub use lib::module as reexported_module;
+            //- /lib.rs crate:lib
+            pub mod module {
+                pub struct S;
+            }
+        ",
+            expect![[r#"
+                main:
+                - reexported_module (t)
+                - reexported_module::S (t)
+                - reexported_module::S (v)
+                lib:
+                - module (t)
+                - module::S (t)
+                - module::S (v)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn cyclic_module_reexport() {
+        // A cyclic reexport does not hang.
+        check(
+            r"
+            //- /lib.rs crate:lib
+            pub mod module {
+                pub struct S;
+                pub use super::sub::*;
+            }
+
+            pub mod sub {
+                pub use super::module;
+            }
+        ",
+            expect![[r#"
+                lib:
+                - module (t)
+                - module::S (t)
+                - module::S (v)
+                - sub (t)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn private_macro() {
+        check(
+            r"
+            //- /lib.rs crate:lib
+            macro_rules! private_macro {
+                () => {};
+            }
+        ",
+            expect![[r#"
+                lib:
+
+            "#]],
+        );
+    }
+
+    #[test]
+    fn namespacing() {
+        check(
+            r"
+            //- /lib.rs crate:lib
+            pub struct Thing;     // t + v
+            #[macro_export]
+            macro_rules! Thing {  // m
+                () => {};
+            }
+        ",
+            expect![[r#"
+                lib:
+                - Thing (m)
+                - Thing (t)
+                - Thing (v)
+            "#]],
+        );
+
+        check(
+            r"
+            //- /lib.rs crate:lib
+            pub mod Thing {}      // t
+            #[macro_export]
+            macro_rules! Thing {  // m
+                () => {};
+            }
+        ",
+            expect![[r#"
+                lib:
+                - Thing (m)
+                - Thing (t)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn search() {
+        let ra_fixture = r#"
+            //- /main.rs crate:main deps:dep
+            //- /dep.rs crate:dep deps:tdep
+            use tdep::fmt as fmt_dep;
+            pub mod fmt {
+                pub trait Display {
+                    fn fmt();
+                }
+            }
+            #[macro_export]
+            macro_rules! Fmt {
+                () => {};
+            }
+            pub struct Fmt;
+
+            pub fn format() {}
+            pub fn no() {}
+
+            //- /tdep.rs crate:tdep
+            pub mod fmt {
+                pub struct NotImportableFromMain;
+            }
+        "#;
+
+        check_search(
+            ra_fixture,
+            "main",
+            Query::new("fmt"),
+            expect![[r#"
+                dep::fmt (t)
+                dep::Fmt (t)
+                dep::Fmt (v)
+                dep::Fmt (m)
+                dep::fmt::Display (t)
+                dep::format (v)
+                dep::fmt::Display (t)
+            "#]],
+        );
+
+        check_search(
+            ra_fixture,
+            "main",
+            Query::new("fmt").anchor_end(),
+            expect![[r#"
+                dep::fmt (t)
+                dep::Fmt (t)
+                dep::Fmt (v)
+                dep::Fmt (m)
+                dep::fmt::Display (t)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn search_casing() {
+        let ra_fixture = r#"
+            //- /main.rs crate:main deps:dep
+            //- /dep.rs crate:dep
+
+            pub struct fmt;
+            pub struct FMT;
+        "#;
+
+        check_search(
+            ra_fixture,
+            "main",
+            Query::new("FMT"),
+            expect![[r#"
+                dep::fmt (t)
+                dep::fmt (v)
+                dep::FMT (t)
+                dep::FMT (v)
+            "#]],
+        );
+
+        check_search(
+            ra_fixture,
+            "main",
+            Query::new("FMT").case_sensitive(),
+            expect![[r#"
+                dep::FMT (t)
+                dep::FMT (v)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn search_limit() {
+        check_search(
+            r#"
+        //- /main.rs crate:main deps:dep
+        //- /dep.rs crate:dep
+        pub mod fmt {
+            pub trait Display {
+                fn fmt();
+            }
+        }
+        #[macro_export]
+        macro_rules! Fmt {
+            () => {};
+        }
+        pub struct Fmt;
+
+        pub fn format() {}
+        pub fn no() {}
+    "#,
+            "main",
+            Query::new("").limit(2),
+            expect![[r#"
+                dep::fmt (t)
+                dep::Fmt (t)
+            "#]],
+        );
+    }
+}