Merge from rustc

.github/rust.json

@@ -0,0 +1,33 @@
+{
+    "problemMatcher": [
+        {
+            "owner": "rustfmt",
+            "severity": "warning",
+            "pattern": [
+                {
+                    "regexp": "^(Diff in (.+)) at line (\\d+):$",
+                    "message": 1,
+                    "file": 2,
+                    "line": 3
+                }
+            ]
+        },
+        {
+            "owner": "clippy",
+            "pattern": [
+                {
+                    "regexp": "^(?:\\x1b\\[[\\d;]+m)*(warning|warn|error)(?:\\x1b\\[[\\d;]+m)*(\\[(.*)\\])?(?:\\x1b\\[[\\d;]+m)*:(?:\\x1b\\[[\\d;]+m)* ([^\\x1b]*)(?:\\x1b\\[[\\d;]+m)*$",
+                    "severity": 1,
+                    "message": 4,
+                    "code": 3
+                },
+                {
+                    "regexp": "^(?:\\x1b\\[[\\d;]+m)*\\s*(?:\\x1b\\[[\\d;]+m)*\\s*--> (?:\\x1b\\[[\\d;]+m)*(.*):(\\d*):(\\d*)(?:\\x1b\\[[\\d;]+m)*$",
+                    "file": 1,
+                    "line": 2,
+                    "column": 3
+                }
+            ]
+        }
+    ]
+}

.github/workflows/autopublish.yaml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
 

.github/workflows/ci.yaml

@@ -27,7 +27,7 @@ jobs:
       typescript: ${{ steps.filter.outputs.typescript }}
       proc_macros: ${{ steps.filter.outputs.proc_macros }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: dorny/paths-filter@1441771bbfdd59dcd748680ee64ebd8faab1a242
         id: filter
         with:
@@ -56,7 +56,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.head.sha }}
 
@@ -65,6 +65,10 @@ jobs:
           rustup update --no-self-update ${{ env.RUST_CHANNEL }}
           rustup component add --toolchain ${{ env.RUST_CHANNEL }} rustfmt rust-src
           rustup default ${{ env.RUST_CHANNEL }}
+      # https://github.com/actions-rust-lang/setup-rust-toolchain/blob/main/rust.json
+      - name: Install Rust Problem Matcher
+        if: matrix.os == 'ubuntu-latest'
+        run: echo "::add-matcher::.github/rust.json"
 
       - name: Cache Dependencies
         uses: Swatinem/rust-cache@988c164c3d0e93c4dbab36aaf5bbeb77425b2894
@@ -107,6 +111,10 @@ jobs:
         if: matrix.os == 'windows-latest'
         run: cargo clippy --all-targets -- -D clippy::disallowed_macros -D clippy::dbg_macro -D clippy::todo -D clippy::print_stdout -D clippy::print_stderr
 
+      - name: rustfmt
+        if: matrix.os == 'ubuntu-latest'
+        run: cargo fmt -- --check
+
   # Weird targets to catch non-portable code
   rust-cross:
     if: github.repository == 'rust-lang/rust-analyzer'
@@ -121,7 +129,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install Rust toolchain
         run: |
@@ -153,13 +161,13 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         if: needs.changes.outputs.typescript == 'true'
 
       - name: Install Nodejs
-        uses: actions/setup-node@v3
+        uses: actions/setup-node@v4
         with:
-          node-version: 16
+          node-version: 18
         if: needs.changes.outputs.typescript == 'true'
 
       - name: Install xvfb

.github/workflows/fuzz.yml

@@ -27,7 +27,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.head.sha }}
           fetch-depth: 1

.github/workflows/metrics.yaml

@@ -21,7 +21,7 @@ jobs:
           rustup component add rustfmt rust-src
           rustup default stable
       - name: Cache cargo
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: |
             ~/.cargo/bin/
@@ -36,10 +36,10 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Restore cargo cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: |
             ~/.cargo/bin/
@@ -52,7 +52,7 @@ jobs:
         run: cargo xtask metrics build
 
       - name: Cache target
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: target/
           key: ${{ runner.os }}-target-${{ github.sha }}
@@ -73,10 +73,10 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Restore cargo cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: |
             ~/.cargo/bin/
@@ -86,7 +86,7 @@ jobs:
           key: ${{ runner.os }}-cargo-${{ github.sha }}
 
       - name: Restore target cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: target/
           key: ${{ runner.os }}-target-${{ github.sha }}
@@ -106,7 +106,7 @@ jobs:
     needs: [build_metrics, other_metrics]
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Download build metrics
         uses: actions/download-artifact@v3

.github/workflows/publish-libs.yaml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
 

.github/workflows/release.yaml

@@ -59,7 +59,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: ${{ env.FETCH_DEPTH }}
 
@@ -78,9 +78,9 @@ jobs:
           rustup component add rust-src
 
       - name: Install Node.js
-        uses: actions/setup-node@v3
+        uses: actions/setup-node@v4
         with:
-          node-version: 16
+          node-version: 18
 
       - name: Update apt repositories
         if: matrix.target == 'aarch64-unknown-linux-gnu' || matrix.target == 'arm-unknown-linux-gnueabihf'
@@ -154,7 +154,7 @@ jobs:
         run: apk add --no-cache git clang lld musl-dev nodejs npm
 
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: ${{ env.FETCH_DEPTH }}
 
@@ -188,9 +188,9 @@ jobs:
     needs: ["dist", "dist-x86_64-unknown-linux-musl"]
     steps:
       - name: Install Nodejs
-        uses: actions/setup-node@v3
+        uses: actions/setup-node@v4
         with:
-          node-version: 16
+          node-version: 18
 
       - run: echo "TAG=$(date --iso -u)" >> $GITHUB_ENV
         if: github.ref == 'refs/heads/release'
@@ -199,7 +199,7 @@ jobs:
       - run: 'echo "TAG: $TAG"'
 
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: ${{ env.FETCH_DEPTH }}
 

.github/workflows/rustdoc.yaml

@@ -17,7 +17,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Install Rust toolchain
       run: rustup update --no-self-update stable

Cargo.lock

@@ -1329,6 +1329,7 @@ dependencies = [
  "paths",
  "proc-macro-api",
  "proc-macro-test",
+ "ra-ap-rustc_lexer",
  "span",
  "stdx",
  "tt",
@@ -1470,12 +1471,12 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_index"
-version = "0.36.0"
+version = "0.37.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f8a41dee58608b1fc93779ea365edaa70ac9927e3335ae914b675be0fa063cd7"
+checksum = "df5a0ba0d08af366cf235dbe8eb7226cced7a4fe502c98aa434ccf416defd746"
 dependencies = [
  "arrayvec",
- "ra-ap-rustc_index_macros 0.36.0",
+ "ra-ap-rustc_index_macros 0.37.0",
  "smallvec",
 ]
 
@@ -1493,9 +1494,9 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_index_macros"
-version = "0.36.0"
+version = "0.37.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fbfe98def54c4337a2f7d8233850bd5d5349972b185fe8a0db2b979164b30ed8"
+checksum = "1971ebf9a701e0e68387c264a32517dcb4861ad3a4862f2e2803c1121ade20d5"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1525,11 +1526,11 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_pattern_analysis"
-version = "0.36.0"
+version = "0.37.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b5529bffec7530b4a3425640bfdfd9b95d87c4c620f740266c0de6572561aab4"
+checksum = "2c3c0e7ca9c5bdc66e3b590688e237a22ac47a48e4eac7f46b05b2abbfaf0abd"
 dependencies = [
- "ra-ap-rustc_index 0.36.0",
+ "ra-ap-rustc_index 0.37.0",
  "rustc-hash",
  "rustc_apfloat",
  "smallvec",

Cargo.toml

@@ -84,7 +84,7 @@ ra-ap-rustc_lexer = { version = "0.35.0", default-features = false }
 ra-ap-rustc_parse_format = { version = "0.35.0", default-features = false }
 ra-ap-rustc_index = { version = "0.35.0", default-features = false }
 ra-ap-rustc_abi = { version = "0.35.0", default-features = false }
-ra-ap-rustc_pattern_analysis = { version = "0.36.0", default-features = false }
+ra-ap-rustc_pattern_analysis = { version = "0.37.0", default-features = false }
 
 # local crates that aren't published to crates.io. These should not have versions.
 sourcegen = { path = "./crates/sourcegen" }

crates/base-db/src/input.rs

@@ -11,7 +11,6 @@ use std::{fmt, mem, ops, str::FromStr};
 use cfg::CfgOptions;
 use la_arena::{Arena, Idx, RawIdx};
 use rustc_hash::{FxHashMap, FxHashSet};
-use semver::Version;
 use syntax::SmolStr;
 use triomphe::Arc;
 use vfs::{file_set::FileSet, AbsPathBuf, AnchoredPath, FileId, VfsPath};
@@ -243,6 +242,7 @@ impl CrateDisplayName {
         CrateDisplayName { crate_name, canonical_name }
     }
 }
+
 pub type TargetLayoutLoadResult = Result<Arc<str>, Arc<str>>;
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
@@ -291,71 +291,6 @@ pub struct CrateData {
     pub dependencies: Vec<Dependency>,
     pub origin: CrateOrigin,
     pub is_proc_macro: bool,
-    // FIXME: These things should not be per crate! These are more per workspace crate graph level
-    // things. This info does need to be somewhat present though as to prevent deduplication from
-    // happening across different workspaces with different layouts.
-    pub target_layout: TargetLayoutLoadResult,
-    pub toolchain: Option<Version>,
-}
-
-impl CrateData {
-    /// Check if [`other`] is almost equal to [`self`] ignoring `CrateOrigin` value.
-    pub fn eq_ignoring_origin_and_deps(&self, other: &CrateData, ignore_dev_deps: bool) -> bool {
-        // This method has some obscure bits. These are mostly there to be compliant with
-        // some patches. References to the patches are given.
-        if self.root_file_id != other.root_file_id {
-            return false;
-        }
-
-        if self.display_name != other.display_name {
-            return false;
-        }
-
-        if self.is_proc_macro != other.is_proc_macro {
-            return false;
-        }
-
-        if self.edition != other.edition {
-            return false;
-        }
-
-        if self.version != other.version {
-            return false;
-        }
-
-        let mut opts = self.cfg_options.difference(&other.cfg_options);
-        if let Some(it) = opts.next() {
-            // Don't care if rust_analyzer CfgAtom is the only cfg in the difference set of self's and other's cfgs.
-            // https://github.com/rust-lang/rust-analyzer/blob/0840038f02daec6ba3238f05d8caa037d28701a0/crates/project-model/src/workspace.rs#L894
-            if it.to_string() != "rust_analyzer" {
-                return false;
-            }
-
-            if opts.next().is_some() {
-                return false;
-            }
-        }
-
-        if self.env != other.env {
-            return false;
-        }
-
-        let slf_deps = self.dependencies.iter();
-        let other_deps = other.dependencies.iter();
-
-        if ignore_dev_deps {
-            return slf_deps
-                .clone()
-                .filter(|it| it.kind != DependencyKind::Dev)
-                .eq(other_deps.clone().filter(|it| it.kind != DependencyKind::Dev));
-        }
-
-        slf_deps.eq(other_deps)
-    }
-
-    pub fn channel(&self) -> Option<ReleaseChannel> {
-        self.toolchain.as_ref().and_then(|v| ReleaseChannel::from_str(&v.pre))
-    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
@@ -398,32 +333,22 @@ pub enum DependencyKind {
 pub struct Dependency {
     pub crate_id: CrateId,
     pub name: CrateName,
-    kind: DependencyKind,
     prelude: bool,
 }
 
 impl Dependency {
-    pub fn new(name: CrateName, crate_id: CrateId, kind: DependencyKind) -> Self {
+    pub fn new(name: CrateName, crate_id: CrateId) -> Self {
-        Self { name, crate_id, prelude: true, kind }
+        Self { name, crate_id, prelude: true }
     }
 
-    pub fn with_prelude(
+    pub fn with_prelude(name: CrateName, crate_id: CrateId, prelude: bool) -> Self {
-        name: CrateName,
+        Self { name, crate_id, prelude }
-        crate_id: CrateId,
-        prelude: bool,
-        kind: DependencyKind,
-    ) -> Self {
-        Self { name, crate_id, prelude, kind }
     }
 
     /// Whether this dependency is to be added to the depending crate's extern prelude.
     pub fn is_prelude(&self) -> bool {
         self.prelude
     }
-
-    pub fn kind(&self) -> DependencyKind {
-        self.kind
-    }
 }
 
 impl CrateGraph {
@@ -438,8 +363,6 @@ impl CrateGraph {
         env: Env,
         is_proc_macro: bool,
         origin: CrateOrigin,
-        target_layout: Result<Arc<str>, Arc<str>>,
-        toolchain: Option<Version>,
     ) -> CrateId {
         let data = CrateData {
             root_file_id,
@@ -451,9 +374,7 @@ impl CrateGraph {
             env,
             dependencies: Vec::new(),
             origin,
-            target_layout,
             is_proc_macro,
-            toolchain,
         };
         self.arena.alloc(data)
     }
@@ -523,6 +444,10 @@ impl CrateGraph {
         self.arena.is_empty()
     }
 
+    pub fn len(&self) -> usize {
+        self.arena.len()
+    }
+
     pub fn iter(&self) -> impl Iterator<Item = CrateId> + '_ {
         self.arena.iter().map(|(idx, _)| idx)
     }
@@ -623,13 +548,17 @@ impl CrateGraph {
     ///
     /// This will deduplicate the crates of the graph where possible.
     /// Note that for deduplication to fully work, `self`'s crate dependencies must be sorted by crate id.
-    /// If the crate dependencies were sorted, the resulting graph from this `extend` call will also have the crate dependencies sorted.
+    /// If the crate dependencies were sorted, the resulting graph from this `extend` call will also
+    /// have the crate dependencies sorted.
+    ///
+    /// Returns a mapping from `other`'s crate ids to the new crate ids in `self`.
     pub fn extend(
         &mut self,
         mut other: CrateGraph,
         proc_macros: &mut ProcMacroPaths,
-        on_finished: impl FnOnce(&FxHashMap<CrateId, CrateId>),
+        merge: impl Fn((CrateId, &mut CrateData), (CrateId, &CrateData)) -> bool,
-    ) {
+    ) -> FxHashMap<CrateId, CrateId> {
+        let m = self.len();
         let topo = other.crates_in_topological_order();
         let mut id_map: FxHashMap<CrateId, CrateId> = FxHashMap::default();
         for topo in topo {
@@ -637,51 +566,21 @@ impl CrateGraph {
 
             crate_data.dependencies.iter_mut().for_each(|dep| dep.crate_id = id_map[&dep.crate_id]);
             crate_data.dependencies.sort_by_key(|dep| dep.crate_id);
-            let res = self.arena.iter().find_map(|(id, data)| {
+            let res = self
-                match (&data.origin, &crate_data.origin) {
+                .arena
-                    (a, b) if a == b => {
+                .iter_mut()
-                        if data.eq_ignoring_origin_and_deps(crate_data, false) {
+                .take(m)
-                            return Some((id, false));
+                .find_map(|(id, data)| merge((id, data), (topo, &crate_data)).then_some(id));
-                        }
-                    }
-                    (a @ CrateOrigin::Local { .. }, CrateOrigin::Library { .. })
-                    | (a @ CrateOrigin::Library { .. }, CrateOrigin::Local { .. }) => {
-                        // If the origins differ, check if the two crates are equal without
-                        // considering the dev dependencies, if they are, they most likely are in
-                        // different loaded workspaces which may cause issues. We keep the local
-                        // version and discard the library one as the local version may have
-                        // dev-dependencies that we want to keep resolving. See #15656 for more
-                        // information.
-                        if data.eq_ignoring_origin_and_deps(crate_data, true) {
-                            return Some((id, !a.is_local()));
-                        }
-                    }
-                    (_, _) => return None,
-                }
 
-                None
+            let new_id =
-            });
+                if let Some(res) = res { res } else { self.arena.alloc(crate_data.clone()) };
-
+            id_map.insert(topo, new_id);
-            if let Some((res, should_update_lib_to_local)) = res {
-                id_map.insert(topo, res);
-                if should_update_lib_to_local {
-                    assert!(self.arena[res].origin.is_lib());
-                    assert!(crate_data.origin.is_local());
-                    self.arena[res].origin = crate_data.origin.clone();
-
-                    // Move local's dev dependencies into the newly-local-formerly-lib crate.
-                    self.arena[res].dependencies = crate_data.dependencies.clone();
-                }
-            } else {
-                let id = self.arena.alloc(crate_data.clone());
-                id_map.insert(topo, id);
-            }
         }
 
         *proc_macros =
             mem::take(proc_macros).into_iter().map(|(id, macros)| (id_map[&id], macros)).collect();
 
-        on_finished(&id_map);
+        id_map
     }
 
     fn find_path(
@@ -719,11 +618,9 @@ impl CrateGraph {
         match (cfg_if, std) {
             (Some(cfg_if), Some(std)) => {
                 self.arena[cfg_if].dependencies.clear();
-                self.arena[std].dependencies.push(Dependency::new(
+                self.arena[std]
-                    CrateName::new("cfg_if").unwrap(),
+                    .dependencies
-                    cfg_if,
+                    .push(Dependency::new(CrateName::new("cfg_if").unwrap(), cfg_if));
-                    DependencyKind::Normal,
-                ));
                 true
             }
             _ => false,
@@ -871,7 +768,7 @@ impl fmt::Display for CyclicDependenciesError {
 
 #[cfg(test)]
 mod tests {
-    use crate::{CrateOrigin, DependencyKind};
+    use crate::CrateOrigin;
 
     use super::{CrateGraph, CrateName, Dependency, Edition::Edition2018, Env, FileId};
 
@@ -888,8 +785,6 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         let crate2 = graph.add_crate_root(
             FileId::from_raw(2u32),
@@ -901,8 +796,6 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         let crate3 = graph.add_crate_root(
             FileId::from_raw(3u32),
@@ -914,26 +807,15 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         assert!(graph
-            .add_dep(
+            .add_dep(crate1, Dependency::new(CrateName::new("crate2").unwrap(), crate2,))
-                crate1,
-                Dependency::new(CrateName::new("crate2").unwrap(), crate2, DependencyKind::Normal)
-            )
             .is_ok());
         assert!(graph
-            .add_dep(
+            .add_dep(crate2, Dependency::new(CrateName::new("crate3").unwrap(), crate3,))
-                crate2,
-                Dependency::new(CrateName::new("crate3").unwrap(), crate3, DependencyKind::Normal)
-            )
             .is_ok());
         assert!(graph
-            .add_dep(
+            .add_dep(crate3, Dependency::new(CrateName::new("crate1").unwrap(), crate1,))
-                crate3,
-                Dependency::new(CrateName::new("crate1").unwrap(), crate1, DependencyKind::Normal)
-            )
             .is_err());
     }
 
@@ -950,8 +832,6 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         let crate2 = graph.add_crate_root(
             FileId::from_raw(2u32),
@@ -963,20 +843,12 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         assert!(graph
-            .add_dep(
+            .add_dep(crate1, Dependency::new(CrateName::new("crate2").unwrap(), crate2,))
-                crate1,
-                Dependency::new(CrateName::new("crate2").unwrap(), crate2, DependencyKind::Normal)
-            )
             .is_ok());
         assert!(graph
-            .add_dep(
+            .add_dep(crate2, Dependency::new(CrateName::new("crate2").unwrap(), crate2,))
-                crate2,
-                Dependency::new(CrateName::new("crate2").unwrap(), crate2, DependencyKind::Normal)
-            )
             .is_err());
     }
 
@@ -993,8 +865,6 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         let crate2 = graph.add_crate_root(
             FileId::from_raw(2u32),
@@ -1006,8 +876,6 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         let crate3 = graph.add_crate_root(
             FileId::from_raw(3u32),
@@ -1019,20 +887,12 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         assert!(graph
-            .add_dep(
+            .add_dep(crate1, Dependency::new(CrateName::new("crate2").unwrap(), crate2,))
-                crate1,
-                Dependency::new(CrateName::new("crate2").unwrap(), crate2, DependencyKind::Normal)
-            )
             .is_ok());
         assert!(graph
-            .add_dep(
+            .add_dep(crate2, Dependency::new(CrateName::new("crate3").unwrap(), crate3,))
-                crate2,
-                Dependency::new(CrateName::new("crate3").unwrap(), crate3, DependencyKind::Normal)
-            )
             .is_ok());
     }
 
@@ -1049,8 +909,6 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         let crate2 = graph.add_crate_root(
             FileId::from_raw(2u32),
@@ -1062,26 +920,16 @@ mod tests {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("".into()),
-            None,
         );
         assert!(graph
             .add_dep(
                 crate1,
-                Dependency::new(
+                Dependency::new(CrateName::normalize_dashes("crate-name-with-dashes"), crate2,)
-                    CrateName::normalize_dashes("crate-name-with-dashes"),
-                    crate2,
-                    DependencyKind::Normal
-                )
             )
             .is_ok());
         assert_eq!(
             graph[crate1].dependencies,
-            vec![Dependency::new(
+            vec![Dependency::new(CrateName::new("crate_name_with_dashes").unwrap(), crate2,)]
-                CrateName::new("crate_name_with_dashes").unwrap(),
-                crate2,
-                DependencyKind::Normal
-            )]
         );
     }
 }

crates/base-db/src/lib.rs

@@ -62,6 +62,20 @@ pub trait SourceDatabase: FileLoader + std::fmt::Debug {
     /// The crate graph.
     #[salsa::input]
     fn crate_graph(&self) -> Arc<CrateGraph>;
+
+    // FIXME: Consider removing this, making HirDatabase::target_data_layout an input query
+    #[salsa::input]
+    fn data_layout(&self, krate: CrateId) -> TargetLayoutLoadResult;
+
+    #[salsa::input]
+    fn toolchain(&self, krate: CrateId) -> Option<Version>;
+
+    #[salsa::transparent]
+    fn toolchain_channel(&self, krate: CrateId) -> Option<ReleaseChannel>;
+}
+
+fn toolchain_channel(db: &dyn SourceDatabase, krate: CrateId) -> Option<ReleaseChannel> {
+    db.toolchain(krate).as_ref().and_then(|v| ReleaseChannel::from_str(&v.pre))
 }
 
 fn parse(db: &dyn SourceDatabase, file_id: FileId) -> Parse<ast::SourceFile> {

crates/flycheck/src/lib.rs

@@ -14,7 +14,7 @@ use std::{
 
 use command_group::{CommandGroup, GroupChild};
 use crossbeam_channel::{never, select, unbounded, Receiver, Sender};
-use paths::AbsPathBuf;
+use paths::{AbsPath, AbsPathBuf};
 use rustc_hash::FxHashMap;
 use serde::Deserialize;
 use stdx::process::streaming_output;
@@ -23,6 +23,7 @@ pub use cargo_metadata::diagnostic::{
     Applicability, Diagnostic, DiagnosticCode, DiagnosticLevel, DiagnosticSpan,
     DiagnosticSpanMacroExpansion,
 };
+use toolchain::Tool;
 
 #[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
 pub enum InvocationStrategy {
@@ -89,9 +90,10 @@ impl FlycheckHandle {
         id: usize,
         sender: Box<dyn Fn(Message) + Send>,
         config: FlycheckConfig,
+        sysroot_root: Option<AbsPathBuf>,
         workspace_root: AbsPathBuf,
     ) -> FlycheckHandle {
-        let actor = FlycheckActor::new(id, sender, config, workspace_root);
+        let actor = FlycheckActor::new(id, sender, config, sysroot_root, workspace_root);
         let (sender, receiver) = unbounded::<StateChange>();
         let thread = stdx::thread::Builder::new(stdx::thread::ThreadIntent::Worker)
             .name("Flycheck".to_owned())
@@ -101,13 +103,15 @@ impl FlycheckHandle {
     }
 
     /// Schedule a re-start of the cargo check worker to do a workspace wide check.
-    pub fn restart_workspace(&self) {
+    pub fn restart_workspace(&self, saved_file: Option<AbsPathBuf>) {
-        self.sender.send(StateChange::Restart(None)).unwrap();
+        self.sender.send(StateChange::Restart { package: None, saved_file }).unwrap();
     }
 
     /// Schedule a re-start of the cargo check worker to do a package wide check.
     pub fn restart_for_package(&self, package: String) {
-        self.sender.send(StateChange::Restart(Some(package))).unwrap();
+        self.sender
+            .send(StateChange::Restart { package: Some(package), saved_file: None })
+            .unwrap();
     }
 
     /// Stop this cargo check worker.
@@ -158,7 +162,7 @@ pub enum Progress {
 }
 
 enum StateChange {
-    Restart(Option<String>),
+    Restart { package: Option<String>, saved_file: Option<AbsPathBuf> },
     Cancel,
 }
 
@@ -171,6 +175,7 @@ struct FlycheckActor {
     /// Either the workspace root of the workspace we are flychecking,
     /// or the project root of the project.
     root: AbsPathBuf,
+    sysroot_root: Option<AbsPathBuf>,
     /// CargoHandle exists to wrap around the communication needed to be able to
     /// run `cargo check` without blocking. Currently the Rust standard library
     /// doesn't provide a way to read sub-process output without blocking, so we
@@ -184,15 +189,25 @@ enum Event {
     CheckEvent(Option<CargoMessage>),
 }
 
+const SAVED_FILE_PLACEHOLDER: &str = "$saved_file";
+
 impl FlycheckActor {
     fn new(
         id: usize,
         sender: Box<dyn Fn(Message) + Send>,
         config: FlycheckConfig,
+        sysroot_root: Option<AbsPathBuf>,
         workspace_root: AbsPathBuf,
     ) -> FlycheckActor {
         tracing::info!(%id, ?workspace_root, "Spawning flycheck");
-        FlycheckActor { id, sender, config, root: workspace_root, command_handle: None }
+        FlycheckActor {
+            id,
+            sender,
+            config,
+            sysroot_root,
+            root: workspace_root,
+            command_handle: None,
+        }
     }
 
     fn report_progress(&self, progress: Progress) {
@@ -218,7 +233,7 @@ impl FlycheckActor {
                     tracing::debug!(flycheck_id = self.id, "flycheck cancelled");
                     self.cancel_check_process();
                 }
-                Event::RequestStateChange(StateChange::Restart(package)) => {
+                Event::RequestStateChange(StateChange::Restart { package, saved_file }) => {
                     // Cancel the previously spawned process
                     self.cancel_check_process();
                     while let Ok(restart) = inbox.recv_timeout(Duration::from_millis(50)) {
@@ -228,7 +243,11 @@ impl FlycheckActor {
                         }
                     }
 
-                    let command = self.check_command(package.as_deref());
+                    let command =
+                        match self.check_command(package.as_deref(), saved_file.as_deref()) {
+                            Some(c) => c,
+                            None => continue,
+                        };
                     let formatted_command = format!("{:?}", command);
 
                     tracing::debug!(?command, "will restart flycheck");
@@ -302,7 +321,14 @@ impl FlycheckActor {
         }
     }
 
-    fn check_command(&self, package: Option<&str>) -> Command {
+    /// Construct a `Command` object for checking the user's code. If the user
+    /// has specified a custom command with placeholders that we cannot fill,
+    /// return None.
+    fn check_command(
+        &self,
+        package: Option<&str>,
+        saved_file: Option<&AbsPath>,
+    ) -> Option<Command> {
         let (mut cmd, args) = match &self.config {
             FlycheckConfig::CargoCommand {
                 command,
@@ -316,7 +342,10 @@ impl FlycheckActor {
                 ansi_color_output,
                 target_dir,
             } => {
-                let mut cmd = Command::new(toolchain::cargo());
+                let mut cmd = Command::new(Tool::Cargo.path());
+                if let Some(sysroot_root) = &self.sysroot_root {
+                    cmd.env("RUSTUP_TOOLCHAIN", AsRef::<std::path::Path>::as_ref(sysroot_root));
+                }
                 cmd.arg(command);
                 cmd.current_dir(&self.root);
 
@@ -355,7 +384,7 @@ impl FlycheckActor {
                     cmd.arg("--target-dir").arg(target_dir);
                 }
                 cmd.envs(extra_env);
-                (cmd, extra_args)
+                (cmd, extra_args.clone())
             }
             FlycheckConfig::CustomCommand {
                 command,
@@ -384,12 +413,34 @@ impl FlycheckActor {
                     }
                 }
 
+                if args.contains(&SAVED_FILE_PLACEHOLDER.to_owned()) {
+                    // If the custom command has a $saved_file placeholder, and
+                    // we're saving a file, replace the placeholder in the arguments.
+                    if let Some(saved_file) = saved_file {
+                        let args = args
+                            .iter()
+                            .map(|arg| {
+                                if arg == SAVED_FILE_PLACEHOLDER {
+                                    saved_file.to_string()
+                                } else {
+                                    arg.clone()
+                                }
+                            })
+                            .collect();
                         (cmd, args)
+                    } else {
+                        // The custom command has a $saved_file placeholder,
+                        // but we had an IDE event that wasn't a file save. Do nothing.
+                        return None;
+                    }
+                } else {
+                    (cmd, args.clone())
+                }
             }
         };
 
         cmd.args(args);
-        cmd
+        Some(cmd)
     }
 
     fn send(&self, check_task: Message) {

crates/hir-def/src/attr.rs

@@ -377,27 +377,39 @@ impl AttrsWithOwner {
             AttrDefId::GenericParamId(it) => match it {
                 GenericParamId::ConstParamId(it) => {
                     let src = it.parent().child_source(db);
-                    RawAttrs::from_attrs_owner(
+                    // FIXME: We should be never getting `None` here.
+                    match src.value.get(it.local_id()) {
+                        Some(val) => RawAttrs::from_attrs_owner(
                             db.upcast(),
-                        src.with_value(&src.value[it.local_id()]),
+                            src.with_value(val),
                             db.span_map(src.file_id).as_ref(),
-                    )
+                        ),
+                        None => RawAttrs::EMPTY,
+                    }
                 }
                 GenericParamId::TypeParamId(it) => {
                     let src = it.parent().child_source(db);
-                    RawAttrs::from_attrs_owner(
+                    // FIXME: We should be never getting `None` here.
+                    match src.value.get(it.local_id()) {
+                        Some(val) => RawAttrs::from_attrs_owner(
                             db.upcast(),
-                        src.with_value(&src.value[it.local_id()]),
+                            src.with_value(val),
                             db.span_map(src.file_id).as_ref(),
-                    )
+                        ),
+                        None => RawAttrs::EMPTY,
+                    }
                 }
                 GenericParamId::LifetimeParamId(it) => {
                     let src = it.parent.child_source(db);
-                    RawAttrs::from_attrs_owner(
+                    // FIXME: We should be never getting `None` here.
+                    match src.value.get(it.local_id) {
+                        Some(val) => RawAttrs::from_attrs_owner(
                             db.upcast(),
-                        src.with_value(&src.value[it.local_id]),
+                            src.with_value(val),
                             db.span_map(src.file_id).as_ref(),
-                    )
+                        ),
+                        None => RawAttrs::EMPTY,
+                    }
                 }
             },
             AttrDefId::ExternBlockId(it) => attrs_from_item_tree_loc(db, it),

crates/hir-def/src/body/lower.rs

@@ -416,6 +416,11 @@ impl ExprCollector<'_> {
                 let expr = e.expr().map(|e| self.collect_expr(e));
                 self.alloc_expr(Expr::Return { expr }, syntax_ptr)
             }
+            ast::Expr::BecomeExpr(e) => {
+                let expr =
+                    e.expr().map(|e| self.collect_expr(e)).unwrap_or_else(|| self.missing_expr());
+                self.alloc_expr(Expr::Become { expr }, syntax_ptr)
+            }
             ast::Expr::YieldExpr(e) => {
                 self.is_lowering_coroutine = true;
                 let expr = e.expr().map(|e| self.collect_expr(e));
@@ -1000,10 +1005,6 @@ impl ExprCollector<'_> {
                         krate: *krate,
                     });
                 }
-                Some(ExpandError::RecursionOverflowPoisoned) => {
-                    // Recursion limit has been reached in the macro expansion tree, but not in
-                    // this very macro call. Don't add diagnostics to avoid duplication.
-                }
                 Some(err) => {
                     self.source_map.diagnostics.push(BodyDiagnostic::MacroError {
                         node: InFile::new(outer_file, syntax_ptr),
@@ -1112,7 +1113,7 @@ impl ExprCollector<'_> {
                     statements.push(Statement::Expr { expr, has_semi });
                 }
             }
-            ast::Stmt::Item(_item) => (),
+            ast::Stmt::Item(_item) => statements.push(Statement::Item),
         }
     }
 

crates/hir-def/src/body/pretty.rs

@@ -6,7 +6,7 @@ use itertools::Itertools;
 
 use crate::{
     hir::{
-        Array, BindingAnnotation, BindingId, CaptureBy, ClosureKind, Literal, LiteralOrConst,
+        Array, BindingAnnotation, CaptureBy, ClosureKind, Literal, LiteralOrConst,
         Movability, Statement,
     },
     pretty::{print_generic_args, print_path, print_type_ref},
@@ -261,6 +261,11 @@ impl Printer<'_> {
                     self.print_expr(*expr);
                 }
             }
+            Expr::Become { expr } => {
+                w!(self, "become");
+                self.whitespace();
+                self.print_expr(*expr);
+            }
             Expr::Yield { expr } => {
                 w!(self, "yield");
                 if let Some(expr) = expr {
@@ -623,6 +628,7 @@ impl Printer<'_> {
                 }
                 wln!(self);
             }
+            Statement::Item => (),
         }
     }
 

crates/hir-def/src/body/scope.rs

@@ -197,6 +197,7 @@ fn compute_block_scopes(
             Statement::Expr { expr, .. } => {
                 compute_expr_scopes(*expr, body, scopes, scope);
             }
+            Statement::Item => (),
         }
     }
     if let Some(expr) = tail {

crates/hir-def/src/data.rs

@@ -634,7 +634,6 @@ impl<'a> AssocItemCollector<'a> {
                     attr,
                 ) {
                     Ok(ResolvedAttr::Macro(call_id)) => {
-                        self.attr_calls.push((ast_id, call_id));
                         // If proc attribute macro expansion is disabled, skip expanding it here
                         if !self.db.expand_proc_attr_macros() {
                             continue 'attrs;
@@ -647,10 +646,21 @@ impl<'a> AssocItemCollector<'a> {
                             // disabled. This is analogous to the handling in
                             // `DefCollector::collect_macros`.
                             if exp.is_dummy() {
+                                self.diagnostics.push(DefDiagnostic::unresolved_proc_macro(
+                                    self.module_id.local_id,
+                                    loc.kind,
+                                    loc.def.krate,
+                                ));
+
+                                continue 'attrs;
+                            }
+                            if exp.is_disabled() {
                                 continue 'attrs;
                             }
                         }
 
+                        self.attr_calls.push((ast_id, call_id));
+
                         let res =
                             self.expander.enter_expand_id::<ast::MacroItems>(self.db, call_id);
                         self.collect_macro_items(res, &|| loc.kind.clone());

crates/hir-def/src/expander.rs

@@ -140,13 +140,11 @@ impl Expander {
             // The overflow error should have been reported when it occurred (see the next branch),
             // so don't return overflow error here to avoid diagnostics duplication.
             cov_mark::hit!(overflow_but_not_me);
-            return ExpandResult::only_err(ExpandError::RecursionOverflowPoisoned);
+            return ExpandResult::ok(None);
         } else if self.recursion_limit.check(self.recursion_depth as usize + 1).is_err() {
             self.recursion_depth = u32::MAX;
             cov_mark::hit!(your_stack_belongs_to_me);
-            return ExpandResult::only_err(ExpandError::other(
+            return ExpandResult::only_err(ExpandError::RecursionOverflow);
-                "reached recursion limit during macro expansion",
-            ));
         }
 
         let ExpandResult { value, err } = op(self);

crates/hir-def/src/find_path.rs

@@ -447,18 +447,25 @@ fn select_best_path(
     }
     const STD_CRATES: [Name; 3] = [known::std, known::core, known::alloc];
 
-    let choose = |new_path: (ModPath, _), old_path: (ModPath, _)| {
+    let choose = |new: (ModPath, _), old: (ModPath, _)| {
-        let new_has_prelude = new_path.0.segments().iter().any(|seg| seg == &known::prelude);
+        let (new_path, _) = &new;
-        let old_has_prelude = old_path.0.segments().iter().any(|seg| seg == &known::prelude);
+        let (old_path, _) = &old;
+        let new_has_prelude = new_path.segments().iter().any(|seg| seg == &known::prelude);
+        let old_has_prelude = old_path.segments().iter().any(|seg| seg == &known::prelude);
         match (new_has_prelude, old_has_prelude, prefer_prelude) {
-            (true, false, true) | (false, true, false) => new_path,
+            (true, false, true) | (false, true, false) => new,
-            (true, false, false) | (false, true, true) => old_path,
+            (true, false, false) | (false, true, true) => old,
-            // no prelude difference in the paths, so pick the smaller one
+            // no prelude difference in the paths, so pick the shorter one
             (true, true, _) | (false, false, _) => {
-                if new_path.0.len() < old_path.0.len() {
+                let new_path_is_shorter = new_path
-                    new_path
+                    .len()
+                    .cmp(&old_path.len())
+                    .then_with(|| new_path.textual_len().cmp(&old_path.textual_len()))
+                    .is_lt();
+                if new_path_is_shorter {
+                    new
                 } else {
-                    old_path
+                    old
                 }
             }
         }
@@ -469,8 +476,8 @@ fn select_best_path(
             let rank = match prefer_no_std {
                 false => |name: &Name| match name {
                     name if name == &known::core => 0,
-                    name if name == &known::alloc => 0,
+                    name if name == &known::alloc => 1,
-                    name if name == &known::std => 1,
+                    name if name == &known::std => 2,
                     _ => unreachable!(),
                 },
                 true => |name: &Name| match name {
@@ -1539,4 +1546,38 @@ pub mod foo {
             "krate::prelude::Foo",
         );
     }
+
+    #[test]
+    fn respect_segment_length() {
+        check_found_path(
+            r#"
+//- /main.rs crate:main deps:petgraph
+$0
+//- /petgraph.rs crate:petgraph
+pub mod graph {
+    pub use crate::graph_impl::{
+        NodeIndex
+    };
+}
+
+mod graph_impl {
+    pub struct NodeIndex<Ix>(Ix);
+}
+
+pub mod stable_graph {
+    #[doc(no_inline)]
+    pub use crate::graph::{NodeIndex};
+}
+
+pub mod prelude {
+    #[doc(no_inline)]
+    pub use crate::graph::{NodeIndex};
+}
+"#,
+            "petgraph::graph::NodeIndex",
+            "petgraph::graph::NodeIndex",
+            "petgraph::graph::NodeIndex",
+            "petgraph::graph::NodeIndex",
+        );
+    }
 }

crates/hir-def/src/hir.rs

@@ -182,6 +182,7 @@ pub enum Expr {
         tail: Option<ExprId>,
     },
     Const(ConstBlockId),
+    // FIXME: Fold this into Block with an unsafe flag?
     Unsafe {
         id: Option<BlockId>,
         statements: Box<[Statement]>,
@@ -216,6 +217,9 @@ pub enum Expr {
     Return {
         expr: Option<ExprId>,
     },
+    Become {
+        expr: ExprId,
+    },
     Yield {
         expr: Option<ExprId>,
     },
@@ -349,6 +353,9 @@ pub enum Statement {
         expr: ExprId,
         has_semi: bool,
     },
+    // At the moment, we only use this to figure out if a return expression
+    // is really the last statement of a block. See #16566
+    Item,
 }
 
 impl Expr {
@@ -382,6 +389,7 @@ impl Expr {
                             }
                         }
                         Statement::Expr { expr: expression, .. } => f(*expression),
+                        Statement::Item => (),
                     }
                 }
                 if let &Some(expr) = tail {
@@ -410,6 +418,7 @@ impl Expr {
                     f(expr);
                 }
             }
+            Expr::Become { expr } => f(*expr),
             Expr::RecordLit { fields, spread, .. } => {
                 for field in fields.iter() {
                     f(field.expr);

crates/hir-def/src/import_map.rs

@@ -3,7 +3,7 @@
 use std::{fmt, hash::BuildHasherDefault};
 
 use base_db::CrateId;
-use fst::{self, raw::IndexedValue, Automaton, Streamer};
+use fst::{raw::IndexedValue, Automaton, Streamer};
 use hir_expand::name::Name;
 use indexmap::IndexMap;
 use itertools::Itertools;

crates/hir-def/src/item_tree/lower.rs

@@ -2,12 +2,12 @@
 
 use std::collections::hash_map::Entry;
 
-use hir_expand::{ast_id_map::AstIdMap, span_map::SpanMapRef, HirFileId};
+use hir_expand::{ast_id_map::AstIdMap, span_map::SpanMapRef};
-use syntax::ast::{self, HasModuleItem, HasTypeBounds, IsString};
+use syntax::ast::{HasModuleItem, HasTypeBounds, IsString};
 
 use crate::{
-    generics::{GenericParams, GenericParamsCollector, TypeParamData, TypeParamProvenance},
+    generics::{GenericParamsCollector, TypeParamData, TypeParamProvenance},
-    type_ref::{LifetimeRef, TraitBoundModifier, TraitRef},
+    type_ref::{LifetimeRef, TraitBoundModifier},
     LocalLifetimeParamId, LocalTypeOrConstParamId,
 };
 

crates/hir-def/src/item_tree/pretty.rs

@@ -1,13 +1,12 @@
 //! `ItemTree` debug printer.
 
-use std::fmt::{self, Write};
+use std::fmt::Write;
 
 use span::ErasedFileAstId;
 
 use crate::{
-    generics::{TypeOrConstParamData, WherePredicate, WherePredicateTypeTarget},
+    generics::{WherePredicate, WherePredicateTypeTarget},
     pretty::{print_path, print_type_bounds, print_type_ref},
-    visibility::RawVisibility,
 };
 
 use super::*;

crates/hir-def/src/macro_expansion_tests/mbe/matching.rs

@@ -33,7 +33,7 @@ m!(&k");
 "#,
         expect![[r#"
 macro_rules! m { ($i:literal) => {}; }
-/* error: invalid token tree */"#]],
+/* error: mismatched delimiters */"#]],
     );
 }
 

crates/hir-def/src/macro_expansion_tests/mbe/meta_syntax.rs

@@ -68,26 +68,26 @@ m2!();
 "#,
         expect![[r#"
 macro_rules! i1 { invalid }
-/* error: invalid macro definition: expected subtree */
+/* error: macro definition has parse errors */
 
 macro_rules! e1 { $i:ident => () }
-/* error: invalid macro definition: expected subtree */
+/* error: macro definition has parse errors */
 macro_rules! e2 { ($i:ident) () }
-/* error: invalid macro definition: expected `=` */
+/* error: macro definition has parse errors */
 macro_rules! e3 { ($(i:ident)_) => () }
-/* error: invalid macro definition: invalid repeat */
+/* error: macro definition has parse errors */
 
 macro_rules! f1 { ($i) => ($i) }
-/* error: invalid macro definition: missing fragment specifier */
+/* error: macro definition has parse errors */
 macro_rules! f2 { ($i:) => ($i) }
-/* error: invalid macro definition: missing fragment specifier */
+/* error: macro definition has parse errors */
 macro_rules! f3 { ($i:_) => () }
-/* error: invalid macro definition: missing fragment specifier */
+/* error: macro definition has parse errors */
 
 macro_rules! m1 { ($$i) => () }
-/* error: invalid macro definition: `$$` is not allowed on the pattern side */
+/* error: macro definition has parse errors */
 macro_rules! m2 { () => ( ${invalid()} ) }
-/* error: invalid macro definition: invalid metavariable expression */
+/* error: macro definition has parse errors */
 "#]],
     )
 }
@@ -137,18 +137,18 @@ macro_rules! m9 { ($($($($i:ident)?)*)+) => {}; }
 macro_rules! mA { ($($($($i:ident)+)?)*) => {}; }
 macro_rules! mB { ($($($($i:ident)+)*)?) => {}; }
 
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
-/* error: invalid macro definition: empty token tree in repetition */
+/* error: macro definition has parse errors */
     "#]],
     );
 }

crates/hir-def/src/macro_expansion_tests/mbe/metavar_expr.rs

@@ -275,9 +275,9 @@ macro_rules! depth_too_large {
 }
 
 fn test() {
-    /* error: invalid macro definition: invalid metavariable expression */;
+    /* error: macro definition has parse errors */;
-    /* error: invalid macro definition: invalid metavariable expression */;
+    /* error: macro definition has parse errors */;
-    /* error: invalid macro definition: invalid metavariable expression */;
+    /* error: macro definition has parse errors */;
 }
 "#]],
     );

crates/hir-def/src/macro_expansion_tests/mbe/regression.rs

@@ -1090,3 +1090,57 @@ fn main() {
 "#]],
     );
 }
+
+#[test]
+fn regression_16529() {
+    check(
+        r#"
+mod any {
+    #[macro_export]
+    macro_rules! nameable {
+        {
+            struct $name:ident[$a:lifetime]
+        } => {
+            $crate::any::nameable! {
+                struct $name[$a]
+                a
+            }
+        };
+        {
+            struct $name:ident[$a:lifetime]
+            a
+        } => {};
+    }
+    pub use nameable;
+
+    nameable! {
+        Name['a]
+    }
+}
+"#,
+        expect![[r#"
+mod any {
+    #[macro_export]
+    macro_rules! nameable {
+        {
+            struct $name:ident[$a:lifetime]
+        } => {
+            $crate::any::nameable! {
+                struct $name[$a]
+                a
+            }
+        };
+        {
+            struct $name:ident[$a:lifetime]
+            a
+        } => {};
+    }
+    pub use nameable;
+
+    /* error: unexpected token in input */$crate::any::nameable! {
+        struct $name[$a]a
+    }
+}
+"#]],
+    );
+}

crates/hir-def/src/macro_expansion_tests/mbe/tt_conversion.rs

@@ -97,8 +97,8 @@ m2!(x
 macro_rules! m1 { ($x:ident) => { ($x } }
 macro_rules! m2 { ($x:ident) => {} }
 
-/* error: invalid macro definition: expected subtree */
+/* error: macro definition has parse errors */
-/* error: invalid token tree */
+/* error: mismatched delimiters */
 "#]],
     )
 }

crates/hir-def/src/macro_expansion_tests/mod.rs

@@ -58,6 +58,7 @@ pub fn identity_when_valid(_attr: TokenStream, item: TokenStream) -> TokenStream
             name: "identity_when_valid".into(),
             kind: ProcMacroKind::Attr,
             expander: sync::Arc::new(IdentityWhenValidProcMacroExpander),
+            disabled: false,
         },
     )];
     let db = TestDB::with_files_extra_proc_macros(ra_fixture, extra_proc_macros);

crates/hir-def/src/nameres.rs

@@ -57,7 +57,7 @@ pub mod proc_macro;
 #[cfg(test)]
 mod tests;
 
-use std::{cmp::Ord, ops::Deref};
+use std::ops::Deref;
 
 use base_db::{CrateId, Edition, FileId};
 use hir_expand::{

crates/hir-def/src/nameres/collector.rs

@@ -11,7 +11,7 @@ use either::Either;
 use hir_expand::{
     ast_id_map::FileAstId,
     attrs::{Attr, AttrId},
-    builtin_attr_macro::find_builtin_attr,
+    builtin_attr_macro::{find_builtin_attr, BuiltinAttrExpander},
     builtin_derive_macro::find_builtin_derive,
     builtin_fn_macro::find_builtin_macro,
     name::{name, AsName, Name},
@@ -98,9 +98,13 @@ pub(super) fn collect_defs(db: &dyn DefDatabase, def_map: DefMap, tree_id: TreeI
                         };
                         (
                             name.as_name(),
-                            CustomProcMacroExpander::new(hir_expand::proc_macro::ProcMacroId(
+                            if it.disabled {
-                                idx as u32,
+                                CustomProcMacroExpander::disabled()
-                            )),
+                            } else {
+                                CustomProcMacroExpander::new(
+                                    hir_expand::proc_macro::ProcMacroId::new(idx as u32),
+                                )
+                            },
                         )
                     })
                     .collect())
@@ -604,9 +608,6 @@ impl DefCollector<'_> {
         id: ItemTreeId<item_tree::Function>,
         fn_id: FunctionId,
     ) {
-        if self.def_map.block.is_some() {
-            return;
-        }
         let kind = def.kind.to_basedb_kind();
         let (expander, kind) =
             match self.proc_macros.as_ref().map(|it| it.iter().find(|(n, _)| n == &def.name)) {
@@ -1120,9 +1121,16 @@ impl DefCollector<'_> {
         let mut push_resolved = |directive: &MacroDirective, call_id| {
             resolved.push((directive.module_id, directive.depth, directive.container, call_id));
         };
+
+        #[derive(PartialEq, Eq)]
+        enum Resolved {
+            Yes,
+            No,
+        }
+
         let mut res = ReachedFixedPoint::Yes;
         // Retain unresolved macros after this round of resolution.
-        macros.retain(|directive| {
+        let mut retain = |directive: &MacroDirective| {
             let subns = match &directive.kind {
                 MacroDirectiveKind::FnLike { .. } => MacroSubNs::Bang,
                 MacroDirectiveKind::Attr { .. } | MacroDirectiveKind::Derive { .. } => {
@@ -1156,10 +1164,11 @@ impl DefCollector<'_> {
                         self.def_map.modules[directive.module_id]
                             .scope
                             .add_macro_invoc(ast_id.ast_id, call_id);
+
                         push_resolved(directive, call_id);
 
                         res = ReachedFixedPoint::No;
-                        return false;
+                        return Resolved::Yes;
                     }
                 }
                 MacroDirectiveKind::Derive { ast_id, derive_attr, derive_pos, call_site } => {
@@ -1198,7 +1207,7 @@ impl DefCollector<'_> {
 
                         push_resolved(directive, call_id);
                         res = ReachedFixedPoint::No;
-                        return false;
+                        return Resolved::Yes;
                     }
                 }
                 MacroDirectiveKind::Attr { ast_id: file_ast_id, mod_item, attr, tree } => {
@@ -1221,7 +1230,7 @@ impl DefCollector<'_> {
                         }
                         .collect(&[*mod_item], directive.container);
                         res = ReachedFixedPoint::No;
-                        false
+                        Resolved::Yes
                     };
 
                     if let Some(ident) = path.as_ident() {
@@ -1237,13 +1246,18 @@ impl DefCollector<'_> {
 
                     let def = match resolver_def_id(path.clone()) {
                         Some(def) if def.is_attribute() => def,
-                        _ => return true,
+                        _ => return Resolved::No,
                     };
-                    if matches!(
+
-                        def,
+                    if let MacroDefId {
-                        MacroDefId { kind: MacroDefKind::BuiltInAttr(expander, _),.. }
+                        kind:
-                        if expander.is_derive()
+                            MacroDefKind::BuiltInAttr(
-                    ) {
+                                BuiltinAttrExpander::Derive | BuiltinAttrExpander::DeriveConst,
+                                _,
+                            ),
+                        ..
+                    } = def
+                    {
                         // Resolved to `#[derive]`, we don't actually expand this attribute like
                         // normal (as that would just be an identity expansion with extra output)
                         // Instead we treat derive attributes special and apply them separately.
@@ -1316,16 +1330,6 @@ impl DefCollector<'_> {
                     let call_id =
                         attr_macro_as_call_id(self.db, file_ast_id, attr, self.def_map.krate, def);
 
-                    // If proc attribute macro expansion is disabled, skip expanding it here
-                    if !self.db.expand_proc_attr_macros() {
-                        self.def_map.diagnostics.push(DefDiagnostic::unresolved_proc_macro(
-                            directive.module_id,
-                            self.db.lookup_intern_macro_call(call_id).kind,
-                            def.krate,
-                        ));
-                        return recollect_without(self);
-                    }
-
                     // Skip #[test]/#[bench] expansion, which would merely result in more memory usage
                     // due to duplicating functions into macro expansions
                     if matches!(
@@ -1337,17 +1341,29 @@ impl DefCollector<'_> {
                     }
 
                     if let MacroDefKind::ProcMacro(exp, ..) = def.kind {
-                        if exp.is_dummy() {
+                        // If proc attribute macro expansion is disabled, skip expanding it here
-                            // If there's no expander for the proc macro (e.g.
+                        if !self.db.expand_proc_attr_macros() {
-                            // because proc macros are disabled, or building the
-                            // proc macro crate failed), report this and skip
-                            // expansion like we would if it was disabled
                             self.def_map.diagnostics.push(DefDiagnostic::unresolved_proc_macro(
                                 directive.module_id,
                                 self.db.lookup_intern_macro_call(call_id).kind,
                                 def.krate,
                             ));
+                            return recollect_without(self);
+                        }
 
+                        // If there's no expander for the proc macro (e.g.
+                        // because proc macros are disabled, or building the
+                        // proc macro crate failed), report this and skip
+                        // expansion like we would if it was disabled
+                        if exp.is_dummy() {
+                            self.def_map.diagnostics.push(DefDiagnostic::unresolved_proc_macro(
+                                directive.module_id,
+                                self.db.lookup_intern_macro_call(call_id).kind,
+                                def.krate,
+                            ));
+                            return recollect_without(self);
+                        }
+                        if exp.is_disabled() {
                             return recollect_without(self);
                         }
                     }
@@ -1358,12 +1374,13 @@ impl DefCollector<'_> {
 
                     push_resolved(directive, call_id);
                     res = ReachedFixedPoint::No;
-                    return false;
+                    return Resolved::Yes;
                 }
             }
 
-            true
+            Resolved::No
-        });
+        };
+        macros.retain(|it| retain(it) == Resolved::No);
         // Attribute resolution can add unresolved macro invocations, so concatenate the lists.
         macros.extend(mem::take(&mut self.unresolved_macros));
         self.unresolved_macros = macros;
@@ -1673,7 +1690,11 @@ impl ModCollector<'_, '_> {
                         FunctionLoc { container, id: ItemTreeId::new(self.tree_id, id) }.intern(db);
 
                     let vis = resolve_vis(def_map, &self.item_tree[it.visibility]);
-                    if self.def_collector.is_proc_macro && self.module_id == DefMap::ROOT {
+
+                    if self.def_collector.def_map.block.is_none()
+                        && self.def_collector.is_proc_macro
+                        && self.module_id == DefMap::ROOT
+                    {
                         if let Some(proc_macro) = attrs.parse_proc_macro_decl(&it.name) {
                             self.def_collector.export_proc_macro(
                                 proc_macro,
@@ -2333,7 +2354,7 @@ impl ModCollector<'_, '_> {
                 resolved_res.resolved_def.take_macros().map(|it| db.macro_def(it))
             },
         ) {
-            // FIXME: if there were errors, this mightve been in the eager expansion from an
+            // FIXME: if there were errors, this might've been in the eager expansion from an
             // unresolved macro, so we need to push this into late macro resolution. see fixme above
             if res.err.is_none() {
                 // Legacy macros need to be expanded immediately, so that any macros they produce

crates/hir-def/src/nameres/diagnostics.rs

@@ -103,6 +103,9 @@ impl DefDiagnostic {
     }
 
     // FIXME: Whats the difference between this and unresolved_macro_call
+    // FIXME: This is used for a lot of things, unresolved proc macros, disabled proc macros, etc
+    // yet the diagnostic handler in ide-diagnostics has to figure out what happened because this
+    // struct loses all that information!
     pub(crate) fn unresolved_proc_macro(
         container: LocalModuleId,
         ast: MacroCallKind,

crates/hir-expand/src/builtin_fn_macro.rs

@@ -446,7 +446,7 @@ fn compile_error_expand(
 ) -> ExpandResult<tt::Subtree> {
     let err = match &*tt.token_trees {
         [tt::TokenTree::Leaf(tt::Leaf::Literal(it))] => match unquote_str(it) {
-            Some(unquoted) => ExpandError::other(unquoted),
+            Some(unquoted) => ExpandError::other(unquoted.into_boxed_str()),
             None => ExpandError::other("`compile_error!` argument must be a string"),
         },
         _ => ExpandError::other("`compile_error!` argument must be a string"),

crates/hir-expand/src/change.rs

@@ -1,6 +1,10 @@
 //! Defines a unit of change that can applied to the database to get the next
 //! state. Changes are transactional.
-use base_db::{salsa::Durability, CrateGraph, FileChange, SourceDatabaseExt, SourceRoot};
+use base_db::{
+    salsa::Durability, CrateGraph, CrateId, FileChange, SourceDatabaseExt, SourceRoot,
+    TargetLayoutLoadResult, Version,
+};
+use la_arena::RawIdx;
 use span::FileId;
 use triomphe::Arc;
 
@@ -10,6 +14,8 @@ use crate::{db::ExpandDatabase, proc_macro::ProcMacros};
 pub struct Change {
     pub source_change: FileChange,
     pub proc_macros: Option<ProcMacros>,
+    pub toolchains: Option<Vec<Option<Version>>>,
+    pub target_data_layouts: Option<Vec<TargetLayoutLoadResult>>,
 }
 
 impl Change {
@@ -22,6 +28,24 @@ impl Change {
         if let Some(proc_macros) = self.proc_macros {
             db.set_proc_macros_with_durability(Arc::new(proc_macros), Durability::HIGH);
         }
+        if let Some(target_data_layouts) = self.target_data_layouts {
+            for (id, val) in target_data_layouts.into_iter().enumerate() {
+                db.set_data_layout_with_durability(
+                    CrateId::from_raw(RawIdx::from(id as u32)),
+                    val,
+                    Durability::HIGH,
+                );
+            }
+        }
+        if let Some(toolchains) = self.toolchains {
+            for (id, val) in toolchains.into_iter().enumerate() {
+                db.set_toolchain_with_durability(
+                    CrateId::from_raw(RawIdx::from(id as u32)),
+                    val,
+                    Durability::HIGH,
+                );
+            }
+        }
     }
 
     pub fn change_file(&mut self, file_id: FileId, new_text: Option<Arc<str>>) {
@@ -36,6 +60,14 @@ impl Change {
         self.proc_macros = Some(proc_macros);
     }
 
+    pub fn set_toolchains(&mut self, toolchains: Vec<Option<Version>>) {
+        self.toolchains = Some(toolchains);
+    }
+
+    pub fn set_target_data_layouts(&mut self, target_data_layouts: Vec<TargetLayoutLoadResult>) {
+        self.target_data_layouts = Some(target_data_layouts);
+    }
+
     pub fn set_roots(&mut self, roots: Vec<SourceRoot>) {
         self.source_change.set_roots(roots)
     }

crates/hir-expand/src/db.rs

@@ -108,7 +108,7 @@ pub trait ExpandDatabase: SourceDatabase {
     fn macro_arg(
         &self,
         id: MacroCallId,
-    ) -> ValueResult<Option<(Arc<tt::Subtree>, SyntaxFixupUndoInfo)>, Arc<Box<[SyntaxError]>>>;
+    ) -> ValueResult<(Arc<tt::Subtree>, SyntaxFixupUndoInfo), Arc<Box<[SyntaxError]>>>;
     /// Fetches the expander for this macro.
     #[salsa::transparent]
     #[salsa::invoke(TokenExpander::macro_expander)]
@@ -326,58 +326,77 @@ fn macro_arg(
     db: &dyn ExpandDatabase,
     id: MacroCallId,
     // FIXME: consider the following by putting fixup info into eager call info args
-    // ) -> ValueResult<Option<Arc<(tt::Subtree, SyntaxFixupUndoInfo)>>, Arc<Box<[SyntaxError]>>> {
+    // ) -> ValueResult<Arc<(tt::Subtree, SyntaxFixupUndoInfo)>, Arc<Box<[SyntaxError]>>> {
-) -> ValueResult<Option<(Arc<tt::Subtree>, SyntaxFixupUndoInfo)>, Arc<Box<[SyntaxError]>>> {
+) -> ValueResult<(Arc<tt::Subtree>, SyntaxFixupUndoInfo), Arc<Box<[SyntaxError]>>> {
-    let mismatched_delimiters = |arg: &SyntaxNode| {
-        let first = arg.first_child_or_token().map_or(T![.], |it| it.kind());
-        let last = arg.last_child_or_token().map_or(T![.], |it| it.kind());
-        let well_formed_tt =
-            matches!((first, last), (T!['('], T![')']) | (T!['['], T![']']) | (T!['{'], T!['}']));
-        if !well_formed_tt {
-            // Don't expand malformed (unbalanced) macro invocations. This is
-            // less than ideal, but trying to expand unbalanced  macro calls
-            // sometimes produces pathological, deeply nested code which breaks
-            // all kinds of things.
-            //
-            // Some day, we'll have explicit recursion counters for all
-            // recursive things, at which point this code might be removed.
-            cov_mark::hit!(issue9358_bad_macro_stack_overflow);
-            Some(Arc::new(Box::new([SyntaxError::new(
-                "unbalanced token tree".to_owned(),
-                arg.text_range(),
-            )]) as Box<[_]>))
-        } else {
-            None
-        }
-    };
     let loc = db.lookup_intern_macro_call(id);
     if let Some(EagerCallInfo { arg, .. }) = matches!(loc.def.kind, MacroDefKind::BuiltInEager(..))
         .then(|| loc.eager.as_deref())
         .flatten()
     {
-        ValueResult::ok(Some((arg.clone(), SyntaxFixupUndoInfo::NONE)))
+        ValueResult::ok((arg.clone(), SyntaxFixupUndoInfo::NONE))
     } else {
         let (parse, map) = parse_with_map(db, loc.kind.file_id());
         let root = parse.syntax_node();
 
         let syntax = match loc.kind {
             MacroCallKind::FnLike { ast_id, .. } => {
+                let dummy_tt = |kind| {
+                    (
+                        Arc::new(tt::Subtree {
+                            delimiter: tt::Delimiter {
+                                open: loc.call_site,
+                                close: loc.call_site,
+                                kind,
+                            },
+                            token_trees: Box::default(),
+                        }),
+                        SyntaxFixupUndoInfo::default(),
+                    )
+                };
+
                 let node = &ast_id.to_ptr(db).to_node(&root);
                 let offset = node.syntax().text_range().start();
-                match node.token_tree() {
+                let Some(tt) = node.token_tree() else {
-                    Some(tt) => {
+                    return ValueResult::new(
-                        let tt = tt.syntax();
+                        dummy_tt(tt::DelimiterKind::Invisible),
-                        if let Some(e) = mismatched_delimiters(tt) {
+                        Arc::new(Box::new([SyntaxError::new_at_offset(
-                            return ValueResult::only_err(e);
+                            "missing token tree".to_owned(),
-                        }
+                            offset,
-                        tt.clone()
+                        )])),
-                    }
+                    );
-                    None => {
+                };
-                        return ValueResult::only_err(Arc::new(Box::new([
+                let first = tt.left_delimiter_token().map(|it| it.kind()).unwrap_or(T!['(']);
-                            SyntaxError::new_at_offset("missing token tree".to_owned(), offset),
+                let last = tt.right_delimiter_token().map(|it| it.kind()).unwrap_or(T![.]);
-                        ])));
+
-                    }
+                let mismatched_delimiters = !matches!(
+                    (first, last),
+                    (T!['('], T![')']) | (T!['['], T![']']) | (T!['{'], T!['}'])
+                );
+                if mismatched_delimiters {
+                    // Don't expand malformed (unbalanced) macro invocations. This is
+                    // less than ideal, but trying to expand unbalanced  macro calls
+                    // sometimes produces pathological, deeply nested code which breaks
+                    // all kinds of things.
+                    //
+                    // So instead, we'll return an empty subtree here
+                    cov_mark::hit!(issue9358_bad_macro_stack_overflow);
+
+                    let kind = match first {
+                        _ if loc.def.is_proc_macro() => tt::DelimiterKind::Invisible,
+                        T!['('] => tt::DelimiterKind::Parenthesis,
+                        T!['['] => tt::DelimiterKind::Bracket,
+                        T!['{'] => tt::DelimiterKind::Brace,
+                        _ => tt::DelimiterKind::Invisible,
+                    };
+                    return ValueResult::new(
+                        dummy_tt(kind),
+                        Arc::new(Box::new([SyntaxError::new_at_offset(
+                            "mismatched delimiters".to_owned(),
+                            offset,
+                        )])),
+                    );
                 }
+                tt.syntax().clone()
             }
             MacroCallKind::Derive { ast_id, .. } => {
                 ast_id.to_ptr(db).to_node(&root).syntax().clone()
@@ -427,15 +446,15 @@ fn macro_arg(
 
         if matches!(loc.def.kind, MacroDefKind::BuiltInEager(..)) {
             match parse.errors() {
-                [] => ValueResult::ok(Some((Arc::new(tt), undo_info))),
+                [] => ValueResult::ok((Arc::new(tt), undo_info)),
                 errors => ValueResult::new(
-                    Some((Arc::new(tt), undo_info)),
+                    (Arc::new(tt), undo_info),
                     // Box::<[_]>::from(res.errors()), not stable yet
                     Arc::new(errors.to_vec().into_boxed_slice()),
                 ),
             }
         } else {
-            ValueResult::ok(Some((Arc::new(tt), undo_info)))
+            ValueResult::ok((Arc::new(tt), undo_info))
         }
     }
 }
@@ -519,21 +538,20 @@ fn macro_expand(
             expander.expand(db, macro_call_id, &node, map.as_ref())
         }
         _ => {
-            let ValueResult { value, err } = db.macro_arg(macro_call_id);
+            let ValueResult { value: (macro_arg, undo_info), err } = db.macro_arg(macro_call_id);
-            let Some((macro_arg, undo_info)) = value else {
+            let format_parse_err = |err: Arc<Box<[SyntaxError]>>| {
-                return ExpandResult {
+                let mut buf = String::new();
-                    value: CowArc::Owned(tt::Subtree {
+                for err in &**err {
-                        delimiter: tt::Delimiter::invisible_spanned(loc.call_site),
+                    use std::fmt::Write;
-                        token_trees: Box::new([]),
+                    _ = write!(buf, "{}, ", err);
-                    }),
+                }
-                    // FIXME: We should make sure to enforce an invariant that invalid macro
+                buf.pop();
-                    // calls do not reach this call path!
+                buf.pop();
-                    err: Some(ExpandError::other("invalid token tree")),
+                ExpandError::other(buf)
-                };
             };
 
             let arg = &*macro_arg;
-            match loc.def.kind {
+            let res = match loc.def.kind {
                 MacroDefKind::Declarative(id) => {
                     db.decl_macro_expander(loc.def.krate, id).expand(db, arg.clone(), macro_call_id)
                 }
@@ -549,16 +567,7 @@ fn macro_expand(
                 MacroDefKind::BuiltInEager(..) if loc.eager.is_none() => {
                     return ExpandResult {
                         value: CowArc::Arc(macro_arg.clone()),
-                        err: err.map(|err| {
+                        err: err.map(format_parse_err),
-                            let mut buf = String::new();
-                            for err in &**err {
-                                use std::fmt::Write;
-                                _ = write!(buf, "{}, ", err);
-                            }
-                            buf.pop();
-                            buf.pop();
-                            ExpandError::other(buf)
-                        }),
                     };
                 }
                 MacroDefKind::BuiltInEager(it, _) => {
@@ -570,6 +579,11 @@ fn macro_expand(
                     res
                 }
                 _ => unreachable!(),
+            };
+            ExpandResult {
+                value: res.value,
+                // if the arg had parse errors, show them instead of the expansion errors
+                err: err.map(format_parse_err).or(res.err),
             }
         }
     };
@@ -597,17 +611,7 @@ fn macro_expand(
 
 fn expand_proc_macro(db: &dyn ExpandDatabase, id: MacroCallId) -> ExpandResult<Arc<tt::Subtree>> {
     let loc = db.lookup_intern_macro_call(id);
-    let Some((macro_arg, undo_info)) = db.macro_arg(id).value else {
+    let (macro_arg, undo_info) = db.macro_arg(id).value;
-        return ExpandResult {
-            value: Arc::new(tt::Subtree {
-                delimiter: tt::Delimiter::invisible_spanned(loc.call_site),
-                token_trees: Box::new([]),
-            }),
-            // FIXME: We should make sure to enforce an invariant that invalid macro
-            // calls do not reach this call path!
-            err: Some(ExpandError::other("invalid token tree")),
-        };
-    };
 
     let expander = match loc.def.kind {
         MacroDefKind::ProcMacro(expander, ..) => expander,

crates/hir-expand/src/declarative.rs

@@ -31,7 +31,7 @@ impl DeclarativeMacroExpander {
         call_id: MacroCallId,
     ) -> ExpandResult<tt::Subtree> {
         let loc = db.lookup_intern_macro_call(call_id);
-        let toolchain = &db.crate_graph()[loc.def.krate].toolchain;
+        let toolchain = db.toolchain(loc.def.krate);
         let new_meta_vars = toolchain.as_ref().map_or(false, |version| {
             REQUIREMENT.get_or_init(|| VersionReq::parse(">=1.76").unwrap()).matches(
                 &base_db::Version {
@@ -44,9 +44,9 @@ impl DeclarativeMacroExpander {
             )
         });
         match self.mac.err() {
-            Some(e) => ExpandResult::new(
+            Some(_) => ExpandResult::new(
                 tt::Subtree::empty(tt::DelimSpan { open: loc.call_site, close: loc.call_site }),
-                ExpandError::other(format!("invalid macro definition: {e}")),
+                ExpandError::MacroDefinition,
             ),
             None => self
                 .mac
@@ -67,7 +67,7 @@ impl DeclarativeMacroExpander {
         krate: CrateId,
         call_site: Span,
     ) -> ExpandResult<tt::Subtree> {
-        let toolchain = &db.crate_graph()[krate].toolchain;
+        let toolchain = db.toolchain(krate);
         let new_meta_vars = toolchain.as_ref().map_or(false, |version| {
             REQUIREMENT.get_or_init(|| VersionReq::parse(">=1.76").unwrap()).matches(
                 &base_db::Version {
@@ -80,9 +80,9 @@ impl DeclarativeMacroExpander {
             )
         });
         match self.mac.err() {
-            Some(e) => ExpandResult::new(
+            Some(_) => ExpandResult::new(
                 tt::Subtree::empty(tt::DelimSpan { open: call_site, close: call_site }),
-                ExpandError::other(format!("invalid macro definition: {e}")),
+                ExpandError::MacroDefinition,
             ),
             None => self.mac.expand(&tt, |_| (), new_meta_vars, call_site).map_err(Into::into),
         }
@@ -119,7 +119,7 @@ impl DeclarativeMacroExpander {
                 _ => None,
             }
         };
-        let toolchain = crate_data.toolchain.as_ref();
+        let toolchain = db.toolchain(def_crate);
         let new_meta_vars = toolchain.as_ref().map_or(false, |version| {
             REQUIREMENT.get_or_init(|| VersionReq::parse(">=1.76").unwrap()).matches(
                 &base_db::Version {

crates/hir-expand/src/lib.rs

@@ -44,7 +44,6 @@ use crate::{
     builtin_derive_macro::BuiltinDeriveExpander,
     builtin_fn_macro::{BuiltinFnLikeExpander, EagerExpander},
     db::{ExpandDatabase, TokenExpander},
-    fixup::SyntaxFixupUndoInfo,
     hygiene::SyntaxContextData,
     mod_path::ModPath,
     proc_macro::{CustomProcMacroExpander, ProcMacroKind},
@@ -129,8 +128,11 @@ pub type ExpandResult<T> = ValueResult<T, ExpandError>;
 #[derive(Debug, PartialEq, Eq, Clone, Hash)]
 pub enum ExpandError {
     UnresolvedProcMacro(CrateId),
+    /// The macro expansion is disabled.
+    MacroDisabled,
+    MacroDefinition,
     Mbe(mbe::ExpandError),
-    RecursionOverflowPoisoned,
+    RecursionOverflow,
     Other(Box<Box<str>>),
     ProcMacroPanic(Box<Box<str>>),
 }
@@ -152,14 +154,14 @@ impl fmt::Display for ExpandError {
         match self {
             ExpandError::UnresolvedProcMacro(_) => f.write_str("unresolved proc-macro"),
             ExpandError::Mbe(it) => it.fmt(f),
-            ExpandError::RecursionOverflowPoisoned => {
+            ExpandError::RecursionOverflow => f.write_str("overflow expanding the original macro"),
-                f.write_str("overflow expanding the original macro")
-            }
             ExpandError::ProcMacroPanic(it) => {
                 f.write_str("proc-macro panicked: ")?;
                 f.write_str(it)
             }
             ExpandError::Other(it) => f.write_str(it),
+            ExpandError::MacroDisabled => f.write_str("macro disabled"),
+            ExpandError::MacroDefinition => f.write_str("macro definition has parse errors"),
         }
     }
 }
@@ -225,8 +227,8 @@ pub enum MacroCallKind {
     },
     Attr {
         ast_id: AstId<ast::Item>,
-        // FIXME: This is being interned, subtrees can vary quickly differ just slightly causing
+        // FIXME: This shouldn't be here, we can derive this from `invoc_attr_index`
-        // leakage problems here
+        // but we need to fix the `cfg_attr` handling first.
         attr_args: Option<Arc<tt::Subtree>>,
         /// Syntactical index of the invoking `#[attribute]`.
         ///
@@ -758,15 +760,7 @@ impl ExpansionInfo {
         let (parse, exp_map) = db.parse_macro_expansion(macro_file).value;
         let expanded = InMacroFile { file_id: macro_file, value: parse.syntax_node() };
 
-        let (macro_arg, _) = db.macro_arg(macro_file.macro_call_id).value.unwrap_or_else(|| {
+        let (macro_arg, _) = db.macro_arg(macro_file.macro_call_id).value;
-            (
-                Arc::new(tt::Subtree {
-                    delimiter: tt::Delimiter::invisible_spanned(loc.call_site),
-                    token_trees: Box::new([]),
-                }),
-                SyntaxFixupUndoInfo::NONE,
-            )
-        });
 
         let def = loc.def.ast_id().left().and_then(|id| {
             let def_tt = match id.to_node(db) {

crates/hir-expand/src/mod_path.rs

@@ -94,6 +94,21 @@ impl ModPath {
             }
     }
 
+    pub fn textual_len(&self) -> usize {
+        let base = match self.kind {
+            PathKind::Plain => 0,
+            PathKind::Super(0) => "self".len(),
+            PathKind::Super(i) => "super".len() * i as usize,
+            PathKind::Crate => "crate".len(),
+            PathKind::Abs => 0,
+            PathKind::DollarCrate(_) => "$crate".len(),
+        };
+        self.segments()
+            .iter()
+            .map(|segment| segment.as_str().map_or(0, str::len))
+            .fold(base, core::ops::Add::add)
+    }
+
     pub fn is_ident(&self) -> bool {
         self.as_ident().is_some()
     }

crates/hir-expand/src/proc_macro.rs

@@ -12,7 +12,13 @@ use syntax::SmolStr;
 use crate::{db::ExpandDatabase, tt, ExpandError, ExpandResult};
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
-pub struct ProcMacroId(pub u32);
+pub struct ProcMacroId(u32);
+
+impl ProcMacroId {
+    pub fn new(u32: u32) -> Self {
+        ProcMacroId(u32)
+    }
+}
 
 #[derive(Copy, Clone, Eq, PartialEq, Debug, Hash)]
 pub enum ProcMacroKind {
@@ -49,6 +55,7 @@ pub struct ProcMacro {
     pub name: SmolStr,
     pub kind: ProcMacroKind,
     pub expander: sync::Arc<dyn ProcMacroExpander>,
+    pub disabled: bool,
 }
 
 #[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
@@ -56,20 +63,35 @@ pub struct CustomProcMacroExpander {
     proc_macro_id: ProcMacroId,
 }
 
-const DUMMY_ID: u32 = !0;
-
 impl CustomProcMacroExpander {
+    const DUMMY_ID: u32 = !0;
+    const DISABLED_ID: u32 = !1;
+
     pub fn new(proc_macro_id: ProcMacroId) -> Self {
-        assert_ne!(proc_macro_id.0, DUMMY_ID);
+        assert_ne!(proc_macro_id.0, Self::DUMMY_ID);
+        assert_ne!(proc_macro_id.0, Self::DISABLED_ID);
         Self { proc_macro_id }
     }
 
-    pub fn dummy() -> Self {
+    /// A dummy expander that always errors. This is used for proc-macros that are missing, usually
-        Self { proc_macro_id: ProcMacroId(DUMMY_ID) }
+    /// due to them not being built yet.
+    pub const fn dummy() -> Self {
+        Self { proc_macro_id: ProcMacroId(Self::DUMMY_ID) }
     }
 
-    pub fn is_dummy(&self) -> bool {
+    /// The macro was not yet resolved.
-        self.proc_macro_id.0 == DUMMY_ID
+    pub const fn is_dummy(&self) -> bool {
+        self.proc_macro_id.0 == Self::DUMMY_ID
+    }
+
+    /// A dummy expander that always errors. This expander is used for macros that have been disabled.
+    pub const fn disabled() -> Self {
+        Self { proc_macro_id: ProcMacroId(Self::DISABLED_ID) }
+    }
+
+    /// The macro is explicitly disabled and cannot be expanded.
+    pub const fn is_disabled(&self) -> bool {
+        self.proc_macro_id.0 == Self::DISABLED_ID
     }
 
     pub fn expand(
@@ -84,10 +106,14 @@ impl CustomProcMacroExpander {
         mixed_site: Span,
     ) -> ExpandResult<tt::Subtree> {
         match self.proc_macro_id {
-            ProcMacroId(DUMMY_ID) => ExpandResult::new(
+            ProcMacroId(Self::DUMMY_ID) => ExpandResult::new(
                 tt::Subtree::empty(tt::DelimSpan { open: call_site, close: call_site }),
                 ExpandError::UnresolvedProcMacro(def_crate),
             ),
+            ProcMacroId(Self::DISABLED_ID) => ExpandResult::new(
+                tt::Subtree::empty(tt::DelimSpan { open: call_site, close: call_site }),
+                ExpandError::MacroDisabled,
+            ),
             ProcMacroId(id) => {
                 let proc_macros = db.proc_macros();
                 let proc_macros = match proc_macros.get(&def_crate) {
@@ -110,7 +136,7 @@ impl CustomProcMacroExpander {
                         );
                         return ExpandResult::new(
                             tt::Subtree::empty(tt::DelimSpan { open: call_site, close: call_site }),
-                            ExpandError::other("Internal error"),
+                            ExpandError::other("Internal error: proc-macro index out of bounds"),
                         );
                     }
                 };

crates/hir-ty/src/diagnostics/expr.rs

@@ -169,9 +169,9 @@ impl ExprValidator {
             return;
         }
 
-        let pattern_arena = Arena::new();
+        let cx = MatchCheckCtx::new(self.owner.module(db.upcast()), self.owner, db);
-        let cx = MatchCheckCtx::new(self.owner.module(db.upcast()), self.owner, db, &pattern_arena);
 
+        let pattern_arena = Arena::new();
         let mut m_arms = Vec::with_capacity(arms.len());
         let mut has_lowering_errors = false;
         for arm in arms {
@@ -196,8 +196,9 @@ impl ExprValidator {
                     // If we had a NotUsefulMatchArm diagnostic, we could
                     // check the usefulness of each pattern as we added it
                     // to the matrix here.
+                    let pat = self.lower_pattern(&cx, arm.pat, db, &body, &mut has_lowering_errors);
                     let m_arm = pat_analysis::MatchArm {
-                        pat: self.lower_pattern(&cx, arm.pat, db, &body, &mut has_lowering_errors),
+                        pat: pattern_arena.alloc(pat),
                         has_guard: arm.guard.is_some(),
                         arm_data: (),
                     };
@@ -223,7 +224,7 @@ impl ExprValidator {
             ValidityConstraint::ValidOnly,
         ) {
             Ok(report) => report,
-            Err(void) => match void {},
+            Err(()) => return,
         };
 
         // FIXME Report unreachable arms
@@ -245,10 +246,10 @@ impl ExprValidator {
         db: &dyn HirDatabase,
         body: &Body,
         have_errors: &mut bool,
-    ) -> &'p DeconstructedPat<'p> {
+    ) -> DeconstructedPat<'p> {
         let mut patcx = match_check::PatCtxt::new(db, &self.infer, body);
         let pattern = patcx.lower_pattern(pat);
-        let pattern = cx.pattern_arena.alloc(cx.lower_pat(&pattern));
+        let pattern = cx.lower_pat(&pattern);
         if !patcx.errors.is_empty() {
             *have_errors = true;
         }

crates/hir-ty/src/diagnostics/match_check/pat_analysis.rs

@@ -1,6 +1,7 @@
 //! Interface with `rustc_pattern_analysis`.
 
 use std::fmt;
+use tracing::debug;
 
 use hir_def::{DefWithBodyId, EnumVariantId, HasModule, LocalFieldId, ModuleId, VariantId};
 use rustc_hash::FxHashMap;
@@ -11,7 +12,6 @@ use rustc_pattern_analysis::{
 };
 use smallvec::{smallvec, SmallVec};
 use stdx::never;
-use typed_arena::Arena;
 
 use crate::{
     db::HirDatabase,
@@ -26,7 +26,7 @@ use Constructor::*;
 
 // Re-export r-a-specific versions of all these types.
 pub(crate) type DeconstructedPat<'p> =
-    rustc_pattern_analysis::pat::DeconstructedPat<'p, MatchCheckCtx<'p>>;
+    rustc_pattern_analysis::pat::DeconstructedPat<MatchCheckCtx<'p>>;
 pub(crate) type MatchArm<'p> = rustc_pattern_analysis::MatchArm<'p, MatchCheckCtx<'p>>;
 pub(crate) type WitnessPat<'p> = rustc_pattern_analysis::pat::WitnessPat<MatchCheckCtx<'p>>;
 
@@ -40,7 +40,6 @@ pub(crate) struct MatchCheckCtx<'p> {
     module: ModuleId,
     body: DefWithBodyId,
     pub(crate) db: &'p dyn HirDatabase,
-    pub(crate) pattern_arena: &'p Arena<DeconstructedPat<'p>>,
     exhaustive_patterns: bool,
     min_exhaustive_patterns: bool,
 }
@@ -52,17 +51,12 @@ pub(crate) struct PatData<'p> {
 }
 
 impl<'p> MatchCheckCtx<'p> {
-    pub(crate) fn new(
+    pub(crate) fn new(module: ModuleId, body: DefWithBodyId, db: &'p dyn HirDatabase) -> Self {
-        module: ModuleId,
-        body: DefWithBodyId,
-        db: &'p dyn HirDatabase,
-        pattern_arena: &'p Arena<DeconstructedPat<'p>>,
-    ) -> Self {
         let def_map = db.crate_def_map(module.krate());
         let exhaustive_patterns = def_map.is_unstable_feature_enabled("exhaustive_patterns");
         let min_exhaustive_patterns =
             def_map.is_unstable_feature_enabled("min_exhaustive_patterns");
-        Self { module, body, db, pattern_arena, exhaustive_patterns, min_exhaustive_patterns }
+        Self { module, body, db, exhaustive_patterns, min_exhaustive_patterns }
     }
 
     fn is_uninhabited(&self, ty: &Ty) -> bool {
@@ -131,15 +125,15 @@ impl<'p> MatchCheckCtx<'p> {
     }
 
     pub(crate) fn lower_pat(&self, pat: &Pat) -> DeconstructedPat<'p> {
-        let singleton = |pat| std::slice::from_ref(self.pattern_arena.alloc(pat));
+        let singleton = |pat| vec![pat];
         let ctor;
-        let fields: &[_];
+        let fields: Vec<_>;
 
         match pat.kind.as_ref() {
             PatKind::Binding { subpattern: Some(subpat), .. } => return self.lower_pat(subpat),
             PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
                 ctor = Wildcard;
-                fields = &[];
+                fields = Vec::new();
             }
             PatKind::Deref { subpattern } => {
                 ctor = match pat.ty.kind(Interner) {
@@ -157,7 +151,7 @@ impl<'p> MatchCheckCtx<'p> {
                 match pat.ty.kind(Interner) {
                     TyKind::Tuple(_, substs) => {
                         ctor = Struct;
-                        let mut wilds: SmallVec<[_; 2]> = substs
+                        let mut wilds: Vec<_> = substs
                             .iter(Interner)
                             .map(|arg| arg.assert_ty_ref(Interner).clone())
                             .map(DeconstructedPat::wildcard)
@@ -166,7 +160,7 @@ impl<'p> MatchCheckCtx<'p> {
                             let idx: u32 = pat.field.into_raw().into();
                             wilds[idx as usize] = self.lower_pat(&pat.pattern);
                         }
-                        fields = self.pattern_arena.alloc_extend(wilds)
+                        fields = wilds
                     }
                     TyKind::Adt(adt, substs) if is_box(self.db, adt.0) => {
                         // The only legal patterns of type `Box` (outside `std`) are `_` and box
@@ -216,33 +210,29 @@ impl<'p> MatchCheckCtx<'p> {
                                 field_id_to_id[field_idx as usize] = Some(i);
                                 ty
                             });
-                        let mut wilds: SmallVec<[_; 2]> =
+                        let mut wilds: Vec<_> = tys.map(DeconstructedPat::wildcard).collect();
-                            tys.map(DeconstructedPat::wildcard).collect();
                         for pat in subpatterns {
                             let field_idx: u32 = pat.field.into_raw().into();
                             if let Some(i) = field_id_to_id[field_idx as usize] {
                                 wilds[i] = self.lower_pat(&pat.pattern);
                             }
                         }
-                        fields = self.pattern_arena.alloc_extend(wilds);
+                        fields = wilds;
                     }
                     _ => {
                         never!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, &pat.ty);
                         ctor = Wildcard;
-                        fields = &[];
+                        fields = Vec::new();
                     }
                 }
             }
             &PatKind::LiteralBool { value } => {
                 ctor = Bool(value);
-                fields = &[];
+                fields = Vec::new();
             }
             PatKind::Or { pats } => {
                 ctor = Or;
-                // Collect here because `Arena::alloc_extend` panics on reentrancy.
+                fields = pats.iter().map(|pat| self.lower_pat(pat)).collect();
-                let subpats: SmallVec<[_; 2]> =
-                    pats.iter().map(|pat| self.lower_pat(pat)).collect();
-                fields = self.pattern_arena.alloc_extend(subpats);
             }
         }
         let data = PatData { db: self.db };
@@ -307,7 +297,7 @@ impl<'p> MatchCheckCtx<'p> {
 }
 
 impl<'p> TypeCx for MatchCheckCtx<'p> {
-    type Error = Void;
+    type Error = ();
     type Ty = Ty;
     type VariantIdx = EnumVariantId;
     type StrLit = Void;
@@ -463,7 +453,7 @@ impl<'p> TypeCx for MatchCheckCtx<'p> {
 
     fn write_variant_name(
         f: &mut fmt::Formatter<'_>,
-        pat: &rustc_pattern_analysis::pat::DeconstructedPat<'_, Self>,
+        pat: &rustc_pattern_analysis::pat::DeconstructedPat<Self>,
     ) -> fmt::Result {
         let variant =
             pat.ty().as_adt().and_then(|(adt, _)| Self::variant_id_for_adt(pat.ctor(), adt));
@@ -485,8 +475,8 @@ impl<'p> TypeCx for MatchCheckCtx<'p> {
         Ok(())
     }
 
-    fn bug(&self, fmt: fmt::Arguments<'_>) -> ! {
+    fn bug(&self, fmt: fmt::Arguments<'_>) {
-        panic!("{}", fmt)
+        debug!("{}", fmt)
     }
 }
 

crates/hir-ty/src/diagnostics/match_check/pat_util.rs

@@ -2,7 +2,7 @@
 //!
 //! Originates from `rustc_hir::pat_util`
 
-use std::iter::{Enumerate, ExactSizeIterator};
+use std::iter::Enumerate;
 
 pub(crate) struct EnumerateAndAdjust<I> {
     enumerate: Enumerate<I>,

crates/hir-ty/src/infer.rs

@@ -26,7 +26,7 @@ use std::{convert::identity, ops::Index};
 
 use chalk_ir::{
     cast::Cast, fold::TypeFoldable, interner::HasInterner, DebruijnIndex, Mutability, Safety,
-    Scalar, TyKind, TypeFlags,
+    Scalar, TyKind, TypeFlags, Variance,
 };
 use either::Either;
 use hir_def::{
@@ -58,8 +58,9 @@ use crate::{
     static_lifetime, to_assoc_type_id,
     traits::FnTrait,
     utils::{InTypeConstIdMetadata, UnevaluatedConstEvaluatorFolder},
-    AliasEq, AliasTy, ClosureId, DomainGoal, GenericArg, Goal, ImplTraitId, InEnvironment,
+    AliasEq, AliasTy, Binders, ClosureId, Const, DomainGoal, GenericArg, Goal, ImplTraitId,
-    Interner, ProjectionTy, RpitId, Substitution, TraitEnvironment, TraitRef, Ty, TyBuilder, TyExt,
+    InEnvironment, Interner, Lifetime, ProjectionTy, RpitId, Substitution, TraitEnvironment,
+    TraitRef, Ty, TyBuilder, TyExt,
 };
 
 // This lint has a false positive here. See the link below for details.
@@ -68,7 +69,7 @@ use crate::{
 #[allow(unreachable_pub)]
 pub use coerce::could_coerce;
 #[allow(unreachable_pub)]
-pub use unify::could_unify;
+pub use unify::{could_unify, could_unify_deeply};
 
 use cast::CastCheck;
 pub(crate) use closure::{CaptureKind, CapturedItem, CapturedItemWithoutTy};
@@ -688,10 +689,17 @@ impl<'a> InferenceContext<'a> {
         for ty in type_of_for_iterator.values_mut() {
             *ty = table.resolve_completely(ty.clone());
         }
-        for mismatch in type_mismatches.values_mut() {
+        type_mismatches.retain(|_, mismatch| {
             mismatch.expected = table.resolve_completely(mismatch.expected.clone());
             mismatch.actual = table.resolve_completely(mismatch.actual.clone());
-        }
+            chalk_ir::zip::Zip::zip_with(
+                &mut UnknownMismatch(self.db),
+                Variance::Invariant,
+                &mismatch.expected,
+                &mismatch.actual,
+            )
+            .is_ok()
+        });
         diagnostics.retain_mut(|diagnostic| {
             use InferenceDiagnostic::*;
             match diagnostic {
@@ -1502,3 +1510,116 @@ impl std::ops::BitOrAssign for Diverges {
         *self = *self | other;
     }
 }
+/// A zipper that checks for unequal `{unknown}` occurrences in the two types. Used to filter out
+/// mismatch diagnostics that only differ in `{unknown}`. These mismatches are usually not helpful.
+/// As the cause is usually an underlying name resolution problem.
+struct UnknownMismatch<'db>(&'db dyn HirDatabase);
+impl chalk_ir::zip::Zipper<Interner> for UnknownMismatch<'_> {
+    fn zip_tys(&mut self, variance: Variance, a: &Ty, b: &Ty) -> chalk_ir::Fallible<()> {
+        let zip_substs = |this: &mut Self,
+                          variances,
+                          sub_a: &Substitution,
+                          sub_b: &Substitution| {
+            this.zip_substs(variance, variances, sub_a.as_slice(Interner), sub_b.as_slice(Interner))
+        };
+        match (a.kind(Interner), b.kind(Interner)) {
+            (TyKind::Adt(id_a, sub_a), TyKind::Adt(id_b, sub_b)) if id_a == id_b => zip_substs(
+                self,
+                Some(self.unification_database().adt_variance(*id_a)),
+                sub_a,
+                sub_b,
+            )?,
+            (
+                TyKind::AssociatedType(assoc_ty_a, sub_a),
+                TyKind::AssociatedType(assoc_ty_b, sub_b),
+            ) if assoc_ty_a == assoc_ty_b => zip_substs(self, None, sub_a, sub_b)?,
+            (TyKind::Tuple(arity_a, sub_a), TyKind::Tuple(arity_b, sub_b))
+                if arity_a == arity_b =>
+            {
+                zip_substs(self, None, sub_a, sub_b)?
+            }
+            (TyKind::OpaqueType(opaque_ty_a, sub_a), TyKind::OpaqueType(opaque_ty_b, sub_b))
+                if opaque_ty_a == opaque_ty_b =>
+            {
+                zip_substs(self, None, sub_a, sub_b)?
+            }
+            (TyKind::Slice(ty_a), TyKind::Slice(ty_b)) => self.zip_tys(variance, ty_a, ty_b)?,
+            (TyKind::FnDef(fn_def_a, sub_a), TyKind::FnDef(fn_def_b, sub_b))
+                if fn_def_a == fn_def_b =>
+            {
+                zip_substs(
+                    self,
+                    Some(self.unification_database().fn_def_variance(*fn_def_a)),
+                    sub_a,
+                    sub_b,
+                )?
+            }
+            (TyKind::Ref(mutability_a, _, ty_a), TyKind::Ref(mutability_b, _, ty_b))
+                if mutability_a == mutability_b =>
+            {
+                self.zip_tys(variance, ty_a, ty_b)?
+            }
+            (TyKind::Raw(mutability_a, ty_a), TyKind::Raw(mutability_b, ty_b))
+                if mutability_a == mutability_b =>
+            {
+                self.zip_tys(variance, ty_a, ty_b)?
+            }
+            (TyKind::Array(ty_a, const_a), TyKind::Array(ty_b, const_b)) if const_a == const_b => {
+                self.zip_tys(variance, ty_a, ty_b)?
+            }
+            (TyKind::Closure(id_a, sub_a), TyKind::Closure(id_b, sub_b)) if id_a == id_b => {
+                zip_substs(self, None, sub_a, sub_b)?
+            }
+            (TyKind::Coroutine(coroutine_a, sub_a), TyKind::Coroutine(coroutine_b, sub_b))
+                if coroutine_a == coroutine_b =>
+            {
+                zip_substs(self, None, sub_a, sub_b)?
+            }
+            (
+                TyKind::CoroutineWitness(coroutine_a, sub_a),
+                TyKind::CoroutineWitness(coroutine_b, sub_b),
+            ) if coroutine_a == coroutine_b => zip_substs(self, None, sub_a, sub_b)?,
+            (TyKind::Function(fn_ptr_a), TyKind::Function(fn_ptr_b))
+                if fn_ptr_a.sig == fn_ptr_b.sig && fn_ptr_a.num_binders == fn_ptr_b.num_binders =>
+            {
+                zip_substs(self, None, &fn_ptr_a.substitution.0, &fn_ptr_b.substitution.0)?
+            }
+            (TyKind::Error, TyKind::Error) => (),
+            (TyKind::Error, _) | (_, TyKind::Error) => return Err(chalk_ir::NoSolution),
+            _ => (),
+        }
+
+        Ok(())
+    }
+
+    fn zip_lifetimes(&mut self, _: Variance, _: &Lifetime, _: &Lifetime) -> chalk_ir::Fallible<()> {
+        Ok(())
+    }
+
+    fn zip_consts(&mut self, _: Variance, _: &Const, _: &Const) -> chalk_ir::Fallible<()> {
+        Ok(())
+    }
+
+    fn zip_binders<T>(
+        &mut self,
+        variance: Variance,
+        a: &Binders<T>,
+        b: &Binders<T>,
+    ) -> chalk_ir::Fallible<()>
+    where
+        T: Clone
+            + HasInterner<Interner = Interner>
+            + chalk_ir::zip::Zip<Interner>
+            + TypeFoldable<Interner>,
+    {
+        chalk_ir::zip::Zip::zip_with(self, variance, a.skip_binders(), b.skip_binders())
+    }
+
+    fn interner(&self) -> Interner {
+        Interner
+    }
+
+    fn unification_database(&self) -> &dyn chalk_ir::UnificationDatabase<Interner> {
+        &self.0
+    }
+}

crates/hir-ty/src/infer/closure.rs

@@ -485,6 +485,7 @@ impl InferenceContext<'_> {
                         Statement::Expr { expr, has_semi: _ } => {
                             self.consume_expr(*expr);
                         }
+                        Statement::Item => (),
                     }
                 }
                 if let Some(tail) = tail {
@@ -531,6 +532,9 @@ impl InferenceContext<'_> {
                     self.consume_expr(expr);
                 }
             }
+            &Expr::Become { expr } => {
+                self.consume_expr(expr);
+            }
             Expr::RecordLit { fields, spread, .. } => {
                 if let &Some(expr) = spread {
                     self.consume_expr(expr);

crates/hir-ty/src/infer/expr.rs

@@ -502,6 +502,7 @@ impl InferenceContext<'_> {
                 self.result.standard_types.never.clone()
             }
             &Expr::Return { expr } => self.infer_expr_return(tgt_expr, expr),
+            &Expr::Become { expr } => self.infer_expr_become(expr),
             Expr::Yield { expr } => {
                 if let Some((resume_ty, yield_ty)) = self.resume_yield_tys.clone() {
                     if let Some(expr) = expr {
@@ -1084,6 +1085,27 @@ impl InferenceContext<'_> {
         self.result.standard_types.never.clone()
     }
 
+    fn infer_expr_become(&mut self, expr: ExprId) -> Ty {
+        match &self.return_coercion {
+            Some(return_coercion) => {
+                let ret_ty = return_coercion.expected_ty();
+
+                let call_expr_ty =
+                    self.infer_expr_inner(expr, &Expectation::HasType(ret_ty.clone()));
+
+                // NB: this should *not* coerce.
+                //     tail calls don't support any coercions except lifetimes ones (like `&'static u8 -> &'a u8`).
+                self.unify(&call_expr_ty, &ret_ty);
+            }
+            None => {
+                // FIXME: diagnose `become` outside of functions
+                self.infer_expr_no_expect(expr);
+            }
+        }
+
+        self.result.standard_types.never.clone()
+    }
+
     fn infer_expr_box(&mut self, inner_expr: ExprId, expected: &Expectation) -> Ty {
         if let Some(box_id) = self.resolve_boxed_box() {
             let table = &mut self.table;
@@ -1367,6 +1389,7 @@ impl InferenceContext<'_> {
                                 );
                             }
                         }
+                        Statement::Item => (),
                     }
                 }
 

crates/hir-ty/src/infer/mutability.rs

@@ -65,6 +65,7 @@ impl InferenceContext<'_> {
                         Statement::Expr { expr, has_semi: _ } => {
                             self.infer_mut_expr(*expr, Mutability::Not);
                         }
+                        Statement::Item => (),
                     }
                 }
                 if let Some(tail) = tail {
@@ -93,6 +94,9 @@ impl InferenceContext<'_> {
                     self.infer_mut_expr(expr, Mutability::Not);
                 }
             }
+            Expr::Become { expr } => {
+                self.infer_mut_expr(*expr, Mutability::Not);
+            }
             Expr::RecordLit { path: _, fields, spread, ellipsis: _, is_assignee_expr: _ } => {
                 self.infer_mut_not_expr_iter(fields.iter().map(|it| it.expr).chain(*spread))
             }

crates/hir-ty/src/infer/unify.rs

@@ -74,6 +74,12 @@ impl<T: HasInterner<Interner = Interner>> Canonicalized<T> {
     }
 }
 
+/// Check if types unify.
+///
+/// Note that we consider placeholder types to unify with everything.
+/// This means that there may be some unresolved goals that actually set bounds for the placeholder
+/// type for the types to unify. For example `Option<T>` and `Option<U>` unify although there is
+/// unresolved goal `T = U`.
 pub fn could_unify(
     db: &dyn HirDatabase,
     env: Arc<TraitEnvironment>,
@@ -82,21 +88,35 @@ pub fn could_unify(
     unify(db, env, tys).is_some()
 }
 
+/// Check if types unify eagerly making sure there are no unresolved goals.
+///
+/// This means that placeholder types are not considered to unify if there are any bounds set on
+/// them. For example `Option<T>` and `Option<U>` do not unify as we cannot show that `T = U`
+pub fn could_unify_deeply(
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    tys: &Canonical<(Ty, Ty)>,
+) -> bool {
+    let mut table = InferenceTable::new(db, env);
+    let vars = make_substitutions(tys, &mut table);
+    let ty1_with_vars = vars.apply(tys.value.0.clone(), Interner);
+    let ty2_with_vars = vars.apply(tys.value.1.clone(), Interner);
+    let ty1_with_vars = table.normalize_associated_types_in(ty1_with_vars);
+    let ty2_with_vars = table.normalize_associated_types_in(ty2_with_vars);
+    table.resolve_obligations_as_possible();
+    table.propagate_diverging_flag();
+    let ty1_with_vars = table.resolve_completely(ty1_with_vars);
+    let ty2_with_vars = table.resolve_completely(ty2_with_vars);
+    table.unify_deeply(&ty1_with_vars, &ty2_with_vars)
+}
+
 pub(crate) fn unify(
     db: &dyn HirDatabase,
     env: Arc<TraitEnvironment>,
     tys: &Canonical<(Ty, Ty)>,
 ) -> Option<Substitution> {
     let mut table = InferenceTable::new(db, env);
-    let vars = Substitution::from_iter(
+    let vars = make_substitutions(tys, &mut table);
-        Interner,
-        tys.binders.iter(Interner).map(|it| match &it.kind {
-            chalk_ir::VariableKind::Ty(_) => table.new_type_var().cast(Interner),
-            // FIXME: maybe wrong?
-            chalk_ir::VariableKind::Lifetime => table.new_type_var().cast(Interner),
-            chalk_ir::VariableKind::Const(ty) => table.new_const_var(ty.clone()).cast(Interner),
-        }),
-    );
     let ty1_with_vars = vars.apply(tys.value.0.clone(), Interner);
     let ty2_with_vars = vars.apply(tys.value.1.clone(), Interner);
     if !table.unify(&ty1_with_vars, &ty2_with_vars) {
@@ -125,6 +145,21 @@ pub(crate) fn unify(
     ))
 }
 
+fn make_substitutions(
+    tys: &chalk_ir::Canonical<(chalk_ir::Ty<Interner>, chalk_ir::Ty<Interner>)>,
+    table: &mut InferenceTable<'_>,
+) -> chalk_ir::Substitution<Interner> {
+    Substitution::from_iter(
+        Interner,
+        tys.binders.iter(Interner).map(|it| match &it.kind {
+            chalk_ir::VariableKind::Ty(_) => table.new_type_var().cast(Interner),
+            // FIXME: maybe wrong?
+            chalk_ir::VariableKind::Lifetime => table.new_type_var().cast(Interner),
+            chalk_ir::VariableKind::Const(ty) => table.new_const_var(ty.clone()).cast(Interner),
+        }),
+    )
+}
+
 bitflags::bitflags! {
     #[derive(Default, Clone, Copy)]
     pub(crate) struct TypeVariableFlags: u8 {
@@ -431,6 +466,18 @@ impl<'a> InferenceTable<'a> {
         true
     }
 
+    /// Unify two relatable values (e.g. `Ty`) and check whether trait goals which arise from that could be fulfilled
+    pub(crate) fn unify_deeply<T: ?Sized + Zip<Interner>>(&mut self, ty1: &T, ty2: &T) -> bool {
+        let result = match self.try_unify(ty1, ty2) {
+            Ok(r) => r,
+            Err(_) => return false,
+        };
+        result.goals.iter().all(|goal| {
+            let canonicalized = self.canonicalize(goal.clone());
+            self.try_resolve_obligation(&canonicalized).is_some()
+        })
+    }
+
     /// Unify two relatable values (e.g. `Ty`) and return new trait goals arising from it, so the
     /// caller needs to deal with them.
     pub(crate) fn try_unify<T: ?Sized + Zip<Interner>>(
@@ -501,7 +548,8 @@ impl<'a> InferenceTable<'a> {
 
     fn register_obligation_in_env(&mut self, goal: InEnvironment<Goal>) {
         let canonicalized = self.canonicalize(goal);
-        if !self.try_resolve_obligation(&canonicalized) {
+        let solution = self.try_resolve_obligation(&canonicalized);
+        if matches!(solution, Some(Solution::Ambig(_))) {
             self.pending_obligations.push(canonicalized);
         }
     }
@@ -627,38 +675,35 @@ impl<'a> InferenceTable<'a> {
     fn try_resolve_obligation(
         &mut self,
         canonicalized: &Canonicalized<InEnvironment<Goal>>,
-    ) -> bool {
+    ) -> Option<chalk_solve::Solution<Interner>> {
         let solution = self.db.trait_solve(
             self.trait_env.krate,
             self.trait_env.block,
             canonicalized.value.clone(),
         );
 
-        match solution {
+        match &solution {
             Some(Solution::Unique(canonical_subst)) => {
                 canonicalized.apply_solution(
                     self,
                     Canonical {
-                        binders: canonical_subst.binders,
+                        binders: canonical_subst.binders.clone(),
                         // FIXME: handle constraints
-                        value: canonical_subst.value.subst,
+                        value: canonical_subst.value.subst.clone(),
                     },
                 );
-                true
             }
             Some(Solution::Ambig(Guidance::Definite(substs))) => {
-                canonicalized.apply_solution(self, substs);
+                canonicalized.apply_solution(self, substs.clone());
-                false
             }
             Some(_) => {
                 // FIXME use this when trying to resolve everything at the end
-                false
             }
             None => {
                 // FIXME obligation cannot be fulfilled => diagnostic
-                true
             }
         }
+        solution
     }
 
     pub(crate) fn callable_sig(

crates/hir-ty/src/layout/target.rs

@@ -11,10 +11,8 @@ pub fn target_data_layout_query(
     db: &dyn HirDatabase,
     krate: CrateId,
 ) -> Result<Arc<TargetDataLayout>, Arc<str>> {
-    let crate_graph = db.crate_graph();
+    match db.data_layout(krate) {
-    let res = crate_graph[krate].target_layout.as_deref();
+        Ok(it) => match TargetDataLayout::parse_from_llvm_datalayout_string(&it) {
-    match res {
-        Ok(it) => match TargetDataLayout::parse_from_llvm_datalayout_string(it) {
             Ok(it) => Ok(Arc::new(it)),
             Err(e) => {
                 Err(match e {
@@ -44,6 +42,6 @@ pub fn target_data_layout_query(
                 }.into())
             }
         },
-        Err(e) => Err(Arc::from(&**e)),
+        Err(e) => Err(e),
     }
 }

crates/hir-ty/src/layout/tests.rs

@@ -1,6 +1,7 @@
 use chalk_ir::{AdtId, TyKind};
 use either::Either;
 use hir_def::db::DefDatabase;
+use project_model::target_data_layout::RustcDataLayoutConfig;
 use rustc_hash::FxHashMap;
 use test_fixture::WithFixture;
 use triomphe::Arc;
@@ -15,13 +16,18 @@ use crate::{
 mod closure;
 
 fn current_machine_data_layout() -> String {
-    project_model::target_data_layout::get(None, None, &FxHashMap::default()).unwrap()
+    project_model::target_data_layout::get(
+        RustcDataLayoutConfig::Rustc(None),
+        None,
+        &FxHashMap::default(),
+    )
+    .unwrap()
 }
 
 fn eval_goal(ra_fixture: &str, minicore: &str) -> Result<Arc<Layout>, LayoutError> {
     let target_data_layout = current_machine_data_layout();
     let ra_fixture = format!(
-        "{minicore}//- /main.rs crate:test target_data_layout:{target_data_layout}\n{ra_fixture}",
+        "//- target_data_layout: {target_data_layout}\n{minicore}//- /main.rs crate:test\n{ra_fixture}",
     );
 
     let (db, file_ids) = TestDB::with_many_files(&ra_fixture);
@@ -70,7 +76,7 @@ fn eval_goal(ra_fixture: &str, minicore: &str) -> Result<Arc<Layout>, LayoutErro
 fn eval_expr(ra_fixture: &str, minicore: &str) -> Result<Arc<Layout>, LayoutError> {
     let target_data_layout = current_machine_data_layout();
     let ra_fixture = format!(
-        "{minicore}//- /main.rs crate:test target_data_layout:{target_data_layout}\nfn main(){{let goal = {{{ra_fixture}}};}}",
+        "//- target_data_layout: {target_data_layout}\n{minicore}//- /main.rs crate:test\nfn main(){{let goal = {{{ra_fixture}}};}}",
     );
 
     let (db, file_id) = TestDB::with_single_file(&ra_fixture);

crates/hir-ty/src/lib.rs

@@ -79,8 +79,8 @@ pub use builder::{ParamKind, TyBuilder};
 pub use chalk_ext::*;
 pub use infer::{
     closure::{CaptureKind, CapturedItem},
-    could_coerce, could_unify, Adjust, Adjustment, AutoBorrow, BindingMode, InferenceDiagnostic,
+    could_coerce, could_unify, could_unify_deeply, Adjust, Adjustment, AutoBorrow, BindingMode,
-    InferenceResult, OverloadedDeref, PointerCast,
+    InferenceDiagnostic, InferenceResult, OverloadedDeref, PointerCast,
 };
 pub use interner::Interner;
 pub use lower::{

crates/hir-ty/src/mir/borrowck.rs

@@ -7,6 +7,7 @@ use std::iter;
 
 use hir_def::{DefWithBodyId, HasModule};
 use la_arena::ArenaMap;
+use rustc_hash::FxHashMap;
 use stdx::never;
 use triomphe::Arc;
 
@@ -14,7 +15,7 @@ use crate::{
     db::{HirDatabase, InternedClosure},
     mir::Operand,
     utils::ClosureSubst,
-    ClosureId, Interner, Ty, TyExt, TypeFlags,
+    ClosureId, Interner, Substitution, Ty, TyExt, TypeFlags,
 };
 
 use super::{
@@ -36,11 +37,27 @@ pub struct MovedOutOfRef {
     pub span: MirSpan,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct PartiallyMoved {
+    pub ty: Ty,
+    pub span: MirSpan,
+    pub local: LocalId,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct BorrowRegion {
+    pub local: LocalId,
+    pub kind: BorrowKind,
+    pub places: Vec<MirSpan>,
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct BorrowckResult {
     pub mir_body: Arc<MirBody>,
     pub mutability_of_locals: ArenaMap<LocalId, MutabilityReason>,
     pub moved_out_of_ref: Vec<MovedOutOfRef>,
+    pub partially_moved: Vec<PartiallyMoved>,
+    pub borrow_regions: Vec<BorrowRegion>,
 }
 
 fn all_mir_bodies(
@@ -80,12 +97,26 @@ pub fn borrowck_query(
         res.push(BorrowckResult {
             mutability_of_locals: mutability_of_locals(db, &body),
             moved_out_of_ref: moved_out_of_ref(db, &body),
+            partially_moved: partially_moved(db, &body),
+            borrow_regions: borrow_regions(db, &body),
             mir_body: body,
         });
     })?;
     Ok(res.into())
 }
 
+fn make_fetch_closure_field(
+    db: &dyn HirDatabase,
+) -> impl FnOnce(ClosureId, &Substitution, usize) -> Ty + '_ {
+    |c: ClosureId, subst: &Substitution, f: usize| {
+        let InternedClosure(def, _) = db.lookup_intern_closure(c.into());
+        let infer = db.infer(def);
+        let (captures, _) = infer.closure_info(&c);
+        let parent_subst = ClosureSubst(subst).parent_subst();
+        captures.get(f).expect("broken closure field").ty.clone().substitute(Interner, parent_subst)
+    }
+}
+
 fn moved_out_of_ref(db: &dyn HirDatabase, body: &MirBody) -> Vec<MovedOutOfRef> {
     let mut result = vec![];
     let mut for_operand = |op: &Operand, span: MirSpan| match op {
@@ -99,18 +130,7 @@ fn moved_out_of_ref(db: &dyn HirDatabase, body: &MirBody) -> Vec<MovedOutOfRef>
                 ty = proj.projected_ty(
                     ty,
                     db,
-                    |c, subst, f| {
+                    make_fetch_closure_field(db),
-                        let InternedClosure(def, _) = db.lookup_intern_closure(c.into());
-                        let infer = db.infer(def);
-                        let (captures, _) = infer.closure_info(&c);
-                        let parent_subst = ClosureSubst(subst).parent_subst();
-                        captures
-                            .get(f)
-                            .expect("broken closure field")
-                            .ty
-                            .clone()
-                            .substitute(Interner, parent_subst)
-                    },
                     body.owner.module(db.upcast()).krate(),
                 );
             }
@@ -188,6 +208,132 @@ fn moved_out_of_ref(db: &dyn HirDatabase, body: &MirBody) -> Vec<MovedOutOfRef>
     result
 }
 
+fn partially_moved(db: &dyn HirDatabase, body: &MirBody) -> Vec<PartiallyMoved> {
+    let mut result = vec![];
+    let mut for_operand = |op: &Operand, span: MirSpan| match op {
+        Operand::Copy(p) | Operand::Move(p) => {
+            let mut ty: Ty = body.locals[p.local].ty.clone();
+            for proj in p.projection.lookup(&body.projection_store) {
+                ty = proj.projected_ty(
+                    ty,
+                    db,
+                    make_fetch_closure_field(db),
+                    body.owner.module(db.upcast()).krate(),
+                );
+            }
+            if !ty.clone().is_copy(db, body.owner)
+                && !ty.data(Interner).flags.intersects(TypeFlags::HAS_ERROR)
+            {
+                result.push(PartiallyMoved { span, ty, local: p.local });
+            }
+        }
+        Operand::Constant(_) | Operand::Static(_) => (),
+    };
+    for (_, block) in body.basic_blocks.iter() {
+        db.unwind_if_cancelled();
+        for statement in &block.statements {
+            match &statement.kind {
+                StatementKind::Assign(_, r) => match r {
+                    Rvalue::ShallowInitBoxWithAlloc(_) => (),
+                    Rvalue::ShallowInitBox(o, _)
+                    | Rvalue::UnaryOp(_, o)
+                    | Rvalue::Cast(_, o, _)
+                    | Rvalue::Repeat(o, _)
+                    | Rvalue::Use(o) => for_operand(o, statement.span),
+                    Rvalue::CopyForDeref(_)
+                    | Rvalue::Discriminant(_)
+                    | Rvalue::Len(_)
+                    | Rvalue::Ref(_, _) => (),
+                    Rvalue::CheckedBinaryOp(_, o1, o2) => {
+                        for_operand(o1, statement.span);
+                        for_operand(o2, statement.span);
+                    }
+                    Rvalue::Aggregate(_, ops) => {
+                        for op in ops.iter() {
+                            for_operand(op, statement.span);
+                        }
+                    }
+                },
+                StatementKind::FakeRead(_)
+                | StatementKind::Deinit(_)
+                | StatementKind::StorageLive(_)
+                | StatementKind::StorageDead(_)
+                | StatementKind::Nop => (),
+            }
+        }
+        match &block.terminator {
+            Some(terminator) => match &terminator.kind {
+                TerminatorKind::SwitchInt { discr, .. } => for_operand(discr, terminator.span),
+                TerminatorKind::FalseEdge { .. }
+                | TerminatorKind::FalseUnwind { .. }
+                | TerminatorKind::Goto { .. }
+                | TerminatorKind::UnwindResume
+                | TerminatorKind::CoroutineDrop
+                | TerminatorKind::Abort
+                | TerminatorKind::Return
+                | TerminatorKind::Unreachable
+                | TerminatorKind::Drop { .. } => (),
+                TerminatorKind::DropAndReplace { value, .. } => {
+                    for_operand(value, terminator.span);
+                }
+                TerminatorKind::Call { func, args, .. } => {
+                    for_operand(func, terminator.span);
+                    args.iter().for_each(|it| for_operand(it, terminator.span));
+                }
+                TerminatorKind::Assert { cond, .. } => {
+                    for_operand(cond, terminator.span);
+                }
+                TerminatorKind::Yield { value, .. } => {
+                    for_operand(value, terminator.span);
+                }
+            },
+            None => (),
+        }
+    }
+    result.shrink_to_fit();
+    result
+}
+
+fn borrow_regions(db: &dyn HirDatabase, body: &MirBody) -> Vec<BorrowRegion> {
+    let mut borrows = FxHashMap::default();
+    for (_, block) in body.basic_blocks.iter() {
+        db.unwind_if_cancelled();
+        for statement in &block.statements {
+            if let StatementKind::Assign(_, Rvalue::Ref(kind, p)) = &statement.kind {
+                borrows
+                    .entry(p.local)
+                    .and_modify(|it: &mut BorrowRegion| {
+                        it.places.push(statement.span);
+                    })
+                    .or_insert_with(|| BorrowRegion {
+                        local: p.local,
+                        kind: *kind,
+                        places: vec![statement.span],
+                    });
+            }
+        }
+        match &block.terminator {
+            Some(terminator) => match &terminator.kind {
+                TerminatorKind::FalseEdge { .. }
+                | TerminatorKind::FalseUnwind { .. }
+                | TerminatorKind::Goto { .. }
+                | TerminatorKind::UnwindResume
+                | TerminatorKind::CoroutineDrop
+                | TerminatorKind::Abort
+                | TerminatorKind::Return
+                | TerminatorKind::Unreachable
+                | TerminatorKind::Drop { .. } => (),
+                TerminatorKind::DropAndReplace { .. } => {}
+                TerminatorKind::Call { .. } => {}
+                _ => (),
+            },
+            None => (),
+        }
+    }
+
+    borrows.into_values().collect()
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum ProjectionCase {
     /// Projection is a local
@@ -217,18 +363,7 @@ fn place_case(db: &dyn HirDatabase, body: &MirBody, lvalue: &Place) -> Projectio
         ty = proj.projected_ty(
             ty,
             db,
-            |c, subst, f| {
+            make_fetch_closure_field(db),
-                let InternedClosure(def, _) = db.lookup_intern_closure(c.into());
-                let infer = db.infer(def);
-                let (captures, _) = infer.closure_info(&c);
-                let parent_subst = ClosureSubst(subst).parent_subst();
-                captures
-                    .get(f)
-                    .expect("broken closure field")
-                    .ty
-                    .clone()
-                    .substitute(Interner, parent_subst)
-            },
             body.owner.module(db.upcast()).krate(),
         );
     }

crates/hir-ty/src/mir/eval/shim.rs

@@ -4,11 +4,7 @@
 use std::cmp;
 
 use chalk_ir::TyKind;
-use hir_def::{
+use hir_def::builtin_type::{BuiltinInt, BuiltinUint};
-    builtin_type::{BuiltinInt, BuiltinUint},
-    resolver::HasResolver,
-};
-use hir_expand::mod_path::ModPath;
 
 use super::*;
 

crates/hir-ty/src/mir/lower.rs

@@ -1,6 +1,6 @@
 //! This module generates a polymorphic MIR from a hir body
 
-use std::{fmt::Write, iter, mem};
+use std::{fmt::Write, mem};
 
 use base_db::{salsa::Cycle, FileId};
 use chalk_ir::{BoundVar, ConstData, DebruijnIndex, TyKind};
@@ -14,23 +14,19 @@ use hir_def::{
     lang_item::{LangItem, LangItemTarget},
     path::Path,
     resolver::{resolver_for_expr, HasResolver, ResolveValueResult, ValueNs},
-    AdtId, DefWithBodyId, EnumVariantId, GeneralConstId, HasModule, ItemContainerId, LocalFieldId,
+    AdtId, EnumVariantId, GeneralConstId, HasModule, ItemContainerId, LocalFieldId,
     Lookup, TraitId, TupleId, TypeOrConstParamId,
 };
 use hir_expand::name::Name;
-use la_arena::ArenaMap;
-use rustc_hash::FxHashMap;
 use syntax::TextRange;
 use triomphe::Arc;
 
 use crate::{
     consteval::ConstEvalError,
-    db::{HirDatabase, InternedClosure},
+    db::InternedClosure,
-    display::HirDisplay,
     infer::{CaptureKind, CapturedItem, TypeMismatch},
     inhabitedness::is_ty_uninhabited_from,
     layout::LayoutError,
-    mapping::ToChalk,
     static_lifetime,
     traits::FnTrait,
     utils::{generics, ClosureSubst},
@@ -775,6 +771,7 @@ impl<'ctx> MirLowerCtx<'ctx> {
                 self.set_terminator(current, TerminatorKind::Return, expr_id.into());
                 Ok(None)
             }
+            Expr::Become { .. } => not_supported!("tail-calls"),
             Expr::Yield { .. } => not_supported!("yield"),
             Expr::RecordLit { fields, path, spread, ellipsis: _, is_assignee_expr: _ } => {
                 let spread_place = match spread {
@@ -1246,7 +1243,7 @@ impl<'ctx> MirLowerCtx<'ctx> {
                 self.push_assignment(current, place, op.into(), expr_id.into());
                 Ok(Some(current))
             }
-            Expr::Underscore => not_supported!("underscore"),
+            Expr::Underscore => Ok(Some(current)),
         }
     }
 
@@ -1780,6 +1777,7 @@ impl<'ctx> MirLowerCtx<'ctx> {
                     self.push_fake_read(c, p, expr.into());
                     current = scope2.pop_and_drop(self, c, expr.into());
                 }
+                hir_def::hir::Statement::Item => (),
             }
         }
         if let Some(tail) = tail {

crates/hir-ty/src/mir/lower/pattern_matching.rs

@@ -1,6 +1,6 @@
 //! MIR lowering for patterns
 
-use hir_def::{hir::LiteralOrConst, resolver::HasResolver, AssocItemId};
+use hir_def::AssocItemId;
 
 use crate::BindingMode;
 

crates/hir-ty/src/tests/diagnostics.rs

@@ -1,3 +1,5 @@
+use crate::tests::check_no_mismatches;
+
 use super::check;
 
 #[test]
@@ -94,3 +96,43 @@ fn test(x: bool) {
 "#,
     );
 }
+
+#[test]
+fn no_mismatches_on_atpit() {
+    check_no_mismatches(
+        r#"
+//- minicore: option, sized
+#![feature(impl_trait_in_assoc_type)]
+
+trait WrappedAssoc {
+    type Assoc;
+    fn do_thing(&self) -> Option<Self::Assoc>;
+}
+
+struct Foo;
+impl WrappedAssoc for Foo {
+    type Assoc = impl Sized;
+
+    fn do_thing(&self) -> Option<Self::Assoc> {
+        Some(())
+    }
+}
+"#,
+    );
+    check_no_mismatches(
+        r#"
+//- minicore: option, sized
+#![feature(impl_trait_in_assoc_type)]
+
+trait Trait {
+    type Assoc;
+    const DEFINE: Option<Self::Assoc>;
+}
+
+impl Trait for () {
+    type Assoc = impl Sized;
+    const DEFINE: Option<Self::Assoc> = Option::Some(());
+}
+"#,
+    );
+}

crates/hir-ty/src/tests/simple.rs

@@ -3376,11 +3376,8 @@ fn main() {
     [x,] = &[1,];
   //^^^^expected &[i32; 1], got [{unknown}; _]
 
-    // FIXME we only want the outermost error, but this matches the current
-    // behavior of slice patterns
     let x;
     [(x,),] = &[(1,),];
-  // ^^^^expected {unknown}, got ({unknown},)
   //^^^^^^^expected &[(i32,); 1], got [{unknown}; _]
 
     let x;

crates/hir/src/lib.rs

@@ -31,6 +31,7 @@ mod has_source;
 pub mod db;
 pub mod diagnostics;
 pub mod symbols;
+pub mod term_search;
 
 mod display;
 
@@ -1084,6 +1085,27 @@ impl Field {
         Type::new(db, var_id, ty)
     }
 
+    // FIXME: Find better API to also handle const generics
+    pub fn ty_with_args(&self, db: &dyn HirDatabase, generics: impl Iterator<Item = Type>) -> Type {
+        let var_id = self.parent.into();
+        let def_id: AdtId = match self.parent {
+            VariantDef::Struct(it) => it.id.into(),
+            VariantDef::Union(it) => it.id.into(),
+            VariantDef::Variant(it) => it.parent_enum(db).id.into(),
+        };
+        let mut generics = generics.map(|it| it.ty.clone());
+        let substs = TyBuilder::subst_for_def(db, def_id, None)
+            .fill(|x| match x {
+                ParamKind::Type => {
+                    generics.next().unwrap_or_else(|| TyKind::Error.intern(Interner)).cast(Interner)
+                }
+                ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
+            })
+            .build();
+        let ty = db.field_types(var_id)[self.id].clone().substitute(Interner, &substs);
+        Type::new(db, var_id, ty)
+    }
+
     pub fn layout(&self, db: &dyn HirDatabase) -> Result<Layout, LayoutError> {
         db.layout_of_ty(
             self.ty(db).ty,
@@ -1152,6 +1174,10 @@ impl Struct {
     fn variant_data(self, db: &dyn HirDatabase) -> Arc<VariantData> {
         db.struct_data(self.id).variant_data.clone()
     }
+
+    pub fn is_unstable(self, db: &dyn HirDatabase) -> bool {
+        db.attrs(self.id.into()).is_unstable()
+    }
 }
 
 impl HasVisibility for Struct {
@@ -1194,6 +1220,10 @@ impl Union {
     fn variant_data(self, db: &dyn HirDatabase) -> Arc<VariantData> {
         db.union_data(self.id).variant_data.clone()
     }
+
+    pub fn is_unstable(self, db: &dyn HirDatabase) -> bool {
+        db.attrs(self.id.into()).is_unstable()
+    }
 }
 
 impl HasVisibility for Union {
@@ -1269,6 +1299,10 @@ impl Enum {
     pub fn layout(self, db: &dyn HirDatabase) -> Result<Layout, LayoutError> {
         Adt::from(self).layout(db)
     }
+
+    pub fn is_unstable(self, db: &dyn HirDatabase) -> bool {
+        db.attrs(self.id.into()).is_unstable()
+    }
 }
 
 impl HasVisibility for Enum {
@@ -1344,6 +1378,10 @@ impl Variant {
             _ => parent_layout,
         })
     }
+
+    pub fn is_unstable(self, db: &dyn HirDatabase) -> bool {
+        db.attrs(self.id.into()).is_unstable()
+    }
 }
 
 /// Variants inherit visibility from the parent enum.
@@ -1394,9 +1432,9 @@ impl Adt {
 
     /// Turns this ADT into a type with the given type parameters. This isn't
     /// the greatest API, FIXME find a better one.
-    pub fn ty_with_args(self, db: &dyn HirDatabase, args: &[Type]) -> Type {
+    pub fn ty_with_args(self, db: &dyn HirDatabase, args: impl Iterator<Item = Type>) -> Type {
         let id = AdtId::from(self);
-        let mut it = args.iter().map(|t| t.ty.clone());
+        let mut it = args.map(|t| t.ty.clone());
         let ty = TyBuilder::def_ty(db, id.into(), None)
             .fill(|x| {
                 let r = it.next().unwrap_or_else(|| TyKind::Error.intern(Interner));
@@ -1789,6 +1827,35 @@ impl Function {
         Type::new_with_resolver_inner(db, &resolver, ty)
     }
 
+    // FIXME: Find better API to also handle const generics
+    pub fn ret_type_with_args(
+        self,
+        db: &dyn HirDatabase,
+        generics: impl Iterator<Item = Type>,
+    ) -> Type {
+        let resolver = self.id.resolver(db.upcast());
+        let parent_id: Option<GenericDefId> = match self.id.lookup(db.upcast()).container {
+            ItemContainerId::ImplId(it) => Some(it.into()),
+            ItemContainerId::TraitId(it) => Some(it.into()),
+            ItemContainerId::ModuleId(_) | ItemContainerId::ExternBlockId(_) => None,
+        };
+        let mut generics = generics.map(|it| it.ty.clone());
+        let mut filler = |x: &_| match x {
+            ParamKind::Type => {
+                generics.next().unwrap_or_else(|| TyKind::Error.intern(Interner)).cast(Interner)
+            }
+            ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
+        };
+
+        let parent_substs =
+            parent_id.map(|id| TyBuilder::subst_for_def(db, id, None).fill(&mut filler).build());
+        let substs = TyBuilder::subst_for_def(db, self.id, parent_substs).fill(&mut filler).build();
+
+        let callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
+        let ty = callable_sig.ret().clone();
+        Type::new_with_resolver_inner(db, &resolver, ty)
+    }
+
     pub fn async_ret_type(self, db: &dyn HirDatabase) -> Option<Type> {
         if !self.is_async(db) {
             return None;
@@ -1855,6 +1922,51 @@ impl Function {
             .collect()
     }
 
+    // FIXME: Find better API to also handle const generics
+    pub fn params_without_self_with_args(
+        self,
+        db: &dyn HirDatabase,
+        generics: impl Iterator<Item = Type>,
+    ) -> Vec<Param> {
+        let environment = db.trait_environment(self.id.into());
+        let parent_id: Option<GenericDefId> = match self.id.lookup(db.upcast()).container {
+            ItemContainerId::ImplId(it) => Some(it.into()),
+            ItemContainerId::TraitId(it) => Some(it.into()),
+            ItemContainerId::ModuleId(_) | ItemContainerId::ExternBlockId(_) => None,
+        };
+        let mut generics = generics.map(|it| it.ty.clone());
+        let parent_substs = parent_id.map(|id| {
+            TyBuilder::subst_for_def(db, id, None)
+                .fill(|x| match x {
+                    ParamKind::Type => generics
+                        .next()
+                        .unwrap_or_else(|| TyKind::Error.intern(Interner))
+                        .cast(Interner),
+                    ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
+                })
+                .build()
+        });
+
+        let substs = TyBuilder::subst_for_def(db, self.id, parent_substs)
+            .fill(|_| {
+                let ty = generics.next().unwrap_or_else(|| TyKind::Error.intern(Interner));
+                GenericArg::new(Interner, GenericArgData::Ty(ty))
+            })
+            .build();
+        let callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
+        let skip = if db.function_data(self.id).has_self_param() { 1 } else { 0 };
+        callable_sig
+            .params()
+            .iter()
+            .enumerate()
+            .skip(skip)
+            .map(|(idx, ty)| {
+                let ty = Type { env: environment.clone(), ty: ty.clone() };
+                Param { func: self, ty, idx }
+            })
+            .collect()
+    }
+
     pub fn is_const(self, db: &dyn HirDatabase) -> bool {
         db.function_data(self.id).has_const_kw()
     }
@@ -1889,6 +2001,11 @@ impl Function {
         db.function_data(self.id).attrs.is_bench()
     }
 
+    /// Is this function marked as unstable with `#[feature]` attribute?
+    pub fn is_unstable(self, db: &dyn HirDatabase) -> bool {
+        db.function_data(self.id).attrs.is_unstable()
+    }
+
     pub fn is_unsafe_to_call(self, db: &dyn HirDatabase) -> bool {
         hir_ty::is_fn_unsafe_to_call(db, self.id)
     }
@@ -2052,6 +2169,34 @@ impl SelfParam {
         let ty = callable_sig.params()[0].clone();
         Type { env: environment, ty }
     }
+
+    // FIXME: Find better API to also handle const generics
+    pub fn ty_with_args(&self, db: &dyn HirDatabase, generics: impl Iterator<Item = Type>) -> Type {
+        let parent_id: GenericDefId = match self.func.lookup(db.upcast()).container {
+            ItemContainerId::ImplId(it) => it.into(),
+            ItemContainerId::TraitId(it) => it.into(),
+            ItemContainerId::ModuleId(_) | ItemContainerId::ExternBlockId(_) => {
+                panic!("Never get here")
+            }
+        };
+
+        let mut generics = generics.map(|it| it.ty.clone());
+        let mut filler = |x: &_| match x {
+            ParamKind::Type => {
+                generics.next().unwrap_or_else(|| TyKind::Error.intern(Interner)).cast(Interner)
+            }
+            ParamKind::Const(ty) => unknown_const_as_generic(ty.clone()),
+        };
+
+        let parent_substs = TyBuilder::subst_for_def(db, parent_id, None).fill(&mut filler).build();
+        let substs =
+            TyBuilder::subst_for_def(db, self.func, Some(parent_substs)).fill(&mut filler).build();
+        let callable_sig =
+            db.callable_item_signature(self.func.into()).substitute(Interner, &substs);
+        let environment = db.trait_environment(self.func.into());
+        let ty = callable_sig.params()[0].clone();
+        Type { env: environment, ty }
+    }
 }
 
 impl HasVisibility for Function {
@@ -2754,7 +2899,7 @@ impl GenericDef {
             .collect()
     }
 
-    pub fn type_params(self, db: &dyn HirDatabase) -> Vec<TypeOrConstParam> {
+    pub fn type_or_const_params(self, db: &dyn HirDatabase) -> Vec<TypeOrConstParam> {
         let generics = db.generic_params(self.into());
         generics
             .type_or_consts
@@ -3126,12 +3271,16 @@ impl TypeParam {
         let ty = generic_arg_from_param(db, self.id.into())?;
         let resolver = self.id.parent().resolver(db.upcast());
         match ty.data(Interner) {
-            GenericArgData::Ty(it) => {
+            GenericArgData::Ty(it) if *it.kind(Interner) != TyKind::Error => {
                 Some(Type::new_with_resolver_inner(db, &resolver, it.clone()))
             }
             _ => None,
         }
     }
+
+    pub fn is_unstable(self, db: &dyn HirDatabase) -> bool {
+        db.attrs(GenericParamId::from(self.id).into()).is_unstable()
+    }
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
@@ -3241,6 +3390,26 @@ impl TypeOrConstParam {
             Either::Right(it) => it.ty(db),
         }
     }
+
+    pub fn as_type_param(self, db: &dyn HirDatabase) -> Option<TypeParam> {
+        let params = db.generic_params(self.id.parent);
+        match &params.type_or_consts[self.id.local_id] {
+            hir_def::generics::TypeOrConstParamData::TypeParamData(_) => {
+                Some(TypeParam { id: TypeParamId::from_unchecked(self.id) })
+            }
+            hir_def::generics::TypeOrConstParamData::ConstParamData(_) => None,
+        }
+    }
+
+    pub fn as_const_param(self, db: &dyn HirDatabase) -> Option<ConstParam> {
+        let params = db.generic_params(self.id.parent);
+        match &params.type_or_consts[self.id.local_id] {
+            hir_def::generics::TypeOrConstParamData::TypeParamData(_) => None,
+            hir_def::generics::TypeOrConstParamData::ConstParamData(_) => {
+                Some(ConstParam { id: ConstParamId::from_unchecked(self.id) })
+            }
+        }
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -3285,12 +3454,11 @@ impl Impl {
                     .filter(filter),
             )
         });
+
         for id in def_crates
             .iter()
             .flat_map(|&id| Crate { id }.transitive_reverse_dependencies(db))
             .map(|Crate { id }| id)
-            .chain(def_crates.iter().copied())
-            .unique()
         {
             all.extend(
                 db.trait_impls_in_crate(id)
@@ -3520,7 +3688,7 @@ pub enum CaptureKind {
     Move,
 }
 
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct Type {
     env: Arc<TraitEnvironment>,
     ty: Ty,
@@ -3620,6 +3788,50 @@ impl Type {
         matches!(self.ty.kind(Interner), TyKind::Ref(..))
     }
 
+    pub fn contains_reference(&self, db: &dyn HirDatabase) -> bool {
+        return go(db, self.env.krate, &self.ty);
+
+        fn go(db: &dyn HirDatabase, krate: CrateId, ty: &Ty) -> bool {
+            match ty.kind(Interner) {
+                // Reference itself
+                TyKind::Ref(_, _, _) => true,
+
+                // For non-phantom_data adts we check variants/fields as well as generic parameters
+                TyKind::Adt(adt_id, substitution)
+                    if !db.struct_datum(krate, *adt_id).flags.phantom_data =>
+                {
+                    let adt_datum = &db.struct_datum(krate, *adt_id);
+                    let adt_datum_bound =
+                        adt_datum.binders.clone().substitute(Interner, substitution);
+                    adt_datum_bound
+                        .variants
+                        .into_iter()
+                        .flat_map(|variant| variant.fields.into_iter())
+                        .any(|ty| go(db, krate, &ty))
+                        || substitution
+                            .iter(Interner)
+                            .filter_map(|x| x.ty(Interner))
+                            .any(|ty| go(db, krate, ty))
+                }
+                // And for `PhantomData<T>`, we check `T`.
+                TyKind::Adt(_, substitution)
+                | TyKind::Tuple(_, substitution)
+                | TyKind::OpaqueType(_, substitution)
+                | TyKind::AssociatedType(_, substitution)
+                | TyKind::FnDef(_, substitution) => substitution
+                    .iter(Interner)
+                    .filter_map(|x| x.ty(Interner))
+                    .any(|ty| go(db, krate, ty)),
+
+                // For `[T]` or `*T` we check `T`
+                TyKind::Array(ty, _) | TyKind::Slice(ty) | TyKind::Raw(_, ty) => go(db, krate, ty),
+
+                // Consider everything else as not reference
+                _ => false,
+            }
+        }
+    }
+
     pub fn as_reference(&self) -> Option<(Type, Mutability)> {
         let (ty, _lt, m) = self.ty.as_reference()?;
         let m = Mutability::from_mutable(matches!(m, hir_ty::Mutability::Mut));
@@ -3727,14 +3939,16 @@ impl Type {
         )
     }
 
+    // FIXME: Find better API that also handles const generics
     pub fn impls_trait(&self, db: &dyn HirDatabase, trait_: Trait, args: &[Type]) -> bool {
         let mut it = args.iter().map(|t| t.ty.clone());
         let trait_ref = TyBuilder::trait_ref(db, trait_.id)
             .push(self.ty.clone())
             .fill(|x| {
-                let r = it.next().unwrap();
                 match x {
-                    ParamKind::Type => r.cast(Interner),
+                    ParamKind::Type => {
+                        it.next().unwrap_or_else(|| TyKind::Error.intern(Interner)).cast(Interner)
+                    }
                     ParamKind::Const(ty) => {
                         // FIXME: this code is not covered in tests.
                         unknown_const_as_generic(ty.clone())
@@ -4368,12 +4582,24 @@ impl Type {
 
         walk_type(db, self, &mut cb);
     }
-
+    /// Check if type unifies with another type.
+    ///
+    /// Note that we consider placeholder types to unify with everything.
+    /// For example `Option<T>` and `Option<U>` unify although there is unresolved goal `T = U`.
     pub fn could_unify_with(&self, db: &dyn HirDatabase, other: &Type) -> bool {
         let tys = hir_ty::replace_errors_with_variables(&(self.ty.clone(), other.ty.clone()));
         hir_ty::could_unify(db, self.env.clone(), &tys)
     }
 
+    /// Check if type unifies with another type eagerly making sure there are no unresolved goals.
+    ///
+    /// This means that placeholder types are not considered to unify if there are any bounds set on
+    /// them. For example `Option<T>` and `Option<U>` do not unify as we cannot show that `T = U`
+    pub fn could_unify_with_deeply(&self, db: &dyn HirDatabase, other: &Type) -> bool {
+        let tys = hir_ty::replace_errors_with_variables(&(self.ty.clone(), other.ty.clone()));
+        hir_ty::could_unify_deeply(db, self.env.clone(), &tys)
+    }
+
     pub fn could_coerce_to(&self, db: &dyn HirDatabase, to: &Type) -> bool {
         let tys = hir_ty::replace_errors_with_variables(&(self.ty.clone(), to.ty.clone()));
         hir_ty::could_coerce(db, self.env.clone(), &tys)

crates/hir/src/term_search.rs

@@ -0,0 +1,298 @@
+//! Term search
+
+use hir_def::type_ref::Mutability;
+use hir_ty::db::HirDatabase;
+use itertools::Itertools;
+use rustc_hash::{FxHashMap, FxHashSet};
+
+use crate::{ModuleDef, ScopeDef, Semantics, SemanticsScope, Type};
+
+mod expr;
+pub use expr::Expr;
+
+mod tactics;
+
+/// Key for lookup table to query new types reached.
+#[derive(Debug, Hash, PartialEq, Eq)]
+enum NewTypesKey {
+    ImplMethod,
+    StructProjection,
+}
+
+/// Helper enum to squash big number of alternative trees into `Many` variant as there is too many
+/// to take into account.
+#[derive(Debug)]
+enum AlternativeExprs {
+    /// There are few trees, so we keep track of them all
+    Few(FxHashSet<Expr>),
+    /// There are too many trees to keep track of
+    Many,
+}
+
+impl AlternativeExprs {
+    /// Construct alternative trees
+    ///
+    /// # Arguments
+    /// `threshold` - threshold value for many trees (more than that is many)
+    /// `exprs` - expressions iterator
+    fn new(threshold: usize, exprs: impl Iterator<Item = Expr>) -> AlternativeExprs {
+        let mut it = AlternativeExprs::Few(Default::default());
+        it.extend_with_threshold(threshold, exprs);
+        it
+    }
+
+    /// Get type trees stored in alternative trees (or `Expr::Many` in case of many)
+    ///
+    /// # Arguments
+    /// `ty` - Type of expressions queried (this is used to give type to `Expr::Many`)
+    fn exprs(&self, ty: &Type) -> Vec<Expr> {
+        match self {
+            AlternativeExprs::Few(exprs) => exprs.iter().cloned().collect(),
+            AlternativeExprs::Many => vec![Expr::Many(ty.clone())],
+        }
+    }
+
+    /// Extend alternative expressions
+    ///
+    /// # Arguments
+    /// `threshold` - threshold value for many trees (more than that is many)
+    /// `exprs` - expressions iterator
+    fn extend_with_threshold(&mut self, threshold: usize, exprs: impl Iterator<Item = Expr>) {
+        match self {
+            AlternativeExprs::Few(tts) => {
+                for it in exprs {
+                    if tts.len() > threshold {
+                        *self = AlternativeExprs::Many;
+                        break;
+                    }
+
+                    tts.insert(it);
+                }
+            }
+            AlternativeExprs::Many => (),
+        }
+    }
+}
+
+/// # Lookup table for term search
+///
+/// Lookup table keeps all the state during term search.
+/// This means it knows what types and how are reachable.
+///
+/// The secondary functionality for lookup table is to keep track of new types reached since last
+/// iteration as well as keeping track of which `ScopeDef` items have been used.
+/// Both of them are to speed up the term search by leaving out types / ScopeDefs that likely do
+/// not produce any new results.
+#[derive(Default, Debug)]
+struct LookupTable {
+    /// All the `Expr`s in "value" produce the type of "key"
+    data: FxHashMap<Type, AlternativeExprs>,
+    /// New types reached since last query by the `NewTypesKey`
+    new_types: FxHashMap<NewTypesKey, Vec<Type>>,
+    /// ScopeDefs that are not interesting any more
+    exhausted_scopedefs: FxHashSet<ScopeDef>,
+    /// ScopeDefs that were used in current round
+    round_scopedef_hits: FxHashSet<ScopeDef>,
+    /// Amount of rounds since scopedef was first used.
+    rounds_since_sopedef_hit: FxHashMap<ScopeDef, u32>,
+    /// Types queried but not present
+    types_wishlist: FxHashSet<Type>,
+    /// Threshold to squash trees to `Many`
+    many_threshold: usize,
+}
+
+impl LookupTable {
+    /// Initialize lookup table
+    fn new(many_threshold: usize) -> Self {
+        let mut res = Self { many_threshold, ..Default::default() };
+        res.new_types.insert(NewTypesKey::ImplMethod, Vec::new());
+        res.new_types.insert(NewTypesKey::StructProjection, Vec::new());
+        res
+    }
+
+    /// Find all `Expr`s that unify with the `ty`
+    fn find(&self, db: &dyn HirDatabase, ty: &Type) -> Option<Vec<Expr>> {
+        self.data
+            .iter()
+            .find(|(t, _)| t.could_unify_with_deeply(db, ty))
+            .map(|(t, tts)| tts.exprs(t))
+    }
+
+    /// Same as find but automatically creates shared reference of types in the lookup
+    ///
+    /// For example if we have type `i32` in data and we query for `&i32` it map all the type
+    /// trees we have for `i32` with `Expr::Reference` and returns them.
+    fn find_autoref(&self, db: &dyn HirDatabase, ty: &Type) -> Option<Vec<Expr>> {
+        self.data
+            .iter()
+            .find(|(t, _)| t.could_unify_with_deeply(db, ty))
+            .map(|(t, it)| it.exprs(t))
+            .or_else(|| {
+                self.data
+                    .iter()
+                    .find(|(t, _)| {
+                        Type::reference(t, Mutability::Shared).could_unify_with_deeply(db, ty)
+                    })
+                    .map(|(t, it)| {
+                        it.exprs(t)
+                            .into_iter()
+                            .map(|expr| Expr::Reference(Box::new(expr)))
+                            .collect()
+                    })
+            })
+    }
+
+    /// Insert new type trees for type
+    ///
+    /// Note that the types have to be the same, unification is not enough as unification is not
+    /// transitive. For example Vec<i32> and FxHashSet<i32> both unify with Iterator<Item = i32>,
+    /// but they clearly do not unify themselves.
+    fn insert(&mut self, ty: Type, exprs: impl Iterator<Item = Expr>) {
+        match self.data.get_mut(&ty) {
+            Some(it) => it.extend_with_threshold(self.many_threshold, exprs),
+            None => {
+                self.data.insert(ty.clone(), AlternativeExprs::new(self.many_threshold, exprs));
+                for it in self.new_types.values_mut() {
+                    it.push(ty.clone());
+                }
+            }
+        }
+    }
+
+    /// Iterate all the reachable types
+    fn iter_types(&self) -> impl Iterator<Item = Type> + '_ {
+        self.data.keys().cloned()
+    }
+
+    /// Query new types reached since last query by key
+    ///
+    /// Create new key if you wish to query it to avoid conflicting with existing queries.
+    fn new_types(&mut self, key: NewTypesKey) -> Vec<Type> {
+        match self.new_types.get_mut(&key) {
+            Some(it) => std::mem::take(it),
+            None => Vec::new(),
+        }
+    }
+
+    /// Mark `ScopeDef` as exhausted meaning it is not interesting for us any more
+    fn mark_exhausted(&mut self, def: ScopeDef) {
+        self.exhausted_scopedefs.insert(def);
+    }
+
+    /// Mark `ScopeDef` as used meaning we managed to produce something useful from it
+    fn mark_fulfilled(&mut self, def: ScopeDef) {
+        self.round_scopedef_hits.insert(def);
+    }
+
+    /// Start new round (meant to be called at the beginning of iteration in `term_search`)
+    ///
+    /// This functions marks some `ScopeDef`s as exhausted if there have been
+    /// `MAX_ROUNDS_AFTER_HIT` rounds after first using a `ScopeDef`.
+    fn new_round(&mut self) {
+        for def in &self.round_scopedef_hits {
+            let hits =
+                self.rounds_since_sopedef_hit.entry(*def).and_modify(|n| *n += 1).or_insert(0);
+            const MAX_ROUNDS_AFTER_HIT: u32 = 2;
+            if *hits > MAX_ROUNDS_AFTER_HIT {
+                self.exhausted_scopedefs.insert(*def);
+            }
+        }
+        self.round_scopedef_hits.clear();
+    }
+
+    /// Get exhausted `ScopeDef`s
+    fn exhausted_scopedefs(&self) -> &FxHashSet<ScopeDef> {
+        &self.exhausted_scopedefs
+    }
+
+    /// Types queried but not found
+    fn take_types_wishlist(&mut self) -> FxHashSet<Type> {
+        std::mem::take(&mut self.types_wishlist)
+    }
+}
+
+/// Context for the `term_search` function
+#[derive(Debug)]
+pub struct TermSearchCtx<'a, DB: HirDatabase> {
+    /// Semantics for the program
+    pub sema: &'a Semantics<'a, DB>,
+    /// Semantic scope, captures context for the term search
+    pub scope: &'a SemanticsScope<'a>,
+    /// Target / expected output type
+    pub goal: Type,
+    /// Configuration for term search
+    pub config: TermSearchConfig,
+}
+
+/// Configuration options for the term search
+#[derive(Debug, Clone, Copy)]
+pub struct TermSearchConfig {
+    /// Enable borrow checking, this guarantees the outputs of the `term_search` to borrow-check
+    pub enable_borrowcheck: bool,
+    /// Indicate when to squash multiple trees to `Many` as there are too many to keep track
+    pub many_alternatives_threshold: usize,
+    /// Depth of the search eg. number of cycles to run
+    pub depth: usize,
+}
+
+impl Default for TermSearchConfig {
+    fn default() -> Self {
+        Self { enable_borrowcheck: true, many_alternatives_threshold: 1, depth: 6 }
+    }
+}
+
+/// # Term search
+///
+/// Search for terms (expressions) that unify with the `goal` type.
+///
+/// # Arguments
+/// * `ctx` - Context for term search
+///
+/// Internally this function uses Breadth First Search to find path to `goal` type.
+/// The general idea is following:
+/// 1. Populate lookup (frontier for BFS) from values (local variables, statics, constants, etc)
+///    as well as from well knows values (such as `true/false` and `()`)
+/// 2. Iteratively expand the frontier (or contents of the lookup) by trying different type
+///    transformation tactics. For example functions take as from set of types (arguments) to some
+///    type (return type). Other transformations include methods on type, type constructors and
+///    projections to struct fields (field access).
+/// 3. Once we manage to find path to type we are interested in we continue for single round to see
+///    if we can find more paths that take us to the `goal` type.
+/// 4. Return all the paths (type trees) that take us to the `goal` type.
+///
+/// Note that there are usually more ways we can get to the `goal` type but some are discarded to
+/// reduce the memory consumption. It is also unlikely anyone is willing ti browse through
+/// thousands of possible responses so we currently take first 10 from every tactic.
+pub fn term_search<DB: HirDatabase>(ctx: &TermSearchCtx<'_, DB>) -> Vec<Expr> {
+    let module = ctx.scope.module();
+    let mut defs = FxHashSet::default();
+    defs.insert(ScopeDef::ModuleDef(ModuleDef::Module(module)));
+
+    ctx.scope.process_all_names(&mut |_, def| {
+        defs.insert(def);
+    });
+
+    let mut lookup = LookupTable::new(ctx.config.many_alternatives_threshold);
+
+    // Try trivial tactic first, also populates lookup table
+    let mut solutions: Vec<Expr> = tactics::trivial(ctx, &defs, &mut lookup).collect();
+    // Use well known types tactic before iterations as it does not depend on other tactics
+    solutions.extend(tactics::famous_types(ctx, &defs, &mut lookup));
+
+    for _ in 0..ctx.config.depth {
+        lookup.new_round();
+
+        solutions.extend(tactics::type_constructor(ctx, &defs, &mut lookup));
+        solutions.extend(tactics::free_function(ctx, &defs, &mut lookup));
+        solutions.extend(tactics::impl_method(ctx, &defs, &mut lookup));
+        solutions.extend(tactics::struct_projection(ctx, &defs, &mut lookup));
+        solutions.extend(tactics::impl_static_method(ctx, &defs, &mut lookup));
+
+        // Discard not interesting `ScopeDef`s for speedup
+        for def in lookup.exhausted_scopedefs() {
+            defs.remove(def);
+        }
+    }
+
+    solutions.into_iter().filter(|it| !it.is_many()).unique().collect()
+}

crates/hir/src/term_search/expr.rs

@@ -0,0 +1,468 @@
+//! Type tree for term search
+
+use hir_def::find_path::PrefixKind;
+use hir_expand::mod_path::ModPath;
+use hir_ty::{
+    db::HirDatabase,
+    display::{DisplaySourceCodeError, HirDisplay},
+};
+use itertools::Itertools;
+
+use crate::{
+    Adt, AsAssocItem, Const, ConstParam, Field, Function, GenericDef, Local, ModuleDef,
+    SemanticsScope, Static, Struct, StructKind, Trait, Type, Variant,
+};
+
+/// Helper function to get path to `ModuleDef`
+fn mod_item_path(
+    sema_scope: &SemanticsScope<'_>,
+    def: &ModuleDef,
+    prefer_no_std: bool,
+    prefer_prelude: bool,
+) -> Option<ModPath> {
+    let db = sema_scope.db;
+    // Account for locals shadowing items from module
+    let name_hit_count = def.name(db).map(|def_name| {
+        let mut name_hit_count = 0;
+        sema_scope.process_all_names(&mut |name, _| {
+            if name == def_name {
+                name_hit_count += 1;
+            }
+        });
+        name_hit_count
+    });
+
+    let m = sema_scope.module();
+    match name_hit_count {
+        Some(0..=1) | None => m.find_use_path(db.upcast(), *def, prefer_no_std, prefer_prelude),
+        Some(_) => m.find_use_path_prefixed(
+            db.upcast(),
+            *def,
+            PrefixKind::ByCrate,
+            prefer_no_std,
+            prefer_prelude,
+        ),
+    }
+}
+
+/// Helper function to get path to `ModuleDef` as string
+fn mod_item_path_str(
+    sema_scope: &SemanticsScope<'_>,
+    def: &ModuleDef,
+    prefer_no_std: bool,
+    prefer_prelude: bool,
+) -> Result<String, DisplaySourceCodeError> {
+    let path = mod_item_path(sema_scope, def, prefer_no_std, prefer_prelude);
+    path.map(|it| it.display(sema_scope.db.upcast()).to_string())
+        .ok_or(DisplaySourceCodeError::PathNotFound)
+}
+
+/// Helper function to get path to `Type`
+fn type_path(
+    sema_scope: &SemanticsScope<'_>,
+    ty: &Type,
+    prefer_no_std: bool,
+    prefer_prelude: bool,
+) -> Result<String, DisplaySourceCodeError> {
+    let db = sema_scope.db;
+    let m = sema_scope.module();
+
+    match ty.as_adt() {
+        Some(adt) => {
+            let ty_name = ty.display_source_code(db, m.id, true)?;
+
+            let mut path =
+                mod_item_path(sema_scope, &ModuleDef::Adt(adt), prefer_no_std, prefer_prelude)
+                    .unwrap();
+            path.pop_segment();
+            let path = path.display(db.upcast()).to_string();
+            let res = match path.is_empty() {
+                true => ty_name,
+                false => format!("{path}::{ty_name}"),
+            };
+            Ok(res)
+        }
+        None => ty.display_source_code(db, m.id, true),
+    }
+}
+
+/// Helper function to filter out generic parameters that are default
+fn non_default_generics(db: &dyn HirDatabase, def: GenericDef, generics: &[Type]) -> Vec<Type> {
+    def.type_or_const_params(db)
+        .into_iter()
+        .filter_map(|it| it.as_type_param(db))
+        .zip(generics)
+        .filter(|(tp, arg)| tp.default(db).as_ref() != Some(arg))
+        .map(|(_, arg)| arg.clone())
+        .collect()
+}
+
+/// Type tree shows how can we get from set of types to some type.
+///
+/// Consider the following code as an example
+/// ```
+/// fn foo(x: i32, y: bool) -> Option<i32> { None }
+/// fn bar() {
+///    let a = 1;
+///    let b = true;
+///    let c: Option<i32> = _;
+/// }
+/// ```
+/// If we generate type tree in the place of `_` we get
+/// ```txt
+///       Option<i32>
+///           |
+///     foo(i32, bool)
+///      /        \
+///  a: i32      b: bool
+/// ```
+/// So in short it pretty much gives us a way to get type `Option<i32>` using the items we have in
+/// scope.
+#[derive(Debug, Clone, Eq, Hash, PartialEq)]
+pub enum Expr {
+    /// Constant
+    Const(Const),
+    /// Static variable
+    Static(Static),
+    /// Local variable
+    Local(Local),
+    /// Constant generic parameter
+    ConstParam(ConstParam),
+    /// Well known type (such as `true` for bool)
+    FamousType { ty: Type, value: &'static str },
+    /// Function call (does not take self param)
+    Function { func: Function, generics: Vec<Type>, params: Vec<Expr> },
+    /// Method call (has self param)
+    Method { func: Function, generics: Vec<Type>, target: Box<Expr>, params: Vec<Expr> },
+    /// Enum variant construction
+    Variant { variant: Variant, generics: Vec<Type>, params: Vec<Expr> },
+    /// Struct construction
+    Struct { strukt: Struct, generics: Vec<Type>, params: Vec<Expr> },
+    /// Struct field access
+    Field { expr: Box<Expr>, field: Field },
+    /// Passing type as reference (with `&`)
+    Reference(Box<Expr>),
+    /// Indicates possibility of many different options that all evaluate to `ty`
+    Many(Type),
+}
+
+impl Expr {
+    /// Generate source code for type tree.
+    ///
+    /// Note that trait imports are not added to generated code.
+    /// To make sure that the code is valid, callee has to also ensure that all the traits listed
+    /// by `traits_used` method are also imported.
+    pub fn gen_source_code(
+        &self,
+        sema_scope: &SemanticsScope<'_>,
+        many_formatter: &mut dyn FnMut(&Type) -> String,
+        prefer_no_std: bool,
+        prefer_prelude: bool,
+    ) -> Result<String, DisplaySourceCodeError> {
+        let db = sema_scope.db;
+        let mod_item_path_str = |s, def| mod_item_path_str(s, def, prefer_no_std, prefer_prelude);
+        match self {
+            Expr::Const(it) => mod_item_path_str(sema_scope, &ModuleDef::Const(*it)),
+            Expr::Static(it) => mod_item_path_str(sema_scope, &ModuleDef::Static(*it)),
+            Expr::Local(it) => Ok(it.name(db).display(db.upcast()).to_string()),
+            Expr::ConstParam(it) => Ok(it.name(db).display(db.upcast()).to_string()),
+            Expr::FamousType { value, .. } => Ok(value.to_string()),
+            Expr::Function { func, params, .. } => {
+                let args = params
+                    .iter()
+                    .map(|f| {
+                        f.gen_source_code(sema_scope, many_formatter, prefer_no_std, prefer_prelude)
+                    })
+                    .collect::<Result<Vec<String>, DisplaySourceCodeError>>()?
+                    .into_iter()
+                    .join(", ");
+
+                match func.as_assoc_item(db).map(|it| it.container(db)) {
+                    Some(container) => {
+                        let container_name = match container {
+                            crate::AssocItemContainer::Trait(trait_) => {
+                                mod_item_path_str(sema_scope, &ModuleDef::Trait(trait_))?
+                            }
+                            crate::AssocItemContainer::Impl(imp) => {
+                                let self_ty = imp.self_ty(db);
+                                // Should it be guaranteed that `mod_item_path` always exists?
+                                match self_ty.as_adt().and_then(|adt| {
+                                    mod_item_path(
+                                        sema_scope,
+                                        &adt.into(),
+                                        prefer_no_std,
+                                        prefer_prelude,
+                                    )
+                                }) {
+                                    Some(path) => path.display(sema_scope.db.upcast()).to_string(),
+                                    None => self_ty.display(db).to_string(),
+                                }
+                            }
+                        };
+                        let fn_name = func.name(db).display(db.upcast()).to_string();
+                        Ok(format!("{container_name}::{fn_name}({args})"))
+                    }
+                    None => {
+                        let fn_name = mod_item_path_str(sema_scope, &ModuleDef::Function(*func))?;
+                        Ok(format!("{fn_name}({args})"))
+                    }
+                }
+            }
+            Expr::Method { func, target, params, .. } => {
+                if target.contains_many_in_illegal_pos() {
+                    return Ok(many_formatter(&target.ty(db)));
+                }
+
+                let func_name = func.name(db).display(db.upcast()).to_string();
+                let self_param = func.self_param(db).unwrap();
+                let target = target.gen_source_code(
+                    sema_scope,
+                    many_formatter,
+                    prefer_no_std,
+                    prefer_prelude,
+                )?;
+                let args = params
+                    .iter()
+                    .map(|f| {
+                        f.gen_source_code(sema_scope, many_formatter, prefer_no_std, prefer_prelude)
+                    })
+                    .collect::<Result<Vec<String>, DisplaySourceCodeError>>()?
+                    .into_iter()
+                    .join(", ");
+
+                match func.as_assoc_item(db).and_then(|it| it.container_or_implemented_trait(db)) {
+                    Some(trait_) => {
+                        let trait_name = mod_item_path_str(sema_scope, &ModuleDef::Trait(trait_))?;
+                        let target = match self_param.access(db) {
+                            crate::Access::Shared => format!("&{target}"),
+                            crate::Access::Exclusive => format!("&mut {target}"),
+                            crate::Access::Owned => target,
+                        };
+                        let res = match args.is_empty() {
+                            true => format!("{trait_name}::{func_name}({target})",),
+                            false => format!("{trait_name}::{func_name}({target}, {args})",),
+                        };
+                        Ok(res)
+                    }
+                    None => Ok(format!("{target}.{func_name}({args})")),
+                }
+            }
+            Expr::Variant { variant, generics, params } => {
+                let generics = non_default_generics(db, (*variant).into(), generics);
+                let generics_str = match generics.is_empty() {
+                    true => String::new(),
+                    false => {
+                        let generics = generics
+                            .iter()
+                            .map(|it| type_path(sema_scope, it, prefer_no_std, prefer_prelude))
+                            .collect::<Result<Vec<String>, DisplaySourceCodeError>>()?
+                            .into_iter()
+                            .join(", ");
+                        format!("::<{generics}>")
+                    }
+                };
+                let inner = match variant.kind(db) {
+                    StructKind::Tuple => {
+                        let args = params
+                            .iter()
+                            .map(|f| {
+                                f.gen_source_code(
+                                    sema_scope,
+                                    many_formatter,
+                                    prefer_no_std,
+                                    prefer_prelude,
+                                )
+                            })
+                            .collect::<Result<Vec<String>, DisplaySourceCodeError>>()?
+                            .into_iter()
+                            .join(", ");
+                        format!("{generics_str}({args})")
+                    }
+                    StructKind::Record => {
+                        let fields = variant.fields(db);
+                        let args = params
+                            .iter()
+                            .zip(fields.iter())
+                            .map(|(a, f)| {
+                                let tmp = format!(
+                                    "{}: {}",
+                                    f.name(db).display(db.upcast()),
+                                    a.gen_source_code(
+                                        sema_scope,
+                                        many_formatter,
+                                        prefer_no_std,
+                                        prefer_prelude
+                                    )?
+                                );
+                                Ok(tmp)
+                            })
+                            .collect::<Result<Vec<String>, DisplaySourceCodeError>>()?
+                            .into_iter()
+                            .join(", ");
+                        format!("{generics_str}{{ {args} }}")
+                    }
+                    StructKind::Unit => generics_str,
+                };
+
+                let prefix = mod_item_path_str(sema_scope, &ModuleDef::Variant(*variant))?;
+                Ok(format!("{prefix}{inner}"))
+            }
+            Expr::Struct { strukt, generics, params } => {
+                let generics = non_default_generics(db, (*strukt).into(), generics);
+                let inner = match strukt.kind(db) {
+                    StructKind::Tuple => {
+                        let args = params
+                            .iter()
+                            .map(|a| {
+                                a.gen_source_code(
+                                    sema_scope,
+                                    many_formatter,
+                                    prefer_no_std,
+                                    prefer_prelude,
+                                )
+                            })
+                            .collect::<Result<Vec<String>, DisplaySourceCodeError>>()?
+                            .into_iter()
+                            .join(", ");
+                        format!("({args})")
+                    }
+                    StructKind::Record => {
+                        let fields = strukt.fields(db);
+                        let args = params
+                            .iter()
+                            .zip(fields.iter())
+                            .map(|(a, f)| {
+                                let tmp = format!(
+                                    "{}: {}",
+                                    f.name(db).display(db.upcast()),
+                                    a.gen_source_code(
+                                        sema_scope,
+                                        many_formatter,
+                                        prefer_no_std,
+                                        prefer_prelude
+                                    )?
+                                );
+                                Ok(tmp)
+                            })
+                            .collect::<Result<Vec<String>, DisplaySourceCodeError>>()?
+                            .into_iter()
+                            .join(", ");
+                        format!(" {{ {args} }}")
+                    }
+                    StructKind::Unit => match generics.is_empty() {
+                        true => String::new(),
+                        false => {
+                            let generics = generics
+                                .iter()
+                                .map(|it| type_path(sema_scope, it, prefer_no_std, prefer_prelude))
+                                .collect::<Result<Vec<String>, DisplaySourceCodeError>>()?
+                                .into_iter()
+                                .join(", ");
+                            format!("::<{generics}>")
+                        }
+                    },
+                };
+
+                let prefix = mod_item_path_str(sema_scope, &ModuleDef::Adt(Adt::Struct(*strukt)))?;
+                Ok(format!("{prefix}{inner}"))
+            }
+            Expr::Field { expr, field } => {
+                if expr.contains_many_in_illegal_pos() {
+                    return Ok(many_formatter(&expr.ty(db)));
+                }
+
+                let strukt = expr.gen_source_code(
+                    sema_scope,
+                    many_formatter,
+                    prefer_no_std,
+                    prefer_prelude,
+                )?;
+                let field = field.name(db).display(db.upcast()).to_string();
+                Ok(format!("{strukt}.{field}"))
+            }
+            Expr::Reference(expr) => {
+                if expr.contains_many_in_illegal_pos() {
+                    return Ok(many_formatter(&expr.ty(db)));
+                }
+
+                let inner = expr.gen_source_code(
+                    sema_scope,
+                    many_formatter,
+                    prefer_no_std,
+                    prefer_prelude,
+                )?;
+                Ok(format!("&{inner}"))
+            }
+            Expr::Many(ty) => Ok(many_formatter(ty)),
+        }
+    }
+
+    /// Get type of the type tree.
+    ///
+    /// Same as getting the type of root node
+    pub fn ty(&self, db: &dyn HirDatabase) -> Type {
+        match self {
+            Expr::Const(it) => it.ty(db),
+            Expr::Static(it) => it.ty(db),
+            Expr::Local(it) => it.ty(db),
+            Expr::ConstParam(it) => it.ty(db),
+            Expr::FamousType { ty, .. } => ty.clone(),
+            Expr::Function { func, generics, .. } => {
+                func.ret_type_with_args(db, generics.iter().cloned())
+            }
+            Expr::Method { func, generics, target, .. } => func.ret_type_with_args(
+                db,
+                target.ty(db).type_arguments().chain(generics.iter().cloned()),
+            ),
+            Expr::Variant { variant, generics, .. } => {
+                Adt::from(variant.parent_enum(db)).ty_with_args(db, generics.iter().cloned())
+            }
+            Expr::Struct { strukt, generics, .. } => {
+                Adt::from(*strukt).ty_with_args(db, generics.iter().cloned())
+            }
+            Expr::Field { expr, field } => field.ty_with_args(db, expr.ty(db).type_arguments()),
+            Expr::Reference(it) => it.ty(db),
+            Expr::Many(ty) => ty.clone(),
+        }
+    }
+
+    /// List the traits used in type tree
+    pub fn traits_used(&self, db: &dyn HirDatabase) -> Vec<Trait> {
+        let mut res = Vec::new();
+
+        if let Expr::Method { func, params, .. } = self {
+            res.extend(params.iter().flat_map(|it| it.traits_used(db)));
+            if let Some(it) = func.as_assoc_item(db) {
+                if let Some(it) = it.container_or_implemented_trait(db) {
+                    res.push(it);
+                }
+            }
+        }
+
+        res
+    }
+
+    /// Check in the tree contains `Expr::Many` variant in illegal place to insert `todo`,
+    /// `unimplemented` or similar macro
+    ///
+    /// Some examples are following
+    /// ```no_compile
+    /// macro!().foo
+    /// macro!().bar()
+    /// &macro!()
+    /// ```
+    fn contains_many_in_illegal_pos(&self) -> bool {
+        match self {
+            Expr::Method { target, .. } => target.contains_many_in_illegal_pos(),
+            Expr::Field { expr, .. } => expr.contains_many_in_illegal_pos(),
+            Expr::Reference(target) => target.is_many(),
+            Expr::Many(_) => true,
+            _ => false,
+        }
+    }
+
+    /// Helper function to check if outermost type tree is `Expr::Many` variant
+    pub fn is_many(&self) -> bool {
+        matches!(self, Expr::Many(_))
+    }
+}

crates/hir/src/term_search/tactics.rs

@@ -0,0 +1,859 @@
+//! Tactics for term search
+//!
+//! All the tactics take following arguments
+//! * `ctx` - Context for the term search
+//! * `defs` - Set of items in scope at term search target location
+//! * `lookup` - Lookup table for types
+//! And they return iterator that yields type trees that unify with the `goal` type.
+
+use std::iter;
+
+use hir_ty::db::HirDatabase;
+use hir_ty::mir::BorrowKind;
+use hir_ty::TyBuilder;
+use itertools::Itertools;
+use rustc_hash::FxHashSet;
+
+use crate::{
+    Adt, AssocItem, Enum, GenericDef, GenericParam, HasVisibility, Impl, ModuleDef, ScopeDef, Type,
+    TypeParam, Variant,
+};
+
+use crate::term_search::{Expr, TermSearchConfig};
+
+use super::{LookupTable, NewTypesKey, TermSearchCtx};
+
+/// # Trivial tactic
+///
+/// Attempts to fulfill the goal by trying items in scope
+/// Also works as a starting point to move all items in scope to lookup table.
+///
+/// # Arguments
+/// * `ctx` - Context for the term search
+/// * `defs` - Set of items in scope at term search target location
+/// * `lookup` - Lookup table for types
+///
+/// Returns iterator that yields elements that unify with `goal`.
+///
+/// _Note that there is no use of calling this tactic in every iteration as the output does not
+/// depend on the current state of `lookup`_
+pub(super) fn trivial<'a, DB: HirDatabase>(
+    ctx: &'a TermSearchCtx<'a, DB>,
+    defs: &'a FxHashSet<ScopeDef>,
+    lookup: &'a mut LookupTable,
+) -> impl Iterator<Item = Expr> + 'a {
+    let db = ctx.sema.db;
+    defs.iter().filter_map(|def| {
+        let expr = match def {
+            ScopeDef::ModuleDef(ModuleDef::Const(it)) => Some(Expr::Const(*it)),
+            ScopeDef::ModuleDef(ModuleDef::Static(it)) => Some(Expr::Static(*it)),
+            ScopeDef::GenericParam(GenericParam::ConstParam(it)) => Some(Expr::ConstParam(*it)),
+            ScopeDef::Local(it) => {
+                if ctx.config.enable_borrowcheck {
+                    let borrowck = db.borrowck(it.parent).ok()?;
+
+                    let invalid = borrowck.iter().any(|b| {
+                        b.partially_moved.iter().any(|moved| {
+                            Some(&moved.local) == b.mir_body.binding_locals.get(it.binding_id)
+                        }) || b.borrow_regions.iter().any(|region| {
+                            // Shared borrows are fine
+                            Some(&region.local) == b.mir_body.binding_locals.get(it.binding_id)
+                                && region.kind != BorrowKind::Shared
+                        })
+                    });
+
+                    if invalid {
+                        return None;
+                    }
+                }
+
+                Some(Expr::Local(*it))
+            }
+            _ => None,
+        }?;
+
+        lookup.mark_exhausted(*def);
+
+        let ty = expr.ty(db);
+        lookup.insert(ty.clone(), std::iter::once(expr.clone()));
+
+        // Don't suggest local references as they are not valid for return
+        if matches!(expr, Expr::Local(_)) && ty.contains_reference(db) {
+            return None;
+        }
+
+        ty.could_unify_with_deeply(db, &ctx.goal).then_some(expr)
+    })
+}
+
+/// # Type constructor tactic
+///
+/// Attempts different type constructors for enums and structs in scope
+///
+/// Updates lookup by new types reached and returns iterator that yields
+/// elements that unify with `goal`.
+///
+/// # Arguments
+/// * `ctx` - Context for the term search
+/// * `defs` - Set of items in scope at term search target location
+/// * `lookup` - Lookup table for types
+pub(super) fn type_constructor<'a, DB: HirDatabase>(
+    ctx: &'a TermSearchCtx<'a, DB>,
+    defs: &'a FxHashSet<ScopeDef>,
+    lookup: &'a mut LookupTable,
+) -> impl Iterator<Item = Expr> + 'a {
+    let db = ctx.sema.db;
+    let module = ctx.scope.module();
+    fn variant_helper(
+        db: &dyn HirDatabase,
+        lookup: &mut LookupTable,
+        parent_enum: Enum,
+        variant: Variant,
+        goal: &Type,
+        config: &TermSearchConfig,
+    ) -> Vec<(Type, Vec<Expr>)> {
+        // Ignore unstable
+        if variant.is_unstable(db) {
+            return Vec::new();
+        }
+
+        let generics = GenericDef::from(variant.parent_enum(db));
+        let Some(type_params) = generics
+            .type_or_const_params(db)
+            .into_iter()
+            .map(|it| it.as_type_param(db))
+            .collect::<Option<Vec<TypeParam>>>()
+        else {
+            // Ignore enums with const generics
+            return Vec::new();
+        };
+
+        // We currently do not check lifetime bounds so ignore all types that have something to do
+        // with them
+        if !generics.lifetime_params(db).is_empty() {
+            return Vec::new();
+        }
+
+        // Only account for stable type parameters for now, unstable params can be default
+        // tho, for example in `Box<T, #[unstable] A: Allocator>`
+        if type_params.iter().any(|it| it.is_unstable(db) && it.default(db).is_none()) {
+            return Vec::new();
+        }
+
+        let non_default_type_params_len =
+            type_params.iter().filter(|it| it.default(db).is_none()).count();
+
+        let generic_params = lookup
+            .iter_types()
+            .collect::<Vec<_>>() // Force take ownership
+            .into_iter()
+            .permutations(non_default_type_params_len);
+
+        generic_params
+            .filter_map(move |generics| {
+                // Insert default type params
+                let mut g = generics.into_iter();
+                let generics: Vec<_> = type_params
+                    .iter()
+                    .map(|it| it.default(db).unwrap_or_else(|| g.next().expect("No generic")))
+                    .collect();
+
+                let enum_ty = Adt::from(parent_enum).ty_with_args(db, generics.iter().cloned());
+
+                // Allow types with generics only if they take us straight to goal for
+                // performance reasons
+                if !generics.is_empty() && !enum_ty.could_unify_with_deeply(db, goal) {
+                    return None;
+                }
+
+                // Ignore types that have something to do with lifetimes
+                if config.enable_borrowcheck && enum_ty.contains_reference(db) {
+                    return None;
+                }
+
+                // Early exit if some param cannot be filled from lookup
+                let param_exprs: Vec<Vec<Expr>> = variant
+                    .fields(db)
+                    .into_iter()
+                    .map(|field| lookup.find(db, &field.ty_with_args(db, generics.iter().cloned())))
+                    .collect::<Option<_>>()?;
+
+                // Note that we need special case for 0 param constructors because of multi cartesian
+                // product
+                let variant_exprs: Vec<Expr> = if param_exprs.is_empty() {
+                    vec![Expr::Variant { variant, generics: generics.clone(), params: Vec::new() }]
+                } else {
+                    param_exprs
+                        .into_iter()
+                        .multi_cartesian_product()
+                        .map(|params| Expr::Variant { variant, generics: generics.clone(), params })
+                        .collect()
+                };
+                lookup.insert(enum_ty.clone(), variant_exprs.iter().cloned());
+
+                Some((enum_ty, variant_exprs))
+            })
+            .collect()
+    }
+    defs.iter()
+        .filter_map(move |def| match def {
+            ScopeDef::ModuleDef(ModuleDef::Variant(it)) => {
+                let variant_exprs =
+                    variant_helper(db, lookup, it.parent_enum(db), *it, &ctx.goal, &ctx.config);
+                if variant_exprs.is_empty() {
+                    return None;
+                }
+                lookup.mark_fulfilled(ScopeDef::ModuleDef(ModuleDef::Variant(*it)));
+                Some(variant_exprs)
+            }
+            ScopeDef::ModuleDef(ModuleDef::Adt(Adt::Enum(enum_))) => {
+                let exprs: Vec<(Type, Vec<Expr>)> = enum_
+                    .variants(db)
+                    .into_iter()
+                    .flat_map(|it| variant_helper(db, lookup, *enum_, it, &ctx.goal, &ctx.config))
+                    .collect();
+
+                if !exprs.is_empty() {
+                    lookup.mark_fulfilled(ScopeDef::ModuleDef(ModuleDef::Adt(Adt::Enum(*enum_))));
+                }
+
+                Some(exprs)
+            }
+            ScopeDef::ModuleDef(ModuleDef::Adt(Adt::Struct(it))) => {
+                // Ignore unstable and not visible
+                if it.is_unstable(db) || !it.is_visible_from(db, module) {
+                    return None;
+                }
+
+                let generics = GenericDef::from(*it);
+
+                // Ignore const params for now
+                let type_params = generics
+                    .type_or_const_params(db)
+                    .into_iter()
+                    .map(|it| it.as_type_param(db))
+                    .collect::<Option<Vec<TypeParam>>>()?;
+
+                // We currently do not check lifetime bounds so ignore all types that have something to do
+                // with them
+                if !generics.lifetime_params(db).is_empty() {
+                    return None;
+                }
+
+                // Only account for stable type parameters for now, unstable params can be default
+                // tho, for example in `Box<T, #[unstable] A: Allocator>`
+                if type_params.iter().any(|it| it.is_unstable(db) && it.default(db).is_none()) {
+                    return None;
+                }
+
+                let non_default_type_params_len =
+                    type_params.iter().filter(|it| it.default(db).is_none()).count();
+
+                let generic_params = lookup
+                    .iter_types()
+                    .collect::<Vec<_>>() // Force take ownership
+                    .into_iter()
+                    .permutations(non_default_type_params_len);
+
+                let exprs = generic_params
+                    .filter_map(|generics| {
+                        // Insert default type params
+                        let mut g = generics.into_iter();
+                        let generics: Vec<_> = type_params
+                            .iter()
+                            .map(|it| {
+                                it.default(db)
+                                    .unwrap_or_else(|| g.next().expect("Missing type param"))
+                            })
+                            .collect();
+
+                        let struct_ty = Adt::from(*it).ty_with_args(db, generics.iter().cloned());
+
+                        // Allow types with generics only if they take us straight to goal for
+                        // performance reasons
+                        if non_default_type_params_len != 0
+                            && struct_ty.could_unify_with_deeply(db, &ctx.goal)
+                        {
+                            return None;
+                        }
+
+                        // Ignore types that have something to do with lifetimes
+                        if ctx.config.enable_borrowcheck && struct_ty.contains_reference(db) {
+                            return None;
+                        }
+                        let fileds = it.fields(db);
+                        // Check if all fields are visible, otherwise we cannot fill them
+                        if fileds.iter().any(|it| !it.is_visible_from(db, module)) {
+                            return None;
+                        }
+
+                        // Early exit if some param cannot be filled from lookup
+                        let param_exprs: Vec<Vec<Expr>> = fileds
+                            .into_iter()
+                            .map(|field| lookup.find(db, &field.ty(db)))
+                            .collect::<Option<_>>()?;
+
+                        // Note that we need special case for 0 param constructors because of multi cartesian
+                        // product
+                        let struct_exprs: Vec<Expr> = if param_exprs.is_empty() {
+                            vec![Expr::Struct { strukt: *it, generics, params: Vec::new() }]
+                        } else {
+                            param_exprs
+                                .into_iter()
+                                .multi_cartesian_product()
+                                .map(|params| Expr::Struct {
+                                    strukt: *it,
+                                    generics: generics.clone(),
+                                    params,
+                                })
+                                .collect()
+                        };
+
+                        lookup
+                            .mark_fulfilled(ScopeDef::ModuleDef(ModuleDef::Adt(Adt::Struct(*it))));
+                        lookup.insert(struct_ty.clone(), struct_exprs.iter().cloned());
+
+                        Some((struct_ty, struct_exprs))
+                    })
+                    .collect();
+                Some(exprs)
+            }
+            _ => None,
+        })
+        .flatten()
+        .filter_map(|(ty, exprs)| ty.could_unify_with_deeply(db, &ctx.goal).then_some(exprs))
+        .flatten()
+}
+
+/// # Free function tactic
+///
+/// Attempts to call different functions in scope with parameters from lookup table.
+/// Functions that include generics are not used for performance reasons.
+///
+/// Updates lookup by new types reached and returns iterator that yields
+/// elements that unify with `goal`.
+///
+/// # Arguments
+/// * `ctx` - Context for the term search
+/// * `defs` - Set of items in scope at term search target location
+/// * `lookup` - Lookup table for types
+pub(super) fn free_function<'a, DB: HirDatabase>(
+    ctx: &'a TermSearchCtx<'a, DB>,
+    defs: &'a FxHashSet<ScopeDef>,
+    lookup: &'a mut LookupTable,
+) -> impl Iterator<Item = Expr> + 'a {
+    let db = ctx.sema.db;
+    let module = ctx.scope.module();
+    defs.iter()
+        .filter_map(move |def| match def {
+            ScopeDef::ModuleDef(ModuleDef::Function(it)) => {
+                let generics = GenericDef::from(*it);
+
+                // Ignore const params for now
+                let type_params = generics
+                    .type_or_const_params(db)
+                    .into_iter()
+                    .map(|it| it.as_type_param(db))
+                    .collect::<Option<Vec<TypeParam>>>()?;
+
+                // Ignore lifetimes as we do not check them
+                if !generics.lifetime_params(db).is_empty() {
+                    return None;
+                }
+
+                // Only account for stable type parameters for now, unstable params can be default
+                // tho, for example in `Box<T, #[unstable] A: Allocator>`
+                if type_params.iter().any(|it| it.is_unstable(db) && it.default(db).is_none()) {
+                    return None;
+                }
+
+                let non_default_type_params_len =
+                    type_params.iter().filter(|it| it.default(db).is_none()).count();
+
+                // Ignore bigger number of generics for now as they kill the performance
+                if non_default_type_params_len > 0 {
+                    return None;
+                }
+
+                let generic_params = lookup
+                    .iter_types()
+                    .collect::<Vec<_>>() // Force take ownership
+                    .into_iter()
+                    .permutations(non_default_type_params_len);
+
+                let exprs: Vec<_> = generic_params
+                    .filter_map(|generics| {
+                        // Insert default type params
+                        let mut g = generics.into_iter();
+                        let generics: Vec<_> = type_params
+                            .iter()
+                            .map(|it| match it.default(db) {
+                                Some(ty) => Some(ty),
+                                None => {
+                                    let generic = g.next().expect("Missing type param");
+                                    // Filter out generics that do not unify due to trait bounds
+                                    it.ty(db).could_unify_with(db, &generic).then_some(generic)
+                                }
+                            })
+                            .collect::<Option<_>>()?;
+
+                        let ret_ty = it.ret_type_with_args(db, generics.iter().cloned());
+                        // Filter out private and unsafe functions
+                        if !it.is_visible_from(db, module)
+                            || it.is_unsafe_to_call(db)
+                            || it.is_unstable(db)
+                            || ctx.config.enable_borrowcheck && ret_ty.contains_reference(db)
+                            || ret_ty.is_raw_ptr()
+                        {
+                            return None;
+                        }
+
+                        // Early exit if some param cannot be filled from lookup
+                        let param_exprs: Vec<Vec<Expr>> = it
+                            .params_without_self_with_args(db, generics.iter().cloned())
+                            .into_iter()
+                            .map(|field| {
+                                let ty = field.ty();
+                                match ty.is_mutable_reference() {
+                                    true => None,
+                                    false => lookup.find_autoref(db, ty),
+                                }
+                            })
+                            .collect::<Option<_>>()?;
+
+                        // Note that we need special case for 0 param constructors because of multi cartesian
+                        // product
+                        let fn_exprs: Vec<Expr> = if param_exprs.is_empty() {
+                            vec![Expr::Function { func: *it, generics, params: Vec::new() }]
+                        } else {
+                            param_exprs
+                                .into_iter()
+                                .multi_cartesian_product()
+                                .map(|params| Expr::Function {
+                                    func: *it,
+                                    generics: generics.clone(),
+
+                                    params,
+                                })
+                                .collect()
+                        };
+
+                        lookup.mark_fulfilled(ScopeDef::ModuleDef(ModuleDef::Function(*it)));
+                        lookup.insert(ret_ty.clone(), fn_exprs.iter().cloned());
+                        Some((ret_ty, fn_exprs))
+                    })
+                    .collect();
+                Some(exprs)
+            }
+            _ => None,
+        })
+        .flatten()
+        .filter_map(|(ty, exprs)| ty.could_unify_with_deeply(db, &ctx.goal).then_some(exprs))
+        .flatten()
+}
+
+/// # Impl method tactic
+///
+/// Attempts to to call methods on types from lookup table.
+/// This includes both functions from direct impl blocks as well as functions from traits.
+/// Methods defined in impl blocks that are generic and methods that are themselves have
+/// generics are ignored for performance reasons.
+///
+/// Updates lookup by new types reached and returns iterator that yields
+/// elements that unify with `goal`.
+///
+/// # Arguments
+/// * `ctx` - Context for the term search
+/// * `defs` - Set of items in scope at term search target location
+/// * `lookup` - Lookup table for types
+pub(super) fn impl_method<'a, DB: HirDatabase>(
+    ctx: &'a TermSearchCtx<'a, DB>,
+    _defs: &'a FxHashSet<ScopeDef>,
+    lookup: &'a mut LookupTable,
+) -> impl Iterator<Item = Expr> + 'a {
+    let db = ctx.sema.db;
+    let module = ctx.scope.module();
+    lookup
+        .new_types(NewTypesKey::ImplMethod)
+        .into_iter()
+        .flat_map(|ty| {
+            Impl::all_for_type(db, ty.clone()).into_iter().map(move |imp| (ty.clone(), imp))
+        })
+        .flat_map(|(ty, imp)| imp.items(db).into_iter().map(move |item| (imp, ty.clone(), item)))
+        .filter_map(|(imp, ty, it)| match it {
+            AssocItem::Function(f) => Some((imp, ty, f)),
+            _ => None,
+        })
+        .filter_map(move |(imp, ty, it)| {
+            let fn_generics = GenericDef::from(it);
+            let imp_generics = GenericDef::from(imp);
+
+            // Ignore const params for now
+            let imp_type_params = imp_generics
+                .type_or_const_params(db)
+                .into_iter()
+                .map(|it| it.as_type_param(db))
+                .collect::<Option<Vec<TypeParam>>>()?;
+
+            // Ignore const params for now
+            let fn_type_params = fn_generics
+                .type_or_const_params(db)
+                .into_iter()
+                .map(|it| it.as_type_param(db))
+                .collect::<Option<Vec<TypeParam>>>()?;
+
+            // Ignore all functions that have something to do with lifetimes as we don't check them
+            if !fn_generics.lifetime_params(db).is_empty() {
+                return None;
+            }
+
+            // Ignore functions without self param
+            if !it.has_self_param(db) {
+                return None;
+            }
+
+            // Filter out private and unsafe functions
+            if !it.is_visible_from(db, module) || it.is_unsafe_to_call(db) || it.is_unstable(db) {
+                return None;
+            }
+
+            // Only account for stable type parameters for now, unstable params can be default
+            // tho, for example in `Box<T, #[unstable] A: Allocator>`
+            if imp_type_params.iter().any(|it| it.is_unstable(db) && it.default(db).is_none())
+                || fn_type_params.iter().any(|it| it.is_unstable(db) && it.default(db).is_none())
+            {
+                return None;
+            }
+
+            let non_default_type_params_len = imp_type_params
+                .iter()
+                .chain(fn_type_params.iter())
+                .filter(|it| it.default(db).is_none())
+                .count();
+
+            // Ignore bigger number of generics for now as they kill the performance
+            if non_default_type_params_len > 0 {
+                return None;
+            }
+
+            let generic_params = lookup
+                .iter_types()
+                .collect::<Vec<_>>() // Force take ownership
+                .into_iter()
+                .permutations(non_default_type_params_len);
+
+            let exprs: Vec<_> = generic_params
+                .filter_map(|generics| {
+                    // Insert default type params
+                    let mut g = generics.into_iter();
+                    let generics: Vec<_> = imp_type_params
+                        .iter()
+                        .chain(fn_type_params.iter())
+                        .map(|it| match it.default(db) {
+                            Some(ty) => Some(ty),
+                            None => {
+                                let generic = g.next().expect("Missing type param");
+                                // Filter out generics that do not unify due to trait bounds
+                                it.ty(db).could_unify_with(db, &generic).then_some(generic)
+                            }
+                        })
+                        .collect::<Option<_>>()?;
+
+                    let ret_ty = it.ret_type_with_args(
+                        db,
+                        ty.type_arguments().chain(generics.iter().cloned()),
+                    );
+                    // Filter out functions that return references
+                    if ctx.config.enable_borrowcheck && ret_ty.contains_reference(db)
+                        || ret_ty.is_raw_ptr()
+                    {
+                        return None;
+                    }
+
+                    // Ignore functions that do not change the type
+                    if ty.could_unify_with_deeply(db, &ret_ty) {
+                        return None;
+                    }
+
+                    let self_ty = it
+                        .self_param(db)
+                        .expect("No self param")
+                        .ty_with_args(db, ty.type_arguments().chain(generics.iter().cloned()));
+
+                    // Ignore functions that have different self type
+                    if !self_ty.autoderef(db).any(|s_ty| ty == s_ty) {
+                        return None;
+                    }
+
+                    let target_type_exprs = lookup.find(db, &ty).expect("Type not in lookup");
+
+                    // Early exit if some param cannot be filled from lookup
+                    let param_exprs: Vec<Vec<Expr>> = it
+                        .params_without_self_with_args(
+                            db,
+                            ty.type_arguments().chain(generics.iter().cloned()),
+                        )
+                        .into_iter()
+                        .map(|field| lookup.find_autoref(db, field.ty()))
+                        .collect::<Option<_>>()?;
+
+                    let fn_exprs: Vec<Expr> = std::iter::once(target_type_exprs)
+                        .chain(param_exprs)
+                        .multi_cartesian_product()
+                        .map(|params| {
+                            let mut params = params.into_iter();
+                            let target = Box::new(params.next().unwrap());
+                            Expr::Method {
+                                func: it,
+                                generics: generics.clone(),
+                                target,
+                                params: params.collect(),
+                            }
+                        })
+                        .collect();
+
+                    lookup.insert(ret_ty.clone(), fn_exprs.iter().cloned());
+                    Some((ret_ty, fn_exprs))
+                })
+                .collect();
+            Some(exprs)
+        })
+        .flatten()
+        .filter_map(|(ty, exprs)| ty.could_unify_with_deeply(db, &ctx.goal).then_some(exprs))
+        .flatten()
+}
+
+/// # Struct projection tactic
+///
+/// Attempts different struct fields (`foo.bar.baz`)
+///
+/// Updates lookup by new types reached and returns iterator that yields
+/// elements that unify with `goal`.
+///
+/// # Arguments
+/// * `ctx` - Context for the term search
+/// * `defs` - Set of items in scope at term search target location
+/// * `lookup` - Lookup table for types
+pub(super) fn struct_projection<'a, DB: HirDatabase>(
+    ctx: &'a TermSearchCtx<'a, DB>,
+    _defs: &'a FxHashSet<ScopeDef>,
+    lookup: &'a mut LookupTable,
+) -> impl Iterator<Item = Expr> + 'a {
+    let db = ctx.sema.db;
+    let module = ctx.scope.module();
+    lookup
+        .new_types(NewTypesKey::StructProjection)
+        .into_iter()
+        .map(|ty| (ty.clone(), lookup.find(db, &ty).expect("Expr not in lookup")))
+        .flat_map(move |(ty, targets)| {
+            ty.fields(db).into_iter().filter_map(move |(field, filed_ty)| {
+                if !field.is_visible_from(db, module) {
+                    return None;
+                }
+                let exprs = targets
+                    .clone()
+                    .into_iter()
+                    .map(move |target| Expr::Field { field, expr: Box::new(target) });
+                Some((filed_ty, exprs))
+            })
+        })
+        .filter_map(|(ty, exprs)| ty.could_unify_with_deeply(db, &ctx.goal).then_some(exprs))
+        .flatten()
+}
+
+/// # Famous types tactic
+///
+/// Attempts different values of well known types such as `true` or `false`.
+///
+/// Updates lookup by new types reached and returns iterator that yields
+/// elements that unify with `goal`.
+///
+/// _Note that there is no point of calling it iteratively as the output is always the same_
+///
+/// # Arguments
+/// * `ctx` - Context for the term search
+/// * `defs` - Set of items in scope at term search target location
+/// * `lookup` - Lookup table for types
+pub(super) fn famous_types<'a, DB: HirDatabase>(
+    ctx: &'a TermSearchCtx<'a, DB>,
+    _defs: &'a FxHashSet<ScopeDef>,
+    lookup: &'a mut LookupTable,
+) -> impl Iterator<Item = Expr> + 'a {
+    let db = ctx.sema.db;
+    let module = ctx.scope.module();
+    [
+        Expr::FamousType { ty: Type::new(db, module.id, TyBuilder::bool()), value: "true" },
+        Expr::FamousType { ty: Type::new(db, module.id, TyBuilder::bool()), value: "false" },
+        Expr::FamousType { ty: Type::new(db, module.id, TyBuilder::unit()), value: "()" },
+    ]
+    .into_iter()
+    .map(|exprs| {
+        lookup.insert(exprs.ty(db), std::iter::once(exprs.clone()));
+        exprs
+    })
+    .filter(|expr| expr.ty(db).could_unify_with_deeply(db, &ctx.goal))
+}
+
+/// # Impl static method (without self type) tactic
+///
+/// Attempts different functions from impl blocks that take no self parameter.
+///
+/// Updates lookup by new types reached and returns iterator that yields
+/// elements that unify with `goal`.
+///
+/// # Arguments
+/// * `ctx` - Context for the term search
+/// * `defs` - Set of items in scope at term search target location
+/// * `lookup` - Lookup table for types
+pub(super) fn impl_static_method<'a, DB: HirDatabase>(
+    ctx: &'a TermSearchCtx<'a, DB>,
+    _defs: &'a FxHashSet<ScopeDef>,
+    lookup: &'a mut LookupTable,
+) -> impl Iterator<Item = Expr> + 'a {
+    let db = ctx.sema.db;
+    let module = ctx.scope.module();
+    lookup
+        .take_types_wishlist()
+        .into_iter()
+        .chain(iter::once(ctx.goal.clone()))
+        .flat_map(|ty| {
+            Impl::all_for_type(db, ty.clone()).into_iter().map(move |imp| (ty.clone(), imp))
+        })
+        .filter(|(_, imp)| !imp.is_unsafe(db))
+        .flat_map(|(ty, imp)| imp.items(db).into_iter().map(move |item| (imp, ty.clone(), item)))
+        .filter_map(|(imp, ty, it)| match it {
+            AssocItem::Function(f) => Some((imp, ty, f)),
+            _ => None,
+        })
+        .filter_map(move |(imp, ty, it)| {
+            let fn_generics = GenericDef::from(it);
+            let imp_generics = GenericDef::from(imp);
+
+            // Ignore const params for now
+            let imp_type_params = imp_generics
+                .type_or_const_params(db)
+                .into_iter()
+                .map(|it| it.as_type_param(db))
+                .collect::<Option<Vec<TypeParam>>>()?;
+
+            // Ignore const params for now
+            let fn_type_params = fn_generics
+                .type_or_const_params(db)
+                .into_iter()
+                .map(|it| it.as_type_param(db))
+                .collect::<Option<Vec<TypeParam>>>()?;
+
+            // Ignore all functions that have something to do with lifetimes as we don't check them
+            if !fn_generics.lifetime_params(db).is_empty()
+                || !imp_generics.lifetime_params(db).is_empty()
+            {
+                return None;
+            }
+
+            // Ignore functions with self param
+            if it.has_self_param(db) {
+                return None;
+            }
+
+            // Filter out private and unsafe functions
+            if !it.is_visible_from(db, module) || it.is_unsafe_to_call(db) || it.is_unstable(db) {
+                return None;
+            }
+
+            // Only account for stable type parameters for now, unstable params can be default
+            // tho, for example in `Box<T, #[unstable] A: Allocator>`
+            if imp_type_params.iter().any(|it| it.is_unstable(db) && it.default(db).is_none())
+                || fn_type_params.iter().any(|it| it.is_unstable(db) && it.default(db).is_none())
+            {
+                return None;
+            }
+
+            let non_default_type_params_len = imp_type_params
+                .iter()
+                .chain(fn_type_params.iter())
+                .filter(|it| it.default(db).is_none())
+                .count();
+
+            // Ignore bigger number of generics for now as they kill the performance
+            if non_default_type_params_len > 1 {
+                return None;
+            }
+
+            let generic_params = lookup
+                .iter_types()
+                .collect::<Vec<_>>() // Force take ownership
+                .into_iter()
+                .permutations(non_default_type_params_len);
+
+            let exprs: Vec<_> = generic_params
+                .filter_map(|generics| {
+                    // Insert default type params
+                    let mut g = generics.into_iter();
+                    let generics: Vec<_> = imp_type_params
+                        .iter()
+                        .chain(fn_type_params.iter())
+                        .map(|it| match it.default(db) {
+                            Some(ty) => Some(ty),
+                            None => {
+                                let generic = g.next().expect("Missing type param");
+                                it.trait_bounds(db)
+                                    .into_iter()
+                                    .all(|bound| generic.impls_trait(db, bound, &[]));
+                                // Filter out generics that do not unify due to trait bounds
+                                it.ty(db).could_unify_with(db, &generic).then_some(generic)
+                            }
+                        })
+                        .collect::<Option<_>>()?;
+
+                    let ret_ty = it.ret_type_with_args(
+                        db,
+                        ty.type_arguments().chain(generics.iter().cloned()),
+                    );
+                    // Filter out functions that return references
+                    if ctx.config.enable_borrowcheck && ret_ty.contains_reference(db)
+                        || ret_ty.is_raw_ptr()
+                    {
+                        return None;
+                    }
+
+                    // Ignore functions that do not change the type
+                    // if ty.could_unify_with_deeply(db, &ret_ty) {
+                    //     return None;
+                    // }
+
+                    // Early exit if some param cannot be filled from lookup
+                    let param_exprs: Vec<Vec<Expr>> = it
+                        .params_without_self_with_args(
+                            db,
+                            ty.type_arguments().chain(generics.iter().cloned()),
+                        )
+                        .into_iter()
+                        .map(|field| lookup.find_autoref(db, field.ty()))
+                        .collect::<Option<_>>()?;
+
+                    // Note that we need special case for 0 param constructors because of multi cartesian
+                    // product
+                    let fn_exprs: Vec<Expr> = if param_exprs.is_empty() {
+                        vec![Expr::Function { func: it, generics, params: Vec::new() }]
+                    } else {
+                        param_exprs
+                            .into_iter()
+                            .multi_cartesian_product()
+                            .map(|params| Expr::Function {
+                                func: it,
+                                generics: generics.clone(),
+                                params,
+                            })
+                            .collect()
+                    };
+
+                    lookup.insert(ret_ty.clone(), fn_exprs.iter().cloned());
+                    Some((ret_ty, fn_exprs))
+                })
+                .collect();
+            Some(exprs)
+        })
+        .flatten()
+        .filter_map(|(ty, exprs)| ty.could_unify_with_deeply(db, &ctx.goal).then_some(exprs))
+        .flatten()
+}

crates/ide-assists/src/handlers/fix_visibility.rs

@@ -79,7 +79,7 @@ fn add_vis_to_referenced_module_def(acc: &mut Assists, ctx: &AssistContext<'_>)
         edit.edit_file(target_file);
 
         let vis_owner = edit.make_mut(vis_owner);
-        vis_owner.set_visibility(missing_visibility.clone_for_update());
+        vis_owner.set_visibility(Some(missing_visibility.clone_for_update()));
 
         if let Some((cap, vis)) = ctx.config.snippet_cap.zip(vis_owner.visibility()) {
             edit.add_tabstop_before(cap, vis);
@@ -131,7 +131,7 @@ fn add_vis_to_referenced_record_field(acc: &mut Assists, ctx: &AssistContext<'_>
         edit.edit_file(target_file);
 
         let vis_owner = edit.make_mut(vis_owner);
-        vis_owner.set_visibility(missing_visibility.clone_for_update());
+        vis_owner.set_visibility(Some(missing_visibility.clone_for_update()));
 
         if let Some((cap, vis)) = ctx.config.snippet_cap.zip(vis_owner.visibility()) {
             edit.add_tabstop_before(cap, vis);

crates/ide-assists/src/handlers/generate_delegate_methods.rs

@@ -1,4 +1,4 @@
-use hir::{self, HasCrate, HasVisibility};
+use hir::{HasCrate, HasVisibility};
 use ide_db::{path_transform::PathTransform, FxHashSet};
 use syntax::{
     ast::{

crates/ide-assists/src/handlers/generate_trait_from_impl.rs

@@ -1,8 +1,13 @@
 use crate::assist_context::{AssistContext, Assists};
 use ide_db::assists::AssistId;
 use syntax::{
-    ast::{self, edit::IndentLevel, make, HasGenericParams, HasVisibility},
+    ast::{
-    ted, AstNode, SyntaxKind,
+        self,
+        edit_in_place::{HasVisibilityEdit, Indent},
+        make, HasGenericParams, HasName,
+    },
+    ted::{self, Position},
+    AstNode, SyntaxKind, T,
 };
 
 // NOTES :
@@ -44,7 +49,7 @@ use syntax::{
 //     };
 // }
 //
-// trait ${0:TraitName}<const N: usize> {
+// trait ${0:NewTrait}<const N: usize> {
 //     // Used as an associated constant.
 //     const CONST_ASSOC: usize = N * 4;
 //
@@ -53,7 +58,7 @@ use syntax::{
 //     const_maker! {i32, 7}
 // }
 //
-// impl<const N: usize> ${0:TraitName}<N> for Foo<N> {
+// impl<const N: usize> ${0:NewTrait}<N> for Foo<N> {
 //     // Used as an associated constant.
 //     const CONST_ASSOC: usize = N * 4;
 //
@@ -94,8 +99,10 @@ pub(crate) fn generate_trait_from_impl(acc: &mut Assists, ctx: &AssistContext<'_
         "Generate trait from impl",
         impl_ast.syntax().text_range(),
         |builder| {
+            let impl_ast = builder.make_mut(impl_ast);
             let trait_items = assoc_items.clone_for_update();
-            let impl_items = assoc_items.clone_for_update();
+            let impl_items = builder.make_mut(assoc_items);
+            let impl_name = builder.make_mut(impl_name);
 
             trait_items.assoc_items().for_each(|item| {
                 strip_body(&item);
@@ -112,46 +119,42 @@ pub(crate) fn generate_trait_from_impl(acc: &mut Assists, ctx: &AssistContext<'_
                 impl_ast.generic_param_list(),
                 impl_ast.where_clause(),
                 trait_items,
-            );
+            )
+            .clone_for_update();
+
+            let trait_name = trait_ast.name().expect("new trait should have a name");
+            let trait_name_ref = make::name_ref(&trait_name.to_string()).clone_for_update();
 
             // Change `impl Foo` to `impl NewTrait for Foo`
-            let arg_list = if let Some(genpars) = impl_ast.generic_param_list() {
+            let mut elements = vec![
-                genpars.to_generic_args().to_string()
+                trait_name_ref.syntax().clone().into(),
-            } else {
+                make::tokens::single_space().into(),
-                "".to_owned()
+                make::token(T![for]).into(),
-            };
+            ];
 
-            if let Some(snippet_cap) = ctx.config.snippet_cap {
+            if let Some(params) = impl_ast.generic_param_list() {
-                builder.replace_snippet(
+                let gen_args = &params.to_generic_args().clone_for_update();
-                    snippet_cap,
+                elements.insert(1, gen_args.syntax().clone().into());
-                    impl_name.syntax().text_range(),
-                    format!("${{0:TraitName}}{} for {}", arg_list, impl_name),
-                );
-
-                // Insert trait before TraitImpl
-                builder.insert_snippet(
-                    snippet_cap,
-                    impl_ast.syntax().text_range().start(),
-                    format!(
-                        "{}\n\n{}",
-                        trait_ast.to_string().replace("NewTrait", "${0:TraitName}"),
-                        IndentLevel::from_node(impl_ast.syntax())
-                    ),
-                );
-            } else {
-                builder.replace(
-                    impl_name.syntax().text_range(),
-                    format!("NewTrait{} for {}", arg_list, impl_name),
-                );
-
-                // Insert trait before TraitImpl
-                builder.insert(
-                    impl_ast.syntax().text_range().start(),
-                    format!("{}\n\n{}", trait_ast, IndentLevel::from_node(impl_ast.syntax())),
-                );
             }
 
-            builder.replace(assoc_items.syntax().text_range(), impl_items.to_string());
+            ted::insert_all(Position::before(impl_name.syntax()), elements);
+
+            // Insert trait before TraitImpl
+            ted::insert_all_raw(
+                Position::before(impl_ast.syntax()),
+                vec![
+                    trait_ast.syntax().clone().into(),
+                    make::tokens::whitespace(&format!("\n\n{}", impl_ast.indent_level())).into(),
+                ],
+            );
+
+            // Link the trait name & trait ref names together as a placeholder snippet group
+            if let Some(cap) = ctx.config.snippet_cap {
+                builder.add_placeholder_snippet_group(
+                    cap,
+                    vec![trait_name.syntax().clone(), trait_name_ref.syntax().clone()],
+                );
+            }
         },
     );
 
@@ -160,23 +163,8 @@ pub(crate) fn generate_trait_from_impl(acc: &mut Assists, ctx: &AssistContext<'_
 
 /// `E0449` Trait items always share the visibility of their trait
 fn remove_items_visibility(item: &ast::AssocItem) {
-    match item {
+    if let Some(has_vis) = ast::AnyHasVisibility::cast(item.syntax().clone()) {
-        ast::AssocItem::Const(c) => {
+        has_vis.set_visibility(None);
-            if let Some(vis) = c.visibility() {
-                ted::remove(vis.syntax());
-            }
-        }
-        ast::AssocItem::Fn(f) => {
-            if let Some(vis) = f.visibility() {
-                ted::remove(vis.syntax());
-            }
-        }
-        ast::AssocItem::TypeAlias(t) => {
-            if let Some(vis) = t.visibility() {
-                ted::remove(vis.syntax());
-            }
-        }
-        _ => (),
     }
 }
 
@@ -404,12 +392,12 @@ impl<const N: usize> F$0oo<N> {
             r#"
 struct Foo<const N: usize>([i32; N]);
 
-trait ${0:TraitName}<const N: usize> {
+trait ${0:NewTrait}<const N: usize> {
     // Used as an associated constant.
     const CONST: usize = N * 4;
 }
 
-impl<const N: usize> ${0:TraitName}<N> for Foo<N> {
+impl<const N: usize> ${0:NewTrait}<N> for Foo<N> {
     // Used as an associated constant.
     const CONST: usize = N * 4;
 }

crates/ide-assists/src/handlers/term_search.rs

@@ -0,0 +1,253 @@
+//! Term search assist
+use hir::term_search::TermSearchCtx;
+use ide_db::{
+    assists::{AssistId, AssistKind, GroupLabel},
+    famous_defs::FamousDefs,
+};
+
+use itertools::Itertools;
+use syntax::{ast, AstNode};
+
+use crate::assist_context::{AssistContext, Assists};
+
+pub(crate) fn term_search(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let unexpanded = ctx.find_node_at_offset::<ast::MacroCall>()?;
+    let syntax = unexpanded.syntax();
+    let goal_range = syntax.text_range();
+
+    let parent = syntax.parent()?;
+    let scope = ctx.sema.scope(&parent)?;
+
+    let macro_call = ctx.sema.resolve_macro_call(&unexpanded)?;
+
+    let famous_defs = FamousDefs(&ctx.sema, scope.krate());
+    let std_todo = famous_defs.core_macros_todo()?;
+    let std_unimplemented = famous_defs.core_macros_unimplemented()?;
+
+    if macro_call != std_todo && macro_call != std_unimplemented {
+        return None;
+    }
+
+    let target_ty = ctx.sema.type_of_expr(&ast::Expr::cast(parent.clone())?)?.adjusted();
+
+    let term_search_ctx = TermSearchCtx {
+        sema: &ctx.sema,
+        scope: &scope,
+        goal: target_ty,
+        config: Default::default(),
+    };
+    let paths = hir::term_search::term_search(&term_search_ctx);
+
+    if paths.is_empty() {
+        return None;
+    }
+
+    let mut formatter = |_: &hir::Type| String::from("todo!()");
+
+    let paths = paths
+        .into_iter()
+        .filter_map(|path| {
+            path.gen_source_code(
+                &scope,
+                &mut formatter,
+                ctx.config.prefer_no_std,
+                ctx.config.prefer_prelude,
+            )
+            .ok()
+        })
+        .unique();
+
+    for code in paths {
+        acc.add_group(
+            &GroupLabel(String::from("Term search")),
+            AssistId("term_search", AssistKind::Generate),
+            format!("Replace todo!() with {code}"),
+            goal_range,
+            |builder| {
+                builder.replace(goal_range, code);
+            },
+        );
+    }
+
+    Some(())
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_complete_local() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+fn f() { let a: u128 = 1; let b: u128 = todo$0!() }"#,
+            r#"fn f() { let a: u128 = 1; let b: u128 = a }"#,
+        )
+    }
+
+    #[test]
+    fn test_complete_todo_with_msg() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+fn f() { let a: u128 = 1; let b: u128 = todo$0!("asd") }"#,
+            r#"fn f() { let a: u128 = 1; let b: u128 = a }"#,
+        )
+    }
+
+    #[test]
+    fn test_complete_unimplemented_with_msg() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+fn f() { let a: u128 = 1; let b: u128 = todo$0!("asd") }"#,
+            r#"fn f() { let a: u128 = 1; let b: u128 = a }"#,
+        )
+    }
+
+    #[test]
+    fn test_complete_unimplemented() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+fn f() { let a: u128 = 1; let b: u128 = todo$0!("asd") }"#,
+            r#"fn f() { let a: u128 = 1; let b: u128 = a }"#,
+        )
+    }
+
+    #[test]
+    fn test_complete_struct_field() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+struct A { pub x: i32, y: bool }
+fn f() { let a = A { x: 1, y: true }; let b: i32 = todo$0!(); }"#,
+            r#"struct A { pub x: i32, y: bool }
+fn f() { let a = A { x: 1, y: true }; let b: i32 = a.x; }"#,
+        )
+    }
+
+    #[test]
+    fn test_enum_with_generics() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented, option
+fn f() { let a: i32 = 1; let b: Option<i32> = todo$0!(); }"#,
+            r#"fn f() { let a: i32 = 1; let b: Option<i32> = None; }"#,
+        )
+    }
+
+    #[test]
+    fn test_enum_with_generics2() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+enum Option<T> { None, Some(T) }
+fn f() { let a: i32 = 1; let b: Option<i32> = todo$0!(); }"#,
+            r#"enum Option<T> { None, Some(T) }
+fn f() { let a: i32 = 1; let b: Option<i32> = Option::Some(a); }"#,
+        )
+    }
+
+    #[test]
+    fn test_enum_with_generics3() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+enum Option<T> { None, Some(T) }
+fn f() { let a: Option<i32> = Option::None; let b: Option<Option<i32>> = todo$0!(); }"#,
+            r#"enum Option<T> { None, Some(T) }
+fn f() { let a: Option<i32> = Option::None; let b: Option<Option<i32>> = Option::Some(a); }"#,
+        )
+    }
+
+    #[test]
+    fn test_enum_with_generics4() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+enum Foo<T = i32> { Foo(T) }
+fn f() { let a = 0; let b: Foo = todo$0!(); }"#,
+            r#"enum Foo<T = i32> { Foo(T) }
+fn f() { let a = 0; let b: Foo = Foo::Foo(a); }"#,
+        );
+
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+enum Foo<T = i32> { Foo(T) }
+fn f() { let a: Foo<u32> = Foo::Foo(0); let b: Foo<u32> = todo$0!(); }"#,
+            r#"enum Foo<T = i32> { Foo(T) }
+fn f() { let a: Foo<u32> = Foo::Foo(0); let b: Foo<u32> = a; }"#,
+        )
+    }
+
+    #[test]
+    fn test_newtype() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+struct Foo(i32);
+fn f() { let a: i32 = 1; let b: Foo = todo$0!(); }"#,
+            r#"struct Foo(i32);
+fn f() { let a: i32 = 1; let b: Foo = Foo(a); }"#,
+        )
+    }
+
+    #[test]
+    fn test_shadowing() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+fn f() { let a: i32 = 1; let b: i32 = 2; let a: u32 = 0; let c: i32 = todo$0!(); }"#,
+            r#"fn f() { let a: i32 = 1; let b: i32 = 2; let a: u32 = 0; let c: i32 = b; }"#,
+        )
+    }
+
+    #[test]
+    fn test_famous_bool() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+fn f() { let a: bool = todo$0!(); }"#,
+            r#"fn f() { let a: bool = false; }"#,
+        )
+    }
+
+    #[test]
+    fn test_fn_with_reference_types() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+fn f(a: &i32) -> f32 { a as f32 }
+fn g() { let a = 1; let b: f32 = todo$0!(); }"#,
+            r#"fn f(a: &i32) -> f32 { a as f32 }
+fn g() { let a = 1; let b: f32 = f(&a); }"#,
+        )
+    }
+
+    #[test]
+    fn test_fn_with_reference_types2() {
+        check_assist(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+fn f(a: &i32) -> f32 { a as f32 }
+fn g() { let a = &1; let b: f32 = todo$0!(); }"#,
+            r#"fn f(a: &i32) -> f32 { a as f32 }
+fn g() { let a = &1; let b: f32 = f(a); }"#,
+        )
+    }
+
+    #[test]
+    fn test_fn_with_reference_types3() {
+        check_assist_not_applicable(
+            term_search,
+            r#"//- minicore: todo, unimplemented
+            fn f(a: &i32) -> f32 { a as f32 }
+            fn g() { let a = &mut 1; let b: f32 = todo$0!(); }"#,
+        )
+    }
+}

crates/ide-assists/src/lib.rs

@@ -60,11 +60,6 @@
 
 #![warn(rust_2018_idioms, unused_lifetimes)]
 
-#[allow(unused)]
-macro_rules! eprintln {
-    ($($tt:tt)*) => { stdx::eprintln!($($tt)*) };
-}
-
 mod assist_config;
 mod assist_context;
 #[cfg(test)]
@@ -210,6 +205,7 @@ mod handlers {
     mod replace_turbofish_with_explicit_type;
     mod sort_items;
     mod split_import;
+    mod term_search;
     mod toggle_ignore;
     mod unmerge_match_arm;
     mod unmerge_use;
@@ -332,6 +328,7 @@ mod handlers {
             replace_arith_op::replace_arith_with_saturating,
             sort_items::sort_items,
             split_import::split_import,
+            term_search::term_search,
             toggle_ignore::toggle_ignore,
             unmerge_match_arm::unmerge_match_arm,
             unmerge_use::unmerge_use,

crates/ide-assists/src/tests/generated.rs

@@ -1665,7 +1665,7 @@ macro_rules! const_maker {
     };
 }
 
-trait ${0:TraitName}<const N: usize> {
+trait ${0:NewTrait}<const N: usize> {
     // Used as an associated constant.
     const CONST_ASSOC: usize = N * 4;
 
@@ -1674,7 +1674,7 @@ trait ${0:TraitName}<const N: usize> {
     const_maker! {i32, 7}
 }
 
-impl<const N: usize> ${0:TraitName}<N> for Foo<N> {
+impl<const N: usize> ${0:NewTrait}<N> for Foo<N> {
     // Used as an associated constant.
     const CONST_ASSOC: usize = N * 4;
 

crates/ide-completion/src/completions.rs

@@ -40,7 +40,8 @@ use crate::{
         literal::{render_struct_literal, render_variant_lit},
         macro_::render_macro,
         pattern::{render_struct_pat, render_variant_pat},
-        render_field, render_path_resolution, render_pattern_resolution, render_tuple_field,
+        render_expr, render_field, render_path_resolution, render_pattern_resolution,
+        render_tuple_field,
         type_alias::{render_type_alias, render_type_alias_with_eq},
         union_literal::render_union_literal,
         RenderContext,
@@ -157,6 +158,12 @@ impl Completions {
         item.add_to(self, ctx.db);
     }
 
+    pub(crate) fn add_expr(&mut self, ctx: &CompletionContext<'_>, expr: &hir::term_search::Expr) {
+        if let Some(item) = render_expr(ctx, expr) {
+            item.add_to(self, ctx.db)
+        }
+    }
+
     pub(crate) fn add_crate_roots(
         &mut self,
         ctx: &CompletionContext<'_>,
@@ -694,6 +701,7 @@ pub(super) fn complete_name_ref(
             match &path_ctx.kind {
                 PathKind::Expr { expr_ctx } => {
                     expr::complete_expr_path(acc, ctx, path_ctx, expr_ctx);
+                    expr::complete_expr(acc, ctx);
 
                     dot::complete_undotted_self(acc, ctx, path_ctx, expr_ctx);
                     item_list::complete_item_list_in_expr(acc, ctx, path_ctx, expr_ctx);

crates/ide-completion/src/completions/expr.rs

@@ -328,3 +328,59 @@ pub(crate) fn complete_expr_path(
         }
     }
 }
+
+pub(crate) fn complete_expr(acc: &mut Completions, ctx: &CompletionContext<'_>) {
+    let _p = tracing::span!(tracing::Level::INFO, "complete_expr").entered();
+
+    if !ctx.config.enable_term_search {
+        return;
+    }
+
+    if !ctx.qualifier_ctx.none() {
+        return;
+    }
+
+    if let Some(ty) = &ctx.expected_type {
+        // Ignore unit types as they are not very interesting
+        if ty.is_unit() || ty.is_unknown() {
+            return;
+        }
+
+        let term_search_ctx = hir::term_search::TermSearchCtx {
+            sema: &ctx.sema,
+            scope: &ctx.scope,
+            goal: ty.clone(),
+            config: hir::term_search::TermSearchConfig {
+                enable_borrowcheck: false,
+                many_alternatives_threshold: 1,
+                depth: 6,
+            },
+        };
+        let exprs = hir::term_search::term_search(&term_search_ctx);
+        for expr in exprs {
+            // Expand method calls
+            match expr {
+                hir::term_search::Expr::Method { func, generics, target, params }
+                    if target.is_many() =>
+                {
+                    let target_ty = target.ty(ctx.db);
+                    let term_search_ctx =
+                        hir::term_search::TermSearchCtx { goal: target_ty, ..term_search_ctx };
+                    let target_exprs = hir::term_search::term_search(&term_search_ctx);
+
+                    for expr in target_exprs {
+                        let expanded_expr = hir::term_search::Expr::Method {
+                            func,
+                            generics: generics.clone(),
+                            target: Box::new(expr),
+                            params: params.clone(),
+                        };
+
+                        acc.add_expr(ctx, &expanded_expr)
+                    }
+                }
+                _ => acc.add_expr(ctx, &expr),
+            }
+        }
+    }
+}

crates/ide-completion/src/completions/flyimport.rs

@@ -238,6 +238,8 @@ fn import_on_the_fly(
             (PathKind::Type { location }, ItemInNs::Types(ty)) => {
                 if matches!(location, TypeLocation::TypeBound) {
                     matches!(ty, ModuleDef::Trait(_))
+                } else if matches!(location, TypeLocation::ImplTrait) {
+                    matches!(ty, ModuleDef::Trait(_) | ModuleDef::Module(_))
                 } else {
                     true
                 }

crates/ide-completion/src/completions/item_list/trait_impl.rs

@@ -31,7 +31,7 @@
 //! }
 //! ```
 
-use hir::{self, HasAttrs};
+use hir::HasAttrs;
 use ide_db::{
     documentation::HasDocs, path_transform::PathTransform,
     syntax_helpers::insert_whitespace_into_node, traits::get_missing_assoc_items, SymbolKind,

crates/ide-completion/src/completions/type.rs

@@ -31,6 +31,11 @@ pub(crate) fn complete_type_path(
             ScopeDef::ImplSelfType(_) => location.complete_self_type(),
             // Don't suggest attribute macros and derives.
             ScopeDef::ModuleDef(Macro(mac)) => mac.is_fn_like(ctx.db),
+            ScopeDef::ModuleDef(Trait(_) | Module(_))
+                if matches!(location, TypeLocation::ImplTrait) =>
+            {
+                true
+            }
             // Type things are fine
             ScopeDef::ModuleDef(
                 BuiltinType(_) | Adt(_) | Module(_) | Trait(_) | TraitAlias(_) | TypeAlias(_),
@@ -184,6 +189,21 @@ pub(crate) fn complete_type_path(
                         }
                     }
                 }
+                TypeLocation::ImplTrait => {
+                    acc.add_nameref_keywords_with_colon(ctx);
+                    ctx.process_all_names(&mut |name, def, doc_aliases| {
+                        let is_trait_or_module = matches!(
+                            def,
+                            ScopeDef::ModuleDef(
+                                hir::ModuleDef::Module(_) | hir::ModuleDef::Trait(_)
+                            )
+                        );
+                        if is_trait_or_module {
+                            acc.add_path_resolution(ctx, path_ctx, name, def, doc_aliases);
+                        }
+                    });
+                    return;
+                }
                 _ => {}
             };
 

crates/ide-completion/src/config.rs

@@ -14,6 +14,7 @@ pub struct CompletionConfig {
     pub enable_imports_on_the_fly: bool,
     pub enable_self_on_the_fly: bool,
     pub enable_private_editable: bool,
+    pub enable_term_search: bool,
     pub full_function_signatures: bool,
     pub callable: Option<CallableSnippets>,
     pub snippet_cap: Option<SnippetCap>,

crates/ide-completion/src/context.rs

@@ -202,6 +202,7 @@ impl TypeLocation {
             }
             TypeLocation::AssocConstEq => false,
             TypeLocation::AssocTypeEq => true,
+            TypeLocation::ImplTrait => false,
             _ => true,
         }
     }
@@ -716,7 +717,7 @@ impl<'a> CompletionContext<'a> {
         let krate = scope.krate();
         let module = scope.module();
 
-        let toolchain = db.crate_graph()[krate.into()].channel();
+        let toolchain = db.toolchain_channel(krate.into());
         // `toolchain == None` means we're in some detached files. Since we have no information on
         // the toolchain being used, let's just allow unstable items to be listed.
         let is_nightly = matches!(toolchain, Some(base_db::ReleaseChannel::Nightly) | None);

crates/ide-completion/src/item.rs

@@ -166,6 +166,8 @@ pub struct CompletionRelevance {
     pub postfix_match: Option<CompletionRelevancePostfixMatch>,
     /// This is set for type inference results
     pub is_definite: bool,
+    /// This is set for items that are function (associated or method)
+    pub function: Option<CompletionRelevanceFn>,
 }
 
 #[derive(Debug, Clone, Copy, Eq, PartialEq)]
@@ -207,6 +209,24 @@ pub enum CompletionRelevancePostfixMatch {
     Exact,
 }
 
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+pub struct CompletionRelevanceFn {
+    pub has_params: bool,
+    pub has_self_param: bool,
+    pub return_type: CompletionRelevanceReturnType,
+}
+
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+pub enum CompletionRelevanceReturnType {
+    Other,
+    /// Returns the Self type of the impl/trait
+    DirectConstructor,
+    /// Returns something that indirectly constructs the `Self` type of the impl/trait e.g. `Result<Self, ()>`, `Option<Self>`
+    Constructor,
+    /// Returns a possible builder for the type
+    Builder,
+}
+
 impl CompletionRelevance {
     /// Provides a relevance score. Higher values are more relevant.
     ///
@@ -231,6 +251,7 @@ impl CompletionRelevance {
             postfix_match,
             is_definite,
             is_item_from_notable_trait,
+            function,
         } = self;
 
         // lower rank private things
@@ -275,6 +296,33 @@ impl CompletionRelevance {
         if is_definite {
             score += 10;
         }
+
+        score += function
+            .map(|asf| {
+                let mut fn_score = match asf.return_type {
+                    CompletionRelevanceReturnType::DirectConstructor => 15,
+                    CompletionRelevanceReturnType::Builder => 10,
+                    CompletionRelevanceReturnType::Constructor => 5,
+                    CompletionRelevanceReturnType::Other => 0,
+                };
+
+                // When a fn is bumped due to return type:
+                // Bump Constructor or Builder methods with no arguments,
+                // over them tha with self arguments
+                if fn_score > 0 {
+                    if !asf.has_params {
+                        // bump associated functions
+                        fn_score += 1;
+                    } else if asf.has_self_param {
+                        // downgrade methods (below Constructor)
+                        fn_score = 1;
+                    }
+                }
+
+                fn_score
+            })
+            .unwrap_or_default();
+
         score
     }
 
@@ -297,6 +345,7 @@ pub enum CompletionItemKind {
     Method,
     Snippet,
     UnresolvedReference,
+    Expression,
 }
 
 impl_from!(SymbolKind for CompletionItemKind);
@@ -341,6 +390,7 @@ impl CompletionItemKind {
             CompletionItemKind::Method => "me",
             CompletionItemKind::Snippet => "sn",
             CompletionItemKind::UnresolvedReference => "??",
+            CompletionItemKind::Expression => "ex",
         }
     }
 }

crates/ide-completion/src/render.rs

@@ -17,7 +17,7 @@ use ide_db::{
     imports::import_assets::LocatedImport,
     RootDatabase, SnippetCap, SymbolKind,
 };
-use syntax::{format_smolstr, AstNode, SmolStr, SyntaxKind, TextRange};
+use syntax::{ast, format_smolstr, AstNode, SmolStr, SyntaxKind, TextRange};
 use text_edit::TextEdit;
 
 use crate::{
@@ -272,6 +272,82 @@ pub(crate) fn render_resolution_with_import_pat(
     Some(render_resolution_pat(ctx, pattern_ctx, local_name, Some(import_edit), resolution))
 }
 
+pub(crate) fn render_expr(
+    ctx: &CompletionContext<'_>,
+    expr: &hir::term_search::Expr,
+) -> Option<Builder> {
+    let mut i = 1;
+    let mut snippet_formatter = |ty: &hir::Type| {
+        let arg_name = ty
+            .as_adt()
+            .and_then(|adt| adt.name(ctx.db).as_text())
+            .map(|s| stdx::to_lower_snake_case(s.as_str()))
+            .unwrap_or_else(|| String::from("_"));
+        let res = format!("${{{i}:{arg_name}}}");
+        i += 1;
+        res
+    };
+
+    let mut label_formatter = |ty: &hir::Type| {
+        ty.as_adt()
+            .and_then(|adt| adt.name(ctx.db).as_text())
+            .map(|s| stdx::to_lower_snake_case(s.as_str()))
+            .unwrap_or_else(|| String::from("..."))
+    };
+
+    let label = expr
+        .gen_source_code(
+            &ctx.scope,
+            &mut label_formatter,
+            ctx.config.prefer_no_std,
+            ctx.config.prefer_prelude,
+        )
+        .ok()?;
+
+    let source_range = match ctx.original_token.parent() {
+        Some(node) => match node.ancestors().find_map(ast::Path::cast) {
+            Some(path) => path.syntax().text_range(),
+            None => node.text_range(),
+        },
+        None => ctx.source_range(),
+    };
+
+    let mut item = CompletionItem::new(CompletionItemKind::Expression, source_range, label.clone());
+
+    let snippet = format!(
+        "{}$0",
+        expr.gen_source_code(
+            &ctx.scope,
+            &mut snippet_formatter,
+            ctx.config.prefer_no_std,
+            ctx.config.prefer_prelude
+        )
+        .ok()?
+    );
+    let edit = TextEdit::replace(source_range, snippet);
+    item.snippet_edit(ctx.config.snippet_cap?, edit);
+    item.documentation(Documentation::new(String::from("Autogenerated expression by term search")));
+    item.set_relevance(crate::CompletionRelevance {
+        type_match: compute_type_match(ctx, &expr.ty(ctx.db)),
+        ..Default::default()
+    });
+    for trait_ in expr.traits_used(ctx.db) {
+        let trait_item = hir::ItemInNs::from(hir::ModuleDef::from(trait_));
+        let Some(path) = ctx.module.find_use_path(
+            ctx.db,
+            trait_item,
+            ctx.config.prefer_no_std,
+            ctx.config.prefer_prelude,
+        ) else {
+            continue;
+        };
+
+        item.add_import(LocatedImport::new(path, trait_item, trait_item));
+    }
+
+    Some(item)
+}
+
 fn scope_def_to_name(
     resolution: ScopeDef,
     ctx: &RenderContext<'_>,
@@ -599,6 +675,16 @@ mod tests {
         expect.assert_debug_eq(&actual);
     }
 
+    #[track_caller]
+    fn check_function_relevance(ra_fixture: &str, expect: Expect) {
+        let actual: Vec<_> = do_completion(ra_fixture, CompletionItemKind::Method)
+            .into_iter()
+            .map(|item| (item.detail.unwrap_or_default(), item.relevance.function))
+            .collect();
+
+        expect.assert_debug_eq(&actual);
+    }
+
     #[track_caller]
     fn check_relevance_for_kinds(ra_fixture: &str, kinds: &[CompletionItemKind], expect: Expect) {
         let mut actual = get_all_items(TEST_CONFIG, ra_fixture, None);
@@ -961,6 +1047,7 @@ fn func(input: Struct) { }
                 st Self [type]
                 sp Self [type]
                 st Struct [type]
+                ex Struct [type]
                 lc self [local]
                 fn func(…) []
                 me self.test() []
@@ -985,6 +1072,9 @@ fn main() {
 "#,
             expect![[r#"
                 lc input [type+name+local]
+                ex input [type]
+                ex true [type]
+                ex false [type]
                 lc inputbad [local]
                 fn main() []
                 fn test(…) []
@@ -1174,6 +1264,7 @@ fn main() { let _: m::Spam = S$0 }
                             is_private_editable: false,
                             postfix_match: None,
                             is_definite: false,
+                            function: None,
                         },
                         trigger_call_info: true,
                     },
@@ -1201,6 +1292,7 @@ fn main() { let _: m::Spam = S$0 }
                             is_private_editable: false,
                             postfix_match: None,
                             is_definite: false,
+                            function: None,
                         },
                         trigger_call_info: true,
                     },
@@ -1280,6 +1372,7 @@ fn foo() { A { the$0 } }
                             is_private_editable: false,
                             postfix_match: None,
                             is_definite: false,
+                            function: None,
                         },
                     },
                 ]
@@ -1313,6 +1406,26 @@ impl S {
                         documentation: Documentation(
                             "Method docs",
                         ),
+                        relevance: CompletionRelevance {
+                            exact_name_match: false,
+                            type_match: None,
+                            is_local: false,
+                            is_item_from_trait: false,
+                            is_item_from_notable_trait: false,
+                            is_name_already_imported: false,
+                            requires_import: false,
+                            is_op_method: false,
+                            is_private_editable: false,
+                            postfix_match: None,
+                            is_definite: false,
+                            function: Some(
+                                CompletionRelevanceFn {
+                                    has_params: true,
+                                    has_self_param: true,
+                                    return_type: Other,
+                                },
+                            ),
+                        },
                     },
                     CompletionItem {
                         label: "foo",
@@ -1418,6 +1531,26 @@ fn foo(s: S) { s.$0 }
                         kind: Method,
                         lookup: "the_method",
                         detail: "fn(&self)",
+                        relevance: CompletionRelevance {
+                            exact_name_match: false,
+                            type_match: None,
+                            is_local: false,
+                            is_item_from_trait: false,
+                            is_item_from_notable_trait: false,
+                            is_name_already_imported: false,
+                            requires_import: false,
+                            is_op_method: false,
+                            is_private_editable: false,
+                            postfix_match: None,
+                            is_definite: false,
+                            function: Some(
+                                CompletionRelevanceFn {
+                                    has_params: true,
+                                    has_self_param: true,
+                                    return_type: Other,
+                                },
+                            ),
+                        },
                     },
                 ]
             "#]],
@@ -1665,6 +1798,10 @@ fn f() { A { bar: b$0 }; }
             expect![[r#"
                 fn bar() [type+name]
                 fn baz() [type]
+                ex baz() [type]
+                ex bar() [type]
+                ex A { bar: baz() }.bar [type]
+                ex A { bar: bar() }.bar [type]
                 st A []
                 fn f() []
             "#]],
@@ -1749,6 +1886,8 @@ fn main() {
                 lc s [type+name+local]
                 st S [type]
                 st S [type]
+                ex s [type]
+                ex S [type]
                 fn foo(…) []
                 fn main() []
             "#]],
@@ -1766,6 +1905,8 @@ fn main() {
                 lc ssss [type+local]
                 st S [type]
                 st S [type]
+                ex ssss [type]
+                ex S [type]
                 fn foo(…) []
                 fn main() []
             "#]],
@@ -1798,6 +1939,8 @@ fn main() {
 }
             "#,
             expect![[r#"
+                ex core::ops::Deref::deref(&T(S)) (use core::ops::Deref) [type_could_unify]
+                ex core::ops::Deref::deref(&t) (use core::ops::Deref) [type_could_unify]
                 lc m [local]
                 lc t [local]
                 lc &t [type+local]
@@ -1846,6 +1989,8 @@ fn main() {
 }
             "#,
             expect![[r#"
+                ex core::ops::DerefMut::deref_mut(&mut T(S)) (use core::ops::DerefMut) [type_could_unify]
+                ex core::ops::DerefMut::deref_mut(&mut t) (use core::ops::DerefMut) [type_could_unify]
                 lc m [local]
                 lc t [local]
                 lc &mut t [type+local]
@@ -1894,6 +2039,8 @@ fn bar(t: Foo) {}
                 ev Foo::A [type]
                 ev Foo::B [type]
                 en Foo [type]
+                ex Foo::A [type]
+                ex Foo::B [type]
                 fn bar(…) []
                 fn foo() []
             "#]],
@@ -1947,6 +2094,8 @@ fn main() {
 }
 "#,
             expect![[r#"
+                ex core::ops::Deref::deref(&T(S)) (use core::ops::Deref) [type_could_unify]
+                ex core::ops::Deref::deref(&bar()) (use core::ops::Deref) [type_could_unify]
                 st S []
                 st &S [type]
                 st S []
@@ -2002,6 +2151,254 @@ fn main() {
         );
     }
 
+    #[test]
+    fn constructor_order_simple() {
+        check_relevance(
+            r#"
+struct Foo;
+struct Other;
+struct Option<T>(T);
+
+impl Foo {
+    fn fn_ctr() -> Foo { unimplemented!() }
+    fn fn_another(n: u32) -> Other { unimplemented!() }
+    fn fn_ctr_self() -> Option<Self> { unimplemented!() }
+}
+
+fn test() {
+    let a = Foo::$0;
+}
+"#,
+            expect![[r#"
+                fn fn_ctr() [type_could_unify]
+                fn fn_ctr_self() [type_could_unify]
+                fn fn_another(…) [type_could_unify]
+            "#]],
+        );
+    }
+
+    #[test]
+    fn constructor_order_kind() {
+        check_function_relevance(
+            r#"
+struct Foo;
+struct Bar;
+struct Option<T>(T);
+enum Result<T, E> { Ok(T), Err(E) };
+
+impl Foo {
+    fn fn_ctr(&self) -> Foo { unimplemented!() }
+    fn fn_ctr_with_args(&self, n: u32) -> Foo { unimplemented!() }
+    fn fn_another(&self, n: u32) -> Bar { unimplemented!() }
+    fn fn_ctr_wrapped(&self, ) -> Option<Self> { unimplemented!() }
+    fn fn_ctr_wrapped_2(&self, ) -> Result<Self, Bar> { unimplemented!() }
+    fn fn_ctr_wrapped_3(&self, ) -> Result<Bar, Self> { unimplemented!() } // Self is not the first type
+    fn fn_ctr_wrapped_with_args(&self, m: u32) -> Option<Self> { unimplemented!() }
+    fn fn_another_unit(&self) { unimplemented!() }
+}
+
+fn test() {
+    let a = self::Foo::$0;
+}
+"#,
+            expect![[r#"
+                [
+                    (
+                        "fn(&self, u32) -> Bar",
+                        Some(
+                            CompletionRelevanceFn {
+                                has_params: true,
+                                has_self_param: true,
+                                return_type: Other,
+                            },
+                        ),
+                    ),
+                    (
+                        "fn(&self)",
+                        Some(
+                            CompletionRelevanceFn {
+                                has_params: true,
+                                has_self_param: true,
+                                return_type: Other,
+                            },
+                        ),
+                    ),
+                    (
+                        "fn(&self) -> Foo",
+                        Some(
+                            CompletionRelevanceFn {
+                                has_params: true,
+                                has_self_param: true,
+                                return_type: DirectConstructor,
+                            },
+                        ),
+                    ),
+                    (
+                        "fn(&self, u32) -> Foo",
+                        Some(
+                            CompletionRelevanceFn {
+                                has_params: true,
+                                has_self_param: true,
+                                return_type: DirectConstructor,
+                            },
+                        ),
+                    ),
+                    (
+                        "fn(&self) -> Option<Foo>",
+                        Some(
+                            CompletionRelevanceFn {
+                                has_params: true,
+                                has_self_param: true,
+                                return_type: Constructor,
+                            },
+                        ),
+                    ),
+                    (
+                        "fn(&self) -> Result<Foo, Bar>",
+                        Some(
+                            CompletionRelevanceFn {
+                                has_params: true,
+                                has_self_param: true,
+                                return_type: Constructor,
+                            },
+                        ),
+                    ),
+                    (
+                        "fn(&self) -> Result<Bar, Foo>",
+                        Some(
+                            CompletionRelevanceFn {
+                                has_params: true,
+                                has_self_param: true,
+                                return_type: Constructor,
+                            },
+                        ),
+                    ),
+                    (
+                        "fn(&self, u32) -> Option<Foo>",
+                        Some(
+                            CompletionRelevanceFn {
+                                has_params: true,
+                                has_self_param: true,
+                                return_type: Constructor,
+                            },
+                        ),
+                    ),
+                ]
+            "#]],
+        );
+    }
+
+    #[test]
+    fn constructor_order_relevance() {
+        check_relevance(
+            r#"
+struct Foo;
+struct FooBuilder;
+struct Result<T>(T);
+
+impl Foo {
+    fn fn_no_ret(&self) {}
+    fn fn_ctr_with_args(input: u32) -> Foo { unimplemented!() }
+    fn fn_direct_ctr() -> Self { unimplemented!() }
+    fn fn_ctr() -> Result<Self> { unimplemented!() }
+    fn fn_other() -> Result<u32> { unimplemented!() }
+    fn fn_builder() -> FooBuilder { unimplemented!() }
+}
+
+fn test() {
+    let a = self::Foo::$0;
+}
+"#,
+            // preference:
+            // Direct Constructor
+            // Direct Constructor with args
+            // Builder
+            // Constructor
+            // Others
+            expect![[r#"
+                fn fn_direct_ctr() [type_could_unify]
+                fn fn_ctr_with_args(…) [type_could_unify]
+                fn fn_builder() [type_could_unify]
+                fn fn_ctr() [type_could_unify]
+                me fn_no_ret(…) [type_could_unify]
+                fn fn_other() [type_could_unify]
+            "#]],
+        );
+
+        //
+    }
+
+    #[test]
+    fn function_relevance_generic_1() {
+        check_relevance(
+            r#"
+struct Foo<T: Default>(T);
+struct FooBuilder;
+struct Option<T>(T);
+enum Result<T, E>{Ok(T), Err(E)};
+
+impl<T: Default> Foo<T> {
+    fn fn_returns_unit(&self) {}
+    fn fn_ctr_with_args(input: T) -> Foo<T> { unimplemented!() }
+    fn fn_direct_ctr() -> Self { unimplemented!() }
+    fn fn_ctr_wrapped() -> Option<Self> { unimplemented!() }
+    fn fn_ctr_wrapped_2() -> Result<Self, u32> { unimplemented!() }
+    fn fn_other() -> Option<u32> { unimplemented!() }
+    fn fn_builder() -> FooBuilder { unimplemented!() }
+}
+
+fn test() {
+    let a = self::Foo::<u32>::$0;
+}
+                "#,
+            expect![[r#"
+                        fn fn_direct_ctr() [type_could_unify]
+                        fn fn_ctr_with_args(…) [type_could_unify]
+                        fn fn_builder() [type_could_unify]
+                        fn fn_ctr_wrapped() [type_could_unify]
+                        fn fn_ctr_wrapped_2() [type_could_unify]
+                        me fn_returns_unit(…) [type_could_unify]
+                        fn fn_other() [type_could_unify]
+                    "#]],
+        );
+    }
+
+    #[test]
+    fn function_relevance_generic_2() {
+        // Generic 2
+        check_relevance(
+            r#"
+struct Foo<T: Default>(T);
+struct FooBuilder;
+struct Option<T>(T);
+enum Result<T, E>{Ok(T), Err(E)};
+
+impl<T: Default> Foo<T> {
+    fn fn_no_ret(&self) {}
+    fn fn_ctr_with_args(input: T) -> Foo<T> { unimplemented!() }
+    fn fn_direct_ctr() -> Self { unimplemented!() }
+    fn fn_ctr() -> Option<Self> { unimplemented!() }
+    fn fn_ctr2() -> Result<Self, u32> { unimplemented!() }
+    fn fn_other() -> Option<u32> { unimplemented!() }
+    fn fn_builder() -> FooBuilder { unimplemented!() }
+}
+
+fn test() {
+    let a : Res<Foo<u32>> = Foo::$0;
+}
+                "#,
+            expect![[r#"
+                fn fn_direct_ctr() [type_could_unify]
+                fn fn_ctr_with_args(…) [type_could_unify]
+                fn fn_builder() [type_could_unify]
+                fn fn_ctr() [type_could_unify]
+                fn fn_ctr2() [type_could_unify]
+                me fn_no_ret(…) [type_could_unify]
+                fn fn_other() [type_could_unify]
+            "#]],
+        );
+    }
+
     #[test]
     fn struct_field_method_ref() {
         check_kinds(
@@ -2022,6 +2419,26 @@ fn foo(f: Foo) { let _: &u32 = f.b$0 }
                         kind: Method,
                         lookup: "baz",
                         detail: "fn(&self) -> u32",
+                        relevance: CompletionRelevance {
+                            exact_name_match: false,
+                            type_match: None,
+                            is_local: false,
+                            is_item_from_trait: false,
+                            is_item_from_notable_trait: false,
+                            is_name_already_imported: false,
+                            requires_import: false,
+                            is_op_method: false,
+                            is_private_editable: false,
+                            postfix_match: None,
+                            is_definite: false,
+                            function: Some(
+                                CompletionRelevanceFn {
+                                    has_params: true,
+                                    has_self_param: true,
+                                    return_type: Other,
+                                },
+                            ),
+                        },
                         ref_match: "&@107",
                     },
                     CompletionItem {
@@ -2096,6 +2513,7 @@ fn foo() {
                             is_private_editable: false,
                             postfix_match: None,
                             is_definite: false,
+                            function: None,
                         },
                     },
                 ]
@@ -2133,6 +2551,26 @@ fn main() {
                         ),
                         lookup: "foo",
                         detail: "fn() -> S",
+                        relevance: CompletionRelevance {
+                            exact_name_match: false,
+                            type_match: None,
+                            is_local: false,
+                            is_item_from_trait: false,
+                            is_item_from_notable_trait: false,
+                            is_name_already_imported: false,
+                            requires_import: false,
+                            is_op_method: false,
+                            is_private_editable: false,
+                            postfix_match: None,
+                            is_definite: false,
+                            function: Some(
+                                CompletionRelevanceFn {
+                                    has_params: false,
+                                    has_self_param: false,
+                                    return_type: Other,
+                                },
+                            ),
+                        },
                         ref_match: "&@92",
                     },
                 ]
@@ -2160,6 +2598,7 @@ fn foo() {
 "#,
             expect![[r#"
                 lc foo [type+local]
+                ex foo [type]
                 ev Foo::A(…) [type_could_unify]
                 ev Foo::B [type_could_unify]
                 en Foo [type_could_unify]
@@ -2493,6 +2932,7 @@ fn main() {
                             is_private_editable: false,
                             postfix_match: None,
                             is_definite: false,
+                            function: None,
                         },
                     },
                     CompletionItem {
@@ -2515,6 +2955,7 @@ fn main() {
                             is_private_editable: false,
                             postfix_match: None,
                             is_definite: false,
+                            function: None,
                         },
                     },
                 ]

crates/ide-completion/src/render/function.rs

@@ -8,8 +8,13 @@ use syntax::{format_smolstr, AstNode, SmolStr};
 
 use crate::{
     context::{CompletionContext, DotAccess, DotAccessKind, PathCompletionCtx, PathKind},
-    item::{Builder, CompletionItem, CompletionItemKind, CompletionRelevance},
+    item::{
-    render::{compute_exact_name_match, compute_ref_match, compute_type_match, RenderContext},
+        Builder, CompletionItem, CompletionItemKind, CompletionRelevance, CompletionRelevanceFn,
+        CompletionRelevanceReturnType,
+    },
+    render::{
+        compute_exact_name_match, compute_ref_match, compute_type_match, match_types, RenderContext,
+    },
     CallableSnippets,
 };
 
@@ -61,9 +66,9 @@ fn render(
         ),
         _ => (name.unescaped().to_smol_str(), name.to_smol_str()),
     };
-
+    let has_self_param = func.self_param(db).is_some();
     let mut item = CompletionItem::new(
-        if func.self_param(db).is_some() {
+        if has_self_param {
             CompletionItemKind::Method
         } else {
             CompletionItemKind::SymbolKind(SymbolKind::Function)
@@ -99,6 +104,15 @@ fn render(
         .filter(|_| !has_call_parens)
         .and_then(|cap| Some((cap, params(ctx.completion, func, &func_kind, has_dot_receiver)?)));
 
+    let function = assoc_item
+        .and_then(|assoc_item| assoc_item.implementing_ty(db))
+        .map(|self_type| compute_return_type_match(db, &ctx, self_type, &ret_type))
+        .map(|return_type| CompletionRelevanceFn {
+            has_params: has_self_param || func.num_params(db) > 0,
+            has_self_param,
+            return_type,
+        });
+
     item.set_relevance(CompletionRelevance {
         type_match: if has_call_parens || complete_call_parens.is_some() {
             compute_type_match(completion, &ret_type)
@@ -106,6 +120,7 @@ fn render(
             compute_type_match(completion, &func.ty(db))
         },
         exact_name_match: compute_exact_name_match(completion, &call),
+        function,
         is_op_method,
         is_item_from_notable_trait,
         ..ctx.completion_relevance()
@@ -156,6 +171,33 @@ fn render(
     item
 }
 
+fn compute_return_type_match(
+    db: &dyn HirDatabase,
+    ctx: &RenderContext<'_>,
+    self_type: hir::Type,
+    ret_type: &hir::Type,
+) -> CompletionRelevanceReturnType {
+    if match_types(ctx.completion, &self_type, ret_type).is_some() {
+        // fn([..]) -> Self
+        CompletionRelevanceReturnType::DirectConstructor
+    } else if ret_type
+        .type_arguments()
+        .any(|ret_type_arg| match_types(ctx.completion, &self_type, &ret_type_arg).is_some())
+    {
+        // fn([..]) -> Result<Self, E> OR Wrapped<Foo, Self>
+        CompletionRelevanceReturnType::Constructor
+    } else if ret_type
+        .as_adt()
+        .and_then(|adt| adt.name(db).as_str().map(|name| name.ends_with("Builder")))
+        .unwrap_or(false)
+    {
+        // fn([..]) -> [..]Builder
+        CompletionRelevanceReturnType::Builder
+    } else {
+        CompletionRelevanceReturnType::Other
+    }
+}
+
 pub(super) fn add_call_parens<'b>(
     builder: &'b mut Builder,
     ctx: &CompletionContext<'_>,

crates/ide-completion/src/tests.rs

@@ -65,6 +65,7 @@ pub(crate) const TEST_CONFIG: CompletionConfig = CompletionConfig {
     enable_imports_on_the_fly: true,
     enable_self_on_the_fly: true,
     enable_private_editable: false,
+    enable_term_search: true,
     full_function_signatures: false,
     callable: Some(CallableSnippets::FillArguments),
     snippet_cap: SnippetCap::new(true),

crates/ide-completion/src/tests/expression.rs

@@ -97,6 +97,11 @@ fn func(param0 @ (param1, param2): (i32, i32)) {
             kw unsafe
             kw while
             kw while let
+            ex ifletlocal
+            ex letlocal
+            ex matcharm
+            ex param1
+            ex param2
         "#]],
     );
 }
@@ -241,6 +246,8 @@ fn complete_in_block() {
             sn macro_rules
             sn pd
             sn ppd
+            ex false
+            ex true
         "#]],
     )
 }
@@ -542,7 +549,26 @@ fn quux(x: i32) {
     m!(x$0
 }
 "#,
-        expect![[r#""#]],
+        expect![[r#"
+            fn quux(…)   fn(i32)
+            lc x         i32
+            lc y         i32
+            ma m!(…)     macro_rules! m
+            bt u32       u32
+            kw crate::
+            kw false
+            kw for
+            kw if
+            kw if let
+            kw loop
+            kw match
+            kw return
+            kw self::
+            kw true
+            kw unsafe
+            kw while
+            kw while let
+        "#]],
     );
 }
 
@@ -683,6 +709,8 @@ fn main() {
 "#,
         expect![[r#"
             fn test()       fn() -> Zulu
+            ex Zulu
+            ex Zulu::test()
         "#]],
     );
 }

crates/ide-completion/src/tests/flyimport.rs

@@ -1397,3 +1397,22 @@ pub use bridge2::server2::Span2;
         "#]],
     );
 }
+
+#[test]
+fn flyimport_only_traits_in_impl_trait_block() {
+    check(
+        r#"
+//- /main.rs crate:main deps:dep
+pub struct Bar;
+
+impl Foo$0 for Bar { }
+//- /lib.rs crate:dep
+pub trait FooTrait;
+
+pub struct FooStruct;
+"#,
+        expect![[r#"
+            tt FooTrait (use dep::FooTrait)
+        "#]],
+    );
+}

crates/ide-completion/src/tests/record.rs

@@ -192,6 +192,8 @@ fn main() {
             bt u32                  u32
             kw crate::
             kw self::
+            ex Foo::default()
+            ex foo
         "#]],
     );
     check(

crates/ide-completion/src/tests/special.rs

@@ -695,6 +695,8 @@ fn bar() -> Bar {
 "#,
         expect![[r#"
             fn foo() (as Foo) fn() -> Self
+            ex Bar
+            ex bar()
         "#]],
     );
 }
@@ -722,6 +724,8 @@ fn bar() -> Bar {
         expect![[r#"
             fn bar()          fn()
             fn foo() (as Foo) fn() -> Self
+            ex Bar
+            ex bar()
         "#]],
     );
 }
@@ -748,6 +752,8 @@ fn bar() -> Bar {
 "#,
         expect![[r#"
             fn foo() (as Foo) fn() -> Self
+            ex Bar
+            ex bar()
         "#]],
     );
 }

crates/ide-completion/src/tests/type_pos.rs

@@ -989,3 +989,43 @@ fn foo<'a>() { S::<'static, F$0, _, _>; }
         "#]],
     );
 }
+
+#[test]
+fn complete_traits_on_impl_trait_block() {
+    check(
+        r#"
+trait Foo {}
+
+struct Bar;
+
+impl $0 for Bar { }
+"#,
+        expect![[r#"
+            md module
+            tt Foo
+            tt Trait
+            kw crate::
+            kw self::
+        "#]],
+    );
+}
+
+#[test]
+fn complete_traits_with_path_on_impl_trait_block() {
+    check(
+        r#"
+mod outer {
+    pub trait Foo {}
+    pub struct Bar;
+    pub mod inner {
+    }
+}
+
+impl outer::$0 for Bar { }
+"#,
+        expect![[r#"
+            md inner
+            tt Foo
+        "#]],
+    );
+}

crates/ide-db/src/famous_defs.rs

@@ -114,6 +114,14 @@ impl FamousDefs<'_, '_> {
         self.find_function("core:mem:drop")
     }
 
+    pub fn core_macros_todo(&self) -> Option<Macro> {
+        self.find_macro("core:todo")
+    }
+
+    pub fn core_macros_unimplemented(&self) -> Option<Macro> {
+        self.find_macro("core:unimplemented")
+    }
+
     pub fn builtin_crates(&self) -> impl Iterator<Item = Crate> {
         IntoIterator::into_iter([
             self.std(),

crates/ide-db/src/path_transform.rs

@@ -148,7 +148,7 @@ impl<'a> PathTransform<'a> {
         let mut defaulted_params: Vec<DefaultedParam> = Default::default();
         self.generic_def
             .into_iter()
-            .flat_map(|it| it.type_params(db))
+            .flat_map(|it| it.type_or_const_params(db))
             .skip(skip)
             // The actual list of trait type parameters may be longer than the one
             // used in the `impl` block due to trailing default type parameters.

crates/ide-db/src/rename.rs

@@ -71,7 +71,6 @@ impl Definition {
         &self,
         sema: &Semantics<'_, RootDatabase>,
         new_name: &str,
-        rename_external: bool,
     ) -> Result<SourceChange> {
         // self.krate() returns None if
         // self is a built-in attr, built-in type or tool module.
@@ -80,8 +79,8 @@ impl Definition {
         if let Some(krate) = self.krate(sema.db) {
             // Can we not rename non-local items?
             // Then bail if non-local
-            if !rename_external && !krate.origin(sema.db).is_local() {
+            if !krate.origin(sema.db).is_local() {
-                bail!("Cannot rename a non-local definition as the config for it is disabled")
+                bail!("Cannot rename a non-local definition")
             }
         }
 

crates/ide-db/src/source_change.rs

@@ -138,7 +138,7 @@ impl SnippetEdit {
             .into_iter()
             .zip(1..)
             .with_position()
-            .map(|pos| {
+            .flat_map(|pos| {
                 let (snippet, index) = match pos {
                     (itertools::Position::First, it) | (itertools::Position::Middle, it) => it,
                     // last/only snippet gets index 0
@@ -146,11 +146,13 @@ impl SnippetEdit {
                     | (itertools::Position::Only, (snippet, _)) => (snippet, 0),
                 };
 
-                let range = match snippet {
+                match snippet {
-                    Snippet::Tabstop(pos) => TextRange::empty(pos),
+                    Snippet::Tabstop(pos) => vec![(index, TextRange::empty(pos))],
-                    Snippet::Placeholder(range) => range,
+                    Snippet::Placeholder(range) => vec![(index, range)],
-                };
+                    Snippet::PlaceholderGroup(ranges) => {
-                (index, range)
+                        ranges.into_iter().map(|range| (index, range)).collect()
+                    }
+                }
             })
             .collect_vec();
 
@@ -248,7 +250,7 @@ impl SourceChangeBuilder {
     fn commit(&mut self) {
         let snippet_edit = self.snippet_builder.take().map(|builder| {
             SnippetEdit::new(
-                builder.places.into_iter().map(PlaceSnippet::finalize_position).collect_vec(),
+                builder.places.into_iter().flat_map(PlaceSnippet::finalize_position).collect(),
             )
         });
 
@@ -287,30 +289,10 @@ impl SourceChangeBuilder {
     pub fn insert(&mut self, offset: TextSize, text: impl Into<String>) {
         self.edit.insert(offset, text.into())
     }
-    /// Append specified `snippet` at the given `offset`
-    pub fn insert_snippet(
-        &mut self,
-        _cap: SnippetCap,
-        offset: TextSize,
-        snippet: impl Into<String>,
-    ) {
-        self.source_change.is_snippet = true;
-        self.insert(offset, snippet);
-    }
     /// Replaces specified `range` of text with a given string.
     pub 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 fn replace_snippet(
-        &mut self,
-        _cap: SnippetCap,
-        range: TextRange,
-        snippet: impl Into<String>,
-    ) {
-        self.source_change.is_snippet = true;
-        self.replace(range, snippet);
-    }
     pub fn replace_ast<N: AstNode>(&mut self, old: N, new: N) {
         algo::diff(old.syntax(), new.syntax()).into_text_edit(&mut self.edit)
     }
@@ -356,6 +338,17 @@ impl SourceChangeBuilder {
         self.add_snippet(PlaceSnippet::Over(node.syntax().clone().into()))
     }
 
+    /// Adds a snippet to move the cursor selected over `nodes`
+    ///
+    /// This allows for renaming newly generated items without having to go
+    /// through a separate rename step.
+    pub fn add_placeholder_snippet_group(&mut self, _cap: SnippetCap, nodes: Vec<SyntaxNode>) {
+        assert!(nodes.iter().all(|node| node.parent().is_some()));
+        self.add_snippet(PlaceSnippet::OverGroup(
+            nodes.into_iter().map(|node| node.into()).collect(),
+        ))
+    }
+
     fn add_snippet(&mut self, snippet: PlaceSnippet) {
         let snippet_builder = self.snippet_builder.get_or_insert(SnippetBuilder { places: vec![] });
         snippet_builder.places.push(snippet);
@@ -400,6 +393,13 @@ pub enum Snippet {
     Tabstop(TextSize),
     /// A placeholder snippet (e.g. `${0:placeholder}`).
     Placeholder(TextRange),
+    /// A group of placeholder snippets, e.g.
+    ///
+    /// ```no_run
+    /// let ${0:new_var} = 4;
+    /// fun(1, 2, 3, ${0:new_var});
+    /// ```
+    PlaceholderGroup(Vec<TextRange>),
 }
 
 enum PlaceSnippet {
@@ -409,14 +409,20 @@ enum PlaceSnippet {
     After(SyntaxElement),
     /// Place a placeholder snippet in place of the element
     Over(SyntaxElement),
+    /// Place a group of placeholder snippets which are linked together
+    /// in place of the elements
+    OverGroup(Vec<SyntaxElement>),
 }
 
 impl PlaceSnippet {
-    fn finalize_position(self) -> Snippet {
+    fn finalize_position(self) -> Vec<Snippet> {
         match self {
-            PlaceSnippet::Before(it) => Snippet::Tabstop(it.text_range().start()),
+            PlaceSnippet::Before(it) => vec![Snippet::Tabstop(it.text_range().start())],
-            PlaceSnippet::After(it) => Snippet::Tabstop(it.text_range().end()),
+            PlaceSnippet::After(it) => vec![Snippet::Tabstop(it.text_range().end())],
-            PlaceSnippet::Over(it) => Snippet::Placeholder(it.text_range()),
+            PlaceSnippet::Over(it) => vec![Snippet::Placeholder(it.text_range())],
+            PlaceSnippet::OverGroup(it) => {
+                vec![Snippet::PlaceholderGroup(it.into_iter().map(|it| it.text_range()).collect())]
+            }
         }
     }
 }

crates/ide-db/src/symbol_index.rs

@@ -31,7 +31,7 @@ use base_db::{
     salsa::{self, ParallelDatabase},
     SourceDatabaseExt, SourceRootId, Upcast,
 };
-use fst::{self, raw::IndexedValue, Automaton, Streamer};
+use fst::{raw::IndexedValue, Automaton, Streamer};
 use hir::{
     db::HirDatabase,
     import_map::{AssocSearchMode, SearchMode},

crates/ide-db/src/syntax_helpers/node_ext.rs

@@ -329,6 +329,7 @@ pub fn for_each_tail_expr(expr: &ast::Expr, cb: &mut dyn FnMut(&ast::Expr)) {
         | ast::Expr::RecordExpr(_)
         | ast::Expr::RefExpr(_)
         | ast::Expr::ReturnExpr(_)
+        | ast::Expr::BecomeExpr(_)
         | ast::Expr::TryExpr(_)
         | ast::Expr::TupleExpr(_)
         | ast::Expr::LetExpr(_)

crates/ide-diagnostics/src/handlers/incorrect_case.rs

@@ -43,7 +43,7 @@ fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::IncorrectCase) -> Option<Vec<Ass
     let label = format!("Rename to {}", d.suggested_text);
     let mut res = unresolved_fix("change_case", &label, frange.range);
     if ctx.resolve.should_resolve(&res.id) {
-        let source_change = def.rename(&ctx.sema, &d.suggested_text, true);
+        let source_change = def.rename(&ctx.sema, &d.suggested_text);
         res.source_change = Some(source_change.ok().unwrap_or_default());
     }
 

crates/ide-diagnostics/src/handlers/macro_error.rs

@@ -242,7 +242,7 @@ macro_rules! foo {
 
 fn f() {
     foo!();
-  //^^^ error: invalid macro definition: expected subtree
+  //^^^ error: macro definition has parse errors
 
 }
 "#,

crates/ide-diagnostics/src/handlers/missing_match_arms.rs

@@ -310,6 +310,24 @@ fn main() {
         );
     }
 
+    #[test]
+    fn mismatched_types_issue_15883() {
+        // Check we don't panic.
+        check_diagnostics_no_bails(
+            r#"
+//- minicore: option
+fn main() {
+    match Some((true, false)) {
+        Some(true) | Some(false) => {}
+        //   ^^^^ error: expected (bool, bool), found bool
+        //                ^^^^^ error: expected (bool, bool), found bool
+        None => {}
+    }
+}
+            "#,
+        );
+    }
+
     #[test]
     fn mismatched_types_in_or_patterns() {
         cov_mark::check_count!(validate_match_bailed_out, 2);

crates/ide-diagnostics/src/handlers/remove_trailing_return.rs

@@ -182,6 +182,18 @@ fn foo() -> u8 {
         );
     }
 
+    #[test]
+    fn no_diagnostic_if_not_last_statement2() {
+        check_diagnostics(
+            r#"
+fn foo() -> u8 {
+    return 2;
+    fn bar() {}
+}
+"#,
+        );
+    }
+
     #[test]
     fn replace_with_expr() {
         check_fix(

crates/ide-diagnostics/src/handlers/type_mismatch.rs

@@ -112,7 +112,8 @@ fn add_missing_ok_or_some(
 
     let variant_name = if Some(expected_enum) == core_result { "Ok" } else { "Some" };
 
-    let wrapped_actual_ty = expected_adt.ty_with_args(ctx.sema.db, &[d.actual.clone()]);
+    let wrapped_actual_ty =
+        expected_adt.ty_with_args(ctx.sema.db, std::iter::once(d.actual.clone()));
 
     if !d.expected.could_unify_with(ctx.sema.db, &wrapped_actual_ty) {
         return None;

crates/ide-diagnostics/src/handlers/typed_hole.rs

@@ -1,14 +1,20 @@
-use hir::{db::ExpandDatabase, ClosureStyle, HirDisplay, StructKind};
+use hir::{
+    db::ExpandDatabase,
+    term_search::{term_search, TermSearchCtx},
+    ClosureStyle, HirDisplay,
+};
 use ide_db::{
     assists::{Assist, AssistId, AssistKind, GroupLabel},
     label::Label,
     source_change::SourceChange,
 };
-use syntax::AstNode;
+use itertools::Itertools;
 use text_edit::TextEdit;
 
 use crate::{Diagnostic, DiagnosticCode, DiagnosticsContext};
 
+use syntax::AstNode;
+
 // Diagnostic: typed-hole
 //
 // This diagnostic is triggered when an underscore expression is used in an invalid position.
@@ -36,50 +42,54 @@ fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::TypedHole) -> Option<Vec<Assist>
     let (original_range, _) =
         d.expr.as_ref().map(|it| it.to_node(&root)).syntax().original_file_range_opt(db)?;
     let scope = ctx.sema.scope(d.expr.value.to_node(&root).syntax())?;
-    let mut assists = vec![];
+
-    scope.process_all_names(&mut |name, def| {
+    let term_search_ctx = TermSearchCtx {
-        let ty = match def {
+        sema: &ctx.sema,
-            hir::ScopeDef::ModuleDef(it) => match it {
+        scope: &scope,
-                hir::ModuleDef::Function(it) => it.ty(db),
+        goal: d.expected.clone(),
-                hir::ModuleDef::Adt(hir::Adt::Struct(it)) if it.kind(db) != StructKind::Record => {
+        config: Default::default(),
-                    it.constructor_ty(db)
-                }
-                hir::ModuleDef::Variant(it) if it.kind(db) != StructKind::Record => {
-                    it.constructor_ty(db)
-                }
-                hir::ModuleDef::Const(it) => it.ty(db),
-                hir::ModuleDef::Static(it) => it.ty(db),
-                _ => return,
-            },
-            hir::ScopeDef::GenericParam(hir::GenericParam::ConstParam(it)) => it.ty(db),
-            hir::ScopeDef::Local(it) => it.ty(db),
-            _ => return,
     };
-        // FIXME: should also check coercions if it is at a coercion site
+    let paths = term_search(&term_search_ctx);
-        if !ty.contains_unknown() && ty.could_unify_with(db, &d.expected) {
+
-            assists.push(Assist {
+    let mut formatter = |_: &hir::Type| String::from("_");
+
+    let assists: Vec<Assist> = paths
+        .into_iter()
+        .filter_map(|path| {
+            path.gen_source_code(
+                &scope,
+                &mut formatter,
+                ctx.config.prefer_no_std,
+                ctx.config.prefer_prelude,
+            )
+            .ok()
+        })
+        .unique()
+        .map(|code| Assist {
             id: AssistId("typed-hole", AssistKind::QuickFix),
-                label: Label::new(format!("Replace `_` with `{}`", name.display(db))),
+            label: Label::new(format!("Replace `_` with `{}`", &code)),
-                group: Some(GroupLabel("Replace `_` with a matching entity in scope".to_owned())),
+            group: Some(GroupLabel("Replace `_` with a term".to_owned())),
             target: original_range.range,
             source_change: Some(SourceChange::from_text_edit(
                 original_range.file_id,
-                    TextEdit::replace(original_range.range, name.display(db).to_string()),
+                TextEdit::replace(original_range.range, code),
             )),
             trigger_signature_help: false,
-            });
+        })
-        }
+        .collect();
-    });
+
-    if assists.is_empty() {
+    if !assists.is_empty() {
-        None
-    } else {
         Some(assists)
+    } else {
+        None
     }
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::tests::{check_diagnostics, check_fixes};
+    use crate::tests::{
+        check_diagnostics, check_fixes_unordered, check_has_fix, check_has_single_fix,
+    };
 
     #[test]
     fn unknown() {
@@ -99,7 +109,7 @@ fn main() {
             r#"
 fn main() {
     if _ {}
-     //^ error: invalid `_` expression, expected type `bool`
+     //^ 💡 error: invalid `_` expression, expected type `bool`
     let _: fn() -> i32 = _;
                        //^ error: invalid `_` expression, expected type `fn() -> i32`
     let _: fn() -> () = _; // FIXME: This should trigger an assist because `main` matches via *coercion*
@@ -129,7 +139,7 @@ fn main() {
 fn main() {
     let mut x = t();
     x = _;
-      //^ 💡 error: invalid `_` expression, expected type `&str`
+      //^ error: invalid `_` expression, expected type `&str`
     x = "";
 }
 fn t<T>() -> T { loop {} }
@@ -143,7 +153,8 @@ fn t<T>() -> T { loop {} }
             r#"
 fn main() {
     let _x = [(); _];
-    let _y: [(); 10] = [(); _];
+    // FIXME: This should trigger error
+    // let _y: [(); 10] = [(); _];
     _ = 0;
     (_,) = (1,);
 }
@@ -153,7 +164,7 @@ fn main() {
 
     #[test]
     fn check_quick_fix() {
-        check_fixes(
+        check_fixes_unordered(
             r#"
 enum Foo {
     Bar
@@ -173,6 +184,18 @@ enum Foo {
 }
 use Foo::Bar;
 const C: Foo = Foo::Bar;
+fn main<const CP: Foo>(param: Foo) {
+    let local = Foo::Bar;
+    let _: Foo = Bar;
+               //^ error: invalid `_` expression, expected type `fn()`
+}
+"#,
+                r#"
+enum Foo {
+    Bar
+}
+use Foo::Bar;
+const C: Foo = Foo::Bar;
 fn main<const CP: Foo>(param: Foo) {
     let local = Foo::Bar;
     let _: Foo = local;
@@ -209,18 +232,6 @@ enum Foo {
 }
 use Foo::Bar;
 const C: Foo = Foo::Bar;
-fn main<const CP: Foo>(param: Foo) {
-    let local = Foo::Bar;
-    let _: Foo = Bar;
-               //^ error: invalid `_` expression, expected type `fn()`
-}
-"#,
-                r#"
-enum Foo {
-    Bar
-}
-use Foo::Bar;
-const C: Foo = Foo::Bar;
 fn main<const CP: Foo>(param: Foo) {
     let local = Foo::Bar;
     let _: Foo = C;
@@ -230,4 +241,153 @@ fn main<const CP: Foo>(param: Foo) {
             ],
         );
     }
+
+    #[test]
+    fn local_item_use_trait() {
+        check_has_fix(
+            r#"
+struct Bar;
+struct Baz;
+trait Foo {
+    fn foo(self) -> Bar;
+}
+impl Foo for Baz {
+    fn foo(self) -> Bar {
+        unimplemented!()
+    }
+}
+fn asd() -> Bar {
+    let a = Baz;
+    _$0
+}
+"#,
+            r"
+struct Bar;
+struct Baz;
+trait Foo {
+    fn foo(self) -> Bar;
+}
+impl Foo for Baz {
+    fn foo(self) -> Bar {
+        unimplemented!()
+    }
+}
+fn asd() -> Bar {
+    let a = Baz;
+    Foo::foo(a)
+}
+",
+        );
+    }
+
+    #[test]
+    fn init_struct() {
+        check_has_fix(
+            r#"struct Abc {}
+struct Qwe { a: i32, b: Abc }
+fn main() {
+    let a: i32 = 1;
+    let c: Qwe = _$0;
+}"#,
+            r#"struct Abc {}
+struct Qwe { a: i32, b: Abc }
+fn main() {
+    let a: i32 = 1;
+    let c: Qwe = Qwe { a: a, b: Abc {  } };
+}"#,
+        );
+    }
+
+    #[test]
+    fn ignore_impl_func_with_incorrect_return() {
+        check_has_single_fix(
+            r#"
+struct Bar {}
+trait Foo {
+    type Res;
+    fn foo(&self) -> Self::Res;
+}
+impl Foo for i32 {
+    type Res = Self;
+    fn foo(&self) -> Self::Res { 1 }
+}
+fn main() {
+    let a: i32 = 1;
+    let c: Bar = _$0;
+}"#,
+            r#"
+struct Bar {}
+trait Foo {
+    type Res;
+    fn foo(&self) -> Self::Res;
+}
+impl Foo for i32 {
+    type Res = Self;
+    fn foo(&self) -> Self::Res { 1 }
+}
+fn main() {
+    let a: i32 = 1;
+    let c: Bar = Bar {  };
+}"#,
+        );
+    }
+
+    #[test]
+    fn use_impl_func_with_correct_return() {
+        check_has_fix(
+            r#"
+struct Bar {}
+struct A;
+trait Foo {
+    type Res;
+    fn foo(&self) -> Self::Res;
+}
+impl Foo for A {
+    type Res = Bar;
+    fn foo(&self) -> Self::Res { Bar { } }
+}
+fn main() {
+    let a = A;
+    let c: Bar = _$0;
+}"#,
+            r#"
+struct Bar {}
+struct A;
+trait Foo {
+    type Res;
+    fn foo(&self) -> Self::Res;
+}
+impl Foo for A {
+    type Res = Bar;
+    fn foo(&self) -> Self::Res { Bar { } }
+}
+fn main() {
+    let a = A;
+    let c: Bar = Foo::foo(&a);
+}"#,
+        );
+    }
+
+    #[test]
+    fn local_shadow_fn() {
+        check_fixes_unordered(
+            r#"
+fn f() {
+    let f: i32 = 0;
+    _$0
+}"#,
+            vec![
+                r#"
+fn f() {
+    let f: i32 = 0;
+    ()
+}"#,
+                r#"
+fn f() {
+    let f: i32 = 0;
+    crate::f()
+}"#,
+            ],
+        );
+    }
 }

crates/ide-diagnostics/src/tests.rs

@@ -91,6 +91,91 @@ fn check_nth_fix_with_config(
     assert_eq_text!(&after, &actual);
 }
 
+pub(crate) fn check_fixes_unordered(ra_fixture_before: &str, ra_fixtures_after: Vec<&str>) {
+    for ra_fixture_after in ra_fixtures_after.iter() {
+        check_has_fix(ra_fixture_before, ra_fixture_after)
+    }
+}
+
+#[track_caller]
+pub(crate) fn check_has_fix(ra_fixture_before: &str, ra_fixture_after: &str) {
+    let after = trim_indent(ra_fixture_after);
+
+    let (db, file_position) = RootDatabase::with_position(ra_fixture_before);
+    let mut conf = DiagnosticsConfig::test_sample();
+    conf.expr_fill_default = ExprFillDefaultMode::Default;
+    let fix = super::diagnostics(&db, &conf, &AssistResolveStrategy::All, file_position.file_id)
+        .into_iter()
+        .find(|d| {
+            d.fixes
+                .as_ref()
+                .and_then(|fixes| {
+                    fixes.iter().find(|fix| {
+                        if !fix.target.contains_inclusive(file_position.offset) {
+                            return false;
+                        }
+                        let actual = {
+                            let source_change = fix.source_change.as_ref().unwrap();
+                            let file_id = *source_change.source_file_edits.keys().next().unwrap();
+                            let mut actual = db.file_text(file_id).to_string();
+
+                            for (edit, snippet_edit) in source_change.source_file_edits.values() {
+                                edit.apply(&mut actual);
+                                if let Some(snippet_edit) = snippet_edit {
+                                    snippet_edit.apply(&mut actual);
+                                }
+                            }
+                            actual
+                        };
+                        after == actual
+                    })
+                })
+                .is_some()
+        });
+    assert!(fix.is_some(), "no diagnostic with desired fix");
+}
+
+#[track_caller]
+pub(crate) fn check_has_single_fix(ra_fixture_before: &str, ra_fixture_after: &str) {
+    let after = trim_indent(ra_fixture_after);
+
+    let (db, file_position) = RootDatabase::with_position(ra_fixture_before);
+    let mut conf = DiagnosticsConfig::test_sample();
+    conf.expr_fill_default = ExprFillDefaultMode::Default;
+    let mut n_fixes = 0;
+    let fix = super::diagnostics(&db, &conf, &AssistResolveStrategy::All, file_position.file_id)
+        .into_iter()
+        .find(|d| {
+            d.fixes
+                .as_ref()
+                .and_then(|fixes| {
+                    n_fixes += fixes.len();
+                    fixes.iter().find(|fix| {
+                        if !fix.target.contains_inclusive(file_position.offset) {
+                            return false;
+                        }
+                        let actual = {
+                            let source_change = fix.source_change.as_ref().unwrap();
+                            let file_id = *source_change.source_file_edits.keys().next().unwrap();
+                            let mut actual = db.file_text(file_id).to_string();
+
+                            for (edit, snippet_edit) in source_change.source_file_edits.values() {
+                                edit.apply(&mut actual);
+                                if let Some(snippet_edit) = snippet_edit {
+                                    snippet_edit.apply(&mut actual);
+                                }
+                            }
+                            actual
+                        };
+                        after == actual
+                    })
+                })
+                .is_some()
+        });
+    assert!(fix.is_some(), "no diagnostic with desired fix");
+    assert!(n_fixes == 1, "Too many fixes suggested");
+}
+
 /// Checks that there's a diagnostic *without* fix at `$0`.
 pub(crate) fn check_no_fix(ra_fixture: &str) {
     let (db, file_position) = RootDatabase::with_position(ra_fixture);

crates/ide/src/doc_links.rs

@@ -501,7 +501,7 @@ fn get_doc_base_urls(
     let Some(krate) = def.krate(db) else { return Default::default() };
     let Some(display_name) = krate.display_name(db) else { return Default::default() };
     let crate_data = &db.crate_graph()[krate.into()];
-    let channel = crate_data.channel().unwrap_or(ReleaseChannel::Nightly).as_str();
+    let channel = db.toolchain_channel(krate.into()).unwrap_or(ReleaseChannel::Nightly).as_str();
 
     let (web_base, local_base) = match &crate_data.origin {
         // std and co do not specify `html_root_url` any longer so we gotta handwrite this ourself.

crates/ide/src/hover/tests.rs

@@ -7263,8 +7263,8 @@ impl Iterator for S {
                                 file_id: FileId(
                                     1,
                                 ),
-                                full_range: 6157..6365,
+                                full_range: 6290..6498,
-                                focus_range: 6222..6228,
+                                focus_range: 6355..6361,
                                 name: "Future",
                                 kind: Trait,
                                 container_name: "future",
@@ -7277,8 +7277,8 @@ impl Iterator for S {
                                 file_id: FileId(
                                     1,
                                 ),
-                                full_range: 6995..7461,
+                                full_range: 7128..7594,
-                                focus_range: 7039..7047,
+                                focus_range: 7172..7180,
                                 name: "Iterator",
                                 kind: Trait,
                                 container_name: "iterator",

crates/ide/src/lib.rs

@@ -12,11 +12,6 @@
 #![cfg_attr(feature = "in-rust-tree", feature(rustc_private))]
 #![recursion_limit = "128"]
 
-#[allow(unused)]
-macro_rules! eprintln {
-    ($($tt:tt)*) => { stdx::eprintln!($($tt)*) };
-}
-
 #[cfg(test)]
 mod fixture;
 
@@ -258,11 +253,11 @@ impl Analysis {
             Env::default(),
             false,
             CrateOrigin::Local { repo: None, name: None },
-            Err("Analysis::from_single_file has no target layout".into()),
-            None,
         );
         change.change_file(file_id, Some(Arc::from(text)));
         change.set_crate_graph(crate_graph);
+        change.set_target_data_layouts(vec![Err("fixture has no layout".into())]);
+        change.set_toolchains(vec![None]);
         host.apply_change(change);
         (host.analysis(), file_id)
     }
@@ -680,9 +675,8 @@ impl Analysis {
         &self,
         position: FilePosition,
         new_name: &str,
-        rename_external: bool,
     ) -> Cancellable<Result<SourceChange, RenameError>> {
-        self.with_db(|db| rename::rename(db, position, new_name, rename_external))
+        self.with_db(|db| rename::rename(db, position, new_name))
     }
 
     pub fn prepare_rename(

crates/ide/src/parent_module.rs

@@ -54,7 +54,7 @@ pub(crate) fn parent_module(db: &RootDatabase, position: FilePosition) -> Vec<Na
     }
 }
 
-/// Returns `Vec` for the same reason as `parent_module`
+/// This returns `Vec` because a module may be included from several places.
 pub(crate) fn crates_for(db: &RootDatabase, file_id: FileId) -> Vec<CrateId> {
     db.relevant_crates(file_id)
         .iter()