Merge branch 'master' into sync-from-rust

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

@@ -54,7 +54,7 @@ pub(super) fn print_body_hir(db: &dyn DefDatabase, body: &Body, owner: DefWithBo
     let mut p = Printer { db, body, buf: header, indent_level: 0, needs_indent: false };
     if let DefWithBodyId::FunctionId(it) = owner {
         p.buf.push('(');
-        body.params.iter().zip(&db.function_data(it).params).for_each(|(&param, ty)| {
+        body.params.iter().zip(db.function_data(it).params.iter()).for_each(|(&param, ty)| {
             p.print_pat(param);
             p.buf.push(':');
             p.print_type_ref(ty);

crates/hir-def/src/data.rs

@@ -34,7 +34,7 @@ use crate::{
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct FunctionData {
     pub name: Name,
-    pub params: Vec<Interned<TypeRef>>,
+    pub params: Box<[Interned<TypeRef>]>,
     pub ret_type: Interned<TypeRef>,
     pub attrs: Attrs,
     pub visibility: RawVisibility,
@@ -177,7 +177,7 @@ pub struct TypeAliasData {
     pub rustc_has_incoherent_inherent_impls: bool,
     pub rustc_allow_incoherent_impl: bool,
     /// Bounds restricting the type alias itself (eg. `type Ty: Bound;` in a trait or impl).
-    pub bounds: Vec<Interned<TypeBound>>,
+    pub bounds: Box<[Interned<TypeBound>]>,
 }
 
 impl TypeAliasData {
@@ -210,7 +210,7 @@ impl TypeAliasData {
             is_extern: matches!(loc.container, ItemContainerId::ExternBlockId(_)),
             rustc_has_incoherent_inherent_impls,
             rustc_allow_incoherent_impl,
-            bounds: typ.bounds.to_vec(),
+            bounds: typ.bounds.clone(),
         })
     }
 }
@@ -327,6 +327,7 @@ pub struct ImplData {
     pub self_ty: Interned<TypeRef>,
     pub items: Vec<AssocItemId>,
     pub is_negative: bool,
+    pub is_unsafe: bool,
     // box it as the vec is usually empty anyways
     pub attribute_calls: Option<Box<Vec<(AstId<ast::Item>, MacroCallId)>>>,
 }
@@ -348,6 +349,7 @@ impl ImplData {
         let target_trait = impl_def.target_trait.clone();
         let self_ty = impl_def.self_ty.clone();
         let is_negative = impl_def.is_negative;
+        let is_unsafe = impl_def.is_unsafe;
 
         let mut collector =
             AssocItemCollector::new(db, module_id, tree_id.file_id(), ItemContainerId::ImplId(id));
@@ -357,7 +359,14 @@ impl ImplData {
         let items = items.into_iter().map(|(_, item)| item).collect();
 
         (
-            Arc::new(ImplData { target_trait, self_ty, items, is_negative, attribute_calls }),
+            Arc::new(ImplData {
+                target_trait,
+                self_ty,
+                items,
+                is_negative,
+                is_unsafe,
+                attribute_calls,
+            }),
             diagnostics.into(),
         )
     }

crates/hir-def/src/find_path.rs

@@ -21,9 +21,10 @@ pub fn find_path(
     item: ItemInNs,
     from: ModuleId,
     prefer_no_std: bool,
+    prefer_prelude: bool,
 ) -> Option<ModPath> {
     let _p = profile::span("find_path");
-    find_path_inner(db, item, from, None, prefer_no_std)
+    find_path_inner(db, item, from, None, prefer_no_std, prefer_prelude)
 }
 
 pub fn find_path_prefixed(
@@ -32,9 +33,10 @@ pub fn find_path_prefixed(
     from: ModuleId,
     prefix_kind: PrefixKind,
     prefer_no_std: bool,
+    prefer_prelude: bool,
 ) -> Option<ModPath> {
     let _p = profile::span("find_path_prefixed");
-    find_path_inner(db, item, from, Some(prefix_kind), prefer_no_std)
+    find_path_inner(db, item, from, Some(prefix_kind), prefer_no_std, prefer_prelude)
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -88,6 +90,7 @@ fn find_path_inner(
     from: ModuleId,
     prefixed: Option<PrefixKind>,
     prefer_no_std: bool,
+    prefer_prelude: bool,
 ) -> Option<ModPath> {
     // - if the item is a builtin, it's in scope
     if let ItemInNs::Types(ModuleDefId::BuiltinType(builtin)) = item {
@@ -109,6 +112,7 @@ fn find_path_inner(
             MAX_PATH_LEN,
             prefixed,
             prefer_no_std || db.crate_supports_no_std(crate_root.krate),
+            prefer_prelude,
         )
         .map(|(item, _)| item);
     }
@@ -134,6 +138,7 @@ fn find_path_inner(
             from,
             prefixed,
             prefer_no_std,
+            prefer_prelude,
         ) {
             let data = db.enum_data(variant.parent);
             path.push_segment(data.variants[variant.local_id].name.clone());
@@ -156,6 +161,7 @@ fn find_path_inner(
         from,
         prefixed,
         prefer_no_std || db.crate_supports_no_std(crate_root.krate),
+        prefer_prelude,
         scope_name,
     )
     .map(|(item, _)| item)
@@ -171,6 +177,7 @@ fn find_path_for_module(
     max_len: usize,
     prefixed: Option<PrefixKind>,
     prefer_no_std: bool,
+    prefer_prelude: bool,
 ) -> Option<(ModPath, Stability)> {
     if max_len == 0 {
         return None;
@@ -236,6 +243,7 @@ fn find_path_for_module(
         from,
         prefixed,
         prefer_no_std,
+        prefer_prelude,
         scope_name,
     )
 }
@@ -316,6 +324,7 @@ fn calculate_best_path(
     from: ModuleId,
     mut prefixed: Option<PrefixKind>,
     prefer_no_std: bool,
+    prefer_prelude: bool,
     scope_name: Option<Name>,
 ) -> Option<(ModPath, Stability)> {
     if max_len <= 1 {
@@ -351,11 +360,14 @@ fn calculate_best_path(
                 best_path_len - 1,
                 prefixed,
                 prefer_no_std,
+                prefer_prelude,
             ) {
                 path.0.push_segment(name);
 
                 let new_path = match best_path.take() {
-                    Some(best_path) => select_best_path(best_path, path, prefer_no_std),
+                    Some(best_path) => {
+                        select_best_path(best_path, path, prefer_no_std, prefer_prelude)
+                    }
                     None => path,
                 };
                 best_path_len = new_path.0.len();
@@ -367,18 +379,18 @@ fn calculate_best_path(
         // too (unless we can't name it at all). It could *also* be (re)exported by the same crate
         // that wants to import it here, but we always prefer to use the external path here.
 
-        let crate_graph = db.crate_graph();
+        for dep in &db.crate_graph()[from.krate].dependencies {
-        let extern_paths = crate_graph[from.krate].dependencies.iter().filter_map(|dep| {
             let import_map = db.import_map(dep.crate_id);
-            import_map.import_info_for(item).and_then(|info| {
+            let Some(import_info_for) = import_map.import_info_for(item) else { continue };
+            for info in import_info_for {
                 if info.is_doc_hidden {
                     // the item or import is `#[doc(hidden)]`, so skip it as it is in an external crate
-                    return None;
+                    continue;
                 }
 
                 // Determine best path for containing module and append last segment from `info`.
                 // FIXME: we should guide this to look up the path locally, or from the same crate again?
-                let (mut path, path_stability) = find_path_for_module(
+                let Some((mut path, path_stability)) = find_path_for_module(
                     db,
                     def_map,
                     visited_modules,
@@ -388,22 +400,26 @@ fn calculate_best_path(
                     max_len - 1,
                     prefixed,
                     prefer_no_std,
-                )?;
+                    prefer_prelude,
+                ) else {
+                    continue;
+                };
                 cov_mark::hit!(partially_imported);
                 path.push_segment(info.name.clone());
-                Some((
+
+                let path_with_stab = (
                     path,
                     zip_stability(path_stability, if info.is_unstable { Unstable } else { Stable }),
-                ))
+                );
-            })
-        });
 
-        for path in extern_paths {
+                let new_path_with_stab = match best_path.take() {
-            let new_path = match best_path.take() {
+                    Some(best_path) => {
-                Some(best_path) => select_best_path(best_path, path, prefer_no_std),
+                        select_best_path(best_path, path_with_stab, prefer_no_std, prefer_prelude)
-                None => path,
+                    }
-            };
+                    None => path_with_stab,
-            update_best_path(&mut best_path, new_path);
+                };
+                update_best_path(&mut best_path, new_path_with_stab);
+            }
         }
     }
     if let Some(module) = item.module(db) {
@@ -420,17 +436,39 @@ fn calculate_best_path(
     }
 }
 
+/// Select the best (most relevant) path between two paths.
+/// This accounts for stability, path length whether std should be chosen over alloc/core paths as
+/// well as ignoring prelude like paths or not.
 fn select_best_path(
-    old_path: (ModPath, Stability),
+    old_path @ (_, old_stability): (ModPath, Stability),
-    new_path: (ModPath, Stability),
+    new_path @ (_, new_stability): (ModPath, Stability),
     prefer_no_std: bool,
+    prefer_prelude: bool,
 ) -> (ModPath, Stability) {
-    match (old_path.1, new_path.1) {
+    match (old_stability, new_stability) {
         (Stable, Unstable) => return old_path,
         (Unstable, Stable) => return new_path,
         _ => {}
     }
     const STD_CRATES: [Name; 3] = [known::std, known::core, known::alloc];
+
+    let choose = |new_path: (ModPath, _), old_path: (ModPath, _)| {
+        let new_has_prelude = new_path.0.segments().iter().any(|seg| seg == &known::prelude);
+        let old_has_prelude = old_path.0.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, false) | (false, true, true) => old_path,
+            // no prelude difference in the paths, so pick the smaller one
+            (true, true, _) | (false, false, _) => {
+                if new_path.0.len() < old_path.0.len() {
+                    new_path
+                } else {
+                    old_path
+                }
+            }
+        }
+    };
+
     match (old_path.0.segments().first(), new_path.0.segments().first()) {
         (Some(old), Some(new)) if STD_CRATES.contains(old) && STD_CRATES.contains(new) => {
             let rank = match prefer_no_std {
@@ -451,23 +489,11 @@ fn select_best_path(
             let orank = rank(old);
             match nrank.cmp(&orank) {
                 Ordering::Less => old_path,
-                Ordering::Equal => {
+                Ordering::Equal => choose(new_path, old_path),
-                    if new_path.0.len() < old_path.0.len() {
-                        new_path
-                    } else {
-                        old_path
-                    }
-                }
                 Ordering::Greater => new_path,
             }
         }
-        _ => {
+        _ => choose(new_path, old_path),
-            if new_path.0.len() < old_path.0.len() {
-                new_path
-            } else {
-                old_path
-            }
-        }
     }
 }
 
@@ -570,7 +596,13 @@ mod tests {
     /// `code` needs to contain a cursor marker; checks that `find_path` for the
     /// item the `path` refers to returns that same path when called from the
     /// module the cursor is in.
-    fn check_found_path_(ra_fixture: &str, path: &str, prefix_kind: Option<PrefixKind>) {
+    #[track_caller]
+    fn check_found_path_(
+        ra_fixture: &str,
+        path: &str,
+        prefix_kind: Option<PrefixKind>,
+        prefer_prelude: bool,
+    ) {
         let (db, pos) = TestDB::with_position(ra_fixture);
         let module = db.module_at_position(pos);
         let parsed_path_file = syntax::SourceFile::parse(&format!("use {path};"));
@@ -589,11 +621,17 @@ mod tests {
             )
             .0
             .take_types()
-            .unwrap();
+            .expect("path does not resolve to a type");
 
-        let found_path =
+        let found_path = find_path_inner(
-            find_path_inner(&db, ItemInNs::Types(resolved), module, prefix_kind, false);
+            &db,
-        assert_eq!(found_path, Some(mod_path), "{prefix_kind:?}");
+            ItemInNs::Types(resolved),
+            module,
+            prefix_kind,
+            false,
+            prefer_prelude,
+        );
+        assert_eq!(found_path, Some(mod_path), "on kind: {prefix_kind:?}");
     }
 
     fn check_found_path(
@@ -603,10 +641,23 @@ mod tests {
         absolute: &str,
         self_prefixed: &str,
     ) {
-        check_found_path_(ra_fixture, unprefixed, None);
+        check_found_path_(ra_fixture, unprefixed, None, false);
-        check_found_path_(ra_fixture, prefixed, Some(PrefixKind::Plain));
+        check_found_path_(ra_fixture, prefixed, Some(PrefixKind::Plain), false);
-        check_found_path_(ra_fixture, absolute, Some(PrefixKind::ByCrate));
+        check_found_path_(ra_fixture, absolute, Some(PrefixKind::ByCrate), false);
-        check_found_path_(ra_fixture, self_prefixed, Some(PrefixKind::BySelf));
+        check_found_path_(ra_fixture, self_prefixed, Some(PrefixKind::BySelf), false);
+    }
+
+    fn check_found_path_prelude(
+        ra_fixture: &str,
+        unprefixed: &str,
+        prefixed: &str,
+        absolute: &str,
+        self_prefixed: &str,
+    ) {
+        check_found_path_(ra_fixture, unprefixed, None, true);
+        check_found_path_(ra_fixture, prefixed, Some(PrefixKind::Plain), true);
+        check_found_path_(ra_fixture, absolute, Some(PrefixKind::ByCrate), true);
+        check_found_path_(ra_fixture, self_prefixed, Some(PrefixKind::BySelf), true);
     }
 
     #[test]
@@ -1421,4 +1472,34 @@ pub mod error {
             "std::error::Error",
         );
     }
+
+    #[test]
+    fn respects_prelude_setting() {
+        let ra_fixture = r#"
+//- /main.rs crate:main deps:krate
+$0
+//- /krate.rs crate:krate
+pub mod prelude {
+    pub use crate::foo::*;
+}
+
+pub mod foo {
+    pub struct Foo;
+}
+"#;
+        check_found_path(
+            ra_fixture,
+            "krate::foo::Foo",
+            "krate::foo::Foo",
+            "krate::foo::Foo",
+            "krate::foo::Foo",
+        );
+        check_found_path_prelude(
+            ra_fixture,
+            "krate::prelude::Foo",
+            "krate::prelude::Foo",
+            "krate::prelude::Foo",
+            "krate::prelude::Foo",
+        );
+    }
 }

crates/hir-def/src/generics.rs

@@ -227,7 +227,7 @@ impl GenericParams {
                 let mut expander = Lazy::new(|| {
                     (module.def_map(db), Expander::new(db, loc.source(db).file_id, module))
                 });
-                for param in &func_data.params {
+                for param in func_data.params.iter() {
                     generic_params.fill_implicit_impl_trait_args(db, &mut expander, param);
                 }
 

crates/hir-def/src/import_map.rs

@@ -1,13 +1,14 @@
 //! A map of all publicly exported items in a crate.
 
-use std::{collections::hash_map::Entry, fmt, hash::BuildHasherDefault};
+use std::{fmt, hash::BuildHasherDefault};
 
 use base_db::CrateId;
-use fst::{self, Streamer};
+use fst::{self, raw::IndexedValue, Streamer};
 use hir_expand::name::Name;
 use indexmap::IndexMap;
 use itertools::Itertools;
-use rustc_hash::{FxHashMap, FxHashSet, FxHasher};
+use rustc_hash::{FxHashSet, FxHasher};
+use smallvec::SmallVec;
 use triomphe::Arc;
 
 use crate::{
@@ -20,31 +21,28 @@ use crate::{
 
 type FxIndexMap<K, V> = IndexMap<K, V, BuildHasherDefault<FxHasher>>;
 
-// FIXME: Support aliases: an item may be exported under multiple names, so `ImportInfo` should
-// have `Vec<(Name, ModuleId)>` instead of `(Name, ModuleId)`.
 /// Item import details stored in the `ImportMap`.
-#[derive(Debug, Clone, Eq, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub struct ImportInfo {
     /// A name that can be used to import the item, relative to the crate's root.
     pub name: Name,
     /// The module containing this item.
     pub container: ModuleId,
-    /// Whether the import is a trait associated item or not.
-    pub is_trait_assoc_item: bool,
     /// Whether this item is annotated with `#[doc(hidden)]`.
     pub is_doc_hidden: bool,
     /// Whether this item is annotated with `#[unstable(..)]`.
     pub is_unstable: bool,
 }
 
+type ImportMapIndex = FxIndexMap<ItemInNs, (SmallVec<[ImportInfo; 1]>, IsTraitAssocItem)>;
+
 /// A map from publicly exported items to its name.
 ///
 /// Reexports of items are taken into account, ie. if something is exported under multiple
 /// names, the one with the shortest import path will be used.
 #[derive(Default)]
 pub struct ImportMap {
-    map: FxIndexMap<ItemInNs, ImportInfo>,
+    map: ImportMapIndex,
-
     /// List of keys stored in `map`, sorted lexicographically by their `ModPath`. Indexed by the
     /// values returned by running `fst`.
     ///
@@ -55,6 +53,12 @@ pub struct ImportMap {
     fst: fst::Map<Vec<u8>>,
 }
 
+#[derive(Copy, Clone, PartialEq, Eq)]
+enum IsTraitAssocItem {
+    Yes,
+    No,
+}
+
 impl ImportMap {
     pub(crate) fn import_map_query(db: &dyn DefDatabase, krate: CrateId) -> Arc<Self> {
         let _p = profile::span("import_map_query");
@@ -64,13 +68,18 @@ impl ImportMap {
         let mut importables: Vec<_> = map
             .iter()
             // We've only collected items, whose name cannot be tuple field.
-            .map(|(&item, info)| (item, info.name.as_str().unwrap().to_ascii_lowercase()))
+            .flat_map(|(&item, (info, _))| {
+                info.iter()
+                    .map(move |info| (item, info.name.as_str().unwrap().to_ascii_lowercase()))
+            })
             .collect();
         importables.sort_by(|(_, lhs_name), (_, rhs_name)| lhs_name.cmp(rhs_name));
+        importables.dedup();
 
         // Build the FST, taking care not to insert duplicate values.
         let mut builder = fst::MapBuilder::memory();
-        let iter = importables.iter().enumerate().dedup_by(|lhs, rhs| lhs.1 .1 == rhs.1 .1);
+        let iter =
+            importables.iter().enumerate().dedup_by(|(_, (_, lhs)), (_, (_, rhs))| lhs == rhs);
         for (start_idx, (_, name)) in iter {
             let _ = builder.insert(name, start_idx as u64);
         }
@@ -82,12 +91,12 @@ impl ImportMap {
         })
     }
 
-    pub fn import_info_for(&self, item: ItemInNs) -> Option<&ImportInfo> {
+    pub fn import_info_for(&self, item: ItemInNs) -> Option<&[ImportInfo]> {
-        self.map.get(&item)
+        self.map.get(&item).map(|(info, _)| &**info)
     }
 }
 
-fn collect_import_map(db: &dyn DefDatabase, krate: CrateId) -> FxIndexMap<ItemInNs, ImportInfo> {
+fn collect_import_map(db: &dyn DefDatabase, krate: CrateId) -> ImportMapIndex {
     let _p = profile::span("collect_import_map");
 
     let def_map = db.crate_def_map(krate);
@@ -95,11 +104,13 @@ fn collect_import_map(db: &dyn DefDatabase, krate: CrateId) -> FxIndexMap<ItemIn
 
     // We look only into modules that are public(ly reexported), starting with the crate root.
     let root = def_map.module_id(DefMap::ROOT);
-    let mut worklist = vec![(root, 0u32)];
+    let mut worklist = vec![root];
-    // Records items' minimum module depth.
+    let mut visited = FxHashSet::default();
-    let mut depth_map = FxHashMap::default();
 
-    while let Some((module, depth)) = worklist.pop() {
+    while let Some(module) = worklist.pop() {
+        if !visited.insert(module) {
+            continue;
+        }
         let ext_def_map;
         let mod_data = if module.krate == krate {
             &def_map[module.local_id]
@@ -131,62 +142,18 @@ fn collect_import_map(db: &dyn DefDatabase, krate: CrateId) -> FxIndexMap<ItemIn
                         ItemInNs::Macros(id) => Some(id.into()),
                     }
                 };
-                let status @ (is_doc_hidden, is_unstable) =
+                let (is_doc_hidden, is_unstable) = attr_id.map_or((false, false), |attr_id| {
-                    attr_id.map_or((false, false), |attr_id| {
+                    let attrs = db.attrs(attr_id);
-                        let attrs = db.attrs(attr_id);
+                    (attrs.has_doc_hidden(), attrs.is_unstable())
-                        (attrs.has_doc_hidden(), attrs.is_unstable())
+                });
-                    });
 
                 let import_info = ImportInfo {
                     name: name.clone(),
                     container: module,
-                    is_trait_assoc_item: false,
                     is_doc_hidden,
                     is_unstable,
                 };
 
-                match depth_map.entry(item) {
-                    Entry::Vacant(entry) => _ = entry.insert((depth, status)),
-                    Entry::Occupied(mut entry) => {
-                        let &(occ_depth, (occ_is_doc_hidden, occ_is_unstable)) = entry.get();
-                        (depth, occ_depth);
-                        let overwrite = match (
-                            is_doc_hidden,
-                            occ_is_doc_hidden,
-                            is_unstable,
-                            occ_is_unstable,
-                        ) {
-                            // no change of hiddeness or unstableness
-                            (true, true, true, true)
-                            | (true, true, false, false)
-                            | (false, false, true, true)
-                            | (false, false, false, false) => depth < occ_depth,
-
-                            // either less hidden or less unstable, accept
-                            (true, true, false, true)
-                            | (false, true, true, true)
-                            | (false, true, false, true)
-                            | (false, true, false, false)
-                            | (false, false, false, true) => true,
-                            // more hidden or unstable, discard
-                            (true, true, true, false)
-                            | (true, false, true, true)
-                            | (true, false, true, false)
-                            | (true, false, false, false)
-                            | (false, false, true, false) => false,
-
-                            // exchanges doc(hidden) for unstable (and vice-versa),
-                            (true, false, false, true) | (false, true, true, false) => {
-                                depth < occ_depth
-                            }
-                        };
-                        if !overwrite {
-                            continue;
-                        }
-                        entry.insert((depth, status));
-                    }
-                }
-
                 if let Some(ModuleDefId::TraitId(tr)) = item.as_module_def_id() {
                     collect_trait_assoc_items(
                         db,
@@ -197,13 +164,14 @@ fn collect_import_map(db: &dyn DefDatabase, krate: CrateId) -> FxIndexMap<ItemIn
                     );
                 }
 
-                map.insert(item, import_info);
+                let (infos, _) =
+                    map.entry(item).or_insert_with(|| (SmallVec::new(), IsTraitAssocItem::No));
+                infos.reserve_exact(1);
+                infos.push(import_info);
 
-                // If we've just added a module, descend into it. We might traverse modules
+                // If we've just added a module, descend into it.
-                // multiple times, but only if the module depth is smaller (else we `continue`
-                // above).
                 if let Some(ModuleDefId::ModuleId(mod_id)) = item.as_module_def_id() {
-                    worklist.push((mod_id, depth + 1));
+                    worklist.push(mod_id);
                 }
             }
         }
@@ -214,7 +182,7 @@ fn collect_import_map(db: &dyn DefDatabase, krate: CrateId) -> FxIndexMap<ItemIn
 
 fn collect_trait_assoc_items(
     db: &dyn DefDatabase,
-    map: &mut FxIndexMap<ItemInNs, ImportInfo>,
+    map: &mut ImportMapIndex,
     tr: TraitId,
     is_type_in_ns: bool,
     trait_import_info: &ImportInfo,
@@ -241,11 +209,14 @@ fn collect_trait_assoc_items(
         let assoc_item_info = ImportInfo {
             container: trait_import_info.container,
             name: assoc_item_name.clone(),
-            is_trait_assoc_item: true,
             is_doc_hidden: attrs.has_doc_hidden(),
             is_unstable: attrs.is_unstable(),
         };
-        map.insert(assoc_item, assoc_item_info);
+
+        let (infos, _) =
+            map.entry(assoc_item).or_insert_with(|| (SmallVec::new(), IsTraitAssocItem::Yes));
+        infos.reserve_exact(1);
+        infos.push(assoc_item_info);
     }
 }
 
@@ -263,10 +234,13 @@ impl fmt::Debug for ImportMap {
         let mut importable_names: Vec<_> = self
             .map
             .iter()
-            .map(|(item, _)| match item {
+            .map(|(item, (infos, _))| {
-                ItemInNs::Types(it) => format!("- {it:?} (t)",),
+                let l = infos.len();
-                ItemInNs::Values(it) => format!("- {it:?} (v)",),
+                match item {
-                ItemInNs::Macros(it) => format!("- {it:?} (m)",),
+                    ItemInNs::Types(it) => format!("- {it:?} (t) [{l}]",),
+                    ItemInNs::Values(it) => format!("- {it:?} (v) [{l}]",),
+                    ItemInNs::Macros(it) => format!("- {it:?} (m) [{l}]",),
+                }
             })
             .collect();
 
@@ -276,7 +250,7 @@ impl fmt::Debug for ImportMap {
 }
 
 /// A way to match import map contents against the search query.
-#[derive(Debug)]
+#[derive(Copy, Clone, Debug)]
 enum SearchMode {
     /// Import map entry should strictly match the query string.
     Exact,
@@ -349,6 +323,15 @@ impl Query {
         Self { case_sensitive: true, ..self }
     }
 
+    fn matches_assoc_mode(&self, is_trait_assoc_item: IsTraitAssocItem) -> bool {
+        match (is_trait_assoc_item, self.assoc_mode) {
+            (IsTraitAssocItem::Yes, AssocSearchMode::Exclude)
+            | (IsTraitAssocItem::No, AssocSearchMode::AssocItemsOnly) => false,
+            _ => true,
+        }
+    }
+
+    /// Checks whether the import map entry matches the query.
     fn import_matches(
         &self,
         db: &dyn DefDatabase,
@@ -356,12 +339,8 @@ impl Query {
         enforce_lowercase: bool,
     ) -> bool {
         let _p = profile::span("import_map::Query::import_matches");
-        match (import.is_trait_assoc_item, self.assoc_mode) {
-            (true, AssocSearchMode::Exclude) => return false,
-            (false, AssocSearchMode::AssocItemsOnly) => return false,
-            _ => {}
-        }
 
+        // FIXME: Can we get rid of the alloc here?
         let mut input = import.name.display(db.upcast()).to_string();
         let case_insensitive = enforce_lowercase || !self.case_sensitive;
         if case_insensitive {
@@ -392,7 +371,7 @@ impl Query {
 pub fn search_dependencies(
     db: &dyn DefDatabase,
     krate: CrateId,
-    query: Query,
+    ref query: Query,
 ) -> FxHashSet<ItemInNs> {
     let _p = profile::span("search_dependencies").detail(|| format!("{query:?}"));
 
@@ -410,31 +389,58 @@ pub fn search_dependencies(
     let mut stream = op.union();
 
     let mut res = FxHashSet::default();
+    let mut common_importable_data_scratch = vec![];
     while let Some((_, indexed_values)) = stream.next() {
-        for indexed_value in indexed_values {
+        for &IndexedValue { index, value } in indexed_values {
-            let import_map = &import_maps[indexed_value.index];
+            let import_map = &import_maps[index];
-            let importables = &import_map.importables[indexed_value.value as usize..];
+            let importables @ [importable, ..] = &import_map.importables[value as usize..] else {
+                continue;
+            };
 
-            let common_importable_data = &import_map.map[&importables[0]];
+            let &(ref importable_data, is_trait_assoc_item) = &import_map.map[importable];
-            if !query.import_matches(db, common_importable_data, true) {
+            if !query.matches_assoc_mode(is_trait_assoc_item) {
                 continue;
             }
 
-            // Name shared by the importable items in this group.
+            common_importable_data_scratch.extend(
-            let common_importable_name =
+                importable_data
-                common_importable_data.name.to_smol_str().to_ascii_lowercase();
+                    .iter()
-            // Add the items from this name group. Those are all subsequent items in
+                    .filter(|&info| query.import_matches(db, info, true))
-            // `importables` whose name match `common_importable_name`.
+                    // Name shared by the importable items in this group.
-            let iter = importables
+                    .map(|info| info.name.to_smol_str()),
-                .iter()
+            );
-                .copied()
+            if common_importable_data_scratch.is_empty() {
-                .take_while(|item| {
+                continue;
-                    common_importable_name
+            }
-                        == import_map.map[item].name.to_smol_str().to_ascii_lowercase()
+            common_importable_data_scratch.sort();
-                })
+            common_importable_data_scratch.dedup();
-                .filter(|item| {
+
-                    !query.case_sensitive // we've already checked the common importables name case-insensitively
+            let iter =
-                        || query.import_matches(db, &import_map.map[item], false)
+                common_importable_data_scratch.drain(..).flat_map(|common_importable_name| {
+                    // Add the items from this name group. Those are all subsequent items in
+                    // `importables` whose name match `common_importable_name`.
+                    importables
+                        .iter()
+                        .copied()
+                        .take_while(move |item| {
+                            let &(ref import_infos, assoc_mode) = &import_map.map[item];
+                            query.matches_assoc_mode(assoc_mode)
+                                && import_infos.iter().any(|info| {
+                                    info.name
+                                        .to_smol_str()
+                                        .eq_ignore_ascii_case(&common_importable_name)
+                                })
+                        })
+                        .filter(move |item| {
+                            !query.case_sensitive || {
+                                // we've already checked the common importables name case-insensitively
+                                let &(ref import_infos, assoc_mode) = &import_map.map[item];
+                                query.matches_assoc_mode(assoc_mode)
+                                    && import_infos
+                                        .iter()
+                                        .any(|info| query.import_matches(db, info, false))
+                            }
+                        })
                 });
             res.extend(iter);
 
@@ -461,6 +467,7 @@ mod tests {
             let mut importable_paths: Vec<_> = self
                 .map
                 .iter()
+                .flat_map(|(item, (info, _))| info.iter().map(move |info| (item, info)))
                 .map(|(item, info)| {
                     let path = render_path(db, info);
                     let ns = match item {
@@ -499,7 +506,7 @@ mod tests {
                 let (path, mark) = match assoc_item_path(&db, &dependency_imports, dependency) {
                     Some(assoc_item_path) => (assoc_item_path, "a"),
                     None => (
-                        render_path(&db, dependency_imports.import_info_for(dependency)?),
+                        render_path(&db, &dependency_imports.import_info_for(dependency)?[0]),
                         match dependency {
                             ItemInNs::Types(ModuleDefId::FunctionId(_))
                             | ItemInNs::Values(ModuleDefId::FunctionId(_)) => "f",
@@ -547,7 +554,12 @@ mod tests {
             .items
             .iter()
             .find(|(_, assoc_item_id)| &dependency_assoc_item_id == assoc_item_id)?;
-        Some(format!("{}::{}", render_path(db, trait_info), assoc_item_name.display(db.upcast())))
+        // FIXME: This should check all import infos, not just the first
+        Some(format!(
+            "{}::{}",
+            render_path(db, &trait_info[0]),
+            assoc_item_name.display(db.upcast())
+        ))
     }
 
     fn check(ra_fixture: &str, expect: Expect) {
@@ -623,6 +635,7 @@ mod tests {
                 main:
                 - publ1 (t)
                 - real_pu2 (t)
+                - real_pu2::Pub (t)
                 - real_pub (t)
                 - real_pub::Pub (t)
             "#]],
@@ -648,6 +661,7 @@ mod tests {
                 - sub (t)
                 - sub::Def (t)
                 - sub::subsub (t)
+                - sub::subsub::Def (t)
             "#]],
         );
     }
@@ -747,7 +761,9 @@ mod tests {
                 - module (t)
                 - module::S (t)
                 - module::S (v)
+                - module::module (t)
                 - sub (t)
+                - sub::module (t)
             "#]],
         );
     }

crates/hir-def/src/item_tree.rs

@@ -709,6 +709,7 @@ pub struct Impl {
     pub target_trait: Option<Interned<TraitRef>>,
     pub self_ty: Interned<TypeRef>,
     pub is_negative: bool,
+    pub is_unsafe: bool,
     pub items: Box<[AssocItem]>,
     pub ast_id: FileAstId<ast::Impl>,
 }

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

@@ -396,14 +396,7 @@ impl<'a> Ctx<'a> {
         let bounds = self.lower_type_bounds(type_alias);
         let generic_params = self.lower_generic_params(HasImplicitSelf::No, type_alias);
         let ast_id = self.source_ast_id_map.ast_id(type_alias);
-        let res = TypeAlias {
+        let res = TypeAlias { name, visibility, bounds, generic_params, type_ref, ast_id };
-            name,
-            visibility,
-            bounds: bounds.into_boxed_slice(),
-            generic_params,
-            type_ref,
-            ast_id,
-        };
         Some(id(self.data().type_aliases.alloc(res)))
     }
 
@@ -499,6 +492,7 @@ impl<'a> Ctx<'a> {
         let target_trait = impl_def.trait_().and_then(|tr| self.lower_trait_ref(&tr));
         let self_ty = self.lower_type_ref(&impl_def.self_ty()?);
         let is_negative = impl_def.excl_token().is_some();
+        let is_unsafe = impl_def.unsafe_token().is_some();
 
         // We cannot use `assoc_items()` here as that does not include macro calls.
         let items = impl_def
@@ -513,7 +507,8 @@ impl<'a> Ctx<'a> {
             })
             .collect();
         let ast_id = self.source_ast_id_map.ast_id(impl_def);
-        let res = Impl { generic_params, target_trait, self_ty, is_negative, items, ast_id };
+        let res =
+            Impl { generic_params, target_trait, self_ty, is_negative, is_unsafe, items, ast_id };
         Some(id(self.data().impls.alloc(res)))
     }
 
@@ -637,13 +632,13 @@ impl<'a> Ctx<'a> {
         Interned::new(generics)
     }
 
-    fn lower_type_bounds(&mut self, node: &dyn ast::HasTypeBounds) -> Vec<Interned<TypeBound>> {
+    fn lower_type_bounds(&mut self, node: &dyn ast::HasTypeBounds) -> Box<[Interned<TypeBound>]> {
         match node.type_bound_list() {
             Some(bound_list) => bound_list
                 .bounds()
                 .map(|it| Interned::new(TypeBound::from_ast(&self.body_ctx, it)))
                 .collect(),
-            None => Vec::new(),
+            None => Box::default(),
         }
     }
 

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

@@ -388,8 +388,18 @@ impl Printer<'_> {
                 wln!(self);
             }
             ModItem::Impl(it) => {
-                let Impl { target_trait, self_ty, is_negative, items, generic_params, ast_id: _ } =
+                let Impl {
-                    &self.tree[it];
+                    target_trait,
+                    self_ty,
+                    is_negative,
+                    is_unsafe,
+                    items,
+                    generic_params,
+                    ast_id: _,
+                } = &self.tree[it];
+                if *is_unsafe {
+                    w!(self, "unsafe");
+                }
                 w!(self, "impl");
                 self.print_generic_params(generic_params);
                 w!(self, " ");

crates/hir-def/src/lib.rs

@@ -152,7 +152,7 @@ impl TryFrom<ModuleId> for CrateRootModuleId {
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
 pub struct ModuleId {
     krate: CrateId,
     /// If this `ModuleId` was derived from a `DefMap` for a block expression, this stores the

crates/hir-expand/src/db.rs

@@ -12,15 +12,11 @@ use syntax::{
 use triomphe::Arc;
 
 use crate::{
-    ast_id_map::AstIdMap,
+    ast_id_map::AstIdMap, builtin_attr_macro::pseudo_derive_attr_expansion,
-    builtin_attr_macro::pseudo_derive_attr_expansion,
+    builtin_fn_macro::EagerExpander, fixup, hygiene::HygieneFrame, tt, AstId, BuiltinAttrExpander,
-    builtin_fn_macro::EagerExpander,
+    BuiltinDeriveExpander, BuiltinFnLikeExpander, EagerCallInfo, ExpandError, ExpandResult,
-    fixup,
+    ExpandTo, HirFileId, HirFileIdRepr, MacroCallId, MacroCallKind, MacroCallLoc, MacroDefId,
-    hygiene::HygieneFrame,
+    MacroDefKind, MacroFile, ProcMacroExpander,
-    name::{name, AsName},
-    tt, AstId, BuiltinAttrExpander, BuiltinDeriveExpander, BuiltinFnLikeExpander, EagerCallInfo,
-    ExpandError, ExpandResult, ExpandTo, HirFileId, HirFileIdRepr, MacroCallId, MacroCallKind,
-    MacroCallLoc, MacroDefId, MacroDefKind, MacroFile, ProcMacroExpander,
 };
 
 /// Total limit on the number of tokens produced by any macro invocation.
@@ -619,20 +615,7 @@ fn macro_expand(db: &dyn ExpandDatabase, id: MacroCallId) -> ExpandResult<Arc<tt
     }
 
     // Skip checking token tree limit for include! macro call
-    let skip_check_tt_count = match loc.kind {
+    if !loc.def.is_include() {
-        MacroCallKind::FnLike { ast_id, expand_to: _ } => {
-            if let Some(name_ref) =
-                ast_id.to_node(db).path().and_then(|p| p.segment()).and_then(|s| s.name_ref())
-            {
-                name_ref.as_name() == name!(include)
-            } else {
-                false
-            }
-        }
-        _ => false,
-    };
-
-    if !skip_check_tt_count {
         // Set a hard limit for the expanded tt
         if let Err(value) = check_tt_count(&tt) {
             return value;

crates/hir-ty/src/db.rs

@@ -20,8 +20,8 @@ use crate::{
     method_resolution::{InherentImpls, TraitImpls, TyFingerprint},
     mir::{BorrowckResult, MirBody, MirLowerError},
     Binders, CallableDefId, ClosureId, Const, FnDefId, GenericArg, ImplTraitId, InferenceResult,
-    Interner, PolyFnSig, QuantifiedWhereClause, ReturnTypeImplTraits, Substitution, TraitRef, Ty,
+    Interner, PolyFnSig, QuantifiedWhereClause, ReturnTypeImplTraits, Substitution,
-    TyDefId, ValueTyDefId,
+    TraitEnvironment, TraitRef, Ty, TyDefId, ValueTyDefId,
 };
 use hir_expand::name::Name;
 
@@ -47,7 +47,7 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
         &self,
         def: DefWithBodyId,
         subst: Substitution,
-        env: Arc<crate::TraitEnvironment>,
+        env: Arc<TraitEnvironment>,
     ) -> Result<Arc<MirBody>, MirLowerError>;
 
     #[salsa::invoke(crate::mir::monomorphized_mir_body_for_closure_query)]
@@ -55,7 +55,7 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
         &self,
         def: ClosureId,
         subst: Substitution,
-        env: Arc<crate::TraitEnvironment>,
+        env: Arc<TraitEnvironment>,
     ) -> Result<Arc<MirBody>, MirLowerError>;
 
     #[salsa::invoke(crate::mir::borrowck_query)]
@@ -81,7 +81,7 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
         &self,
         def: GeneralConstId,
         subst: Substitution,
-        trait_env: Option<Arc<crate::TraitEnvironment>>,
+        trait_env: Option<Arc<TraitEnvironment>>,
     ) -> Result<Const, ConstEvalError>;
 
     #[salsa::invoke(crate::consteval::const_eval_static_query)]
@@ -104,16 +104,12 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
         &self,
         def: AdtId,
         subst: Substitution,
-        env: Arc<crate::TraitEnvironment>,
+        env: Arc<TraitEnvironment>,
     ) -> Result<Arc<Layout>, LayoutError>;
 
     #[salsa::invoke(crate::layout::layout_of_ty_query)]
     #[salsa::cycle(crate::layout::layout_of_ty_recover)]
-    fn layout_of_ty(
+    fn layout_of_ty(&self, ty: Ty, env: Arc<TraitEnvironment>) -> Result<Arc<Layout>, LayoutError>;
-        &self,
-        ty: Ty,
-        env: Arc<crate::TraitEnvironment>,
-    ) -> Result<Arc<Layout>, LayoutError>;
 
     #[salsa::invoke(crate::layout::target_data_layout_query)]
     fn target_data_layout(&self, krate: CrateId) -> Option<Arc<TargetDataLayout>>;
@@ -121,7 +117,7 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[salsa::invoke(crate::method_resolution::lookup_impl_method_query)]
     fn lookup_impl_method(
         &self,
-        env: Arc<crate::TraitEnvironment>,
+        env: Arc<TraitEnvironment>,
         func: FunctionId,
         fn_subst: Substitution,
     ) -> (FunctionId, Substitution);
@@ -149,10 +145,10 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
 
     #[salsa::invoke(crate::lower::trait_environment_for_body_query)]
     #[salsa::transparent]
-    fn trait_environment_for_body(&self, def: DefWithBodyId) -> Arc<crate::TraitEnvironment>;
+    fn trait_environment_for_body(&self, def: DefWithBodyId) -> Arc<TraitEnvironment>;
 
     #[salsa::invoke(crate::lower::trait_environment_query)]
-    fn trait_environment(&self, def: GenericDefId) -> Arc<crate::TraitEnvironment>;
+    fn trait_environment(&self, def: GenericDefId) -> Arc<TraitEnvironment>;
 
     #[salsa::invoke(crate::lower::generic_defaults_query)]
     #[salsa::cycle(crate::lower::generic_defaults_recover)]
@@ -249,7 +245,7 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     fn normalize_projection(
         &self,
         projection: crate::ProjectionTy,
-        env: Arc<crate::TraitEnvironment>,
+        env: Arc<TraitEnvironment>,
     ) -> Ty;
 
     #[salsa::invoke(trait_solve_wait)]

crates/hir-ty/src/diagnostics.rs

@@ -11,9 +11,3 @@ pub use crate::diagnostics::{
     },
     unsafe_check::{missing_unsafe, unsafe_expressions, UnsafeExpr},
 };
-
-#[derive(Debug, PartialEq, Eq)]
-pub struct IncoherentImpl {
-    pub file_id: hir_expand::HirFileId,
-    pub impl_: syntax::AstPtr<syntax::ast::Impl>,
-}

crates/hir-ty/src/display.rs

@@ -945,6 +945,7 @@ impl HirDisplay for Ty {
                             ItemInNs::Types((*def_id).into()),
                             module_id,
                             false,
+                            true,
                         ) {
                             write!(f, "{}", path.display(f.db.upcast()))?;
                         } else {

crates/hir-ty/src/layout.rs

@@ -1,5 +1,7 @@
 //! Compute the binary representation of a type
 
+use std::fmt;
+
 use chalk_ir::{AdtId, FloatTy, IntTy, TyKind, UintTy};
 use hir_def::{
     layout::{
@@ -26,12 +28,6 @@ pub use self::{
     target::target_data_layout_query,
 };
 
-macro_rules! user_error {
-    ($it: expr) => {
-        return Err(LayoutError::UserError(format!($it).into()))
-    };
-}
-
 mod adt;
 mod target;
 
@@ -73,13 +69,38 @@ pub type Variants = hir_def::layout::Variants<RustcFieldIdx, RustcEnumVariantIdx
 
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum LayoutError {
-    UserError(Box<str>),
+    HasErrorConst,
+    HasErrorType,
+    HasPlaceholder,
+    InvalidSimdType,
+    NotImplemented,
+    RecursiveTypeWithoutIndirection,
     SizeOverflow,
     TargetLayoutNotAvailable,
-    HasPlaceholder,
-    HasErrorType,
-    NotImplemented,
     Unknown,
+    UserReprTooSmall,
+}
+
+impl std::error::Error for LayoutError {}
+impl fmt::Display for LayoutError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            LayoutError::HasErrorConst => write!(f, "type contains an unevaluatable const"),
+            LayoutError::HasErrorType => write!(f, "type contains an error"),
+            LayoutError::HasPlaceholder => write!(f, "type contains placeholders"),
+            LayoutError::InvalidSimdType => write!(f, "invalid simd type definition"),
+            LayoutError::NotImplemented => write!(f, "not implemented"),
+            LayoutError::RecursiveTypeWithoutIndirection => {
+                write!(f, "recursive type without indirection")
+            }
+            LayoutError::SizeOverflow => write!(f, "size overflow"),
+            LayoutError::TargetLayoutNotAvailable => write!(f, "target layout not available"),
+            LayoutError::Unknown => write!(f, "unknown"),
+            LayoutError::UserReprTooSmall => {
+                write!(f, "the `#[repr]` hint is too small to hold the discriminants of the enum")
+            }
+        }
+    }
 }
 
 struct LayoutCx<'a> {
@@ -118,9 +139,7 @@ fn layout_of_simd_ty(
 
     let f0_ty = match fields.iter().next() {
         Some(it) => it.1.clone().substitute(Interner, subst),
-        None => {
+        None => return Err(LayoutError::InvalidSimdType),
-            user_error!("simd type with zero fields");
-        }
     };
 
     // The element type and number of elements of the SIMD vector
@@ -134,7 +153,7 @@ fn layout_of_simd_ty(
         // Extract the number of elements from the layout of the array field:
         let FieldsShape::Array { count, .. } = db.layout_of_ty(f0_ty.clone(), env.clone())?.fields
         else {
-            user_error!("Array with non array layout");
+            return Err(LayoutError::Unknown);
         };
 
         (e_ty.clone(), count, true)
@@ -146,7 +165,7 @@ fn layout_of_simd_ty(
     // Compute the ABI of the element type:
     let e_ly = db.layout_of_ty(e_ty, env.clone())?;
     let Abi::Scalar(e_abi) = e_ly.abi else {
-        user_error!("simd type with inner non scalar type");
+        return Err(LayoutError::Unknown);
     };
 
     // Compute the size and alignment of the vector:
@@ -259,9 +278,7 @@ pub fn layout_of_ty_query(
             cx.univariant(dl, &fields, &ReprOptions::default(), kind).ok_or(LayoutError::Unknown)?
         }
         TyKind::Array(element, count) => {
-            let count = try_const_usize(db, &count).ok_or(LayoutError::UserError(Box::from(
+            let count = try_const_usize(db, &count).ok_or(LayoutError::HasErrorConst)? as u64;
-                "unevaluated or mistyped const generic parameter",
-            )))? as u64;
             let element = db.layout_of_ty(element.clone(), trait_env.clone())?;
             let size = element.size.checked_mul(count, dl).ok_or(LayoutError::SizeOverflow)?;
 
@@ -352,7 +369,7 @@ pub fn layout_of_ty_query(
             let mut unit = layout_of_unit(&cx, dl)?;
             match unit.abi {
                 Abi::Aggregate { ref mut sized } => *sized = false,
-                _ => user_error!("bug"),
+                _ => return Err(LayoutError::Unknown),
             }
             unit
         }
@@ -418,7 +435,7 @@ pub fn layout_of_ty_recover(
     _: &Ty,
     _: &Arc<TraitEnvironment>,
 ) -> Result<Arc<Layout>, LayoutError> {
-    user_error!("infinite sized recursive type");
+    Err(LayoutError::RecursiveTypeWithoutIndirection)
 }
 
 fn layout_of_unit(cx: &LayoutCx<'_>, dl: &TargetDataLayout) -> Result<Layout, LayoutError> {

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

@@ -145,7 +145,7 @@ pub fn layout_of_adt_recover(
     _: &Substitution,
     _: &Arc<TraitEnvironment>,
 ) -> Result<Arc<Layout>, LayoutError> {
-    user_error!("infinite sized recursive type");
+    Err(LayoutError::RecursiveTypeWithoutIndirection)
 }
 
 /// Finds the appropriate Integer type and signedness for the given
@@ -169,11 +169,7 @@ fn repr_discr(
         let discr = Integer::from_attr(dl, ity);
         let fit = if ity.is_signed() { signed_fit } else { unsigned_fit };
         if discr < fit {
-            return Err(LayoutError::UserError(
+            return Err(LayoutError::UserReprTooSmall);
-                "Integer::repr_discr: `#[repr]` hint too small for \
-                      discriminant range of enum "
-                    .into(),
-            ));
         }
         return Ok((discr, ity.is_signed()));
     }

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

@@ -210,16 +210,13 @@ fn recursive() {
         struct BoxLike<T: ?Sized>(*mut T);
         struct Goal(BoxLike<Goal>);
     }
-    check_fail(
+    check_fail(r#"struct Goal(Goal);"#, LayoutError::RecursiveTypeWithoutIndirection);
-        r#"struct Goal(Goal);"#,
-        LayoutError::UserError("infinite sized recursive type".into()),
-    );
     check_fail(
         r#"
         struct Foo<T>(Foo<T>);
         struct Goal(Foo<i32>);
         "#,
-        LayoutError::UserError("infinite sized recursive type".into()),
+        LayoutError::RecursiveTypeWithoutIndirection,
     );
 }
 

crates/hir-ty/src/lib.rs

@@ -81,6 +81,7 @@ pub use mapping::{
     lt_from_placeholder_idx, to_assoc_type_id, to_chalk_trait_id, to_foreign_def_id,
     to_placeholder_idx,
 };
+pub use method_resolution::check_orphan_rules;
 pub use traits::TraitEnvironment;
 pub use utils::{all_super_traits, is_fn_unsafe_to_call};
 

crates/hir-ty/src/lower.rs

@@ -1383,51 +1383,50 @@ pub(crate) fn generic_predicates_for_param_query(
     let ctx = TyLoweringContext::new(db, &resolver, def.into())
         .with_type_param_mode(ParamLoweringMode::Variable);
     let generics = generics(db.upcast(), def);
+
+    // we have to filter out all other predicates *first*, before attempting to lower them
+    let predicate = |pred: &&_| match pred {
+        WherePredicate::ForLifetime { target, bound, .. }
+        | WherePredicate::TypeBound { target, bound, .. } => {
+            let invalid_target = match target {
+                WherePredicateTypeTarget::TypeRef(type_ref) => {
+                    ctx.lower_ty_only_param(type_ref) != Some(param_id)
+                }
+                &WherePredicateTypeTarget::TypeOrConstParam(local_id) => {
+                    let target_id = TypeOrConstParamId { parent: def, local_id };
+                    target_id != param_id
+                }
+            };
+            if invalid_target {
+                return false;
+            }
+
+            match &**bound {
+                TypeBound::ForLifetime(_, path) | TypeBound::Path(path, _) => {
+                    // Only lower the bound if the trait could possibly define the associated
+                    // type we're looking for.
+
+                    let Some(assoc_name) = &assoc_name else { return true };
+                    let Some(TypeNs::TraitId(tr)) =
+                        resolver.resolve_path_in_type_ns_fully(db.upcast(), path)
+                    else {
+                        return false;
+                    };
+
+                    all_super_traits(db.upcast(), tr).iter().any(|tr| {
+                        db.trait_data(*tr).items.iter().any(|(name, item)| {
+                            matches!(item, AssocItemId::TypeAliasId(_)) && name == assoc_name
+                        })
+                    })
+                }
+                TypeBound::Lifetime(_) | TypeBound::Error => false,
+            }
+        }
+        WherePredicate::Lifetime { .. } => false,
+    };
     let mut predicates: Vec<_> = resolver
         .where_predicates_in_scope()
-        // we have to filter out all other predicates *first*, before attempting to lower them
+        .filter(predicate)
-        .filter(|pred| match pred {
-            WherePredicate::ForLifetime { target, bound, .. }
-            | WherePredicate::TypeBound { target, bound, .. } => {
-                match target {
-                    WherePredicateTypeTarget::TypeRef(type_ref) => {
-                        if ctx.lower_ty_only_param(type_ref) != Some(param_id) {
-                            return false;
-                        }
-                    }
-                    &WherePredicateTypeTarget::TypeOrConstParam(local_id) => {
-                        let target_id = TypeOrConstParamId { parent: def, local_id };
-                        if target_id != param_id {
-                            return false;
-                        }
-                    }
-                };
-
-                match &**bound {
-                    TypeBound::ForLifetime(_, path) | TypeBound::Path(path, _) => {
-                        // Only lower the bound if the trait could possibly define the associated
-                        // type we're looking for.
-
-                        let assoc_name = match &assoc_name {
-                            Some(it) => it,
-                            None => return true,
-                        };
-                        let tr = match resolver.resolve_path_in_type_ns_fully(db.upcast(), path) {
-                            Some(TypeNs::TraitId(tr)) => tr,
-                            _ => return false,
-                        };
-
-                        all_super_traits(db.upcast(), tr).iter().any(|tr| {
-                            db.trait_data(*tr).items.iter().any(|(name, item)| {
-                                matches!(item, AssocItemId::TypeAliasId(_)) && name == assoc_name
-                            })
-                        })
-                    }
-                    TypeBound::Lifetime(_) | TypeBound::Error => false,
-                }
-            }
-            WherePredicate::Lifetime { .. } => false,
-        })
         .flat_map(|pred| {
             ctx.lower_where_predicate(pred, true).map(|p| make_binders(db, &generics, p))
         })
@@ -1519,7 +1518,12 @@ pub(crate) fn trait_environment_query(
 
     let env = chalk_ir::Environment::new(Interner).add_clauses(Interner, clauses);
 
-    Arc::new(TraitEnvironment { krate, block: None, traits_from_clauses: traits_in_scope, env })
+    Arc::new(TraitEnvironment {
+        krate,
+        block: None,
+        traits_from_clauses: traits_in_scope.into_boxed_slice(),
+        env,
+    })
 }
 
 /// Resolve the where clause(s) of an item with generics.

crates/hir-ty/src/method_resolution.rs

@@ -862,6 +862,62 @@ fn is_inherent_impl_coherent(
     }
 }
 
+/// Checks whether the impl satisfies the orphan rules.
+///
+/// Given `impl<P1..=Pn> Trait<T1..=Tn> for T0`, an `impl`` is valid only if at least one of the following is true:
+/// - Trait is a local trait
+/// - All of
+///   - At least one of the types `T0..=Tn`` must be a local type. Let `Ti`` be the first such type.
+///   - No uncovered type parameters `P1..=Pn` may appear in `T0..Ti`` (excluding `Ti`)
+pub fn check_orphan_rules(db: &dyn HirDatabase, impl_: ImplId) -> bool {
+    let substs = TyBuilder::placeholder_subst(db, impl_);
+    let Some(impl_trait) = db.impl_trait(impl_) else {
+        // not a trait impl
+        return true;
+    };
+
+    let local_crate = impl_.lookup(db.upcast()).container.krate();
+    let is_local = |tgt_crate| tgt_crate == local_crate;
+
+    let trait_ref = impl_trait.substitute(Interner, &substs);
+    let trait_id = from_chalk_trait_id(trait_ref.trait_id);
+    if is_local(trait_id.module(db.upcast()).krate()) {
+        // trait to be implemented is local
+        return true;
+    }
+
+    let unwrap_fundamental = |ty: Ty| match ty.kind(Interner) {
+        TyKind::Ref(_, _, referenced) => referenced.clone(),
+        &TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), ref subs) => {
+            let struct_data = db.struct_data(s);
+            if struct_data.flags.contains(StructFlags::IS_FUNDAMENTAL) {
+                let next = subs.type_parameters(Interner).next();
+                match next {
+                    Some(ty) => ty,
+                    None => ty,
+                }
+            } else {
+                ty
+            }
+        }
+        _ => ty,
+    };
+    //   - At least one of the types `T0..=Tn`` must be a local type. Let `Ti`` be the first such type.
+    let is_not_orphan = trait_ref.substitution.type_parameters(Interner).any(|ty| {
+        match unwrap_fundamental(ty).kind(Interner) {
+            &TyKind::Adt(AdtId(id), _) => is_local(id.module(db.upcast()).krate()),
+            TyKind::Error => true,
+            TyKind::Dyn(it) => it.principal().map_or(false, |trait_ref| {
+                is_local(from_chalk_trait_id(trait_ref.trait_id).module(db.upcast()).krate())
+            }),
+            _ => false,
+        }
+    });
+    // FIXME: param coverage
+    //   - No uncovered type parameters `P1..=Pn` may appear in `T0..Ti`` (excluding `Ti`)
+    is_not_orphan
+}
+
 pub fn iterate_path_candidates(
     ty: &Canonical<Ty>,
     db: &dyn HirDatabase,

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

@@ -4439,42 +4439,42 @@ fn test(v: S<i32>) {
 fn associated_type_in_argument() {
     check(
         r#"
-    trait A {
+trait A {
-        fn m(&self) -> i32;
+    fn m(&self) -> i32;
-    }
+}
 
-    fn x<T: B>(k: &<T as B>::Ty) {
+fn x<T: B>(k: &<T as B>::Ty) {
-        k.m();
+    k.m();
-    }
+}
 
-    struct X;
+struct X;
-    struct Y;
+struct Y;
 
-    impl A for X {
+impl A for X {
-        fn m(&self) -> i32 {
+    fn m(&self) -> i32 {
-            8
+        8
-        }
     }
+}
 
-    impl A for Y {
+impl A for Y {
-        fn m(&self) -> i32 {
+    fn m(&self) -> i32 {
-            32
+        32
-        }
     }
+}
 
-    trait B {
+trait B {
-        type Ty: A;
+    type Ty: A;
-    }
+}
 
-    impl B for u16 {
+impl B for u16 {
-        type Ty = X;
+    type Ty = X;
-    }
+}
 
-    fn ttt() {
+fn ttt() {
-        let inp = Y;
+    let inp = Y;
-        x::<u16>(&inp);
+    x::<u16>(&inp);
-               //^^^^ expected &X, got &Y
+           //^^^^ expected &X, got &Y
-    }
+}
-    "#,
+"#,
     );
 }

crates/hir-ty/src/traits.rs

@@ -48,7 +48,7 @@ pub struct TraitEnvironment {
     pub krate: CrateId,
     pub block: Option<BlockId>,
     // FIXME make this a BTreeMap
-    pub(crate) traits_from_clauses: Vec<(Ty, TraitId)>,
+    pub(crate) traits_from_clauses: Box<[(Ty, TraitId)]>,
     pub env: chalk_ir::Environment<Interner>,
 }
 
@@ -57,7 +57,7 @@ impl TraitEnvironment {
         TraitEnvironment {
             krate,
             block: None,
-            traits_from_clauses: Vec::new(),
+            traits_from_clauses: Box::default(),
             env: chalk_ir::Environment::new(Interner),
         }
     }

crates/hir/src/diagnostics.rs

@@ -3,7 +3,7 @@
 //!
 //! This probably isn't the best way to do this -- ideally, diagnostics should
 //! be expressed in terms of hir types themselves.
-pub use hir_ty::diagnostics::{CaseType, IncoherentImpl, IncorrectCase};
+pub use hir_ty::diagnostics::{CaseType, IncorrectCase};
 
 use base_db::CrateId;
 use cfg::{CfgExpr, CfgOptions};
@@ -53,6 +53,9 @@ diagnostics![
     PrivateAssocItem,
     PrivateField,
     ReplaceFilterMapNextWithFindMap,
+    TraitImplIncorrectSafety,
+    TraitImplMissingAssocItems,
+    TraitImplOrphan,
     TypedHole,
     TypeMismatch,
     UndeclaredLabel,
@@ -280,3 +283,30 @@ pub struct MovedOutOfRef {
     pub ty: Type,
     pub span: InFile<SyntaxNodePtr>,
 }
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct IncoherentImpl {
+    pub file_id: HirFileId,
+    pub impl_: AstPtr<ast::Impl>,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct TraitImplOrphan {
+    pub file_id: HirFileId,
+    pub impl_: AstPtr<ast::Impl>,
+}
+
+// FIXME: Split this off into the corresponding 4 rustc errors
+#[derive(Debug, PartialEq, Eq)]
+pub struct TraitImplIncorrectSafety {
+    pub file_id: HirFileId,
+    pub impl_: AstPtr<ast::Impl>,
+    pub should_be_safe: bool,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct TraitImplMissingAssocItems {
+    pub file_id: HirFileId,
+    pub impl_: AstPtr<ast::Impl>,
+    pub missing: Vec<(Name, AssocItem)>,
+}

crates/hir/src/display.rs

@@ -616,7 +616,7 @@ impl HirDisplay for TypeAlias {
         write_where_clause(def_id, f)?;
         if !data.bounds.is_empty() {
             f.write_str(": ")?;
-            f.write_joined(&data.bounds, " + ")?;
+            f.write_joined(data.bounds.iter(), " + ")?;
         }
         if let Some(ty) = &data.type_ref {
             f.write_str(" = ")?;

crates/hir/src/lib.rs

@@ -34,7 +34,7 @@ pub mod symbols;
 
 mod display;
 
-use std::{iter, ops::ControlFlow};
+use std::{iter, mem::discriminant, ops::ControlFlow};
 
 use arrayvec::ArrayVec;
 use base_db::{CrateDisplayName, CrateId, CrateOrigin, Edition, FileId, ProcMacroKind};
@@ -54,14 +54,14 @@ use hir_def::{
     resolver::{HasResolver, Resolver},
     src::HasSource as _,
     AssocItemId, AssocItemLoc, AttrDefId, ConstId, ConstParamId, CrateRootModuleId, DefWithBodyId,
-    EnumId, EnumVariantId, ExternCrateId, FunctionId, GenericDefId, HasModule, ImplId,
+    EnumId, EnumVariantId, ExternCrateId, FunctionId, GenericDefId, GenericParamId, HasModule,
-    InTypeConstId, ItemContainerId, LifetimeParamId, LocalEnumVariantId, LocalFieldId, Lookup,
+    ImplId, InTypeConstId, ItemContainerId, LifetimeParamId, LocalEnumVariantId, LocalFieldId,
-    MacroExpander, MacroId, ModuleId, StaticId, StructId, TraitAliasId, TraitId, TypeAliasId,
+    Lookup, MacroExpander, MacroId, ModuleId, StaticId, StructId, TraitAliasId, TraitId,
-    TypeOrConstParamId, TypeParamId, UnionId,
+    TypeAliasId, TypeOrConstParamId, TypeParamId, UnionId,
 };
 use hir_expand::{name::name, MacroCallKind};
 use hir_ty::{
-    all_super_traits, autoderef,
+    all_super_traits, autoderef, check_orphan_rules,
     consteval::{try_const_usize, unknown_const_as_generic, ConstEvalError, ConstExt},
     diagnostics::BodyValidationDiagnostic,
     known_const_to_ast,
@@ -90,17 +90,7 @@ use crate::db::{DefDatabase, HirDatabase};
 
 pub use crate::{
     attrs::{resolve_doc_path_on, HasAttrs},
-    diagnostics::{
+    diagnostics::*,
-        AnyDiagnostic, BreakOutsideOfLoop, CaseType, ExpectedFunction, InactiveCode,
-        IncoherentImpl, IncorrectCase, InvalidDeriveTarget, MacroDefError, MacroError,
-        MacroExpansionParseError, MalformedDerive, MismatchedArgCount,
-        MismatchedTupleStructPatArgCount, MissingFields, MissingMatchArms, MissingUnsafe,
-        MovedOutOfRef, NeedMut, NoSuchField, PrivateAssocItem, PrivateField,
-        ReplaceFilterMapNextWithFindMap, TypeMismatch, TypedHole, UndeclaredLabel,
-        UnimplementedBuiltinMacro, UnreachableLabel, UnresolvedExternCrate, UnresolvedField,
-        UnresolvedImport, UnresolvedMacroCall, UnresolvedMethodCall, UnresolvedModule,
-        UnresolvedProcMacro, UnusedMut, UnusedVariable,
-    },
     has_source::HasSource,
     semantics::{PathResolution, Semantics, SemanticsScope, TypeInfo, VisibleTraits},
 };
@@ -604,6 +594,7 @@ impl Module {
 
         let inherent_impls = db.inherent_impls_in_crate(self.id.krate());
 
+        let mut impl_assoc_items_scratch = vec![];
         for impl_def in self.impl_defs(db) {
             let loc = impl_def.id.lookup(db.upcast());
             let tree = loc.id.item_tree(db.upcast());
@@ -614,19 +605,109 @@ impl Module {
                 // FIXME: Once we diagnose the inputs to builtin derives, we should at least extract those diagnostics somehow
                 continue;
             }
+            let ast_id_map = db.ast_id_map(file_id);
 
             for diag in db.impl_data_with_diagnostics(impl_def.id).1.iter() {
                 emit_def_diagnostic(db, acc, diag);
             }
 
             if inherent_impls.invalid_impls().contains(&impl_def.id) {
-                let ast_id_map = db.ast_id_map(file_id);
-
                 acc.push(IncoherentImpl { impl_: ast_id_map.get(node.ast_id()), file_id }.into())
             }
 
-            for item in impl_def.items(db) {
+            if !impl_def.check_orphan_rules(db) {
-                let def: DefWithBody = match item {
+                acc.push(TraitImplOrphan { impl_: ast_id_map.get(node.ast_id()), file_id }.into())
+            }
+
+            let trait_ = impl_def.trait_(db);
+            let trait_is_unsafe = trait_.map_or(false, |t| t.is_unsafe(db));
+            let impl_is_negative = impl_def.is_negative(db);
+            let impl_is_unsafe = impl_def.is_unsafe(db);
+
+            let drop_maybe_dangle = (|| {
+                // FIXME: This can be simplified a lot by exposing hir-ty's utils.rs::Generics helper
+                let trait_ = trait_?;
+                let drop_trait = db.lang_item(self.krate().into(), LangItem::Drop)?.as_trait()?;
+                if drop_trait != trait_.into() {
+                    return None;
+                }
+                let parent = impl_def.id.into();
+                let generic_params = db.generic_params(parent);
+                let lifetime_params = generic_params.lifetimes.iter().map(|(local_id, _)| {
+                    GenericParamId::LifetimeParamId(LifetimeParamId { parent, local_id })
+                });
+                let type_params = generic_params
+                    .iter()
+                    .filter(|(_, it)| it.type_param().is_some())
+                    .map(|(local_id, _)| {
+                        GenericParamId::TypeParamId(TypeParamId::from_unchecked(
+                            TypeOrConstParamId { parent, local_id },
+                        ))
+                    });
+                let res = type_params
+                    .chain(lifetime_params)
+                    .any(|p| db.attrs(AttrDefId::GenericParamId(p)).by_key("may_dangle").exists());
+                Some(res)
+            })()
+            .unwrap_or(false);
+
+            match (impl_is_unsafe, trait_is_unsafe, impl_is_negative, drop_maybe_dangle) {
+                // unsafe negative impl
+                (true, _, true, _) |
+                // unsafe impl for safe trait
+                (true, false, _, false) => acc.push(TraitImplIncorrectSafety { impl_: ast_id_map.get(node.ast_id()), file_id, should_be_safe: true }.into()),
+                // safe impl for unsafe trait
+                (false, true, false, _) |
+                // safe impl of dangling drop
+                (false, false, _, true) => acc.push(TraitImplIncorrectSafety { impl_: ast_id_map.get(node.ast_id()), file_id, should_be_safe: false }.into()),
+                _ => (),
+            };
+
+            if let Some(trait_) = trait_ {
+                let items = &db.trait_data(trait_.into()).items;
+                let required_items = items.iter().filter(|&(_, assoc)| match *assoc {
+                    AssocItemId::FunctionId(it) => !db.function_data(it).has_body(),
+                    AssocItemId::ConstId(_) => true,
+                    AssocItemId::TypeAliasId(it) => db.type_alias_data(it).type_ref.is_none(),
+                });
+                impl_assoc_items_scratch.extend(db.impl_data(impl_def.id).items.iter().map(
+                    |&item| {
+                        (
+                            item,
+                            match item {
+                                AssocItemId::FunctionId(it) => db.function_data(it).name.clone(),
+                                AssocItemId::ConstId(it) => {
+                                    db.const_data(it).name.as_ref().unwrap().clone()
+                                }
+                                AssocItemId::TypeAliasId(it) => db.type_alias_data(it).name.clone(),
+                            },
+                        )
+                    },
+                ));
+
+                let missing: Vec<_> = required_items
+                    .filter(|(name, id)| {
+                        !impl_assoc_items_scratch.iter().any(|(impl_item, impl_name)| {
+                            discriminant(impl_item) == discriminant(id) && impl_name == name
+                        })
+                    })
+                    .map(|(name, item)| (name.clone(), AssocItem::from(*item)))
+                    .collect();
+                if !missing.is_empty() {
+                    acc.push(
+                        TraitImplMissingAssocItems {
+                            impl_: ast_id_map.get(node.ast_id()),
+                            file_id,
+                            missing,
+                        }
+                        .into(),
+                    )
+                }
+                impl_assoc_items_scratch.clear();
+            }
+
+            for &item in &db.impl_data(impl_def.id).items {
+                let def: DefWithBody = match AssocItem::from(item) {
                     AssocItem::Function(it) => it.into(),
                     AssocItem::Const(it) => it.into(),
                     AssocItem::TypeAlias(_) => continue,
@@ -665,8 +746,15 @@ impl Module {
         db: &dyn DefDatabase,
         item: impl Into<ItemInNs>,
         prefer_no_std: bool,
+        prefer_prelude: bool,
     ) -> Option<ModPath> {
-        hir_def::find_path::find_path(db, item.into().into(), self.into(), prefer_no_std)
+        hir_def::find_path::find_path(
+            db,
+            item.into().into(),
+            self.into(),
+            prefer_no_std,
+            prefer_prelude,
+        )
     }
 
     /// Finds a path that can be used to refer to the given item from within
@@ -677,6 +765,7 @@ impl Module {
         item: impl Into<ItemInNs>,
         prefix_kind: PrefixKind,
         prefer_no_std: bool,
+        prefer_prelude: bool,
     ) -> Option<ModPath> {
         hir_def::find_path::find_path_prefixed(
             db,
@@ -684,6 +773,7 @@ impl Module {
             self.into(),
             prefix_kind,
             prefer_no_std,
+            prefer_prelude,
         )
     }
 }
@@ -3390,6 +3480,10 @@ impl Impl {
         db.impl_data(self.id).is_negative
     }
 
+    pub fn is_unsafe(self, db: &dyn HirDatabase) -> bool {
+        db.impl_data(self.id).is_unsafe
+    }
+
     pub fn module(self, db: &dyn HirDatabase) -> Module {
         self.id.lookup(db.upcast()).container.into()
     }
@@ -3398,6 +3492,10 @@ impl Impl {
         let src = self.source(db)?;
         src.file_id.as_builtin_derive_attr_node(db.upcast())
     }
+
+    pub fn check_orphan_rules(self, db: &dyn HirDatabase) -> bool {
+        check_orphan_rules(db, self.id)
+    }
 }
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]

crates/ide-assists/src/assist_config.rs

@@ -14,5 +14,6 @@ pub struct AssistConfig {
     pub allowed: Option<Vec<AssistKind>>,
     pub insert_use: InsertUseConfig,
     pub prefer_no_std: bool,
+    pub prefer_prelude: bool,
     pub assist_emit_must_use: bool,
 }

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

@@ -2245,6 +2245,37 @@ impl b::LocalTrait for B {
     fn no_skip_default_2() -> Option<()> {
         todo!()
     }
+}
+            "#,
+        )
+    }
+
+    #[test]
+    fn doc_hidden_nondefault_member() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+//- /lib.rs crate:b new_source_root:local
+trait LocalTrait {
+    #[doc(hidden)]
+    fn no_skip_non_default() -> Option<()>;
+
+    #[doc(hidden)]
+    fn skip_default() -> Option<()> {
+        todo!()
+    }
+}
+
+//- /main.rs crate:a deps:b
+struct B;
+impl b::Loc$0alTrait for B {}
+            "#,
+            r#"
+struct B;
+impl b::LocalTrait for B {
+    fn no_skip_non_default() -> Option<()> {
+        ${0:todo!()}
+    }
 }
             "#,
         )

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

@@ -88,7 +88,13 @@ pub(crate) fn add_missing_match_arms(acc: &mut Assists, ctx: &AssistContext<'_>)
             .into_iter()
             .filter_map(|variant| {
                 Some((
-                    build_pat(ctx.db(), module, variant, ctx.config.prefer_no_std)?,
+                    build_pat(
+                        ctx.db(),
+                        module,
+                        variant,
+                        ctx.config.prefer_no_std,
+                        ctx.config.prefer_prelude,
+                    )?,
                     variant.should_be_hidden(ctx.db(), module.krate()),
                 ))
             })
@@ -140,7 +146,13 @@ pub(crate) fn add_missing_match_arms(acc: &mut Assists, ctx: &AssistContext<'_>)
                     .iter()
                     .any(|variant| variant.should_be_hidden(ctx.db(), module.krate()));
                 let patterns = variants.into_iter().filter_map(|variant| {
-                    build_pat(ctx.db(), module, variant, ctx.config.prefer_no_std)
+                    build_pat(
+                        ctx.db(),
+                        module,
+                        variant,
+                        ctx.config.prefer_no_std,
+                        ctx.config.prefer_prelude,
+                    )
                 });
 
                 (ast::Pat::from(make::tuple_pat(patterns)), is_hidden)
@@ -173,7 +185,13 @@ pub(crate) fn add_missing_match_arms(acc: &mut Assists, ctx: &AssistContext<'_>)
                     .iter()
                     .any(|variant| variant.should_be_hidden(ctx.db(), module.krate()));
                 let patterns = variants.into_iter().filter_map(|variant| {
-                    build_pat(ctx.db(), module, variant.clone(), ctx.config.prefer_no_std)
+                    build_pat(
+                        ctx.db(),
+                        module,
+                        variant.clone(),
+                        ctx.config.prefer_no_std,
+                        ctx.config.prefer_prelude,
+                    )
                 });
                 (ast::Pat::from(make::slice_pat(patterns)), is_hidden)
             })
@@ -440,11 +458,16 @@ fn build_pat(
     module: hir::Module,
     var: ExtendedVariant,
     prefer_no_std: bool,
+    prefer_prelude: bool,
 ) -> Option<ast::Pat> {
     match var {
         ExtendedVariant::Variant(var) => {
-            let path =
+            let path = mod_path_to_ast(&module.find_use_path(
-                mod_path_to_ast(&module.find_use_path(db, ModuleDef::from(var), prefer_no_std)?);
+                db,
+                ModuleDef::from(var),
+                prefer_no_std,
+                prefer_prelude,
+            )?);
 
             // FIXME: use HIR for this; it doesn't currently expose struct vs. tuple vs. unit variants though
             Some(match var.source(db)?.value.kind() {

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

@@ -93,6 +93,7 @@ pub(crate) fn auto_import(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<
         &ctx.sema,
         ctx.config.insert_use.prefix_kind,
         ctx.config.prefer_no_std,
+        ctx.config.prefer_no_std,
     );
     if proposed_imports.is_empty() {
         return None;

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

@@ -348,6 +348,7 @@ fn augment_references_with_imports(
                         ModuleDef::Module(*target_module),
                         ctx.config.insert_use.prefix_kind,
                         ctx.config.prefer_no_std,
+                        ctx.config.prefer_prelude,
                     )
                     .map(|mod_path| {
                         make::path_concat(mod_path_to_ast(&mod_path), make::path_from_text("Bool"))

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

@@ -50,7 +50,12 @@ pub(crate) fn convert_into_to_from(acc: &mut Assists, ctx: &AssistContext<'_>) -
             _ => return None,
         };
 
-        mod_path_to_ast(&module.find_use_path(ctx.db(), src_type_def, ctx.config.prefer_no_std)?)
+        mod_path_to_ast(&module.find_use_path(
+            ctx.db(),
+            src_type_def,
+            ctx.config.prefer_no_std,
+            ctx.config.prefer_prelude,
+        )?)
     };
 
     let dest_type = match &ast_trait {

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

@@ -205,6 +205,7 @@ fn augment_references_with_imports(
                         ModuleDef::Module(*target_module),
                         ctx.config.insert_use.prefix_kind,
                         ctx.config.prefer_no_std,
+                        ctx.config.prefer_prelude,
                     )
                     .map(|mod_path| {
                         make::path_concat(

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

@@ -163,6 +163,7 @@ pub(crate) fn extract_function(acc: &mut Assists, ctx: &AssistContext<'_>) -> Op
                         ModuleDef::from(control_flow_enum),
                         ctx.config.insert_use.prefix_kind,
                         ctx.config.prefer_no_std,
+                        ctx.config.prefer_prelude,
                     );
 
                     if let Some(mod_path) = mod_path {

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

@@ -384,6 +384,7 @@ fn process_references(
                     *enum_module_def,
                     ctx.config.insert_use.prefix_kind,
                     ctx.config.prefer_no_std,
+                    ctx.config.prefer_prelude,
                 );
                 if let Some(mut mod_path) = mod_path {
                     mod_path.pop_segment();

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

@@ -58,8 +58,12 @@ fn generate_record_deref(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<(
 
     let module = ctx.sema.to_def(&strukt)?.module(ctx.db());
     let trait_ = deref_type_to_generate.to_trait(&ctx.sema, module.krate())?;
-    let trait_path =
+    let trait_path = module.find_use_path(
-        module.find_use_path(ctx.db(), ModuleDef::Trait(trait_), ctx.config.prefer_no_std)?;
+        ctx.db(),
+        ModuleDef::Trait(trait_),
+        ctx.config.prefer_no_std,
+        ctx.config.prefer_prelude,
+    )?;
 
     let field_type = field.ty()?;
     let field_name = field.name()?;
@@ -99,8 +103,12 @@ fn generate_tuple_deref(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()
 
     let module = ctx.sema.to_def(&strukt)?.module(ctx.db());
     let trait_ = deref_type_to_generate.to_trait(&ctx.sema, module.krate())?;
-    let trait_path =
+    let trait_path = module.find_use_path(
-        module.find_use_path(ctx.db(), ModuleDef::Trait(trait_), ctx.config.prefer_no_std)?;
+        ctx.db(),
+        ModuleDef::Trait(trait_),
+        ctx.config.prefer_no_std,
+        ctx.config.prefer_prelude,
+    )?;
 
     let field_type = field.ty()?;
     let target = field.syntax().text_range();

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

@@ -67,6 +67,7 @@ pub(crate) fn generate_new(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option
                     ctx.sema.db,
                     item_for_path_search(ctx.sema.db, item_in_ns)?,
                     ctx.config.prefer_no_std,
+                    ctx.config.prefer_prelude,
                 )?;
 
                 let expr = use_trivial_constructor(

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

@@ -48,6 +48,7 @@ pub(crate) fn qualify_method_call(acc: &mut Assists, ctx: &AssistContext<'_>) ->
         ctx.sema.db,
         item_for_path_search(ctx.sema.db, item_in_ns)?,
         ctx.config.prefer_no_std,
+        ctx.config.prefer_prelude,
     )?;
 
     let qualify_candidate = QualifyCandidate::ImplMethod(ctx.sema.db, call, resolved_call);

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

@@ -37,8 +37,11 @@ use crate::{
 // ```
 pub(crate) fn qualify_path(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
     let (import_assets, syntax_under_caret) = find_importable_node(ctx)?;
-    let mut proposed_imports =
+    let mut proposed_imports = import_assets.search_for_relative_paths(
-        import_assets.search_for_relative_paths(&ctx.sema, ctx.config.prefer_no_std);
+        &ctx.sema,
+        ctx.config.prefer_no_std,
+        ctx.config.prefer_prelude,
+    );
     if proposed_imports.is_empty() {
         return None;
     }

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

@@ -82,7 +82,12 @@ pub(crate) fn replace_derive_with_manual_impl(
     })
     .flat_map(|trait_| {
         current_module
-            .find_use_path(ctx.sema.db, hir::ModuleDef::Trait(trait_), ctx.config.prefer_no_std)
+            .find_use_path(
+                ctx.sema.db,
+                hir::ModuleDef::Trait(trait_),
+                ctx.config.prefer_no_std,
+                ctx.config.prefer_prelude,
+            )
             .as_ref()
             .map(mod_path_to_ast)
             .zip(Some(trait_))

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

@@ -68,6 +68,7 @@ pub(crate) fn replace_qualified_name_with_use(
                 module,
                 ctx.config.insert_use.prefix_kind,
                 ctx.config.prefer_no_std,
+                ctx.config.prefer_prelude,
             )
         })
         .flatten();

crates/ide-assists/src/tests.rs

@@ -30,6 +30,7 @@ pub(crate) const TEST_CONFIG: AssistConfig = AssistConfig {
         skip_glob_imports: true,
     },
     prefer_no_std: false,
+    prefer_prelude: true,
     assist_emit_must_use: false,
 };
 
@@ -44,6 +45,7 @@ pub(crate) const TEST_CONFIG_NO_SNIPPET_CAP: AssistConfig = AssistConfig {
         skip_glob_imports: true,
     },
     prefer_no_std: false,
+    prefer_prelude: true,
     assist_emit_must_use: false,
 };
 

crates/ide-assists/src/utils.rs

@@ -106,8 +106,18 @@ pub fn filter_assoc_items(
         .iter()
         .copied()
         .filter(|assoc_item| {
-            !(ignore_items == IgnoreAssocItems::DocHiddenAttrPresent
+            if ignore_items == IgnoreAssocItems::DocHiddenAttrPresent
-                && assoc_item.attrs(sema.db).has_doc_hidden())
+                && assoc_item.attrs(sema.db).has_doc_hidden()
+            {
+                if let hir::AssocItem::Function(f) = assoc_item {
+                    if !f.has_body(sema.db) {
+                        return true;
+                    }
+                }
+                return false;
+            }
+
+            return true;
         })
         // Note: This throws away items with no source.
         .filter_map(|assoc_item| {

crates/ide-completion/src/completions.rs

@@ -626,6 +626,7 @@ fn enum_variants_with_paths(
             ctx.db,
             hir::ModuleDef::from(variant),
             ctx.config.prefer_no_std,
+            ctx.config.prefer_prelude,
         ) {
             // Variants with trivial paths are already added by the existing completion logic,
             // so we should avoid adding these twice

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

@@ -175,6 +175,7 @@ pub(crate) fn complete_expr_path(
                                 ctx.db,
                                 hir::ModuleDef::from(strukt),
                                 ctx.config.prefer_no_std,
+                                ctx.config.prefer_prelude,
                             )
                             .filter(|it| it.len() > 1);
 
@@ -197,6 +198,7 @@ pub(crate) fn complete_expr_path(
                                 ctx.db,
                                 hir::ModuleDef::from(un),
                                 ctx.config.prefer_no_std,
+                                ctx.config.prefer_prelude,
                             )
                             .filter(|it| it.len() > 1);
 

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

@@ -257,7 +257,12 @@ fn import_on_the_fly(
     let user_input_lowercased = potential_import_name.to_lowercase();
 
     import_assets
-        .search_for_imports(&ctx.sema, ctx.config.insert_use.prefix_kind, ctx.config.prefer_no_std)
+        .search_for_imports(
+            &ctx.sema,
+            ctx.config.insert_use.prefix_kind,
+            ctx.config.prefer_no_std,
+            ctx.config.prefer_prelude,
+        )
         .into_iter()
         .filter(ns_filter)
         .filter(|import| {
@@ -299,7 +304,12 @@ fn import_on_the_fly_pat_(
     let user_input_lowercased = potential_import_name.to_lowercase();
 
     import_assets
-        .search_for_imports(&ctx.sema, ctx.config.insert_use.prefix_kind, ctx.config.prefer_no_std)
+        .search_for_imports(
+            &ctx.sema,
+            ctx.config.insert_use.prefix_kind,
+            ctx.config.prefer_no_std,
+            ctx.config.prefer_prelude,
+        )
         .into_iter()
         .filter(ns_filter)
         .filter(|import| {
@@ -336,7 +346,12 @@ fn import_on_the_fly_method(
     let user_input_lowercased = potential_import_name.to_lowercase();
 
     import_assets
-        .search_for_imports(&ctx.sema, ctx.config.insert_use.prefix_kind, ctx.config.prefer_no_std)
+        .search_for_imports(
+            &ctx.sema,
+            ctx.config.insert_use.prefix_kind,
+            ctx.config.prefer_no_std,
+            ctx.config.prefer_prelude,
+        )
         .into_iter()
         .filter(|import| {
             !ctx.is_item_hidden(&import.item_to_import)

crates/ide-completion/src/config.rs

@@ -19,6 +19,7 @@ pub struct CompletionConfig {
     pub snippet_cap: Option<SnippetCap>,
     pub insert_use: InsertUseConfig,
     pub prefer_no_std: bool,
+    pub prefer_prelude: bool,
     pub snippets: Vec<Snippet>,
     pub limit: Option<usize>,
 }

crates/ide-completion/src/lib.rs

@@ -263,6 +263,7 @@ pub fn resolve_completion_edits(
                     candidate,
                     config.insert_use.prefix_kind,
                     config.prefer_no_std,
+                    config.prefer_prelude,
                 )
             })
             .find(|mod_path| mod_path.display(db).to_string() == full_import_path);

crates/ide-completion/src/snippet.rs

@@ -179,6 +179,7 @@ fn import_edits(ctx: &CompletionContext<'_>, requires: &[GreenNode]) -> Option<V
             item,
             ctx.config.insert_use.prefix_kind,
             ctx.config.prefer_no_std,
+            ctx.config.prefer_prelude,
         )?;
         Some((path.len() > 1).then(|| LocatedImport::new(path.clone(), item, item, None)))
     };

crates/ide-completion/src/tests.rs

@@ -68,6 +68,7 @@ pub(crate) const TEST_CONFIG: CompletionConfig = CompletionConfig {
     callable: Some(CallableSnippets::FillArguments),
     snippet_cap: SnippetCap::new(true),
     prefer_no_std: false,
+    prefer_prelude: true,
     insert_use: InsertUseConfig {
         granularity: ImportGranularity::Crate,
         prefix_kind: PrefixKind::Plain,

crates/ide-db/src/imports/import_assets.rs

@@ -220,9 +220,10 @@ impl ImportAssets {
         sema: &Semantics<'_, RootDatabase>,
         prefix_kind: PrefixKind,
         prefer_no_std: bool,
+        prefer_prelude: bool,
     ) -> Vec<LocatedImport> {
         let _p = profile::span("import_assets::search_for_imports");
-        self.search_for(sema, Some(prefix_kind), prefer_no_std)
+        self.search_for(sema, Some(prefix_kind), prefer_no_std, prefer_prelude)
     }
 
     /// This may return non-absolute paths if a part of the returned path is already imported into scope.
@@ -230,9 +231,10 @@ impl ImportAssets {
         &self,
         sema: &Semantics<'_, RootDatabase>,
         prefer_no_std: bool,
+        prefer_prelude: bool,
     ) -> Vec<LocatedImport> {
         let _p = profile::span("import_assets::search_for_relative_paths");
-        self.search_for(sema, None, prefer_no_std)
+        self.search_for(sema, None, prefer_no_std, prefer_prelude)
     }
 
     /// Requires imports to by prefix instead of fuzzily.
@@ -270,6 +272,7 @@ impl ImportAssets {
         sema: &Semantics<'_, RootDatabase>,
         prefixed: Option<PrefixKind>,
         prefer_no_std: bool,
+        prefer_prelude: bool,
     ) -> Vec<LocatedImport> {
         let _p = profile::span("import_assets::search_for");
 
@@ -281,6 +284,7 @@ impl ImportAssets {
                 &self.module_with_candidate,
                 prefixed,
                 prefer_no_std,
+                prefer_prelude,
             )
         };
 
@@ -594,11 +598,18 @@ fn get_mod_path(
     module_with_candidate: &Module,
     prefixed: Option<PrefixKind>,
     prefer_no_std: bool,
+    prefer_prelude: bool,
 ) -> Option<ModPath> {
     if let Some(prefix_kind) = prefixed {
-        module_with_candidate.find_use_path_prefixed(db, item_to_search, prefix_kind, prefer_no_std)
+        module_with_candidate.find_use_path_prefixed(
+            db,
+            item_to_search,
+            prefix_kind,
+            prefer_no_std,
+            prefer_prelude,
+        )
     } else {
-        module_with_candidate.find_use_path(db, item_to_search, prefer_no_std)
+        module_with_candidate.find_use_path(db, item_to_search, prefer_no_std, prefer_prelude)
     }
 }
 

crates/ide-db/src/path_transform.rs

@@ -277,6 +277,7 @@ impl Ctx<'_> {
                                 self.source_scope.db.upcast(),
                                 hir::ModuleDef::Trait(trait_ref),
                                 false,
+                                true,
                             )?;
                             match make::ty_path(mod_path_to_ast(&found_path)) {
                                 ast::Type::PathType(path_ty) => Some(path_ty),
@@ -311,8 +312,12 @@ impl Ctx<'_> {
                     }
                 }
 
-                let found_path =
+                let found_path = self.target_module.find_use_path(
-                    self.target_module.find_use_path(self.source_scope.db.upcast(), def, false)?;
+                    self.source_scope.db.upcast(),
+                    def,
+                    false,
+                    true,
+                )?;
                 let res = mod_path_to_ast(&found_path).clone_for_update();
                 if let Some(args) = path.segment().and_then(|it| it.generic_arg_list()) {
                     if let Some(segment) = res.segment() {

crates/ide-db/src/search.rs

@@ -584,7 +584,7 @@ impl<'a> FindUsages<'a> {
     ) -> bool {
         match NameRefClass::classify(self.sema, name_ref) {
             Some(NameRefClass::Definition(Definition::SelfType(impl_)))
-                if impl_.self_ty(self.sema.db) == *self_ty =>
+                if impl_.self_ty(self.sema.db).as_adt() == self_ty.as_adt() =>
             {
                 let FileRange { file_id, range } = self.sema.original_range(name_ref.syntax());
                 let reference = FileReference {

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

@@ -136,6 +136,7 @@ pub(crate) fn json_in_items(
                                     it,
                                     config.insert_use.prefix_kind,
                                     config.prefer_no_std,
+                                    config.prefer_prelude,
                                 ) {
                                     insert_use(&scope, mod_path_to_ast(&it), &config.insert_use);
                                 }
@@ -148,6 +149,7 @@ pub(crate) fn json_in_items(
                                     it,
                                     config.insert_use.prefix_kind,
                                     config.prefer_no_std,
+                                    config.prefer_prelude,
                                 ) {
                                     insert_use(&scope, mod_path_to_ast(&it), &config.insert_use);
                                 }

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

@@ -122,6 +122,7 @@ fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::MissingFields) -> Option<Vec<Ass
                             ctx.sema.db,
                             item_for_path_search(ctx.sema.db, item_in_ns)?,
                             ctx.config.prefer_no_std,
+                            ctx.config.prefer_prelude,
                         )?;
 
                         use_trivial_constructor(

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

@@ -0,0 +1,129 @@
+use hir::InFile;
+use syntax::ast;
+
+use crate::{adjusted_display_range, Diagnostic, DiagnosticCode, DiagnosticsContext, Severity};
+
+// Diagnostic: trait-impl-incorrect-safety
+//
+// Diagnoses incorrect safety annotations of trait impls.
+pub(crate) fn trait_impl_incorrect_safety(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::TraitImplIncorrectSafety,
+) -> Diagnostic {
+    Diagnostic::new(
+        DiagnosticCode::Ra("trait-impl-incorrect-safety", Severity::Error),
+        if d.should_be_safe {
+            "unsafe impl for safe trait"
+        } else {
+            "impl for unsafe trait needs to be unsafe"
+        },
+        adjusted_display_range::<ast::Impl>(
+            ctx,
+            InFile { file_id: d.file_id, value: d.impl_.syntax_node_ptr() },
+            &|impl_| {
+                if d.should_be_safe {
+                    Some(match (impl_.unsafe_token(), impl_.impl_token()) {
+                        (None, None) => return None,
+                        (None, Some(t)) | (Some(t), None) => t.text_range(),
+                        (Some(t1), Some(t2)) => t1.text_range().cover(t2.text_range()),
+                    })
+                } else {
+                    impl_.impl_token().map(|t| t.text_range())
+                }
+            },
+        ),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn simple() {
+        check_diagnostics(
+            r#"
+trait Safe {}
+unsafe trait Unsafe {}
+
+  impl Safe for () {}
+
+  impl Unsafe for () {}
+//^^^^  error: impl for unsafe trait needs to be unsafe
+
+  unsafe impl Safe for () {}
+//^^^^^^^^^^^ error: unsafe impl for safe trait
+
+  unsafe impl Unsafe for () {}
+"#,
+        );
+    }
+
+    #[test]
+    fn drop_may_dangle() {
+        check_diagnostics(
+            r#"
+#[lang = "drop"]
+trait Drop {}
+struct S<T>;
+struct L<'l>;
+
+  impl<T> Drop for S<T> {}
+
+  impl<#[may_dangle] T> Drop for S<T> {}
+//^^^^ error: impl for unsafe trait needs to be unsafe
+
+  unsafe impl<T> Drop for S<T> {}
+//^^^^^^^^^^^ error: unsafe impl for safe trait
+
+  unsafe impl<#[may_dangle] T> Drop for S<T> {}
+
+  impl<'l> Drop for L<'l> {}
+
+  impl<#[may_dangle] 'l> Drop for L<'l> {}
+//^^^^ error: impl for unsafe trait needs to be unsafe
+
+  unsafe impl<'l> Drop for L<'l> {}
+//^^^^^^^^^^^ error: unsafe impl for safe trait
+
+  unsafe impl<#[may_dangle] 'l> Drop for L<'l> {}
+"#,
+        );
+    }
+
+    #[test]
+    fn negative() {
+        check_diagnostics(
+            r#"
+trait Trait {}
+
+  impl !Trait for () {}
+
+  unsafe impl !Trait for () {}
+//^^^^^^^^^^^ error: unsafe impl for safe trait
+
+unsafe trait UnsafeTrait {}
+
+  impl !UnsafeTrait for () {}
+
+  unsafe impl !UnsafeTrait for () {}
+//^^^^^^^^^^^ error: unsafe impl for safe trait
+
+"#,
+        );
+    }
+
+    #[test]
+    fn inherent() {
+        check_diagnostics(
+            r#"
+struct S;
+
+  impl S {}
+
+  unsafe impl S {}
+//^^^^^^^^^^^ error: unsafe impl for safe trait
+"#,
+        );
+    }
+}

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

@@ -0,0 +1,102 @@
+use hir::InFile;
+use itertools::Itertools;
+use syntax::{ast, AstNode};
+
+use crate::{adjusted_display_range, Diagnostic, DiagnosticCode, DiagnosticsContext};
+
+// Diagnostic: trait-impl-missing-assoc_item
+//
+// Diagnoses missing trait items in a trait impl.
+pub(crate) fn trait_impl_missing_assoc_item(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::TraitImplMissingAssocItems,
+) -> Diagnostic {
+    let missing = d.missing.iter().format_with(", ", |(name, item), f| {
+        f(&match *item {
+            hir::AssocItem::Function(_) => "`fn ",
+            hir::AssocItem::Const(_) => "`const ",
+            hir::AssocItem::TypeAlias(_) => "`type ",
+        })?;
+        f(&name.display(ctx.sema.db))?;
+        f(&"`")
+    });
+    Diagnostic::new(
+        DiagnosticCode::RustcHardError("E0046"),
+        format!("not all trait items implemented, missing: {missing}"),
+        adjusted_display_range::<ast::Impl>(
+            ctx,
+            InFile { file_id: d.file_id, value: d.impl_.syntax_node_ptr() },
+            &|impl_| impl_.trait_().map(|t| t.syntax().text_range()),
+        ),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn simple() {
+        check_diagnostics(
+            r#"
+trait Trait {
+    const C: ();
+    type T;
+    fn f();
+}
+
+impl Trait for () {
+    const C: () = ();
+    type T = ();
+    fn f() {}
+}
+
+impl Trait for () {
+   //^^^^^ error: not all trait items implemented, missing: `const C`
+    type T = ();
+    fn f() {}
+}
+
+impl Trait for () {
+   //^^^^^ error: not all trait items implemented, missing: `const C`, `type T`, `fn f`
+}
+
+"#,
+        );
+    }
+
+    #[test]
+    fn default() {
+        check_diagnostics(
+            r#"
+trait Trait {
+    const C: ();
+    type T = ();
+    fn f() {}
+}
+
+impl Trait for () {
+    const C: () = ();
+    type T = ();
+    fn f() {}
+}
+
+impl Trait for () {
+   //^^^^^ error: not all trait items implemented, missing: `const C`
+    type T = ();
+    fn f() {}
+}
+
+impl Trait for () {
+   //^^^^^ error: not all trait items implemented, missing: `const C`
+     type T = ();
+ }
+
+impl Trait for () {
+   //^^^^^ error: not all trait items implemented, missing: `const C`
+}
+
+"#,
+        );
+    }
+}

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

@@ -0,0 +1,106 @@
+use hir::InFile;
+
+use crate::{Diagnostic, DiagnosticCode, DiagnosticsContext};
+
+// Diagnostic: trait-impl-orphan
+//
+// Only traits defined in the current crate can be implemented for arbitrary types
+pub(crate) fn trait_impl_orphan(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::TraitImplOrphan,
+) -> Diagnostic {
+    Diagnostic::new_with_syntax_node_ptr(
+        ctx,
+        DiagnosticCode::RustcHardError("E0117"),
+        format!("only traits defined in the current crate can be implemented for arbitrary types"),
+        InFile::new(d.file_id, d.impl_.clone().into()),
+    )
+    // Not yet checked for false positives
+    .experimental()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn simple() {
+        check_diagnostics(
+            r#"
+//- /foo.rs crate:foo
+pub trait Foo {}
+//- /bar.rs crate:bar
+pub struct Bar;
+//- /main.rs crate:main deps:foo,bar
+struct LocalType;
+trait LocalTrait {}
+  impl foo::Foo for bar::Bar {}
+//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: only traits defined in the current crate can be implemented for arbitrary types
+impl foo::Foo for LocalType {}
+impl LocalTrait for bar::Bar {}
+"#,
+        );
+    }
+
+    #[test]
+    fn generics() {
+        check_diagnostics(
+            r#"
+//- /foo.rs crate:foo
+pub trait Foo<T> {}
+//- /bar.rs crate:bar
+pub struct Bar<T>(T);
+//- /main.rs crate:main deps:foo,bar
+struct LocalType<T>;
+trait LocalTrait<T> {}
+  impl<T> foo::Foo<T> for bar::Bar<T> {}
+//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: only traits defined in the current crate can be implemented for arbitrary types
+
+  impl<T> foo::Foo<T> for bar::Bar<LocalType<T>> {}
+//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: only traits defined in the current crate can be implemented for arbitrary types
+
+  impl<T> foo::Foo<LocalType<T>> for bar::Bar<T> {}
+
+  impl<T> foo::Foo<bar::Bar<LocalType<T>>> for bar::Bar<LocalType<T>> {}
+//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: only traits defined in the current crate can be implemented for arbitrary types
+"#,
+        );
+    }
+
+    #[test]
+    fn fundamental() {
+        check_diagnostics(
+            r#"
+//- /foo.rs crate:foo
+pub trait Foo<T> {}
+//- /bar.rs crate:bar
+pub struct Bar<T>(T);
+#[lang = "owned_box"]
+#[fundamental]
+pub struct Box<T>(T);
+//- /main.rs crate:main deps:foo,bar
+struct LocalType;
+  impl<T> foo::Foo<T> for bar::Box<T> {}
+//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: only traits defined in the current crate can be implemented for arbitrary types
+  impl<T> foo::Foo<T> for &LocalType {}
+  impl<T> foo::Foo<T> for bar::Box<LocalType> {}
+"#,
+        );
+    }
+
+    #[test]
+    fn dyn_object() {
+        check_diagnostics(
+            r#"
+//- /foo.rs crate:foo
+pub trait Foo<T> {}
+//- /bar.rs crate:bar
+pub struct Bar;
+//- /main.rs crate:main deps:foo,bar
+trait LocalTrait {}
+impl<T> foo::Foo<T> for dyn LocalTrait {}
+impl<T> foo::Foo<dyn LocalTrait> for Bar {}
+"#,
+        );
+    }
+}

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

@@ -278,6 +278,7 @@ struct Foo;
 struct Bar;
 impl core::ops::Deref for Foo {
     type Target = Bar;
+    fn deref(&self) -> &Self::Target { loop {} }
 }
 
 fn main() {
@@ -290,6 +291,7 @@ struct Foo;
 struct Bar;
 impl core::ops::Deref for Foo {
     type Target = Bar;
+    fn deref(&self) -> &Self::Target { loop {} }
 }
 
 fn main() {

crates/ide-diagnostics/src/lib.rs

@@ -44,6 +44,9 @@ mod handlers {
     pub(crate) mod private_assoc_item;
     pub(crate) mod private_field;
     pub(crate) mod replace_filter_map_next_with_find_map;
+    pub(crate) mod trait_impl_orphan;
+    pub(crate) mod trait_impl_incorrect_safety;
+    pub(crate) mod trait_impl_missing_assoc_item;
     pub(crate) mod typed_hole;
     pub(crate) mod type_mismatch;
     pub(crate) mod unimplemented_builtin_macro;
@@ -225,6 +228,7 @@ pub struct DiagnosticsConfig {
     // FIXME: We may want to include a whole `AssistConfig` here
     pub insert_use: InsertUseConfig,
     pub prefer_no_std: bool,
+    pub prefer_prelude: bool,
 }
 
 impl DiagnosticsConfig {
@@ -247,6 +251,7 @@ impl DiagnosticsConfig {
                 skip_glob_imports: false,
             },
             prefer_no_std: false,
+            prefer_prelude: true,
         }
     }
 }
@@ -356,6 +361,9 @@ pub fn diagnostics(
             AnyDiagnostic::PrivateAssocItem(d) => handlers::private_assoc_item::private_assoc_item(&ctx, &d),
             AnyDiagnostic::PrivateField(d) => handlers::private_field::private_field(&ctx, &d),
             AnyDiagnostic::ReplaceFilterMapNextWithFindMap(d) => handlers::replace_filter_map_next_with_find_map::replace_filter_map_next_with_find_map(&ctx, &d),
+            AnyDiagnostic::TraitImplIncorrectSafety(d) => handlers::trait_impl_incorrect_safety::trait_impl_incorrect_safety(&ctx, &d),
+            AnyDiagnostic::TraitImplMissingAssocItems(d) => handlers::trait_impl_missing_assoc_item::trait_impl_missing_assoc_item(&ctx, &d),
+            AnyDiagnostic::TraitImplOrphan(d) => handlers::trait_impl_orphan::trait_impl_orphan(&ctx, &d),
             AnyDiagnostic::TypedHole(d) => handlers::typed_hole::typed_hole(&ctx, &d),
             AnyDiagnostic::TypeMismatch(d) => handlers::type_mismatch::type_mismatch(&ctx, &d),
             AnyDiagnostic::UndeclaredLabel(d) => handlers::undeclared_label::undeclared_label(&ctx, &d),

crates/ide-diagnostics/src/tests.rs

@@ -5,7 +5,7 @@ use expect_test::Expect;
 use ide_db::{
     assists::AssistResolveStrategy,
     base_db::{fixture::WithFixture, SourceDatabaseExt},
-    RootDatabase,
+    LineIndexDatabase, RootDatabase,
 };
 use stdx::trim_indent;
 use test_utils::{assert_eq_text, extract_annotations, MiniCore};
@@ -43,7 +43,8 @@ fn check_nth_fix(nth: usize, ra_fixture_before: &str, ra_fixture_after: &str) {
         super::diagnostics(&db, &conf, &AssistResolveStrategy::All, file_position.file_id)
             .pop()
             .expect("no diagnostics");
-    let fix = &diagnostic.fixes.expect("diagnostic misses fixes")[nth];
+    let fix =
+        &diagnostic.fixes.expect(&format!("{:?} diagnostic misses fixes", diagnostic.code))[nth];
     let actual = {
         let source_change = fix.source_change.as_ref().unwrap();
         let file_id = *source_change.source_file_edits.keys().next().unwrap();
@@ -103,6 +104,7 @@ pub(crate) fn check_diagnostics(ra_fixture: &str) {
 pub(crate) fn check_diagnostics_with_config(config: DiagnosticsConfig, ra_fixture: &str) {
     let (db, files) = RootDatabase::with_many_files(ra_fixture);
     for file_id in files {
+        let line_index = db.line_index(file_id);
         let diagnostics = super::diagnostics(&db, &config, &AssistResolveStrategy::All, file_id);
 
         let expected = extract_annotations(&db.file_text(file_id));
@@ -136,8 +138,16 @@ pub(crate) fn check_diagnostics_with_config(config: DiagnosticsConfig, ra_fixtur
             }
         }
         if expected != actual {
-            let fneg = expected.iter().filter(|x| !actual.contains(x)).collect::<Vec<_>>();
+            let fneg = expected
-            let fpos = actual.iter().filter(|x| !expected.contains(x)).collect::<Vec<_>>();
+                .iter()
+                .filter(|x| !actual.contains(x))
+                .map(|(range, s)| (line_index.line_col(range.start()), range, s))
+                .collect::<Vec<_>>();
+            let fpos = actual
+                .iter()
+                .filter(|x| !expected.contains(x))
+                .map(|(range, s)| (line_index.line_col(range.start()), range, s))
+                .collect::<Vec<_>>();
 
             panic!("Diagnostic test failed.\nFalse negatives: {fneg:?}\nFalse positives: {fpos:?}");
         }

crates/ide-ssr/src/matching.rs

@@ -651,7 +651,7 @@ impl Match {
         for (path, resolved_path) in &template.resolved_paths {
             if let hir::PathResolution::Def(module_def) = resolved_path.resolution {
                 let mod_path =
-                    module.find_use_path(sema.db, module_def, false).ok_or_else(|| {
+                    module.find_use_path(sema.db, module_def, false, true).ok_or_else(|| {
                         match_error!("Failed to render template path `{}` at match location")
                     })?;
                 self.rendered_template_paths.insert(path.clone(), mod_path);

crates/ide/src/expand_macro.rs

@@ -14,12 +14,12 @@ pub struct ExpandedMacro {
 
 // Feature: Expand Macro Recursively
 //
-// Shows the full macro expansion of the macro at current cursor.
+// Shows the full macro expansion of the macro at the current caret position.
 //
 // |===
 // | Editor  | Action Name
 //
-// | VS Code | **rust-analyzer: Expand macro recursively**
+// | VS Code | **rust-analyzer: Expand macro recursively at caret**
 // |===
 //
 // image::https://user-images.githubusercontent.com/48062697/113020648-b3973180-917a-11eb-84a9-ecb921293dc5.gif[]

crates/ide/src/inlay_hints.rs

@@ -563,6 +563,7 @@ mod tests {
     use hir::ClosureStyle;
     use itertools::Itertools;
     use test_utils::extract_annotations;
+    use text_edit::{TextRange, TextSize};
 
     use crate::inlay_hints::{AdjustmentHints, AdjustmentHintsMode};
     use crate::DiscriminantHints;
@@ -629,6 +630,22 @@ mod tests {
         expect.assert_debug_eq(&inlay_hints)
     }
 
+    #[track_caller]
+    pub(super) fn check_expect_clear_loc(
+        config: InlayHintsConfig,
+        ra_fixture: &str,
+        expect: Expect,
+    ) {
+        let (analysis, file_id) = fixture::file(ra_fixture);
+        let mut inlay_hints = analysis.inlay_hints(&config, file_id, None).unwrap();
+        inlay_hints.iter_mut().flat_map(|hint| &mut hint.label.parts).for_each(|hint| {
+            if let Some(loc) = &mut hint.linked_location {
+                loc.range = TextRange::empty(TextSize::from(0));
+            }
+        });
+        expect.assert_debug_eq(&inlay_hints)
+    }
+
     /// Computes inlay hints for the fixture, applies all the provided text edits and then runs
     /// expect test.
     #[track_caller]

crates/ide/src/inlay_hints/chaining.rs

@@ -78,7 +78,9 @@ mod tests {
     use expect_test::expect;
 
     use crate::{
-        inlay_hints::tests::{check_expect, check_with_config, DISABLED_CONFIG, TEST_CONFIG},
+        inlay_hints::tests::{
+            check_expect, check_expect_clear_loc, check_with_config, DISABLED_CONFIG, TEST_CONFIG,
+        },
         InlayHintsConfig,
     };
 
@@ -444,7 +446,7 @@ fn main() {
 
     #[test]
     fn shorten_iterator_chaining_hints() {
-        check_expect(
+        check_expect_clear_loc(
             InlayHintsConfig { chaining_hints: true, ..DISABLED_CONFIG },
             r#"
 //- minicore: iterators
@@ -484,7 +486,7 @@ fn main() {
                                         file_id: FileId(
                                             1,
                                         ),
-                                        range: 10752..10760,
+                                        range: 0..0,
                                     },
                                 ),
                                 tooltip: "",
@@ -497,7 +499,7 @@ fn main() {
                                         file_id: FileId(
                                             1,
                                         ),
-                                        range: 10784..10788,
+                                        range: 0..0,
                                     },
                                 ),
                                 tooltip: "",
@@ -522,7 +524,7 @@ fn main() {
                                         file_id: FileId(
                                             1,
                                         ),
-                                        range: 10752..10760,
+                                        range: 0..0,
                                     },
                                 ),
                                 tooltip: "",
@@ -535,7 +537,7 @@ fn main() {
                                         file_id: FileId(
                                             1,
                                         ),
-                                        range: 10784..10788,
+                                        range: 0..0,
                                     },
                                 ),
                                 tooltip: "",
@@ -560,7 +562,7 @@ fn main() {
                                         file_id: FileId(
                                             1,
                                         ),
-                                        range: 10752..10760,
+                                        range: 0..0,
                                     },
                                 ),
                                 tooltip: "",
@@ -573,7 +575,7 @@ fn main() {
                                         file_id: FileId(
                                             1,
                                         ),
-                                        range: 10784..10788,
+                                        range: 0..0,
                                     },
                                 ),
                                 tooltip: "",
@@ -598,7 +600,7 @@ fn main() {
                                         file_id: FileId(
                                             0,
                                         ),
-                                        range: 24..30,
+                                        range: 0..0,
                                     },
                                 ),
                                 tooltip: "",

crates/ide/src/references.rs

@@ -683,6 +683,32 @@ enum Foo {
         );
     }
 
+    #[test]
+    fn test_self() {
+        check(
+            r#"
+struct S$0<T> {
+    t: PhantomData<T>,
+}
+
+impl<T> S<T> {
+    fn new() -> Self {
+        Self {
+            t: Default::default(),
+        }
+    }
+}
+"#,
+            expect![[r#"
+            S Struct FileId(0) 0..38 7..8
+
+            FileId(0) 48..49
+            FileId(0) 71..75
+            FileId(0) 86..90
+            "#]],
+        )
+    }
+
     #[test]
     fn test_find_all_refs_two_modules() {
         check(

crates/load-cargo/src/lib.rs

@@ -208,6 +208,7 @@ impl ProjectFolders {
             let entry = {
                 let mut dirs = vfs::loader::Directories::default();
                 dirs.extensions.push("rs".into());
+                dirs.extensions.push("toml".into());
                 dirs.include.extend(root.include);
                 dirs.exclude.extend(root.exclude);
                 for excl in global_excludes {

crates/rust-analyzer/src/cli/analysis_stats.rs

@@ -762,7 +762,8 @@ impl flags::AnalysisStats {
                         group: true,
                         skip_glob_imports: true,
                     },
-                    prefer_no_std: Default::default(),
+                    prefer_no_std: false,
+                    prefer_prelude: true,
                 },
                 ide::AssistResolveStrategy::All,
                 file_id,

crates/rust-analyzer/src/config.rs

@@ -352,7 +352,9 @@ config_data! {
         /// Whether to allow import insertion to merge new imports into single path glob imports like `use std::fmt::*;`.
         imports_merge_glob: bool           = "true",
         /// Prefer to unconditionally use imports of the core and alloc crate, over the std crate.
-        imports_prefer_no_std: bool                     = "false",
+        imports_preferNoStd | imports_prefer_no_std: bool = "false",
+        /// Whether to prefer import paths containing a `prelude` module.
+        imports_preferPrelude: bool                       = "false",
         /// The path structure for newly inserted paths to use.
         imports_prefix: ImportPrefixDef               = "\"plain\"",
 
@@ -1117,7 +1119,8 @@ impl Config {
                 ExprFillDefaultDef::Default => ExprFillDefaultMode::Default,
             },
             insert_use: self.insert_use_config(),
-            prefer_no_std: self.data.imports_prefer_no_std,
+            prefer_no_std: self.data.imports_preferNoStd,
+            prefer_prelude: self.data.imports_preferPrelude,
         }
     }
 
@@ -1486,7 +1489,8 @@ impl Config {
                 CallableCompletionDef::None => None,
             },
             insert_use: self.insert_use_config(),
-            prefer_no_std: self.data.imports_prefer_no_std,
+            prefer_no_std: self.data.imports_preferNoStd,
+            prefer_prelude: self.data.imports_preferPrelude,
             snippet_cap: SnippetCap::new(try_or_def!(
                 self.caps
                     .text_document
@@ -1515,7 +1519,8 @@ impl Config {
             snippet_cap: SnippetCap::new(self.experimental("snippetTextEdit")),
             allowed: None,
             insert_use: self.insert_use_config(),
-            prefer_no_std: self.data.imports_prefer_no_std,
+            prefer_no_std: self.data.imports_preferNoStd,
+            prefer_prelude: self.data.imports_preferPrelude,
             assist_emit_must_use: self.data.assist_emitMustUse,
         }
     }

crates/rust-analyzer/src/integrated_benchmarks.rs

@@ -146,6 +146,7 @@ fn integrated_completion_benchmark() {
             },
             snippets: Vec::new(),
             prefer_no_std: false,
+            prefer_prelude: true,
             limit: None,
         };
         let position =
@@ -186,6 +187,7 @@ fn integrated_completion_benchmark() {
             },
             snippets: Vec::new(),
             prefer_no_std: false,
+            prefer_prelude: true,
             limit: None,
         };
         let position =

crates/test-utils/src/minicore.rs

@@ -44,7 +44,7 @@
 //!     panic: fmt
 //!     phantom_data:
 //!     pin:
-//!     pointee:
+//!     pointee: copy, send, sync, ord, hash, unpin
 //!     range:
 //!     result:
 //!     send: sized
@@ -54,6 +54,7 @@
 //!     sync: sized
 //!     transmute:
 //!     try: infallible
+//!     unpin: sized
 //!     unsize: sized
 
 #![rustc_coherence_is_core]
@@ -89,6 +90,11 @@ pub mod marker {
     pub trait Unsize<T: ?Sized> {}
     // endregion:unsize
 
+    // region:unpin
+    #[lang = "unpin"]
+    pub auto trait Unpin {}
+    // endregion:unpin
+
     // region:copy
     #[lang = "copy"]
     pub trait Copy: Clone {}
@@ -387,9 +393,10 @@ pub mod ptr {
 
     // region:pointee
     #[lang = "pointee_trait"]
+    #[rustc_deny_explicit_impl(implement_via_object = false)]
     pub trait Pointee {
         #[lang = "metadata_type"]
-        type Metadata;
+        type Metadata: Copy + Send + Sync + Ord + Hash + Unpin;
     }
     // endregion:pointee
     // region:non_null

docs/dev/lsp-extensions.md

@@ -57,8 +57,9 @@ export interface TextDocumentEdit {
 }
 ```
 
-When applying such code action or text edit, the editor should insert snippet, with tab stops and placeholder.
+When applying such code action or text edit, the editor should insert snippet, with tab stops and placeholders.
-At the moment, rust-analyzer guarantees that only a single edit will have `InsertTextFormat.Snippet`.
+At the moment, rust-analyzer guarantees that only a single `TextDocumentEdit` will have edits which can be `InsertTextFormat.Snippet`.
+Any additional `TextDocumentEdit`s will only have edits which are `InsertTextFormat.PlainText`.
 
 ### Example
 

docs/user/generated_config.adoc

@@ -493,11 +493,16 @@ Group inserted imports by the https://rust-analyzer.github.io/manual.html#auto-i
 --
 Whether to allow import insertion to merge new imports into single path glob imports like `use std::fmt::*;`.
 --
-[[rust-analyzer.imports.prefer.no.std]]rust-analyzer.imports.prefer.no.std (default: `false`)::
+[[rust-analyzer.imports.preferNoStd]]rust-analyzer.imports.preferNoStd (default: `false`)::
 +
 --
 Prefer to unconditionally use imports of the core and alloc crate, over the std crate.
 --
+[[rust-analyzer.imports.preferPrelude]]rust-analyzer.imports.preferPrelude (default: `false`)::
++
+--
+Whether to prefer import paths containing a `prelude` module.
+--
 [[rust-analyzer.imports.prefix]]rust-analyzer.imports.prefix (default: `"plain"`)::
 +
 --

docs/user/manual.adoc

@@ -946,7 +946,7 @@ Or it is possible to specify vars more granularly:
 "rust-analyzer.runnables.extraEnv": [
     {
         // "mask": null, // null mask means that this rule will be applied for all runnables
-        env: {
+        "env": {
              "APP_ID": "1",
              "APP_DATA": "asdf"
         }
@@ -968,7 +968,7 @@ If needed, you can set different values for different platforms:
 "rust-analyzer.runnables.extraEnv": [
     {
         "platform": "win32", // windows only
-        env: {
+        "env": {
              "APP_DATA": "windows specific data"
         }
     },

editors/code/package.json

@@ -156,7 +156,7 @@
             },
             {
                 "command": "rust-analyzer.expandMacro",
-                "title": "Expand macro recursively",
+                "title": "Expand macro recursively at caret",
                 "category": "rust-analyzer"
             },
             {
@@ -1129,11 +1129,16 @@
                     "default": true,
                     "type": "boolean"
                 },
-                "rust-analyzer.imports.prefer.no.std": {
+                "rust-analyzer.imports.preferNoStd": {
                     "markdownDescription": "Prefer to unconditionally use imports of the core and alloc crate, over the std crate.",
                     "default": false,
                     "type": "boolean"
                 },
+                "rust-analyzer.imports.preferPrelude": {
+                    "markdownDescription": "Whether to prefer import paths containing a `prelude` module.",
+                    "default": false,
+                    "type": "boolean"
+                },
                 "rust-analyzer.imports.prefix": {
                     "markdownDescription": "The path structure for newly inserted paths to use.",
                     "default": "plain",