Lower trait aliases to HIR

crates/hir-def/src/data.rs

@@ -245,19 +245,11 @@ impl TraitData {
             attrs.by_key("rustc_skip_array_during_method_dispatch").exists();
         let rustc_has_incoherent_inherent_impls =
             attrs.by_key("rustc_has_incoherent_inherent_impls").exists();
-        let (items, attribute_calls, diagnostics) = match &tr_def.items {
-            Some(items) => {
-                let mut collector = AssocItemCollector::new(
-                    db,
-                    module_id,
-                    tree_id.file_id(),
-                    ItemContainerId::TraitId(tr),
-                );
-                collector.collect(&item_tree, tree_id.tree_id(), items);
-                collector.finish()
-            }
-            None => Default::default(),
-        };
+        let mut collector =
+            AssocItemCollector::new(db, module_id, tree_id.file_id(), ItemContainerId::TraitId(tr));
+        collector.collect(&item_tree, tree_id.tree_id(), &tr_def.items);
+        let (items, attribute_calls, diagnostics) = collector.finish();
+
         (
             Arc::new(TraitData {
                 name,

crates/hir-def/src/item_tree.rs

@@ -676,8 +676,7 @@ pub struct Trait {
     pub generic_params: Interned<GenericParams>,
     pub is_auto: bool,
     pub is_unsafe: bool,
-    /// This is [`None`] if this Trait is a trait alias.
-    pub items: Option<Box<[AssocItem]>>,
+    pub items: Box<[AssocItem]>,
     pub ast_id: FileAstId<ast::Trait>,
 }
 

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

@@ -109,7 +109,7 @@ impl<'a> Ctx<'a> {
             ast::Item::Static(ast) => self.lower_static(ast)?.into(),
             ast::Item::Const(ast) => self.lower_const(ast).into(),
             ast::Item::Module(ast) => self.lower_module(ast)?.into(),
-            ast::Item::Trait(ast) => self.lower_trait(ast)?.into(),
+            ast::Item::Trait(ast) => self.lower_trait(ast)?,
             ast::Item::Impl(ast) => self.lower_impl(ast)?.into(),
             ast::Item::Use(ast) => self.lower_use(ast)?.into(),
             ast::Item::ExternCrate(ast) => self.lower_extern_crate(ast)?.into(),
@@ -439,26 +439,39 @@ impl<'a> Ctx<'a> {
         Some(id(self.data().mods.alloc(res)))
     }
 
-    fn lower_trait(&mut self, trait_def: &ast::Trait) -> Option<FileItemTreeId<Trait>> {
+    fn lower_trait(&mut self, trait_def: &ast::Trait) -> Option<ModItem> {
         let name = trait_def.name()?.as_name();
         let visibility = self.lower_visibility(trait_def);
         let generic_params = self.lower_generic_params(GenericsOwner::Trait(trait_def), trait_def);
         let is_auto = trait_def.auto_token().is_some();
         let is_unsafe = trait_def.unsafe_token().is_some();
-        let items = trait_def.assoc_item_list().map(|list| {
-            list.assoc_items()
+        let ast_id = self.source_ast_id_map.ast_id(trait_def);
+
+        let item = if trait_def.eq_token().is_some() {
+            // trait aliases
+            let bounds = self.lower_type_bounds(trait_def).into_boxed_slice();
+            let alias = TraitAlias { name, visibility, generic_params, bounds, ast_id };
+            id(self.data().trait_aliases.alloc(alias)).into()
+        } else {
+            // trait definition
+            let items = trait_def
+                .assoc_item_list()
+                .into_iter()
+                .flat_map(|list| list.assoc_items())
                 .filter_map(|item| {
                     let attrs = RawAttrs::new(self.db.upcast(), &item, self.hygiene());
                     self.lower_assoc_item(&item).map(|item| {
                         self.add_attrs(ModItem::from(item).into(), attrs);
                         item
                     })
                 })
-                .collect()
-        });
-        let ast_id = self.source_ast_id_map.ast_id(trait_def);
-        let res = Trait { name, visibility, generic_params, is_auto, is_unsafe, items, ast_id };
-        Some(id(self.data().traits.alloc(res)))
+                .collect();
+
+            let def = Trait { name, visibility, generic_params, is_auto, is_unsafe, items, ast_id };
+            id(self.data().traits.alloc(def)).into()
+        };
+
+        Some(item)
     }
 
     fn lower_impl(&mut self, impl_def: &ast::Impl) -> Option<FileItemTreeId<Impl>> {