Resolve assoc. types of supertraits in the IDE layer

crates/hir/src/lib.rs

@@ -54,7 +54,7 @@ use hir_def::{
 };
 use hir_expand::{name::name, MacroCallKind};
 use hir_ty::{
-    autoderef,
+    all_super_traits, autoderef,
     consteval::{unknown_const_as_generic, ComputedExpr, ConstEvalError, ConstExt},
     diagnostics::BodyValidationDiagnostic,
     method_resolution::{self, TyFingerprint},
@@ -1676,6 +1676,11 @@ impl Trait {
         db.trait_data(self.id).items.iter().map(|(_name, it)| (*it).into()).collect()
     }
 
+    pub fn items_with_supertraits(self, db: &dyn HirDatabase) -> Vec<AssocItem> {
+        let traits = all_super_traits(db.upcast(), self.into());
+        traits.iter().flat_map(|tr| Trait::from(*tr).items(db)).collect()
+    }
+
     pub fn is_auto(self, db: &dyn HirDatabase) -> bool {
         db.trait_data(self.id).is_auto
     }

crates/ide-db/src/defs.rs

@@ -386,9 +386,8 @@ impl NameRefClass {
                     let containing_path = name_ref.syntax().ancestors().find_map(ast::Path::cast)?;
                     let resolved = sema.resolve_path(&containing_path)?;
                     if let PathResolution::Def(ModuleDef::Trait(tr)) = resolved {
-                        // FIXME: resolve in supertraits
                         if let Some(ty) = tr
-                            .items(sema.db)
+                            .items_with_supertraits(sema.db)
                             .iter()
                             .filter_map(|&assoc| match assoc {
                                 hir::AssocItem::TypeAlias(it) => Some(it),

crates/ide/src/goto_definition.rs

@@ -1012,6 +1012,22 @@ fn f() -> impl Iterator<Item$0 = u8> {}
         );
     }
 
+    #[test]
+    fn goto_def_for_super_assoc_ty_in_path() {
+        check(
+            r#"
+trait Super {
+    type Item;
+       //^^^^
+}
+
+trait Sub: Super {}
+
+fn f() -> impl Sub<Item$0 = u8> {}
+"#,
+        );
+    }
+
     #[test]
     fn unknown_assoc_ty() {
         check_unresolved(