Fix assertion failure in type inference (#13352)

crates/hir/src/lib.rs

@@ -2807,6 +2807,10 @@ fn from_def(db: &dyn HirDatabase, def: impl HasResolver + Into<TyDefId>) -> Type
                     let subst = TyBuilder::subst_for_def(db, id, None).fill_with_unknown().build();
                     Some(subst)
                 }
+                ItemContainerId::ImplId(id) => {
+                    let subst = TyBuilder::subst_for_def(db, id, None).fill_with_unknown().build();
+                    Some(subst)
+                }
                 _ => None,
             },
             _ => None,

crates/ide/src/highlight_related.rs

@@ -1373,6 +1373,22 @@ fn main() {
     ().func$0();
      //^^^^
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn test_assoc_type_highlighting() {
+        check(
+            r#"
+trait Trait {
+    type Output;
+      // ^^^^^^
+}
+impl Trait for () {
+    type Output$0 = ();
+      // ^^^^^^
+}
 "#,
         );
     }