Check ancestor maps when computing traits in scope

crates/hir_def/src/resolver.rs

@@ -342,6 +342,16 @@ pub fn traits_in_scope(&self, db: &dyn DefDatabase) -> FxHashSet<TraitId> {
                     traits.extend(prelude_def_map[prelude.local_id].scope.traits());
                 }
                 traits.extend(m.def_map[m.module_id].scope.traits());
+
+                // Add all traits that are in scope because of the containing DefMaps
+                m.def_map.with_ancestor_maps(db, m.module_id, &mut |def_map, module| {
+                    if let Some(prelude) = def_map.prelude() {
+                        let prelude_def_map = prelude.def_map(db);
+                        traits.extend(prelude_def_map[prelude.local_id].scope.traits());
+                    }
+                    traits.extend(def_map[module].scope.traits());
+                    None::<()>
+                });
             }
         }
         traits

crates/hir_ty/src/tests/traits.rs

@@ -3173,6 +3173,39 @@ fn f() {
     );
 }
 
+#[test]
+fn trait_in_scope_with_inner_item() {
+    check_infer(
+        r#"
+mod m {
+    pub trait Tr {
+        fn method(&self) -> u8 { 0 }
+    }
+
+    impl Tr for () {}
+}
+
+use m::Tr;
+
+fn f() {
+    fn inner() {
+        ().method();
+      //^^^^^^^^^^^ u8
+    }
+}
+        "#,
+        expect![[r#"
+            46..50 'self': &Self
+            58..63 '{ 0 }': u8
+            60..61 '0': u8
+            115..185 '{     ...   } }': ()
+            132..183 '{     ...     }': ()
+            142..144 '()': ()
+            142..153 '().method()': u8
+        "#]],
+    );
+}
+
 #[test]
 fn inner_use_in_block() {
     check_types(