| // Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file | |
| // for details. All rights reserved. Use of this source code is governed by a | |
| // BSD-style license that can be found in the LICENSE file. | |
| library opted_in_lib; | |
| import 'dart:async'; | |
| class A<X> {} | |
| class B<X> implements A<X?> {} | |
| class B2<X> implements A<X> {} | |
| class FO<X> extends B2<FutureOr<X>> {} | |
| class G<X> {} |