| // Copyright (c) 2018, 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. | |
| // @dart = 2.9 | |
| abstract class I { | |
| foo([a]); | |
| } | |
| abstract class A { | |
| foo() {} | |
| } | |
| abstract class B extends A implements I {} | |
| class C extends B { | |
| foo([a]) {} | |
| } | |
| void main() {} |