| // Copyright (c) 2023, 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. | 
 |  | 
 | import 'package:expect/expect.dart'; | 
 |  | 
 | /// Regression test for https://github.com/dart-lang/sdk/issues/52688. | 
 |  | 
 | class A<T> extends W with C<T> {} | 
 |  | 
 | mixin C<S> on W { | 
 |   foo(M<S> c); | 
 | } | 
 | mixin M<R> on O {} | 
 |  | 
 | class W { | 
 |   foo(covariant O b) {} | 
 | } | 
 |  | 
 | class O {} | 
 |  | 
 | main() { | 
 |   // Expectation only here to ensure test is running. | 
 |   Expect.isNotNull(A()); | 
 | } |