| // 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. | |
| typedef F<X> = X; | |
| typedef F2<X> = F<F<X>>; | |
| extension type E<X>(F2<X> it) {} | |
| typedef F3<X> = F4<X>; | |
| typedef F4<X> = F4<X>; // Error. | |
| extension type E2<X>(F3<X> it) {} |