pkg/front_end/testcases/general/issue43975.dart

// Copyright (c) 2021, 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
typedef F = void Function<X extends F>() Function();
void main() {}