pkg/front_end/testcases/regress/issue_31181.dart

// Copyright (c) 2017, 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 Foo<T> = T Function<T>(T a);

Foo x;

main() {}