pkg/front_end/testcases/nnbd_mixed/infer_from_opt_in_lib.dart

// Copyright (c) 2020, 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.

class Foo {}

Foo createFoo() => new Foo();

void callback(Foo? Function(Foo?) f) {}