pkg/front_end/testcases/extensions/explicit_invalid_access.dart

// Copyright (c) 2019, 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
class Class {}

extension Extension on Class {}

errors(Class c) {
  Extension(c);
  Extension(c) = 42;
  Extension(c) += 42;
  Extension(c)++;
  ++Extension(c);
}

main() {
}