| // 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. |

| /// @assertion The flatten function is modified as follows: |

| /// [flatten(T)] is defined by cases on [T]: |

| /// if [T] is [S?] then [flatten(T) = flatten(S)?] |

| /// otherwise if [T] is [S*] then [flatten(T) = flatten(S)*] |

| /// otherwise if [T] is [FutureOr<S>] then [flatten(T) = S] |

| /// otherwise [if T <: Future] then let [S] be a type such that [T <: |

| /// Future<S>] and for all [R], if [T <: Future<R>] then [S <: R]; then |

| /// otherwise [flatten(T) = T] |

| /// @description Check that future flattening works correctly for |

| /// [Future<Object>] type statically and the expression cannot be null. |

| /// @author iarkh@unipro.ru |

| Future<Future<Object?>>(() => Future<Object>(() => null)); |

| // [analyzer] unspecified |