tests/language/implicit_downcast_during/yield_test.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.

class A {}

class B extends A {}

Iterable<B> f(A a) sync* {
  yield a;
  //    ^
  // [analyzer] COMPILE_TIME_ERROR.YIELD_OF_INVALID_TYPE
  // [cfe] A value of type 'A' can't be assigned to a variable of type 'B'.
}

void main() {
  A a = new B();
  for (var x in f(a)) {}
  a = new A();
  var iterator = f(a).iterator;
}