// 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 We say that a variable x is promotable via type test with type T
/// given variable model VM if
///
/// VM = VariableModel(declared, promoted, tested, assigned, unassigned, captured)
///  and captured is false
///  and S is the current type of x in VM
///  and not S <: T
///  and T <: S or (S is X extends R and T <: R) or (S is X & R and T <: R)
///
/// @description Checks that a variable is promotable to the type T if all
/// requirements above are met. Test S is X & R and T <: R
///
/// @author sgrekhov@unipro.ru

// Requirements=nnbd-strong

class X {}
class R extends X {}
class T extends R {
  int foo() => 42;
}

main() {
  X x = new T();
  if (x is R) {
    if (x is T) {
      x.foo();
    }
  }
}