// 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

/// @assertion To infer the type of element:
/// ...
/// If element is a spreadElement with expression e1:
/// ...
/// If P is Set<Ps> then let S be the inferred type of e1 in context Iterable<Ps>:
/// ...
/// If S is Null and the spread operator is ...?, then the set element type is
/// Null.
///
/// @description Checks that if S is Null and the spread operator is ...?, then
/// the set element type is Null.
/// @author sgrekhov@unipro.ru

import "../../Utils/expect.dart";

Set<X> foo<X>(Set<X> s) => s;

main() {
  Null x = null;
  var s = foo({...?x});
  Expect.isTrue(s is Set<Null>);
}