LanguageFeatures/Set-literals/type_inference_A18_t01.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

/// @assertion To infer the type of element:
/// ...
/// If element is a spreadElement with expression e1:
/// ...
/// If P is Map<Pk, Pv> then let S be the inferred type of e1 in context P:
/// ...
/// If S is Null and the spread operator is ...?, then the key and value element
/// types are Null.
///
/// @description Checks that if S is Null and the spread operator is ...?, then
/// the key and value element types are Null
/// @author sgrekhov@unipro.ru

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

Map<K, V> foo<K, V>(Map<K, V> s) => s;

main() {
  Null x = null;
  var m = foo({...?x});
  Expect.isTrue(m is Map<Null, Null>);
}