LanguageFeatures/nnbd/weak/const_evaluation_A01_t18.dart

/*
 * 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 With sound null safety, all generic const constructors and
 * generic const literals are evaluated using the actual type arguments
 * provided, whether legacy or non-legacy. This ensures that with sound null
 * safety, the final consistent semantics are obeyed.
 *
 * @description Checks dynamically that actual generic class type parameter is
 * evaluated correctly for [Never] type argument in weak mode.
 *
 * This is a question about constant evaluation, and the distinction between
 * sound and unsound null checking pops up: The null safety spec says that with
 * unsound null checking, `const C<Never>()` should treat `Never` as if it were
 * a legacy type. https://github.com/dart-lang/language/issues/1346 is all about
 * this, and we can't resolve that question as long as 1346 hasn't been
 * resolved.
 *
 * One proposal says that in unsound checking mode, `const C<Never>()` means
 * `const C<Null>()`, so the type argument will be unequal to `Never`. Another
 * one is that we should add `*` to types and leave `Never` in opted-in code
 * unchanged, so we'd compare `Never` and `Never*`, which would yield true
 * (according to the run-time semantics of `operator ==` on instances of `Type`
 * that reify types).
 *
 * So we'll have to keep this one on a waiting list, blocked by 1346 (or some
 * issue that can be found looking at 1346, if the discussion is taken somewhere
 * else, say https://github.com/dart-lang/sdk/issues/44246).
 *
 * @Issue 39678
 * @author iarkh@unipro.ru
 */
// Requirements=nnbd-weak

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

class A<T> {
  const A();
  void testme() { Expect.equals(Never, T); }
}

main() {
  const a = A<Never>();
  a.testme();
}