| // 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 The definitions of least and greatest closure are changed in null |
| /// safe libraries to substitute [Never] in positions where previously [Null |
| /// would have been substituted, and [Object?] in positions where previously |
| /// [Object] or [dynamic] would have been substituted. |
| /// @description Check the [class C<X extends C<X>>] case. |
| /// The analyzer explicitly states that [Object?] is the inferred (but |
| /// non-working) value of [X]. |
| /// |
| /// This matches the specified approach for inference of the return type of a |
| /// function literal (here () => captureTypeArgument()): The type R is the |
| /// greatest closure of C<_> which is C<Object?>, so the function literal gets |
| /// the inferred return type C<Object?>, and inference concludes that X gets the |
| /// value Object?. |
| /// |
| /// Also, X == Never would satisfy X <: C<X>, but other possible values of X |
| /// would be classes implementing C (such as class D extends C<D> {}), and it is |
| /// not plausible that inference could (or should) choose any such solution. In |
| /// other words, it is justified for the static analysis to fail to find a |
| /// suitable value for X. |
| /// |
| /// But it is not true that Object? <: C<Object?>, and this means that the |
| /// inferred type does not satisfy the declared bound. A generic function |
| /// invocation cannot be super-bounded, so the choice must be rejected. |
| /// Created #44092 to report the basic issue here (which is expressible without |
| /// any F-bounds). |
| /// |
| /// @note Read more about the least and greatest closure test template: |
| /// https://github.com/dart-lang/co19/issues/575#issuecomment-613542349 |
| /// |
| /// @Issue 44073, 44092 |
| /// @author iarkh@unipro.ru |
| |
| |
| import "../../../../Utils/expect.dart"; |
| |
| abstract class C<X extends C<X>> {} |
| |
| void main() { |
| void f<X extends C<X>>(C<X> Function() g) => g(); |
| |
| // Verify that the captured type has an `x`. |
| f(() => captureTypeArgument()); |
| //^ |
| // [analyzer] unspecified |
| // [cfe] unspecified |
| } |