in return type class with __invoke method is not a callable

Description

The following code:

<?php
interface I {
    public function test(): callable;
}
class Invokable {
    public function __invoke() {}
}
var_dump(is_callable(new Invokable()));
class C implements I {
    public function test(): Invokable {}
}

Resulted in this output:

bool(true)

Fatal error: Declaration of C::test(): Invokable must be compatible with I::test(): callable in /in/PfBWX on line 10

Process exited with code 255.

Methods should be able to restrict callable return types from interfaces and parent classes to more specific types that unconditionally fall within the callable type. Any class or interface that contains an __invoke method should be considered a callable type an be allowed as a more specific subtype of callable in subclasses. Also \Closure should be allowed as well.

PHP Version

8.4.5

Operating System

No response

まず issue の PHP reproducer を実行し、戻り値型の互換性が callable 型とクラス型をどのように扱うかを調べます。__invoke と Closure を持つクラスを callable 宣言のより狭い戻り値型として受け入れられるようになり、報告されたケースをカバーする互換性テストが追加された時点で issue は完了です。