Override static in return types with self in final classes

[rekmixa]

This PR adds the ability to replace static with self in the return types in the final classes, provided that the prototype of the final class has a static return method.

Example of how it should work:

interface A {
    public function someMethod(): static;
}
final class B implements A {
    public function someMethod(): self { /** */ }
}

• There are no changes that break backward compatibility or covariance logic.

More information in the issue: #17725

[dstogov]

@rekmixa please define what exactly you propose. (e.g. some code didn't work as expected and started to work after the patch).

I'm not sure if this patch is a fix or a new feature that requries RFC and discussion, how it's going to coexists with type variance, etc

@iluuu1994 @nielsdos @arnaud-lb please take care about this PR.

[nielsdos]

Conceptually, this seems correct to me. Please see my preliminary review comments.

[rekmixa]

@nielsdos do i need to squash all commits in this PR?

[nielsdos]

do i need to squash all commits in this PR?

No, we will squash on merge. Squashing makes it harder for us to review what has changed since our reviews.

[nielsdos]

I think this is right now, thanks. But I haven't worked with this code a lot, so this needs more eyes, especially since this is deep engine code.
cc @iluuu1994 @arnaud-lb

This may also need discussion on the ML so we know for sure there are no objections.

Requested changes were performed

[rekmixa]

This may also need discussion on the ML so we know for sure there are no objections.

By the way, i already created discussion in the ML: https://externals.io/message/126367

[nielsdos]

This may also need discussion on the ML so we know for sure there are no objections.

By the way, i already created discussion in the ML: https://externals.io/message/126367

Ah good to know, I missed this.

[iluuu1994]

LGTM now. Thank you @rekmixa! Given there were no objections on the list, it should be ok to merge this in a week or so.

[rekmixa]

LGTM now. Thank you @rekmixa! Given there were no objections on the list, it should be ok to merge this in a week or so.

Thanks for your comments. Can you tell me if this PR will be merged in 8.4 or 8.5?

[iluuu1994]

8.5. Stable branches only receive bug fixes.