self is incorrectly resolved when used as a return type in a trait method

[xabbuh]

Description

The following code:

<?php

class CoreTransliterator
{
    public static function create(string $id, int $direction = self::FORWARD): ?CoreTransliterator
    {
    }
}

trait EmojiTransliteratorTrait
{
    public static function create(string $id, int $direction = self::FORWARD): self
    {
    }
}

class EmojiTransliterator extends CoreTransliterator
{
    use EmojiTransliteratorTrait;
}

Resulted in this output:

Fatal error: Declaration of EmojiTransliteratorTrait::create(string $id, int $direction = self::FORWARD): EmojiTransliteratorTrait must be compatible with CoreTransliterator::create(string $id, int $direction = self::FORWARD): ?CoreTransliterator

But I expected this output instead:

The code should continue to work. self in a trait should probably not be resolved at compile time.

PHP Version

8.5

Operating System

No response

Additional information

• behaviour on PHP 8.4: https://3v4l.org/6J3Q9#v8.4.5
• behaviour on PHP 8.5: https://3v4l.org/6J3Q9/rfc#vgit.master

[iluuu1994]

Probably caused by #15878, I'll have a look.

[Girgias]

I did think that I had handled the trait case when doing the resolution to self but had messed it up.

If it does turn out to be that feel free to re-assign to me @iluuu1994

[iluuu1994]

@Girgias I think this is caused by #15878. The issue is that we're only fixing trait scopes after parent inheritance. Even if self remains unresolved, fn->scope still refers to the trait, which makes the type check fail. The right thing is probably to fix the trait scope before parent inheritance, although this changes behavior for inheritance error messages. It also breaks two tests for edge-cases, which I need to look at.