Attempt to fix #6937

[ptomulik]

Just a blind shot, prehaps completely wrong. But maybe a good starting point for discussion.

[orklah]

Seems like it solves the issue without adding more, that's already a huge win!

I don't have much experience in traits handling with Psalm, mind explaining a little what you did in there so we can have an idea of what's going on?

[ptomulik]

The patch is more an effect of experimenting with the example from the original issue than a consciously elaborated solution. I've observed, than for the class Test involving two traits as follows

class Test {
    /** @template-use AggregateTrait<int> */
    use AggregateTrait; // implements getValue()
    
    /** @template-use AnotherTrait<int> */
    use AnotherTrait; // declares abstract getValue()
    
    public function __construct() {
        $this->value = 123;
    }

the method compareMethodDocblockReturnTypes gets called twice. In the first call

$implementer_classlike_storage->name is "AggregateTrait"
$guide_classlike_storage->name is "AnotherTrait"
$implementer_classlike_storage->is_trait is true

And this passes without any problems. But in the second call

$implementer_classlike_storage->name is "Test"
$guide_classlike_storage->name is "AnotherTrait"
$implementer_classlike_storage->is_trait is false

and this fails. It seems that in the second call psalm treated our getValue() method as it was implemented by Test class, not by AggregateTrait. The template parameters were not applied (transformed) and the return type of getValue() was inferred to be a generic T:AggregateTrait instead of int.

What I proposed here is to apply the template parameters (int) to use AggregateTrait in the second call, when the "implementer classlike" is not a trait.

[orklah]

Thanks!