False positives with assertSame on generics with compatible subtypes

[oliverklee]

I have a Collection container class that uses generics:

/**
 * This class represents a list of models.
 *
 * @template M of AbstractModel
 * @extends \SplObjectStorage<M, int>
 */
class Collection extends \SplObjectStorage
{
     …
}

(with AbstractModel being the abstract base class for domain models)

Now I get error messages like this:

  3069   Call to static method PHPUnit\Framework\Assert::assertSame() with      
         OliverKlee\Oelib\DataStructures\Collection<OliverKlee\Oelib\Model\Abs  
         tractModel> and                                                        
         OliverKlee\Oelib\DataStructures\Collection<Tx_Seminars_Model_Organize  
         r> will always evaluate to false.               

(Organizer is a subclass of AbstractModel, as is PaymentMethods used in the example below.)

for code that basically looks like this (simplified):

class Event
{
    /**
     * @return Collection<PaymentMethods>
     */
    public function getPaymentMethods(): Collection;

    /**
     * @param Collection<PaymentMethods> $paymentMethods
     */
    public function setPaymentMethods(Collection $paymentMethods): void;
}

class EvenTest
{
    public function testPaymentMethodsSetsPaymentMethods(): void
    {
        $paymentMethods = new Collection();
        $this->subject->setPaymentMethods($paymentMethods);

        self::assertSame($paymentMethods, $this->subject->getPaymentMethods());
    }
}

So either the check for assertSame should completely disregard the contained type within generics, or it should allow contained types that are compatible to each other.

[oliverklee]

This could also be caused by, a duplicate of, or related to phpstan/phpstan#5726.

[stof]

To me, this is indeed caused by the linked phpstan issue.