Description:
------------
Discovered an issue with narrowing return type using covariance.

I have a chain of inheritance (...ignore implementation details) from which at the lowest level I attempt to narrow the return type for an inherited method. When running the code PHP fails at compilation stating the method is not compatible.

Now the weird part is it seems the covariance check passes if I remove all interfaces from the lowest level (see example).

The attached test script should point you guys in the right direction.

Cheers,
Terence

Test script:
---------------
<?php

interface Poo
{
    public function poo(): Poo;
}

abstract class AbstractPoo implements Poo
{
    public function poo(): Poo
    {
        return new static();
    }
}

class ConcretePoo extends AbstractPoo
{
    
}

interface B
{
    
}

// Fails if interface is present
class ExtendedConcretePoo extends ConcretePoo implements B
{
    public function poo(): ExtendedConcretePoo
    {
        return new static();
    }
}

// Does not fail if no interfaces present
//class ExtendedConcretePoo extends ConcretePoo
//{
//    public function poo(): ExtendedConcretePoo
//    {
//        return new static();
//    }
//}

$e = new ExtendedConcretePoo();
$r = $e->poo();

Expected result:
----------------
No compilation errors.

Actual result:
--------------
Declaration of ExtendedConcretePoo::poo(): ExtendedConcretePoo must be compatible with AbstractPoo::poo()