Description:
------------
Hello,

I have come across some special behaviour in inheritance. I am not sure how to clearly describe the bug, please come to see the example below.

Code below throws following error:

Fatal error: Declaration of ParentType::accept(ParentVisitor $visitor): mixed must be compatible with ChildType::accept(ChildVisitor $visitor): mixed in /in/sYmmm on line 9


BUT the code in the example works correctly when I switch the order of interfaces in extends for the "Final" interface.

interface Final extends ChildType, OtherInterface {}

Compiles successfully.


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

interface ChildVisitor { /* some visiting methods */ }

interface ParentVisitor extends ChildVisitor { /* some extra visiting methods */ }

interface ParentType
{
    public function accept(ParentVisitor $visitor) : mixed;
}

interface ChildType extends ParentType
{
    public function accept(ChildVisitor $visitor) : mixed;
}

interface OtherInterface extends ParentType {}

interface Final extends OtherInterface, ChildType {}

Expected result:
----------------
Compile successfully.

Actual result:
--------------
Fatal error: Declaration of ParentType::accept(ParentVisitor $visitor): mixed must be compatible with ChildType::accept(ChildVisitor $visitor): mixed in /in/sYmmm on line 9