Description:
------------
Going from "has a return value" to "no return value" is certainly not a valid covariant substitution (at least in theory, in practice void is null).

The void RFC doesn't cover the case at all.

https://wiki.php.net/rfc/void_return_type

It is not unlikely that this is currently allowed by accident.

Thank you.


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

class Foo
{
    public function aaa(){}
}

class Bar extends Foo
{
    public function aaa(): void{}
}

Expected result:
----------------
Error

Actual result:
--------------
No error