All classes must be final, except abstract ones and Doctrine entities.
No exception and no configuration are intentional. Beside Doctrine entities and of course abstract classes, there is no single reason not to declare all classes final. If you want to subclass a class, mark the parent class as abstract and create two child classes, one empty if necessary: you'll gain much more fine grained type-hinting. If you need to mock a standalone class, create an interface, or maybe it's a value-object that shouldn't be mocked at all. If you need to extend a standalone class, create an interface and use the Composite pattern. If you aren't ready yet for serious OOP, go with FinalInternalClassFixer, it's fine.
Warning
Using this rule is risky.
Risky when subclassing non-abstract classes.
--- Original
+++ New
<?php
-class MyApp {}
+final class MyApp {}