Fix issue with opcache preload and class_alias

[starred-gijs]

Fixes #128

Q	A
Bugfix	yes
BC Break	no
New Feature	no
RFC	no
QA	no

Description

Not sure how to test this, except the manual tests I ran.

[boesing]

The problem is, that the whole idea of replacing container-interop is to replace it from within THIS repository.
If we now allow other interfaces to replace container-interop, the whole idea of why we made this change won't work anymore. Because your application will break for sure in case that the Interop\ContainerInterop\ContainerInterface is not exactly the same interface as Psr\Container\ContainerInterface.

---

So do I understand correct, that calling class_alias in an opcached application breaks when this was done after the initial loading of that script?

When we do add interface_exists here, we should at least verify that the interface which does exist is pointing the expected PSR-11 interface.

Something like this (which does obv. not work, but I don't know how to verify that):

interface Foo
{}
if (!interface_exists(Bar::class)) {
     class_alias(Foo::class, 'Bar');
}

assert(Bar::class === Foo::class);

Because silently allow projects to have an existing implementation of the interop interface might break projects as we changed the method type-hints to require PSR-11 implementations.

(Is it clear what I want to point out? I am not sure if that was clear...)

[Ocramius]

That's kinda why I wanted to test this: I think this might be a limitation of preloading, which only stores the declarations.