Make class_alias() work with internal classes

[nicolas-grekas]

Description

I was reminded today that class_alias() doesn't work with internal classes.

I have a use case where a class can be defined either by userland or by an optional extension, and I'd ideally need to alias it. Right now, I have to create a proxy class instead of an alias, and proxy classes are tedious to write+maintain.

Could this limitation be removed?

[nikic]

I've run into this as well. I think from a technical perspective, the main complication is that a) we can't increment the refcount of an internal class during a request and b) we will have an internal class appear in the region for userland classes in the class table. Class aliases already use a special flag in the class table to distinguish them, so it would be possible to not increment the refcount and skip the aliases entirely for destruction purposes.