I realize that this will be a controversial PR, I am opening this primarily for discussion.

My main reason for filing this is that it feels silly to add something like this to dynamic ACL plugins:

    @classmethod
    def generate_acls(cls, project, group=None):
        """ Required function that doesn't do anything. """
        pass
    @classmethod
    def remove_acls(cls, session, project):
        """ Required function that is unused. """
        pass

Especially if we want to move to preferring dynamic auth backends (because they would be required for instances that want to get rid of Gitolite).

I have rebased this on top of PR #3853 to make use of the class instantiation to still provide early errors for non-implemented, required functions.

It doesn't seem that silly to me.

:thumbsup:

I'm not quite sure about this one since the __init___ can easily be overwritten and therefore by-passing the checks in place here :(

I'm kinda thinking let's stick with this for now and re-consider when we approach 6.0

Sure, works for me.
It was really just as a suggestion :).