Metaclass lost with slots=True

[YevIgn]

Hello.

Using a metaclass with slots=True, e.g.

@attr.s(slots=True)
class A(metaclass=abc.ABCMeta):
    @abc.abstractmethod
    def f(self):
        pass

Will lead to A being instantiable and type(A) being <class 'type'> (unlike the case with slots=False), as for slots to work the new class is generated in _make.py with:

cls = type(cls.__name__, cls.__bases__, cls_dict) [1]

This doesn't happen if this line is changed to:

cls = type(cls)(cls.__name__, cls.__bases__, cls_dict) [2]

With this change type(A) is <class 'abc.ABCMeta'> and A is no longer instantiable.
Can the class generation for slots be changed to something like [2] to avoid losing metaclasses or it is intentionally written as it is now and I am missing something?

[Tinche]

It's not intentional, it just hasn't come up until now. :)

Could you try applying the change, and if the tests pass contribute a PR? It'd be nice to add a test for this as well.