The assertion fails in the following example, but is ok with slots=False:

import attr, pickle

@attr.s(slots=True)
class MyClass(object):
    a = attr.ib()
    not_picklable = attr.ib()

    def __getstate__(self):
        return self.a, "replacement"

    def __setstate__(self, state):
        self.a, self.not_picklable = state

mc = MyClass("a", "b")
mc_new = pickle.loads(pickle.dumps(mc))
assert mc_new.not_picklable == "replacement"

This is clearly because attrs auto creates these methods on the new slots-class: https://github.com/python-attrs/attrs/blob/master/src/attr/_make.py#L601

Is there another prefered way to solve this, or would it be possible to support these methods also for slots-classes? If not, it would be good to clarify this in the documentation for slotted-classes, it says:

You can support protocol 0 and 1 by implementing __getstate__ and __setstate__ methods yourself. Those methods are created for frozen slotted classes because they won’t pickle otherwise. Think twice before using pickle though.

This is confusing to me, since implementing these methods have no effect for slotted classes?

Somewhat related:
#139
#475