Problem with abstract classes

[Davanum Srinivas (DIMS)]

The following test:

    def test_remove_with_abstract_class_inheritance(self):
        @six.add_metaclass(abc.ABCMeta)
        class AbstractSerializer(object):
            pass

        @removals.remove(version="2.9", removal_version="3.0")
        class ConcreteSerializer(AbstractSerializer):
            pass

        class MyConcreteSerializer(ConcreteSerializer):
            pass

        MyConcreteSerializer()

Ends up with the following error in python 2.7:

Traceback (most recent call last):
  File "debtcollector/tests/test_deprecation.py", line 546, in test_remove_with_abstract_class_inheritance
    class MyConcreteSerializer(ConcreteSerializer):
  File "/Users/dims/openstack/oslo/debtcollector/.tox/py27/bin/../lib/python2.7/abc.py", line 87, in __new__
    cls = super(ABCMeta, mcls).__new__(mcls, name, bases, namespace)
TypeError: Error when calling the metaclass bases
    metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

And ends up with the following error in python 3.4:

Traceback (most recent call last):
  File "/Users/dims/openstack/oslo/debtcollector/debtcollector/tests/test_deprecation.py", line 549, in test_remove_with_abstract_class_inheritance
    MyConcreteSerializer()
TypeError: 'tuple' object is not callable

[Davanum Srinivas (DIMS) (dims-v)]

Note that this showed up in a real life situation :) when we added deprecation to RequestContextSerializer in oslo.messaging and we will be breaking ironic:

https://s3.amazonaws.com/archive.travis-ci.org/jobs/93447606/log.txt
https://s3.amazonaws.com/archive.travis-ci.org/jobs/93447607/log.txt

[Joshua Harlow (harlowja)]

Related to (same as): https://github.com/GrahamDumpleton/wrapt/issues/51

[Matt Riedemann (mriedem)]

This broke ironic, see bug 1524041.

[Joshua Harlow (harlowja)]

https://review.openstack.org/#/c/260117/ is an alternative for this weakness....