CI fails with "AttributeError: type object 'Callable' has no attribute '_abc_registry'"

[bluetech]

Something broke on CI:

    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\pip\_internal\commands\install.py", line 17, in <module>
      from pip._internal.cli.req_command import RequirementCommand, with_cleanup
    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\pip\_internal\cli\req_command.py", line 16, in <module>
      from pip._internal.index.collector import LinkCollector
    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\pip\_internal\index\collector.py", line 14, in <module>
      from pip._vendor import html5lib, requests
    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\pip\_vendor\requests\__init__.py", line 125, in <module>
      from . import utils
    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\pip\_vendor\requests\utils.py", line 25, in <module>
      from . import certs
    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\pip\_vendor\requests\certs.py", line 15, in <module>
      from pip._vendor.certifi import where
    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\pip\_vendor\certifi\__init__.py", line 1, in <module>
      from .core import contents, where
    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\pip\_vendor\certifi\core.py", line 12, in <module>
      from importlib.resources import path as get_path, read_text
    File "c:\hostedtoolcache\windows\python\3.8.5\x64\lib\importlib\resources.py", line 11, in <module>
      from typing import Iterable, Iterator, Optional, Set, Union   # noqa: F401
    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\typing.py", line 1359, in <module>
      class Callable(extra=collections_abc.Callable, metaclass=CallableMeta):
    File "D:\a\pytest\pytest\.tox\py38-unittestextras\lib\site-packages\typing.py", line 1007, in __new__
      self._abc_registry = extra._abc_registry
  AttributeError: type object 'Callable' has no attribute '_abc_registry'

See pypa/pip#8272

Originally posted by @The-Compiler in #7614 (comment)

[bluetech]

I think what happens is:

1. The windows-py38 CI job installs twisted
2. twisted depends on hyperlink
3. hyperlink just released a version with type annotation support: https://github.com/python-hyper/hyperlink/blob/master/CHANGELOG.md#2000
4. hyperlink depends on the typing backport package with typing ; python_version<"3.5"
5. pip has the mentioned bug pip install -e crashes on Python 3.8 when 'typing' is installed from PyPI because it runs a sub-command in such a way that site-packages comes before lib/python3.8 pypa/pip#8272 which causes it to break where the typing package gets used instead of the stdlib typing.

As far as I understand, from the way hyperlink added the typing dependency it should not get installed on Python >= 3.5, but I just tested it and it does indeed get installed, not sure why.

$ virtualenv venv
created virtual environment CPython3.8.5.final.0-64 in 112ms
  creator CPython3Posix(dest=venv, clear=False, global=False)
  seeder FromAppData(download=False, pip=latest, setuptools=latest, wheel=latest, via=copy)
  activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator
$ source venv/bin/activate
(venv) $ pip install hyperlink
Collecting hyperlink
  Using cached hyperlink-20.0.0-py2.py3-none-any.whl (48 kB)
Collecting idna>=2.5
  Using cached idna-2.10-py2.py3-none-any.whl (58 kB)
Processing /home/ran/.cache/pip/wheels/5e/5d/01/3083e091b57809dad979ea543def62d9d878950e3e74f0c930/typing-3.7.4.3-py3-none-any.whl
Installing collected packages: idna, typing, hyperlink
Successfully installed hyperlink-20.0.0 idna-2.10 typing-3.7.4.3

[bluetech]

This has been fixed in hyperlink.

[The-Compiler]

For the curious, here's the hyperlink issue: python-hyper/hyperlink#133