Add setuptools stubs

[srittau]

Still work in progress: There are mypy failures.

[srittau]

I'm unclear why pytype fails, maybe @rchen152 has some ideas.

[rchen152]

Huh, pytype thinks SetuptoolsDeprecationWarning is a module - maybe because of how it's imported? Looking into it.

[rchen152]

Still trying to figure out how to fix this, but in the meantime, I did find a workaround: if you replace all from .. import <SomeClass> statements with from setuptools import <SomeClass>, that appears to make pytype happy.

[srittau]

stubtest crashes. Maybe @hauntsaninja has an idea.

[hauntsaninja]

Looks like something in setuptools that looks like a function raises on inspect.signature. We could also just catch TypeError here: https://github.com/python/mypy/blob/6fd2dc2403889f7104648d8bfbb8df3f5e83b63f/mypy/stubtest.py#L670

[Akuli]

Apparently stubtest has an instance of NonDataProperty:

>>> from setuptools.command.test import NonDataProperty
>>> import inspect
>>> inspect.signature(NonDataProperty)
<Signature (fget)>
>>> inspect.signature(NonDataProperty(print))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.7/inspect.py", line 3083, in signature
    return Signature.from_callable(obj, follow_wrapped=follow_wrapped)
  File "/usr/lib/python3.7/inspect.py", line 2833, in from_callable
    follow_wrapper_chains=follow_wrapped)
  File "/usr/lib/python3.7/inspect.py", line 2208, in _signature_from_callable
    raise TypeError('{!r} is not a callable object'.format(obj))
TypeError: <setuptools.command.test.NonDataProperty object at 0x7f67b94a3ef0> is not a callable object
>>> 

[srittau]

Let's wait for the next mypy release: python/mypy#10884, also this requires updated distutils.

[hauntsaninja]

Here's a fix in stubtest: python/mypy#10884
Might be easiest to just remove setuptools.command.test.test.test_args from this PR to unblock (or avoid typing it as a method)

[hauntsaninja]

@srittau I pushed a workaround, so CI is now green if you want to merge.

[srittau]

Should we merge this, though? It will not work with current mypy as it requires newer stdlib stubs. I'm 50/50 on merging now vs after the next mypy release.

[hauntsaninja]

Well, I figured it's nice to have the option! :-)
I think I'd lean towards merging: other type checkers can benefit, a mypy release probably isn't imminent (if I had to guess, I'd say the next one would be around Python 3.10 release), setuptools.__init__ should work and that's 99% of setuptools usage.

[rchen152]

I know you've already worked around the pytype issue, but anyway, pytype release 2021.08.03 should fix it ^^

[srittau]

I marked it as ready to merge if someone has time to review it and thinks we should merge now.