CI Tests failing (py 3.6 and 3.7) with version conflict: importlib_metadata

[itsayellow]

Describe the bug

Github CI tests are now failing for python 3.6 and python 3.7 with a version conflict. It appears to be due to the requirement for importlib-metadata < 2.0 and the provided importlib-metadata at v2.0.0.

I'm having trouble reading this Traceback. Is this due to virtualenv requiring importlib-metadata < 2.0?

Run nox --non-interactive --session tests-3.6
Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/pkg_resources/__init__.py", line 581, in _build_master
    ws.require(__requires__)
  File "/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/pkg_resources/__init__.py", line 898, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/pkg_resources/__init__.py", line 789, in resolve
    raise VersionConflict(dist, req).with_context(dependent_req)
pkg_resources.ContextualVersionConflict: (importlib-metadata 2.0.0 (/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages), Requirement.parse('importlib-metadata<2,>=0.12; python_version < "3.8"'), {'virtualenv'})

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.6.12/x64/bin/nox", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/pkg_resources/__init__.py", line 3126, in <module>
    @_call_aside
  File "/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/pkg_resources/__init__.py", line 3110, in _call_aside
    f(*args, **kwargs)
  File "/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/pkg_resources/__init__.py", line 3139, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/pkg_resources/__init__.py", line 583, in _build_master
    return cls._build_from_requirements(__requires__)
  File "/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/pkg_resources/__init__.py", line 596, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
  File "/opt/hostedtoolcache/Python/3.6.12/x64/lib/python3.6/site-packages/pkg_resources/__init__.py", line 784, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'importlib-metadata<2,>=0.12; python_version < "3.8"' distribution was not found and is required by virtualenv

How to reproduce

Expected behavior

[uranusjr]

It’s likely due to nox requiring an incompatible importlib-metadata version. Would it help to populate the CI environment (the one containing nox, not the one nox creates) with the new pip resolver (--use-feature=2020-resolver)?

[itsayellow]

I don't quite understand what's going on, because when I run the tests locally using nox, there is no conflict on my local system.

I'm not sure what the mention of virtualenv in the error message means, it's hard to tell what the error is saying. Theoretically our version of nox shouldn't be using virtualenv.

[itsayellow]

Oh I see what's happening on my system. To run my nox I'm using python 3.8 even when the tests use other python versions. So I never have a need for importlib-metadata which is only for python < 3.8.

Even @cs01's native-venv fork of nox still has virtualenv as a requirement. And virtualenv requires importlib-metadata < 2.0.0 for any python < 3.8. So with an existing importlib-metadata (required by something else presumably, or just preinstalled on github?) the virtualenv requirements fail.

[itsayellow]

Looks like on my local system I can replicate the failure using python3.7 running nox.

Also, --use-feature=2020-resolver seems to fix the problem!

Here is what causes the conflict. nox requires both:

• argcomplete requires importlib-metadata>=0.23,<3
• virtualenv requires importlib-metadata>=0.12,<2