Unable to suppress typechecker nitpicks

[jaraco]

When merging 3841656 from jaraco/skeleton#136, the tests started failing.

____________________________ backports/__init__.py _____________________________
1: error: Unused "type: ignore" comment  [unused-ignore]
_________________________________ test session _________________________________
mypy exited with status 1.
_____________________ backports/entry_points_selectable.py _____________________
24: error: Unused "type: ignore" comment  [unused-ignore]
26: error: "type: ignore" comment without error code (consider "type: ignore[attr-defined, no-redef]" instead)  [ignore-without-code]
31: error: Unused "type: ignore" comment  [unused-ignore]
35: error: Unused "type: ignore" comment  [unused-ignore]
38: error: Unused "type: ignore" comment  [unused-ignore]
39: error: Unused "type: ignore" comment  [unused-ignore]
41: error: "type: ignore" comment without error code (consider "type: ignore[import-not-found]" instead)  [ignore-without-code]

I fixed all the errors on Python 3.12 in 6413a18, but now tests fail on Python 3.8 and 3.9.

_____________________ backports/entry_points_selectable.py _____________________
38: error: Name "metadata" already defined (by an import)  [no-redef]
39: error: Incompatible import of "distributions" (imported name has type overloaded function, local name has type "Callable[[KwArg(Any)], Iterable[importlib_metadata.Distribution]]")  [assignment]
39: error: Incompatible import of "EntryPoint" (imported name has type "Type[importlib.metadata.EntryPoint]", local name has type "Type[importlib_metadata.EntryPoint]")  [assignment]
41: error: Unused "type: ignore" comment  [unused-ignore]

@Avasam Can you work out a solution to get mypy checks to pass on all Python versions?

[Avasam]

Just by reading the commit, my initial guess is that you have dependencies (or versions of such) that are installed in some Python environments but not others.
You can either:

• Use sys.version_info and sys.platform checks instead of try-except-ing imports (most recommended when possible)
• Install all dependencies unconditionally in your type testing environment
• Lock mypy's python_version to a specific version (not recommended¹, setuptools only does it currently because of distutils and Type-check on all Python versions pypa/setuptools#4352 intends to solve that)
• Set ignore_missing_imports = True for those modules and deal with it later (like Link to issues in mypy.ini for non py.typed dependencies pypa/setuptools#4561)

You might find this comment relevant: pypa/setuptools#4586 (comment)

Footnotes

1. I actually do recommend setting python_version in the configs so that editors work on the oldest supported Python version by default. BUT only if you have your CI explicitly pass the --python-version flag to override it ↩

[jaraco]

• Use sys.version_info and sys.platform checks instead of try-except-ing imports (most recommended when possible)

I can't use this technique. The implementation needs to remain unchanged.

• Install all dependencies unconditionally in your type testing environment

I didn't think this would work - because importlib_metadata was already installed in Python 3.8, but it does seem to shift the problem such that other exclusions can be made to work.

• Lock mypy's python_version to a specific version (not recommended1, setuptools only does it currently because of distutils and

I'll probably disable mypy checks before going into this kind of customization.

[jaraco]

I'm hoping this fix also works for jaraco/oathtool#4.