bpo-42382: Make sure each EntryPoint carries it's Distribution information

[s0undt3ch]

This avoids a low performance workaround to get the EntryPoint's Distribution, for example:

USE_IMPORTLIB_METADATA_STDLIB = USE_IMPORTLIB_METADATA = False
try:
    # Py3.8+
    import importlib.metadata

    USE_IMPORTLIB_METADATA_STDLIB = True
except ImportError:
    # < Py3.8 backport package
    import importlib_metadata

    USE_IMPORTLIB_METADATA = True


def get_distribution_from_entry_point(entry_point):
    loaded_entry_point = entry_point.load()
    if isinstance(loaded_entry_point, types.ModuleType):
        module_path = loaded_entry_point.__file__
    else:
        module_path = sys.modules[loaded_entry_point.__module__].__file__
    if USE_IMPORTLIB_METADATA_STDLIB:
        distributions = importlib.metadata.distributions
    else:
        distributions = importlib_metadata.distributions

    for distribution in distributions():
        try:
            relative = pathlib.Path(module_path).relative_to(
                distribution.locate_file("")
            )
        except ValueError:
            pass
        else:
            if relative in distribution.files:
                return distribution

https://bugs.python.org/issue42382

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[s0undt3ch]

CLA signed 🎉

Sorry for the direct ping @jaraco but I think you're probably the best person to review?

[s0undt3ch]

Polite ping.

[asvetlov]

@brettcannon you might be interested in review the PR

[jaraco]

Always happy to have a direct ping. I missed the earlier notice (or hadn't yet gotten to it), so the bump helped ;)

[jaraco]

Overall, this looks good. I think it's on the right track. I'd like to explore the possibility of not storing the 'name' separately from the Distribution object (just store the object). I'm unsure what cases that might break though.

Also, I'll probably want to submit the Python 3.6-compatible backport at importlib_metadata first, and then incorporate those changes into CPython as part of the porting process.

That's not strictly necessary, though. It is faster and easier to test in that project.

[jaraco]

Superseded by #23758.