Port `iter_matching_entrypoints` to `importlib.metadata`

[flying-sheep]

When calling _version_from_entrypoints → iter_matching_entrypoints, we should use importlib.metadata instead of pkg_resources, as pkg_resources isn’t the standard way to do this, and is also buggy in this context (see pypa/setuptools#2531)

The changes required would be pretty minimal:

requirements:

importlib_metadata; python_version < "3.8"

code:

try:
    from importlib.metadata import entry_points
except ImportError:
    from importlib_metadata import entry_points

[RonnyPfannschmidt]

i consider this low prio as the issue can't affect setuptools_scm in the intended usage scsenario as of now

additionally this poses a issue as i don't really want to add the extra dependency for old pythons

so i may decide to just leave it be until the pythons that don't have importlib_metadata no longer need to be supported

[flying-sheep]

Can you please elaborate on why that isn’t the intended usage scenario? Your readme says:

In order to use setuptools_scm from code that is one directory deeper than the project's root, you can use:

from setuptools_scm import get_version
version = get_version(root='..', relative_to=__file__)

We do exactly that, and the setuptools maintainers explicitly ask you to no longer use pkg_resources.

If you want to keep it, in order to avoid hard-to-debug breakage, please create a new WorkingSet and use that instead of the global one.

additionally this poses a issue as i don't really want to add the extra dependency for old pythons

why is that?

[RonnyPfannschmidt]

In the use case for setuptools_scm a stale workingset is typically not a issue, in particular with more modern tools around,
However additional dependencies make packaging more painful

That Being said, if a pr is submitted to use importlib on pythons that support it, im happy to merge and release

[jaraco]

Thanks Ronny. I support this initiative. Even though pkg_resources isn't deprecated, I am working toward deprecation and discouraging its use. I'll be happy to shepherd these changes as well. Thanks flying-sheep for the effort.

[flying-sheep]

That Being said, if a pr is submitted to use importlib on pythons that support it, I’m happy to merge and release

Entirely possible!

Are you actually importing anything from setuptools apart from pkg_resources.iter_entry_points? This might actually reduce the amount of runtime dependencies.

[flying-sheep]

pkg_resources is now officially deprecated:

Use of pkg_resources is discouraged in favor of importlib.resources, importlib.metadata, and their backports (resources, metadata). Please consider using those libraries instead of pkg_resources.

@RonnyPfannschmidt what’s the plan?

[RonnyPfannschmidt]

given that setup_requires usage is now deprecated, lets add it for the next feature release

[flying-sheep]

Okay! Since #526 is merged, this should be very simple. I updated #514