Migrate from pkg_resources

[stanislavlevin]

The usage of pkg_resources (subpackage of setuptools distribution) is discouraged.

https://setuptools.pypa.io/en/latest/pkg_resources.html:

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

ipa healthcheck uses several points of pkg_resources:

• pkg_resources.iter_entry_points to access entry points.
  migration: https://importlib-metadata.readthedocs.io/en/latest/migration.html#pkg-resources-iter-entry-points
• pkg_resources.get_distribution to access a distribution.
  migration: https://importlib-metadata.readthedocs.io/en/latest/migration.html#pkg-resources-get-distribution
• __import__('pkg_resources').declare_namespace
  https://packaging.python.org/en/latest/guides/packaging-namespace-packages/#creating-a-namespace-package
  I'm not sure about the purpose of namespace packages here, since the plugin system is build on top of entry points.

Compatibility note: importlib.metadata is in stdlib since Python 3.8:
https://docs.python.org/3/library/importlib.metadata.html

[rcritten]

@stanislavlevin are you going to work on this or just reporting the issue? I ask because sometimes you file an issue and an hour later drop a huge patch :-)

healthcheck is still used on some older python versions, 3.6.8, in RHEL 8. So this may be a reason to do the first branch.

[stanislavlevin]

@rcritten, yes, I have such a bad habit :-)
But this maybe the breaking change, that's why I asked first.

So, if you say ipa-healthcheck must support Python 3.6.8 this issue maybe postponed to the Python3.8 times or as an alternative solution the external importlib_metadata package can be used as a fallback.

[rcritten]

@stanislavlevin I think it's a good idea to keep up with current standards. It just might make backports a bit more tricky. I'll be supporting RHEL 8 for another few years but I don't want that to stop progress.

So I think it's worth looking into and we'll see what ramifications there are. Thanks for bringing this up.

[stanislavlevin]

@rcritten, could you please clarify the purpose of namespace packages in this project? Is it still needed or can be dropped?

[rcritten]

It is to support the cluster checking as a separate namespace. The intention was to share the healthcheck core but keep the cluster plugins separate. The cluster checking never really went anywhere and was de-prioritized. I'm not sure if that work is going to pick up again but the idea was to check things that could only be done when examining the entire IPA topology.