Eliminate dependency on deprecated setuptools.pkg_resources

[ferdnyc]

This PR eliminates use of setuptools' deprecated pkg_resources in hotdoc.utils.utils and hotdoc.extensions.gi.utils, substituting equivalent APIs provided by importlib.metadata.entry_points().

The entry_points() function used is actually imported from backports.entry_points_selectable (a new dependency, added to setup.py), which ensures that calls to entry_points() can take filtering arguments even in Python < 3.10, where importlib.metadata didn't natively support such usage.

(In practice, for recent Python 3.10+ releases, backports.entry_points_selectable.entry_points will be importlib.metadata.entry_points.)

The resulting hotdoc package passes all unit tests in hotdoc.tests on Python 3.12, even in a virtual environment with the setuptools package removed:

$ python3 -m unittest
.............................................................................................................
/usr/lib64/python3.12/tempfile.py:936: ResourceWarning:
 Implicitly cleaning up <TemporaryDirectory '/tmp/tmpe0jsh57p'>
  _warnings.warn(warn_message, ResourceWarning)
............
----------------------------------------------------------------------
Ran 121 tests in 3.232s

OK

hotdoc from the master branch, in that same situation, fails several tests outright, and skips over 80% of them:

$ python3 -m unittest
[...]
======================================================================
ERROR: hotdoc.tests.test_hotdoc (unittest.loader._FailedTest.hotdoc.tests.test_hotdoc)
----------------------------------------------------------------------
ImportError: Failed to import test module: hotdoc.tests.test_hotdoc
Traceback (most recent call last):
  File "/usr/lib64/python3.12/unittest/loader.py", line 394, in _find_test_path
    module = self._get_module_from_name(name)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/unittest/loader.py", line 337, in _get_module_from_name
    __import__(name)
  File ".../hotdoc/tests/test_hotdoc.py", line 30, in <module>
    from hotdoc.utils.utils import touch
  File ".../hotdoc/utils/utils.py", line 37, in <module>
    import pkg_resources
ModuleNotFoundError: No module named 'pkg_resources'


----------------------------------------------------------------------
Ran 19 tests in 0.002s

FAILED (errors=11)

[ferdnyc]

Some notes.

[ferdnyc]

These are added simply because they're used in the get_language_classes() function later on, but would have been undefined if they'd actually been called.

[ferdnyc]

This is here (despite ep_name never being used) because the results of importlib.metadata.entry_points() are documented as not being validated; invoking any property is the suggested means of triggering validation.

[ferdnyc]

By the same token, entry_point.name (the equivalent of entry_point.module_name from pkg_resources isn't necessarily going to exist on every result from entry_points(), so we can't rely on it for logging. Logging the string value of entry_point ensures that it'll be logged even if it isn't a valid EntryPoint object.

[ferdnyc]

Same validation issue here; since we can't be sure entry_point has a .module property, we need to check it inside the try:.

[ferdnyc]

For the record, I didn't regenerate the pinned requirements.txt with pip-compile, because that process seems somewhat broken. Pinning requirements versions, though it sounds nice in theory, often has the unwanted side-effect of locking you in to a particular Python version.

In this case, pip install -r requirements.txt fails under Python 3.12, because the pinned lxml version isn't compatible.

Fortunately, pip install -e . uses the unpinned dependency from setup.py, so it installs an lxml that's compatible with Python 3.12.

[MathieuDuponchelle]

Thanks A TON for looking at this :)

[ferdnyc]

I believe this is now fixed. I also added importlib_metadata as an explicit dependency in Python < 3.10, even though backports.entry_points_selectable will always pull it in if needed.

(I'm now importing it explicitly to access its distributions() function, instead of relying solely on the backports entry_points(), so I figured it made sense to be explicit about the dependency.)

[MathieuDuponchelle]

lgtm now, huge thanks again for performing maintenance on this project :)