Unsupported packaging <22.0

[stanislavlevin]

As of now, system or user installed packaging is imported first:

pyproject_installer/src/pyproject_installer/lib/__init__.py

Lines 7 to 10 in 2adcf3a

	try:
	from packaging import requirements, markers, specifiers
	except ImportError:
	from .._vendor.packaging import requirements, markers, specifiers

This was made to make it possible for distributions to debundle packaging from this project.
But in practice, it can lead to unpredictable results and can't be properly supported by this project.

For example, the tests suite fails against packaging < 22.0:

_______________________ test_config_sync_verify_changed[data3] _______________________

data = (['foo', 'foo1'], ['bar', 'foobar', 'foo1'], {'foo': {'extra_deps': ['foo'], 'new_deps': ['bar', 'foobar']}})
depsconfig = <function depsconfig.<locals>._gen_depsconfig at 0x7f77bb266820>
mock_collector = <function mock_collector.<locals>._collector at 0x7f77bb266af0>
capsys = <_pytest.capture.CaptureFixture object at 0x7f77bb3428e0>

    @pytest.mark.parametrize(
        "data",
        (
            (["foo", "bar"], [], {"foo": {"extra_deps": ["bar", "foo"]}}),
            ([], ["foo", "bar"], {"foo": {"new_deps": ["bar", "foo"]}}),
            (
                ["foo"],
                ["bar", "foobar"],
                {"foo": {"extra_deps": ["foo"], "new_deps": ["bar", "foobar"]}},
            ),
            (
                ["foo", "foo1"],
                ["bar", "foobar", "foo1"],
                {"foo": {"extra_deps": ["foo"], "new_deps": ["bar", "foobar"]}},
            ),
        ),
    )
    def test_config_sync_verify_changed(data, depsconfig, mock_collector, capsys):
        """Sync changed source with verify"""
    
        action = "sync"
        old_reqs, new_reqs, diff = data
    
        # prepare source config
        input_conf = {
            "sources": {
                "foo": {
                    "srctype": "mock_collector",
                    "deps": old_reqs,
                },
            },
        }
        depsconfig_path = depsconfig(json.dumps(input_conf))
    
        mock_collector(new_reqs)
    
        with pytest.raises(DepsUnsyncedError):
            deps_command(action, depsconfig_path, srcnames=[], verify=True)
    
        expected_conf = deepcopy(input_conf)
        expected_conf["sources"]["foo"]["deps"] = sorted(new_reqs)
    
        actual_conf = json.loads(depsconfig_path.read_text(encoding="utf-8"))
        assert actual_conf == expected_conf
    
        expected_out = json.dumps(diff, indent=2) + "\n"
    
        captured = capsys.readouterr()
        assert not captured.err
>       assert captured.out == expected_out
E       assert ('{\n'\n '  "foo": {\n'\n '    "extra_deps": [\n'\n '      "foo",\n'\n '      "foo1"\n'\n '    ],\n'\n '    "new_deps": [\n'\n '      "bar",\n'\n '      "foo1",\n'\n '      "foobar"\n'\n '    ]\n'\n '  }\n'\n '}\n') == ('{\n'\n '  "foo": {\n'\n '    "extra_deps": [\n'\n '      "foo"\n'\n '    ],\n'\n '    "new_deps": [\n'\n '      "bar",\n'\n '      "foobar"\n'\n '    ]\n'\n '  }\n'\n '}\n')
E           {
E             "foo": {
E               "extra_deps": [
E         -       "foo"
E         +       "foo",
E         ?            +
E         +       "foo1"
E               ],
E               "new_deps": [
E                 "bar",
E         +       "foo1",
E                 "foobar"
E               ]
E             }
E           }

/usr/src/RPM/BUILD/python3-module-pyproject-installer-0.5.2/tests/unit/test_deps/test_deps_config.py:443: AssertionError

This happens because packaging < 22.0 doesn't support comparison of requirement objects and sets of those:

pypa/packaging#499