Switch from pkginfo to packaging for parsing distribution metadata

[dnicolodi]

The packaging package is maintained by the PyPA and it is the de-facto reference implementation for the packaging standards. Using packaging for parsing metadata guarantees support for the latest metadata versions.

warehouse, the Python package index implementation used by PyPI, also uses packaging for parsing metadata. This guarantees that metadata parsing is the same on the client and server side, for the most prominent index.

[dnicolodi]

This passes the unit tests, except for this one

twine/tests/test_package.py

Lines 383 to 437 in dd61356

	@pytest.mark.parametrize(
	"read_data, missing_fields",
	[
	pytest.param(
	b"Metadata-Version: 102.3\nName: test-package\nVersion: 1.0.0\n",
	"Name, Version",
	id="unsupported Metadata-Version",
	),
	pytest.param(
	b"Metadata-Version: 2.3\nName: UNKNOWN\nVersion: UNKNOWN\n",
	"Name, Version",
	id="missing Name and Version",
	),
	pytest.param(
	b"Metadata-Version: 2.2\nName: UNKNOWN\nVersion: UNKNOWN\n",
	"Name, Version",
	id="missing Name and Version",
	),
	pytest.param(
	b"Metadata-Version: 2.3\nName: UNKNOWN\nVersion: 1.0.0\n",
	"Name",
	id="missing Name",
	),
	pytest.param(
	b"Metadata-Version: 2.2\nName: UNKNOWN\nVersion: 1.0.0\n",
	"Name",
	id="missing Name",
	),
	pytest.param(
	b"Metadata-Version: 2.3\nName: test-package\nVersion: UNKNOWN\n",
	"Version",
	id="missing Version",
	),
	pytest.param(
	b"Metadata-Version: 2.2\nName: test-package\nVersion: UNKNOWN\n",
	"Version",
	id="missing Version",
	),
	],
	)
	def test_pkginfo_returns_no_metadata(read_data, missing_fields, monkeypatch):
	"""Raise an exception when pkginfo can't interpret the metadata.
	This could be caused by a version number or format it doesn't support yet.
	"""
	monkeypatch.setattr(package_file.wheel.Wheel, "read", lambda _: read_data)
	filename = "tests/fixtures/twine-1.5.0-py2.py3-none-any.whl"
	with pytest.raises(exceptions.InvalidDistribution) as err:
	package_file.PackageFile.from_filename(filename, comment=None)
	assert (
	f"Metadata is missing required fields: {missing_fields}." in err.value.args[0]
	)
	assert "1.0, 1.1, 1.2, 2.0, 2.1, 2.2" in err.value.args[0]

which is not surprising as the metadata validation raises different exceptions now. I don't know whether the new code should be adapted to raise the same exceptions or it is acceptable to adjust the test.

[dnicolodi]

I've adjusted the test mentioned above. The only remaining issue is that packaging and pkginfo and thus twine disagree on the name of two metadata fields: pkginfo uses platform and supported_platform, while packaging uses platforms and supported_platforms. I don't know who is right here. There is a test failing because of this.