tags: MacOS base_version via dynlib files

[pradyunsg]

macOS version dectection via pep425tags.py uses any dynlib files to determine the base_version of macOS to support in the wheel (see calculate_macosx_platform_tag. packaging does not seem to have this ability.

Originally posted by @mattip in pypa/wheel#346 (comment)

And this was one of the biggest road blocks to switching to packaging.

Originally posted by @agronholm in pypa/wheel#346 (comment)

---

This looks like a case of the fork of pep425tags.py in wheel, diverging from the one in pip. Such cases were expected, and (based on a quick skim) I don't see a reason to not add this functionality.

/cc @brettcannon

[Czaki]

Hi. I'm author of this code to detect minimum macos version. If there are some questions I can try to explain it.

[pradyunsg]

For reference, the current MacOS-specific platform code in packaging.tags is:

packaging/packaging/tags.py

Lines 389 to 416 in ed0a58f

	def mac_platforms(version=None, arch=None):
	# type: (Optional[MacVersion], Optional[str]) -> Iterator[str]
	"""
	Yields the platform tags for a macOS system.
	The `version` parameter is a two-item tuple specifying the macOS version to
	generate platform tags for. The `arch` parameter is the CPU architecture to
	generate platform tags for. Both parameters default to the appropriate value
	for the current system.
	"""
	version_str, _, cpu_arch = platform.mac_ver() # type: ignore
	if version is None:
	version = cast("MacVersion", tuple(map(int, version_str.split(".")[:2])))
	else:
	version = version
	if arch is None:
	arch = _mac_arch(cpu_arch)
	else:
	arch = arch
	for minor_version in range(version[1], -1, -1):
	compat_version = version[0], minor_version
	binary_formats = _mac_binary_formats(compat_version, arch)
	for binary_format in binary_formats:
	yield "macosx_{major}_{minor}_{binary_format}".format(
	major=compat_version[0],
	minor=compat_version[1],
	binary_format=binary_format,
	)

And the MacOS-specific platform code in wheel's pep425tags.py is:

https://github.com/pypa/wheel/blob/bb33181c3b3558f3bdf8dc4a526a64e2f73bcd96/src/wheel/pep425tags.py#L107-L172

There is significant difference (which is why this is a blocker for wheel) and the corresponding wheel PR is pypa/wheel#314.

[brettcannon]

Do note that the code in 'wheel' interrogates built files as part of the making of a wheel which we could never do in order to calculate what tags a running interpreter supports.

So while I'm not opposed to incorporating similar code here, it is a shift in what packaging.tags was initially designed around and so the API shift will need handled appropriately as I don't think this is necessarily a drop-in change in the platform detection code.