TST: harden against environment variables affecting meson-python

[dnicolodi]

Fixes #760.

[rgommers]

Thanks @dnicolodi! LGTM, and confirmed locally that it fixes the failures in test_tags.py that show up on main when MACOSX_DEPLOYMENT_TARGET is set.

It's not entirely clear to me why tests in test_wheel.py aren't also failing for the same reason, but they do seem to pass in the Nix CI. So let's get this in and call it good - in case another issue gets reported we can revisit.

[dnicolodi]

It's not entirely clear to me why tests in test_wheel.py aren't also failing for the same reason

Indeed they should. I wonder if they did not show up in the Nix CI as failing because they were disabled already.

[dnicolodi]

The tests fail locally if I set $MACOSX_DEPLOYMENT_TARGET. I'll extend the fix to these tests too.

I've also found an error in the documentation. https://mesonbuild.com/meson-python/reference/environment-variables.html#envvar-MACOSX_DEPLOYMENT_TARGET says that 11 should be a valid value for this environment variable, but it is not parsed correctly, it should be 11.0.

[rgommers]

We have (or had?) some compat code to ensure that both 11 and 11.0 are valid. packaging made a mess in the 10.x -> >=11 transition, and we had users using both. 11.0 is canonical indeed, but that's also weird given that packaging disallows 11.x with x != 0.

[dnicolodi]

We have (or had?) some compat code to ensure that both 11 and 11.0 are valid.

I don't remember having it and I don't find trace of it in the git history. There are a lot of details in the comments in the implementation

meson-python/mesonpy/_tags.py

Lines 94 to 160 in 1e69e7a

	def _get_macosx_platform_tag() -> str:
	ver, _, arch = platform.mac_ver()
	# Override the architecture with the one provided in the
	# _PYTHON_HOST_PLATFORM environment variable. This environment
	# variable affects the sysconfig.get_platform() return value and
	# is used to cross-compile python extensions on macOS for a
	# different architecture. We base the platform tag computation on
	# platform.mac_ver() but respect the content of the environment
	# variable.
	try:
	arch = os.environ.get('_PYTHON_HOST_PLATFORM', '').split('-')[2]
	except IndexError:
	pass
	# Override the macOS version if one is provided via the
	# MACOSX_DEPLOYMENT_TARGET environment variable.
	try:
	version = tuple(map(int, os.environ.get('MACOSX_DEPLOYMENT_TARGET', '').split('.')))[:2]
	except ValueError:
	version = tuple(map(int, ver.split('.')))[:2]
	# Python built with older macOS SDK on macOS 11, reports an
	# unexising macOS 10.16 version instead of the real version.
	#
	# The packaging module introduced a workaround
	# https://github.com/pypa/packaging/commit/67c4a2820c549070bbfc4bfbf5e2a250075048da
	#
	# This results in packaging versions up to 21.3 generating
	# platform tags like "macosx_10_16_x86_64" and later versions
	# generating "macosx_11_0_x86_64". Using the latter would be more
	# correct but prevents the resulting wheel from being installed on
	# systems using packaging 21.3 or earlier (pip 22.3 or earlier).
	#
	# Fortunately packaging versions carrying the workaround still
	# accepts "macosx_10_16_x86_64" as a compatible platform tag. We
	# can therefore ignore the issue and generate the slightly
	# incorrect tag.
	# The minimum macOS ABI version on arm64 is 11.0. The macOS SDK
	# on arm64 silently bumps any compatibility version specified via
	# the MACOSX_DEPLOYMENT_TARGET environment variable to 11.0.
	# Despite the platform ABI tag being intended to be a minimum
	# compatibility version, pip refuses to install wheels with a
	# platform tag specifying an ABI version lower than 11.0. Use
	# 11.0 as minimum ABI version on arm64.
	if arch == 'arm64' and version < (11, 0):
	version = (11, 0)
	major, minor = version
	if major >= 11:
	# For macOS reelases up to 10.15, the major version number is
	# actually part of the OS name and the minor version is the
	# actual OS release. Starting with macOS 11, the major
	# version number is the OS release and the minor version is
	# the patch level. Reset the patch level to zero.
	minor = 0
	if _32_BIT_INTERPRETER:
	# 32-bit Python running on a 64-bit kernel.
	if arch == 'ppc64':
	arch = 'ppc'
	if arch == 'x86_64':
	arch = 'i386'
	return f'macosx_{major}_{minor}_{arch}'

The issue is that here

meson-python/mesonpy/_tags.py

Line 143 in 1e69e7a

major, minor = version

we expect the version to have two components, and 11 has only one.

I don't know whether it is better to fix the implementation or the docs. I don't know how to check which values are accepted by clang.

[dnicolodi]

I don't know how to check which values are accepted by clang.

That was actually easy: clang errors out when it does not understand the env var format. 11, 11.0, 11.0.0 are all valid.

I'll fix the implementation to accept the 11 variant too.