0.9.0 release produces macOS wheel platform tag that cannot be installed on Homebrew Python

[rgommers]

@mkoeppe noticed a problem with macOS wheel tags with Homebrew Python on Sage, see https://github.com/FFY00/meson-python/issues/91#issuecomment-1263004679. The linked Sage issue (https://trac.sagemath.org/ticket/34081#comment:90) shows:

[scipy-1.9.1] Using pip 22.2.2 from /Users/mkoeppe/s/sage/sage-rebasing/worktree-gcc11/local/var/lib/sage/venv-python3.10/lib/python3.10/site-packages/pip (python 3.10)
[scipy-1.9.1] Looking in links: /Users/mkoeppe/s/sage/sage-rebasing/worktree-gcc11/local/var/lib/sage/venv-python3.10/var/lib/sage/wheels
[scipy-1.9.1] ERROR: scipy-1.9.1-cp310-cp310-macosx_12_6_x86_64.whl is not a supported wheel on this platform.

@mkoeppe can you confirm that you built this wheel on macOS 12.6? If so, the wheel tag should be correct. However, there is a problem of course if pip refuses to install it, which we may have to work around.

Also, can you determine when it is installable? If you rename the wheel from 12_6 to say 12_3, 12_0, 11_0, it should become installable.

[rgommers]

So the issue is that packaging is deliberately setting the macOS minor version to zero: https://github.com/pypa/packaging/blob/b8b2f8a/packaging/tags.py#L394-L403

The accepted tags are:

>>> from packaging import tags
>>> list(tags.mac_platforms())
['macosx_12_0_arm64',
 'macosx_12_0_universal2',
 'macosx_11_0_arm64',
 'macosx_11_0_universal2',
 'macosx_10_16_universal2',
 'macosx_10_15_universal2',
 'macosx_10_14_universal2',
 'macosx_10_13_universal2',
 'macosx_10_12_universal2',
 'macosx_10_11_universal2',
 'macosx_10_10_universal2',
 'macosx_10_9_universal2',
 'macosx_10_8_universal2',
 'macosx_10_7_universal2',
 'macosx_10_6_universal2',
 'macosx_10_5_universal2',
 'macosx_10_4_universal2']

That code is then used by pip, and it refuses to install a 12_6 rather than 12_0. The workaround for us is to copy that code exactly, so we also name wheels as 12_0.

Resetting the minor version like that is only justified if it's 100% guaranteed that minor versions are forward and backwards compatible. It's still not a great thing for packaging to be rejecting valid tags in such a strange manner, forcing us to copy-paste unnecessary code to avoid tags that are complying with PEP 3149 just fine. However, the more important question is whether that binary compatibility is actually guaranteed. I have not yet found an authoritative source stating that.

[rgommers]

The main discussion focused on minor versions at the end, and pypa/packaging#319 (comment) says that (as one would expect) this is indeed not guaranteed. So the packaging code is now both unnecessary and buggy.

[rgommers]

More archeology, from pypa/wheel#385:

the numbering of macOS has changed from 10.major.minor to major.minor.minor2.

In order to actually remove the minor version we'd have to coordinate with wheel (and maybe create a PEP?) Instead we just pin the minor version to 0.

Please pin the minor version to 0 and treat MACOSX_DEPLOYMENT_TARGET=N as MACOSX_DEPLOYMENT_TARGET=N.0.

Now let's test if this is actually true. Write a little test file tmp.c:

#include<stdio.h>
int main()
{
printf("\nthis is main file");
}

Now let's build for different minor versions, and see if they are the same:

% clang -mmacosx-version-min=12.0 tmp.c -o 12-0.o
% clang -mmacosx-version-min=12.4 tmp.c -o 12-4.o
% clang tmp.c -o current-os.o  # my machine is on 12.4

% otool -l 12-0.o | grep minos                   
    minos 12.0
% otool -l 12-4.o | grep minos
    minos 12.4
% otool -l current-os.o | grep minos
    minos 12.0

So yes and no. You are allowed to set the deployment target to a minimum version, and that info is kept in the produced binary. And presumably that won't then run on an older minor version - so technically packaging is wrong here. However, if you don't use -mmacosx-version-min explicitly, it defaults to major.0 - so in practice things are going to be mostly fine by pinning to 11_0, 12_0, etc.

[rgommers]

@FFY00 let's copy the relevant lines of the packaging code verbatim and release 0.9.1?

[rgommers]

I did some more testing and verified that both Clang and GCC do honor MACOSX_DEPLOYMENT_TARGET, so Meson actually doesn't need to do anything here. Clang docs, and test:

% echo $MACOSX_DEPLOYMENT_TARGET
                   
% clang tmp.c -o current-os.o              
% otool -l current-os.o | grep minos             
    minos 12.0
% export MACOSX_DEPLOYMENT_TARGET=12.2
% clang tmp.c -o current-os.o         
% otool -l current-os.o | grep minos  
    minos 12.2

So it looks like there's nothing Meson needs to be doing. Not sure what the deal is with CMake explicitly handling that env var, its code is not very understandable.

tl;dr all we should be doing is forcing the minor version to zero for macOS >= 11. And documenting that if the env var is set, please do set the minor version to zero.

[mkoeppe]

I can confirm that this fixes the reported problem (tested with meson-python 0.10.0). Thanks all!

[mkoeppe]

The problem appears to have returned, this time affecting macOS Ventura (13). Reported in https://trac.sagemath.org/ticket/34658#comment:17; I have not reproduced it yet.

[dimpase]

It seems that packaging is not up to date in regard of macOS 13.

[dimpase]

that's what I see on an intel macOS 13

% /usr/local/opt/python@3/bin/python3
Python 3.10.8 (main, Oct 13 2022, 10:17:43) [Clang 14.0.0 (clang-1400.0.29.102)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from packaging import tags
>>> list(filter(lambda t:  "x_13" in t, tags.mac_platforms()))
['macosx_13_0_x86_64', 'macosx_13_0_intel', 'macosx_13_0_fat64', 'macosx_13_0_fat32', 'macosx_13_0_universal2', 'macosx_13_0_universal']
>>> 

With the Python I see scipy build error, I get

['macosx_13_0_arm64', 'macosx_13_0_universal2']

So it seems that _0 piece is gone missing during the build.