Error during build on unguarded use of new symbols on macOS

[zanieb]

Feature or enhancement

Proposal:

CPython builds run against the latest macOS version and unguarded use of new symbols does not throw an error. However, building CPython on older versions of macOS is supported. Consequently, regressions are not caught, e.g.:

• HACL Blake2 implementation does not check for aligned_alloc availability on macOS #128134
• Availability of ptsname_r is not checked at runtime on macOS #123797
• Availability of utimensat, futimens not checked correctly on macOS #75782

Enabling -Werror=unguarded-availability-new would be great to catch these before they become a problem downstream.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

This was discussed briefly in Discord

[zanieb]

Here's an initial patch 36c7da4

I'm not sure if we should be using unguarded-availability or unguarded-availability-new and define an explicit lower bound version? We use the latter downstream, but we also set a minimum version.

I'm having a hard time reproducing failures without cross-compiling via python-build-standalone. Probably user error.

[zanieb]

Another complexity is astral-sh/python-build-standalone#210 / astral-sh/python-build-standalone#422 — if this is in the CFLAGS in sysconfig it is used to build extension modules in some packages which causes failures.

[zanieb]

Perhaps this is dumb to ask, but.. this flag is clang only? I don't think there's an obvious equivalent in gcc?

[picnixz]

I'm not aware of an equivalent one for gcc. Btw, I think we already had an issue for this one: #100384 but I think it's better to keep the latest in this case unless you want to move the discussion out there.

[zanieb]

Ah thank you @picnixz — I don't have a preference for which issue we use but agree it makes sense to close one of them.

[picnixz]

Let's move the discussion on the original one. I'll edit the issue to include your findings.