strxfrm fails on macOS 15 with OSError: [Errno 22] Invalid argument

[nijel]

Bug report

Bug description:

It appears that macOS 15 broke locale.strxfrm for letters outside the latin-1 set:

import locale
locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')
locale.strxfrm('Français') # works
locale.strxfrm('zkouška') # crashes with OSError
locale.strxfrm('中文') # crashes with OSError

This works on Linux and macOS 14 and crashes on macOS 15, tested with Python 3.9–3.14: https://github.com/nijel/python-strxfrm/actions/runs/13541306384/job/37842825809

There are several projects which run into this already:

• Locale aware sorting crashes on macOS 15 with OSError WeblateOrg/weblate#14019
• Nicotine+ crashing when trying to browse public shares (on MacOS 15 Public Beta) nicotine-plus/nicotine-plus#3063
• Zim wont open in macOS Sequoia zim-desktop-wiki/zim-desktop-wiki#2665

In most cases, this is being addressed by completely removing locale-aware sorting.

CPython versions tested on:

3.14

Operating systems tested on:

macOS

Linked PRs

• gh-130567: fix strxfrm memory allocation #130619

[nijel]

Looking more into that I've found https://swi-prolog.discourse.group/t/compiling-swi-prolog-from-git-source-on-next-macos-15-beta/7590/1. They figured out that wcsxfrm does not actually return desired string size in case of the failure, so they ended up allocating double space in that case, see SWI-Prolog/swipl-devel@f0bbfb0.

The following code would have to be changed:

cpython/Modules/_localemodule.c

Line 426 in 263d56e

wchar_t * new_buf = PyMem_Realloc(buf, (n2+1)*sizeof(wchar_t));

[nijel]

I've tried to address this #130619.

[serhiy-storchaka]

What error do you get? What code?