recent `-X` options do not auto-propagate to multiprocessing processes

[gpshead]

Bug report

Bug description:

-X lazy_imports, -X thread_inherit_context, and -X context_aware_warnings are not inherited via subprocess._args_from_interpreter_flags() so multiprocessing spawned child processes do not inherit these -X settings unless the user happens to be using the dangerous non-default "fork" start method.

We should consider this for every -X option added. In general the answer should be "yes". There's a list in Lib/subprocess.py to update. (could we automate this by making the list an opt-out instead of a remember-when-adding-a-feature-to-opt-in list?)

Linked PRs

• gh-146004: propagate all -X options to multiprocessing child processes #146005
• [3.14] gh-146004: propagate all -X options to multiprocessing child processes (GH-146005) #146552
• gh-146004: fix test_args_from_interpreter_flags #146580
• [3.14] gh-146004: fix test_args_from_interpreter_flags on windows (GH-146580) #146585

[gpshead]

Potentially security relevant for -X disable-remote-debug. though i expect people who really want that off build a python without it or at least use the PYTHON_DISABLE_REMOTE_DEBUG= env var.

[gpshead]

-X options that are not yet being propagated to multiprocessing spawned children that the PR would change:

``context_aware_warnings``,
``cpu_count``,
``disable-remote-debug``,
``int_max_str_digits``,
``lazy_imports``,
``no_debug_ranges``,
``pathconfig_warnings``,
``perf``,
``perf_jit``,
``presite``,
``pycache_prefix``,
``thread_inherit_context``,
``warn_default_encoding``.

thoughts on if any of those should not auto-propagate to non-fork'ed children?

[gpshead]

And among those, which ones we should specifically backport propagation as a bugfix?

[vstinner]

thoughts on if any of those should not auto-propagate to non-fork'ed children?

IMO it's safe to propagate all of them to child processes.

And among those, which ones we should specifically backport propagation as a bugfix?

I'm fine with backporting your change which propagate the whole sys._xoptions directory.