PyModule_GetWarningsModule() of pylifecycle.c is useless when _warning module was converted to a builtin module in 2.6. So move it directly now is OK.

It's not part of the C API and it's no longer exported in libpython since we (the default visibility was changed to "hidden"). IMHO it's safe to remove the function. But it would not harm to document the removal in https://docs.python.org/dev/whatsnew/3.10.html#id4 section.

> But it would not harm to document the removal in https://docs.python.org/dev/whatsnew/3.10.html#id4 section.

Copy that. I will update it soon.

When was the visibility changed to hidden?

New changeset 0f91f586ae9b76c3bb44559bd8cd473b1b8de5ff by Hai Shi in branch 'master':
bpo-42599: Remove useless PyModule_GetWarningsModule() (GH-23691)
https://github.com/python/cpython/commit/0f91f586ae9b76c3bb44559bd8cd473b1b8de5ff

> When was the visibility changed to hidden?

In Python 3.9:

commit 0b60f64e4343913b4931dc27379d9808e5b78fe1
Author: Vinay Sajip <vinay_sajip@yahoo.co.uk>
Date:   Tue Oct 15 08:26:12 2019 +0100

    bpo-11410: Standardize and use symbol visibility attributes across POSIX and Windows. (GH-16347)


Symbols which are not declared with PyAPI_FUNC() are no longer exported when using GCC or clang (any compiler supporting -fvisibility=hidden).


PyModule_GetWarningsModule() was not documented nor exported.

I merged the PR. If it breaks too many packages, we can consider to revert the change. But I expect that there are zero project using it.

Note: PyModule_GetWarningsModule() was not part of PC/python3dll.c neither, hopefully ;-)