typing._allow_reckless_class_checks doesn't work when _abc doesn't exist.

Bug report

Bug description:

When typing._caller's sys._getframe fallback is triggered without _abc module, _typing._allow_reckless_class_checks fails to check _py_abc while running abc.ABCMeta.__instancecheck__.

Without _abc module, _typing._allow_reckless_class_checksfails to check _py_abc

Related code in typing.py:
https://github.com/python/cpython/blob/v3.14.0b3/Lib/typing.py#L1846-L1863

This is technically a bug of typing.py, but really hard to be triggered on CPython.

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Solution suggestion

Patch typing._allow_reckless_class_checks to also check _py_abc

This is the most conservative approach. Compatible with all of previous scenarios and additionally fixing the bug.

Patch typing._caller to remove sys._getframe or raise warning when fallback

If the the typing requires to work with sys._getframemodulename, then let the users to know it has a caveat.

Linked PRs

• gh-136115

閱讀 Lib/typing.py 的第 1846-1863 行，並將提議的變更與連結的 PR gh-136115 進行比較。當 _abc 無法使用時，_allow_reckless_class_checks 也能處理 _py_abc，且已在 CPython main 分支上驗證其行為，即表示完成。