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

Lies Lib/typing.py in den Zeilen 1846-1863 und vergleiche die vorgeschlagene Änderung mit dem verlinkten PR gh-136115. Die Aufgabe ist erledigt, wenn _allow_reckless_class_checks auch _py_abc behandelt, sobald _abc nicht verfügbar ist, und das Verhalten im CPython main branch verifiziert wurde.