Improve traceability of assertion errors in common functions

Feature request

(By @picnizx)

While the C API docs explicitly state that functions should usually not be called with an exception set, else some assertion errors may occur and/or the thread state may be invalid, this means that assert(!PyErr_Occurred()) in common macros / functions such as _PyType_LookupRef would just crash. However, in a CI scenario, without a debugger, it's extremely hard to pinpoint the actual cause.

Related: https://github.com/python/cpython/pull/128159 would give the possibility to show the C stack trace with -X faulthandler.

A crude idea: add assert(!PyErr_Occurred()) inside public common C API functions to be sure that the assertion is checked as well, making debugging a bit easier.

Toy Scenario (original request):

I was working on freethread support for pygame-ce, and I finally need to use a python build with debug symbols, and our atexit-registered quit function was causing SIGABRT to be thrown. This took me a while to figure out. Here's all the code you need to run (or just run python -c "import pygame" since pygame.quit() is atexit-registered).

import pygame
pygame.quit()

Here's the guilty block of code in our codebase:

    funcobj = PyObject_GetAttrString(module, "_internal_mod_quit");

    /* If we could not load _internal_mod_quit, load quit function */
    if (!funcobj)
        funcobj = PyObject_GetAttrString(module, "quit");

    /* Silence errors */
    if (PyErr_Occurred())
        PyErr_Clear();

In the 3.12 docs for PyObject_GetAttrString and PyObject_GetAttr. there's no mention at all that there shouldn't be any exceptions set before calling this function, and it works on release versions of python, so nobody has ever questioned this structure. I'll be making a pull request on our end to clear any exceptions between the first call and second call if needed (or use PyObject_GetOptionalAttrString in 3.13+).

The reason for this issue is that I'm not sure throwing a SIGABRT is the best option here.

CPython versions tested on:

3.12, 3.13, 3.14

Operating systems tested on:

Linux

Beginne damit, das Verhalten der C API rund um PyObject_GetAttrString, PyObject_GetAttr, PyErr_Occurred und _PyType_LookupRef sowie den zugehörigen faulthandler-Pull-Request zu überprüfen. Vergleiche die dokumentierten Voraussetzungen mit den im pygame-Szenario gezeigten Assertion-Fehlern. Als abgeschlossen gilt die Aufgabe, wenn ein abgestimmter Ansatz zur Verbesserung der Nachvollziehbarkeit von Assertions und sein erwartetes Verhalten festgelegt ist.