setuptools bdist_egg stub bootstrap code broken

[chrismile]

Since some time between beginning of September and now, for some reason the __bootstrap__ function in https://github.com/pypa/setuptools/blob/main/setuptools/command/bdist_egg.py#L56 seems to have been broken in my CI pipeline (where I build/install a C++ module with setuptools with a pyi stub, using Python 3.13).

I have created a minimal reproducer at https://github.com/chrismile/PyTestModBootstrap, which contains a module modx that wants to import imply.py into its namespace in __init__.py using setuptool's __bootstrap__ function from https://github.com/pypa/setuptools/blob/main/setuptools/command/bdist_egg.py#L56. For some reason (that was not the case in the past), this does not work.

How to reproduce:

1. Clone: https://github.com/chrismile/PyTestModBootstrap
2. Run: python3 main.py
3. See that the function my_function is not imported into the namespace of the package modx.

If someone sees what might be going wrong, that would be very helpful.

[chrismile]

I found the solution: sys.modules[mod.__name__] = mod needs to be added before spec.loader.exec_module(mod). But I am confused why the bootstrap code by setuptools ever worked in the past. I'd leave this open in case somebody knows.