Stubgen recursive mode for module with submodule should generate directory and init for top-level module

[wenjuno]

The recursive stubgen is great but with one problem, it generates a pyi file named after the top-level module name even if there are submodules. For instance, if I have a module mylib and it has a submodule lib, it will generate two files (1) mylib.pyi (2) lib/__init__.pyi. The content of mylib.pyi will have the import for lib: from . import lib as lib. This only works when mylib.pyi is within a package (i.e. is under a directory). I could put these two files under a directory "mylib" to make it a package, but it leads to a new problem, this package does not have __init__.py, so importing mylib will not get access to the submodule lib and any top-level classes/functions. The mylib.pyi needs to be renamed to __init__.py.
I think stubgen recursive mode should either always generate the top-level module as a package or at least does that when there are submodules.

[nurpax]

Yes, I also hit this and fixed it by renaming the produced top-level stub file:

python -m nanobind.stubgen -i build/cp312-abi3-macosx_15_0_arm64 -q -m slimgui_ext -r -O src/slimgui/slimgui_ext
mv src/slimgui/slimgui_ext/slimgui_ext.pyi src/slimgui/slimgui_ext/__init__.pyi

(https://github.com/nurpax/slimgui/blob/main/full_build.sh)

I put build steps into a separate shell script so that I can apply workarounds like this. I thought I was doing something wrong when I had to add this but looks like this a bug/limitation in nanobind's stubgen.