ENH: refactor Cython file generation

[matthew-brett]

Is your feature request related to a problem? Please describe.

See: rgommers#84 (review)

The current state of our Cython generation code could do with cleanup and refactor, and in particular:

• generate_ufuncs,
• generate_ufuncs_type_stubs and
• generate_fused_funcs

The original (pre-meson) code in SciPy gave:

cdef extern from "_ufuncs_defs.h":

from generate_ufuncs, while in the Meson build changes about to be merged, it looks like:

cdef extern from "/home/rgommers/code/bldscipy/build/scipy/special/_ufuncs_defs.h":

This is due to the changes under if __name__ == "__main__":.

Describe the solution you'd like.

Using relative paths in the generated code seems better/safer (e.g., in case we ever go back to shipping pre-generated Cython sources). So rather than this fix, it would be better to improve this script by separating the contents of the files from the location that those files get written to. That probably means a separate outdir argument for generate_ufuncs, generate_ufuncs_type_stubs and generate_fused_funcs, or refactoring those functions to really separate out the code generation from the file writing parts.

Describe alternatives you've considered.

No response

Additional context (e.g. screenshots, GIFs)

No response

[rgommers]

The relative -> absolute path change is actually only present in my meson branch. That doesn't detract from special/_generate_pyx.py being in need of a refactor though, so I'll leave the issue here.