Right now the erfa.pyx (and erfa.py from #3141) are checked in as source code. These files are entirely auto-generated using cython_generator.py, so this seems wasteful of repository bandwidth in the event of future changes to the templates or other aspects of the erfa wrappers (incl. e..g, #3137).

Some discussion of this already has happened in #2992, #3134, and #3141 . Most relevant is an issue pointed out by @astrofrog, that this would then imply a compile-time dependency on jinja2. Presumably we could avoid this for releases by having the tarballs include the autogenerated source, just as we do right now with Cython-generated c code. I personally don't think it's a big deal to require jinja2 at compile-time, because it's already necessary for sphinx, which developers should all have to build the docs.

It also might make sense to include this on astropy_helpers in a slightly more generic form, allowing any cython_generator.py sort of usage. Or we could put it only in the core for now and later generalize if there's call for it.

cc @jwoillez @astrofrog @mdboom @mhvk @embray