Ideas for allowing usage without setup.py

[astrofrog]

I've been thinking into whether we can try and make it so that using setup.py is not required - one possible option to investigate would be to make use of https://setuptools.pypa.io/en/latest/userguide/extension.html#customizing-distribution-options to add extensions to the Distribution object. Since all that extension-helpers really does is:

from extension_helpers import get_extensions
...
setup(..., ext_modules=get_extensions())

why not simply use the entry point above and assign Distribution.ext_modules?

[embray]

That sounds feasible. setuptools.finalize_distribution_options is new I think (at least to me).

I also supplied this proposal some time ago, but haven't had a chance to act on it: pypa/setuptools#2220

However, that may not be sufficient for some extension modules that need some programmatic configuration. There's no generic standard, e.g. for getting things like the path to numpy includes.

[astrofrog]

I was also thinking about how we might define extensions in e.g. setup.cfg or another file - and stumbled on the same conceptual problem of not being sure how to deal with numpy.get_include_path but then I realised that if it's too difficult to implement in setuptools, there's no reason extension-helpers can't have its own way of defining extension modules in setup.cfg or another file and have e.g. a numpy_include=true/false option (since it's up to us what options to define in extension-helpers and we can be more opinionated than setuotools). This would allow us to be able to get rid of the setup_package.py files in a number of packages I believe (it might be a stretch for astropy though).

[Cadair]

I think with this approach extension_helpers could have as many or as few setup.cfg sections as we want, so I see no reason why we couldn't come up with a scheme which works?

[astrofrog]

#33 has been merged and supports enabling extension-helpers via setup.cfg with no changes required to setup_package.py files!