build_ext fails if build_py was not called before

[mgorny]

For example in aesara:

$ python setup.py build_ext -j12
running build_ext
UPDATING build/lib/aesara/_version.py
error: [Errno 2] No such file or directory: 'build/lib/aesara/_version.py'

[effigies]

During standard python setup.py install, I think build_py is called before build_ext, but it is not always the case that someone will want to call build_py implicitly in build_ext. For example, here is a StackOverflow post asking how to avoid running build_py before build_ext.

I note that we do avoid running the update if you use --inplace. Would updating your above command to python setup.py build_ext -j12 --inplace get you what you want?

[mgorny]

Building in-place is not an option for us, as separate build dirs are required to handle different versions of Python.

[mgorny]

For the record, the problem is related to the Python build infrastructure for Gentoo packages. I suppose the alternative "fix" would be to skip updating the version if build_py wasn't called but I'm not really sure how to check that. I suppose checking if build dir could be an option.

[effigies]

Might make sense to warn if the file doesn't exist with an error message that explains that it couldn't be updated and you might need to build_py first.

Setup.py does also allow you to pass multiple commands, each with their own options. For this use case, maybe:

python setup.py build_py build_ext -j12

[mgorny]

The whole point is to avoid calling build_py because it makes everything much slower (and it's very slow anyway), and PEP517 build takes care of calling it anyway.

[effigies]

Your PR proposes including build_py as part of build_ext in any project that uses versioneer, so that seems like that will break your use case as well.

I think the file check and warning is probably the right way to go for your use case.

[mgorny]

Ok, I'll update the PR later today.

[mgorny]

…and updated!