REGR: Conda build breaks in presence of pyproject.toml on aarch/ppc64le

[h-vetinari]

There were weird build-errors in conda-forge/cvxpy-feedstock#30 and conda-forge/cvxpy-feedstock#31, where the aarch/ppc64le builds would seemingly try to install (and compile!) numpy/scipy etc.

Turns out that they were listed under pyproject.toml, and now the build tried to install them from scratch. Note that this was swallowed silently before, because the same underlying files went through on conda-forge/cvxpy-feedstock#29.

Now however it actually breaks on aarch/ppc64le, with errors that were fairly hard to figure out. Could it be that conda-build upgraded its internal pip-version or something?

I first tried to comment out the affected requirements in pyproject.toml, but even the presence of an empty file, the build will then try to install setuptools/wheel (see here, also xref #3507). This resulted in the even weirder error that numpy wasn't found despite being listed as a build requirement.

On a side-note, I seem to remember getting errors when setuptools tried to install dependencies. This has also not produced an error in the cvxpy-build for some time at least.

CC @scopatz, since you were caught off guard by it as well.

[isuruf]

Might be a duplicate of #2951

[jjhelmus]

Did this end up being cause by a non-activated environment rather than conda-build?

[h-vetinari]

@jjhelmus
these jobs failed on azure in the linked PR. Not sure how the mechanism failed exactly, but it was reproducibly only in case that pyproject.toml existed.

[github-actions]

Hi there, thank you for your contribution!

This issue has been automatically marked as stale because it has not had recent activity. It will be closed automatically if no further activity occurs.

If you would like this issue to remain open please:

1. Verify that you can still reproduce the issue at hand
2. Comment that the issue is still reproducible and include:
   - What OS and version you reproduced the issue on
   - What steps you followed to reproduce the issue

NOTE: If this issue was closed prematurely, please leave a comment.

Thanks!