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In https://github.com/scikit-hep/pyhf/pull/1881 I noticed and fixed a SetuptoolsDeprecationWarning that pyhf had in its setup. As pyhf runs build in its CI to ensure things are working I would like to have these warnings get turned into errors so that the dev team is alerted to them in advance (I just noticed this SetuptoolsDeprecationWarning by looking at the logs by chance).

My naive attempt at

$ python -Werror -m build .

doesn't work, but I guess I'm unclear on how one should pass in warning filters to build and the commands that it will run as

$ python -m build --config-setting=-Werror .

also doesn't work (though that makes sense as --config-setting is going to the backend (setuptools) and not to Python).

https://github.com/pypa/packaging-problems/issues/558

As @agoose77 points out, build runs in a new process by default, and Python isn't passing along the warning flag, so by setting the shell environmental variable PYTHONWARNINGS the information can be propagated. So

$ PYTHONWARNINGS=error python -m build .

works as desired. :+1:

So

$ PYTHONWARNINGS=error python -m build .

works as desired. +1

That was spoken too soon. I guess I really just want to turn SetuptoolsDeprecationWarning into errors and not catch DeprecationWarnings of other things.

OK, I looked into this and it looks like the commandline warning configuration is pretty lacklustre right now in Python. You can pass a module.attr string to resolve the classname for PYTHONWARNINGS / -w ... but this happens before the site packages are enabled, so it won't work. You can work around this with PYTHONPATH pointing to the location of setuptools, but that is not easy unless you run build without build isolation.

Can't you use colons? The (little used) fourth colon separated part is a module name, IIRC.

Can't you use colons?

If colons worked, then shouldn't this

$ PYTHONWARNINGS=error::SetuptoolsDeprecationWarning python -m build .

work?

This allows for

/tmp/build-env-mnsbs_hq/lib/python3.10/site-packages/setuptools/config/setupcfg.py:459: SetuptoolsDeprecationWarning: The license_file parameter is deprecated, use license_files instead.

to pass without error.

The (little used) fourth colon separated part is a module name, IIRC.

Yeah, the warnings docs say

Individual warnings filters are specified as a sequence of fields separated by colons:

action:message:category:module:line

but

$ PYTHONWARNINGS=error::SetuptoolsDeprecationWarning:setuptools python -m build .

gives

Invalid -W option ignored: unknown warning category: 'SetuptoolsDeprecationWarning'

You could raise any warnings from setuptools instead of the specific deprecation warning. I think that's what @henryiii is implying?

I've tested that it works, though it will not discriminate between warning kinds.

You could raise any warnings from setuptools instead of the specific deprecation warning.

I've tested that it works, though it will not discriminate between warning kinds.

Hm, I'm confused as to what I'm doing wrong then as

$ PYTHONWARNINGS=error:::setuptools python -m build .

fails to detect

/tmp/build-env-3r3f9oxf/lib/python3.10/site-packages/setuptools/config/setupcfg.py:459: SetuptoolsDeprecationWarning: The license_file parameter is deprecated, use license_files instead.
  warnings.warn(msg, warning_class)

but

$ PYTHONWARNINGS=error python -m build .

properly raises

ERROR Backend subprocess exited when trying to invoke get_requires_for_build_sdist

It expects the fully-qualified module name, which in this case would be setuptools.config.setupcfg. You can filter using regexes with the programmatic API but not with -W or the env var.

You can filter using regexes with the programmatic API but not with -W or the env var.

Thanks @layday — this is the last bit that I was missing.