PEP 517 config settings support

[nschloe]

In #573, support for PEP 517 was added. From what I can tell, config settings support is still missing. Config settings are a dict that is passed to the build backend, e.g., setuptools. Pip implements this as --config-settings/-C, pypa-build as --config-setting/-C.

It'd be great if tox had some way of specifying config settings that a passed to the build backend, e.g.,

[testenv:.pkg]
config-settings = 
  foo = bar
  alpha = omega
  run = 256

[gaborbernat]

PR welcome 👍

[nschloe]

In tox's output, I see that 'config_settings' exist as an entity:

[...]
.pkg: 685 W build_sdist> python /home/nschloe/venv/lib/python3.11/site-packages/pyproject_api/_backend.py True foobar.build_meta [tox/tox_env/api.py:427]
Backend: run command build_sdist with args {'sdist_directory': '/path/to/.tox/.pkg/dist', 'config_settings': None}

I suppose this comes from pyproject-api. I can't quite see right now how this is called.

Edit: This build_sdist call misses a config_settings arg dict.

[nschloe]

I've found where config_settings need to be added, but I have difficulties understanding how tox settings are defined and passed around. Any help?

[gaborbernat]

https://tox.wiki/en/4.6.4/plugins.html#tox.plugin.spec.tox_add_env_config, you should have plenty examples in the code base, check for example https://tox.wiki/en/4.6.4/config.html#package_root-env

[nschloe]

I'm trying to mimick what's in #1891, but don't really know what I'm doing. I'll best open a PR so we can discuss further over there.

[gaborbernat]

Done.