Per requirements `--config-settings`

[sbidoul]

What's the problem this feature will solve?

Currently we can specify --install-options and --global-options per requirement in requirement files.

These options are on the way to deprecation as they trigger the legacy setup.py install code path.

Towards #8102.

Describe the solution you'd like

Allow --config-settings on requirement lines so they can be passed to the build backend.

Evaluate automatically activating PEP 517 build for requirements with such options.

Alternative Solutions

Do not allow configuring build settings per requirements.

Additional context

#9422 (comment)

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[selim-aigoritma]

I too believe this is necessary since --install-options will become deprecated

[uranusjr]

Pull requests are always welcomed :)

[bricker]

The per-requirement --config-settings option is documented in the documentation, apparently supported since version 7.0, but it doesn't work in pip 23.0.1 and this issue/PR are still open. What am I missing?

[sbidoul]

@bricker it looks like a documentation bug indeed.

I'm tentatively adding this to the 23.1 milestone as it would be nice to have at the same time as the removal of --install-option.

[sbidoul]

What should we do if a given config setting is provided on the CLI and per requirement ?
I assume we should extend, per #11681 ?

Which makes me note that the type of config_settings: Optional[Dict[str, str]] is probably wrong. It should now be config_settings: Optional[Dict[str, Union[str, List[str]]]