Setuptools does not pass config_settings through backend

The build project now has a --config-setting flag to pass options to the backend:

$ python -m build --help
usage: python -m build [-h] [--version] [--sdist] [--wheel] [--outdir dir] [--skip-dependencies]
                       [--no-isolation] [--config-setting CONFIG_SETTING]
                       [srcdir]

- - - >8 - - -

  --config-setting CONFIG_SETTING, -C CONFIG_SETTING
                        pass option to the backend

I wanted to use this to set wheel’s --plat-name argument like so:

$ python -m build --wheel --config-setting plat-name=foo

I found that this worked as expected until the settings got to setuptool’s _build_with_temp_dir function:

https://github.com/pypa/setuptools/blob/d368be2b5be8676ba8a3d55045b45b55090f6982/setuptools/build_meta.py#L190-L200

In this example, _build_with_temp_dir gets called with config_settings={'plat-name': 'foo'}, which then gets ‘fixed’ into config_settings={'plat-name': 'foo', '--global-option': []}, and then setuptools ignores everything in config_settings and only considers --global-option.

It almost seems like --global-option itself could be used for this, but unfortunately it doesn’t work as it’s value is passed to lots of things that don’t accept the arguments I’m hoping to pass:

$ python -m build --wheel --config-setting="--global-option=--plat-name" --config-setting="--global-option=foo" -n
usage: _in_process.py [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
   or: _in_process.py --help [cmd1 cmd2 ...]
   or: _in_process.py --help-commands
   or: _in_process.py cmd --help

error: option --plat-name not recognized
...

I created a commit that “fixes” this for me as a proof of concept: https://github.com/pypa/setuptools/commit/fc95b3b83d6d5b561dc0a356995edf4c99785a6f

Possibly related issues:

• this is very similar to the request in https://github.com/pypa/setuptools/issues/1816, but @gaborbernat is asking for the ability to pass options before the setup command, rather than after.
• https://github.com/pypa/setuptools/issues/1928 may also be related

[FFY00]

FYI I am also in favor of removing the dashes, I don’t think they are needed in PEP 517.

[layday]

I commented on this upthread:

Incidentally, global options in setuptools seem to mean something different than they do in pip where they are placed in front of the setuptools command. Here, they are appended to the command. pip users might find the discrepancy surprising.

---

It is not immediately clear to me that the spec mandates that --global-option should come before setup_command […]

This is all setuptools-specific stuff, the spec has no notion of global options nor does it expect that options will be passed to a CLI.