Accept string in PEP 517 `config_settings`

[FFY00]

As discussed in pypa/build#202, it would be great if setuptools could accept strings, instead of only lists, in the PEP 517 config_settings hooks variable.

It would make the following dictionary valid.

{
    '--global-setting': '--something',
}

Currently, setuptools seems to only accept a list.

{
    '--global-setting': ['--something'],
}

Which is difficult to expose in a CLI interface.

[FFY00]

As we've received another bug report that would benefit from this fixed, I would like to ping. It should be fairly straight forward, when I pass a string instead of list, setuptools would just treat it the same as it would a list with a single element.

The code should be as simple as

if isinstance(option, str):
    option = [option]

I can open a PR if you agree with this.

[KOLANICH]

Shouldn't it be in

setuptools/setuptools/build_meta.py

Line 118 in b6bbe23

def _fix_config(self, config_settings):

?