extras_require in setup.cfg doesn't allow hyphen in extras name

I’m porting a setup.py file to declarative setup.cfg. In this package, an extra contains a hyphen. This works when defined in setup.py but does not when defined in setup.cfg. If I change the hyphen to an underscore, it works again, but this would break the extra for users.

To reproduce:

setup.py:

from setuptools import setup

setup()

setup.cfg:

[options.extras_require]
extra-a =
    pytest
extra_b =
    pytest

tox.ini (to automate the virtual env creation)

[testenv:a]
extras = extra-a

[testenv:b]
extras = extra_b

Then run:

$ tox -e a
$ tox -e b

Notice the extras are installed in the “b” environment but not the “a” environment. AFAICT, the only difference is the use of a hyphen instead of an underscore.

[jaraco]

When this bug was filed, setuptools relied on distutils to parse the config files. Since then, in 24be5abd4cbd9d84537c457456f841522d626e14, the code was inlined, so it should be straightforward to adjust the parsing behavior. I believe it’s worth seriously considering just dropping that substitution.

[melissa-kun-li]

As Jason mentioned, since the config parsing code is now within Setuptools, I believe this line is responsible for turning hyphens to underscores: https://github.com/pypa/setuptools/blob/main/setuptools/dist.py#L601. I wonder if we can simply remove the line, but I’m not sure if there are disadvantages to doing this.