Incorrect warning that package "does not provide the extra" when extra contains an underscore

[tjsmart]

Description

If a package's extras contains an underscore pip will warn that the package "does not provide the extra" when in fact it does.

Expected behavior

I expected that whether a package specifies an extra named foo-bar or foo_bar that anyone should be able to pip install the extra dependency foo-bar or foo_bar without any warnings.

pip version

23.3.1

Python version

3.10.1

OS

Ubuntu 20.04.6 LTS

How to Reproduce

1. Create a setup.cfg file with the following contents:

[metadata]
name = hello_hello
version = 0.0.0

[options.extras_require]
bye_bye =
    typing-extensions

2. Create a setup.py file with the following contents:

from setuptools import setup

setup()

3. Then run pip install -e '.[bye_bye]'.

Note:

• A warning is emitted: "WARNING: hello-hello 0.0.0 does not provide the extra 'bye-bye'".
• The bye-bye extras is used, and (in this case) typing-extensions is installed as desired.

Known Workaround

If I instead specify the extras with a hyphen, by making the following change to my setup.cfg:

[options.extras_require]
- bye_bye =
+ bye-bye =
    typing-extensions

The above command pip install -e '.[bye_bye]' runs successfully without any warning.

Also note that in both situations, the behavior does not change if I specify pip install -e '.[bye-bye]' from the command line.

Output

$ pip install -e '.[bye_bye]'
Looking in indexes: https://pypi.org/simple
Obtaining file:///tmp/cfg_extras
  Preparing metadata (setup.py) ... done
WARNING: hello-hello 0.0.0 does not provide the extra 'bye-bye'
Collecting typing-extensions
  Using cached typing_extensions-4.9.0-py3-none-any.whl.metadata (3.0 kB)
Using cached typing_extensions-4.9.0-py3-none-any.whl (32 kB)
Installing collected packages: hello-hello, typing-extensions
  Running setup.py develop for hello-hello
Successfully installed hello-hello-0.0.0 typing-extensions-4.9.0

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[uranusjr]

This is a side effect of #11445.