setuptools: [FR] Improve error feedback for improper one-liner requirement with environment markers in `setup.cfg`

setuptools version

63.2.0

Python version

3.9 and 3.11

OS

Fedora Linux

Additional environment information

No response

Description

Project: https://github.com/thoth-station/micropipenv The line I have a problem with: https://github.com/thoth-station/micropipenv/blob/2127293c4c9fa344fd1535c5189c39ca7ba4594d/setup.cfg#L40

It seems to me that there is a difference between this:

[options.extras_require]
toml = toml;python_version<"3.11"

and this:

[options.extras_require]
toml =
    toml;python_version<"3.11"

Micropipenv version 1.4.0 contains the [toml] definition on a single line and when you try to install micropipenv[toml], it does not work (Python 3.9.13):

Collecting micropipenv[toml]==1.4.0
  Using cached micropipenv-1.4.0-py3-none-any.whl (38 kB)
Requirement already satisfied: pip>=9 in /home/lbalhar/.virtualenvs/micropipenv/lib/python3.9/site-packages (from micropipenv[toml]==1.4.0) (22.2)
Collecting toml
  Using cached toml-0.10.2-py2.py3-none-any.whl (16 kB)
ERROR: Could not find a version that satisfies the requirement python-version<"3.11"; extra == "toml" (from micropipenv[toml]) (from versions: 0.0.2)
ERROR: No matching distribution found for python-version<"3.11"; extra == "toml"

the same happens when you use Python 3.11.

But when I use the multiline definition:

[options.extras_require]
toml =
    toml;python_version<"3.11"

it works correctly and omits toml in env with Python 3.11 and installs it if Python<3.11.

When I build a sdist from the package, there is a difference in requires.txt in egg-info directory: single line definition:

pip>=9

[toml]
toml
python_version<"3.11"

two lines:

pip>=9

[toml]

[toml:python_version < "3.11"]
toml

Expected behavior

I’d expect the two definitions mentioned above to behave the same way.

How to Reproduce

You can try to install “micropipenv[toml]==1.4.0” and then you can change the extras_require definition as described above to see that it fixes the problem.

Output

$ tail -n 3 setup.cfg

[options.extras_require]
toml = toml;python_version<"3.11"

$ pip install .[toml]
Processing /home/lbalhar/Software/micropipenv
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Preparing metadata (pyproject.toml) ... done
Requirement already satisfied: pip>=9 in /home/lbalhar/.virtualenvs/micropipenv/lib/python3.9/site-packages (from micropipenv==1.4.0) (22.2)
Collecting toml
  Using cached toml-0.10.2-py2.py3-none-any.whl (16 kB)
ERROR: Could not find a version that satisfies the requirement python-version<"3.11"; extra == "toml" (from micropipenv[toml]) (from versions: 0.0.2)
ERROR: No matching distribution found for python-version<"3.11"; extra == "toml"

## changed the definition

$ tail -n 3 setup.cfg
[options.extras_require]
toml =
    toml;python_version<"3.11"

$ pip install .[toml]
Processing /home/lbalhar/Software/micropipenv
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Preparing metadata (pyproject.toml) ... done
Requirement already satisfied: pip>=9 in /home/lbalhar/.virtualenvs/micropipenv/lib/python3.9/site-packages (from micropipenv==1.4.0) (22.2)
Collecting toml
  Using cached toml-0.10.2-py2.py3-none-any.whl (16 kB)
Building wheels for collected packages: micropipenv
  Building wheel for micropipenv (pyproject.toml) ... done
  Created wheel for micropipenv: filename=micropipenv-1.4.0-py3-none-any.whl size=23303 sha256=b645cc71f7404f367dabe8c203cf80025f3080c7d2ac6a929aec3ae5bbab2a6a
  Stored in directory: /tmp/pip-ephem-wheel-cache-zh2n98et/wheels/2a/c1/ee/2caed205bb1a97b553aa44d9a5f1966c5bec9edea862cc2c72
Successfully built micropipenv
Installing collected packages: toml, micropipenv
Successfully installed micropipenv-1.4.0 toml-0.10.2