Merge setup.cfg spec with pyproject.toml one and deprecate setup.py and setup.cfg

[KOLANICH]

Now we have a bunch of files. It's a mess:
1 python packages metadata is in fact generated by setup.py script. This means if you need to parse it you'll have to execute the script.
2 Recently pyproject.toml was introduced, which contains for now only the description of the packages needed to build a package and data in backend-specific format. Why don't we have the things which are part of setup.cfg standardized too?

So I propose to
0 ship setuptools with python. I mean preinstall it as if it was installed by pip.
1 integrate setup.cfg spec into pyproject.toml and publish a PEP
2 setuptools should be workable without setup.py, only with pyproject.toml in a dir
3 pyproject.toml is the primary source of metainfo. setup.py should be executed if and only if pyproject.toml uses any variables from it.
4 Write a warning in red that setup.py is deprecated each time setuptools.setup is used

0 ship setuptools with python

Not going to happen. In fact, we're discussing moving distutils into setuptools (@jaraco, see distutils-sig).

[tuukkamustonen]

1 merge setup.cfg into pyproject.toml and publish a PEP

Just noting that setup.cfg is being used also by several other tools like flake8, pytest, etc.

4 pyproject.toml is the primary source of metainfo. setup.py should be executed if and only if it pyproject.toml uses some variables from it.

Care to elaborate how would pyproject.toml use variables from setup.py?

[RonnyPfannschmidt]

as things currently are, setup.py is the entrypoint and could use variables from pyproject.toml

i propose starting with a tool.setuptools.opptions section for putting plain setup.py parameters

a tool.setuptools.metadata for the plain metadata sections and tool.setuptools.comands for commands/aliases

[pganssle]

I'm going to close this in favor of #1688. We are not going to deprecate setup.py, and Nathaniel is probably right that any deprecation period for setup.cfg would probably be "forever" (though it's certainly possible).