Add setuptools.command.build

[isuruf]

Summary of changes

In order to override distutils.command.build on downstream projects
it is good to have a setuptools specific command which allows
downstream projects to avoid importing distutils.

Closes

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d/.
  (See documentation for details)

[abravalheri]

Thank you very much @isuruf, sorry for the confusion with the extra commits, I was trying to fix the error with flake8, I hope that is OK with you.

I am OK with this change, but I will let the other maintainers have a look because I don't know if there are other implications.

[isuruf]

Ping on this

[abravalheri]

Thank you very much @isuruf and sorry for the delay.
Since no one has found any problem with this implementation, I believe we can go ahead...

Should we add any protection/migration warnings for the case an user was previously relying on distutils.command.build to setup subcommands?

For example, how about something like:

_ORIGINAL_SUBCOMMANDS = {"build_py", "build_clib", "build_ext", "build_scripts"}

class build(_build):
    sub_commands = _build.sub_commands[:]  # copy to avoid sharing the object with parent class

    def run(self):
       subcommands = {cmd[0] for cmd in _build.sub_commands}
       if subcommands - _ORIGINAL_SUBCOMMANDS:
           msg = """
           It seems that you are using `distutils.command.build.build` to add new subcommands.
           Using `distutils` directly is considered deprecated, please use `setuptools.command.build`.
           """
           warning.warns(msg, SetuptoolsDeprecationWarning)
           self.subcommands = _build.sub_commands
       super().run()
  ...

What do you think?

[isuruf]

Makes sense to me. There's a small typo in the line before last. self.subcommands should be self.sub_commands. Can you push into this PR or should I?

[abravalheri]

I can do that later today, but if you would like to go ahead and work on it, that would be great (since I would have to spend some time to create a simple test case).

[abravalheri]

Hi @isuruf, I tried to fix the tests failing in the CI.
Please feel free to revert my changes and do something different.