Please do not remove `setup.py install` as it is needed for distribution packagers

As requested in https://github.com/pypa/setuptools/issues/510#issuecomment-623153201 I’m opening a new issue. What I’d like for is that setup.py install --root=... (or a minimal equivalent) remains working as a ‘low-level’ install command for distribution packagers.

Installing packages straight from setuptools (much like distutils) has important advantages for us:

1. The --root= install mode fits just fine the packaging logic we have. We need a command that puts files in a directory we can use. We build distribution packages, and would really like to avoid building a wheel just to have to repack it into plain package.
2. We need minimal dependencies, and certainly have to avoid circular dependencies. While for tools like pip it might be acceptable to employ dirty bootstrap hacks, we really prefer not to have to rely on that to get the initial install working.
3. There are literally thousands of packages calling setup.py install one way or another. At least in Gentoo the majority of them is covered by our Python framework and could be easily swapped to use another install method but I can imagine others are not so lucky. It’s not fair to ask people to change all that.
4. There are many packages that customize the install command, including some high profile ones. If the command is removed, they would all become broken, wouldn’t they?

All that considered, please keep setup.py build and setup.py install commands for us. I don’t care if they output huge warnings, require magical environment variables to be run but they need to stay as backend commands.

[eli-schwartz]

Well, it looks like we could, we would just need to create a second python package just to reimplement main() around Pep517HookCaller without calling pip first.

This is quite awkward, not least because it’s an explosion of tools and Arch Linux dislikes an explosion of custom distro tools (we devoutly avoid build recipe macros, templates, and inferred hooks with the rationale that they’re unreadable and turn the act of packaging into some secret invite-only club of people who actually understand the endless layers). It would be best if pep517 could just… not call pip when it knows all the Distributions are there. The point of this reinvention of the python packaging landscape was to make things less coupled together, right? So it seems silly to couple pep517 to pip for any reason.

[mgorny]

Eh, things are getting even better. I’ve spent significant time trying to figure out how data_files work with wheels. Unless I’m mistaken, this is done completely outside wheel spec, and it was deprecated anyway. So if I write a useful user-facing Python program, I’m not supposed to install .desktop files for it, or a working manpage, right?