setuptools_scm preferences in pyproject.toml

[nstarman]

I'm very much NOT an expert in packaging infrastructure.

This PR does:

1. adds [tool.setuptools_scm] to pyproject.toml, along with the version write-to location.
2. marks for future removal setup_requires in setup.cfg. I don't remove this now because "Many tools, especially those that invoke setup.py for any reason, may continue to rely on setup_requires. For maximum compatibility with those uses, consider also including a setup_requires directive (described below in setup.py usage and setup.cfg)." (https://pypi.org/project/setuptools-scm/). I'm not sure when this no longer applies to Astropy. If it doesn't it would be good to remove.
3. removes stuff from setup.py. Like the above, I think it may be possible to remove use_scm_version, but I'm not sure.

Insight appreciated.

Fixes #12326

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Do the proposed changes actually accomplish desired goals?
• Do the proposed changes follow the Astropy coding guidelines?
• Are tests added/updated as required? If so, do they follow the Astropy testing guidelines?
• Are docs added/updated as required? If so, do they follow the Astropy documentation guidelines?
• Is rebase and/or squash necessary? If so, please provide the author with appropriate instructions. Also see "When to rebase and squash commits".
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• Is a change log needed? If yes, did the change log check pass? If no, add the no-changelog-entry-needed label. If this is a manual backport, use the skip-changelog-checks label unless special changelog handling is necessary.
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• At the time of adding the milestone, if the milestone set requires a backport to release branch(es), apply the appropriate backport-X.Y.x label(s) before merge.

[github-actions]

👋 Thank you for your draft pull request! Do you know that you can use [ci skip] or [skip ci] in your commit messages to skip running continuous integration tests until you are ready?

[Cadair]

Thanks!

[Cadair]

I see no reason why we shouldn't do this.

[saimn]

Any reason for this version requirement ? This forces using the 2 most recent versions released 2 months ago: https://pypi.org/project/setuptools-scm/#history

[Cadair]

I assume because this was the version which added pyproject.toml support? but I didn't check, this is just what the scm docs say to do.

[astrofrog]

I don't think there is any downside to being strict version wise here since it gets installed into the isolated build environment automatically anyway.

[nstarman]

this is just what the scm docs say to do

Yeah, that's where I grabbed it from. I can try to see if any earlier version works.

[nstarman]

It looks like this can be replaced with "setuptools_scm[toml]>=3.4"
Later versions allow for the [toml] to be dropped.

[Cadair]

As @astrofrog says, I don't think this is an issue. We run very modern Cython and other things in this list, I am happy to keep it where it is.

[saimn]

I'm asking because recently they broke our CI (and many others) with their tomli dependency.
e.g. pypa/setuptools_scm#608, pypa/setuptools_scm#624
Indeed they recommend >=6.2 but all the versions between 6.1 and 6.3 have been yanked.
Bu thopefully should be fine 🤞

[Cadair]

We can always hard pin a version if we don't trust them with releases?

[nstarman]

So merge with this version lower-bound? I guess if there's no version 6.2 it just goes up...

[saimn]

Ok, let's merge this. Not sure if we should backport to 5.0, so I set the milestone to 5.1 for now. @astrofrog, what do you think ?

[astrofrog]

I think 5.1 makes sense

[astrofrog]

Actually I think we should backport since we are going to be maintaining 5.0 for two years and we are fixing deprecated behavior

[astrofrog]

@meeseeksdev backport v5.0.x