Better versioning for BOUT++

[dschwoerer]

Inspired by setuptools_scm

[dschwoerer]

Thanks @d7919

[ZedThree]

Thanks @dschwoerer, I finally found some time to have a play with this! This still needs manual bumping of the versions inside the sed command when we release a new version?

EDIT: Could we pull out the v4.0.0 and 5.0.0.alpha into PREVIOUS_VERSION and NEW_VERSION variables?

Making it fall back to the hardcoded version if the git command fails is a neat touch.

One could imagine calling out to another tool to work out the version. In fact, setuptools_scm can actually be called from the command line 🤔
That would need some faff making sure it was installed though, and adding a pyproject.toml to configure it, etc. Looks like it's MIT licensed, so we could just pull out all the bits we need and hardcode our config.

But that can wait for a future PR, this works well for now.

[dschwoerer]

I actually tried setuptools_scm - but that would only bump to 4.4.$(n+1).dev - and there is no option to get 5.0.0.dev - only 5.1.0 or 5.0.1.dev, haven't tested, not sure. The issue is here: pypa/setuptools_scm#523
But that wouldn't work nice, because if we than merge 4.5 into next, it would use that instead of 5.0.0dev, Anyway, I wouldn't know how to programmatically decide on whether this is going to 5.0.0 or 4.5.0 or 4.4.x ...

So, yes, unfortunately, it needs manual bumping.

I think setting BOUT_PREVIOUS_VERSION and BOUT_NEXT_VERSION might be nicer 👍

[dschwoerer]

We will need pyproject.toml at some point, "just" need to get make wheel working 😀

[ZedThree]

Ah, good point. That is a bit of a shame. Also very true that we just decide what the next version will be, and don't really use an algorithm. Nevermind, this is still nice!

[ZedThree]

I've changed the hardcoded versions to variables, and updated the release checklist to reflect this.

I did consider making the variables settable from the command line (by making them cache variables), which would make it easier to test and change the variables for maintainers, but would probably cause more problems than it would solve when the version doesn't update automatically.

[ZedThree]

This can go in as soon as the tests complete