We're instead going to be working on a centralized branch, so closing this in preference for https://github.com/numpy/numpy/tree/meson

Thanks for getting the ball rolling here with a PR Stefan! As we just chatted about, let's come up with an integration strategy. For everyone, to set some expectations, this is probably going to be a 3-6 month long project, with a bunch of moving parts. So it's too much for a single PR. Hence a long-lived feature branch named meson in the main repo seems like a good idea. That allows everyone to follow along and contribute, while avoiding churn in main.

In addition to the diff in this PR, I have a start here on all the configure checks for npymath (a little outdated after the recent cleanups): https://github.com/rgommers/numpy/tree/meson.

Here is a proposal for how to (a) work on build system changes, and (b) track, prioritize and divide up the work:

• We use a meson branch in this repo
• CI:
  • we ensure regular CI does not run on meson, by removing regular CI jobs from the meson branch in order to not trigger a lot of unnecessary CI runs
  • we start with one new Linux CI job in the meson branch, and deal with other platforms and configs once things have started working on Linux
• Branch rules:
  • for simple changes where the author is fairly sure that the changes are correct, pushing directly to the meson branch is fine,
  • for more complex changes, let's work via PRs to ensure that we get at least cursory review early on
  • since it's a branch in the main repo, merging main into meson is preferred over rebases. @stefanv, @mattip and @rgommers will align in case the meson branch needs rebasing or other history rewriting, to ensure that we don't lose anyone's work.
  • we should avoid making code changes other than build/CI/docs in the meson branch; if we need fixes in NumPy itself, we should open separate PRs for those, get them merged quickly, and then merge main into meson
• Once we are ready to merge initial Meson support into main, we will make a careful PR with granular commits and co-authorship for folks who contributed to the code in that commit.
• For tracking the work, we will have:
  • One tracking issue (I can create it after the project board is done)
  • A project board with status per topic and assigned dev; @mattip made a start of that in Move build to Meson (view) and I'll add to that soon.
  • Documentation on how to test/use the build will live in the meson branch itself.
  • Writing a NEP may be useful at some point, but I'd like to postpone that.