Build bottles via GitHub Actions only one new arch

[mahrud]

Description of issue

Now that GitHub Actions has macos-15 (arm64) runners, I want to build a number bottles on them, but ideally without rebuilding bottles on older runners (in particular, I still have bottles for macos-12 which won't be rebuilt anymore since libtool doesn't have a monterey bottle anymore). Is this possible in some way?

Alternatively, if I rebuild all bottles including for macos-15, can I manually reupload the old macos-12 bottle, or is that going to break everything?

[carlocab]

You can try adapting the dispatch-build-bottle workflow in Homebrew/core which does exactly this.

There's a lot of extra logic that's probably specific only to Homebrew/core, but the specific bits to look at are the bottle job, which builds a bottle, and the upload job, which uploads it.

[mahrud]

Thank you!