macOS 12 GitHub-hosted runners will stop working from 2024-12-03

[huonw]

https://github.blog/changelog/2024-08-19-notice-of-upcoming-deprecations-and-breaking-changes-in-github-actions-runners/

macOS12 runner image We are beginning the deprecation process for the macOS 12 runner image, which allows us to balance our fleet capacity ahead of our upcoming macOS 15 launch. This image will be fully retired by the December 3rd, 2024. We recommend updating workflows to use macos-14, macos-13, or macos-latest.

See also:

• 21074

• 21003

[huonw]

Hm, I don't think this is properly completed:

• 21569 just deprecated running on macOS-12, we need to switch main to macOS-13/14...

• even once we do that, we still use the macOS-12 runner on the 2.23.x branch, and on the upcoming 2.24.x one (note we haven't released 2.23.0 stable yet)

We do not have much time before the deadline of Dec 3, and this is the platform support for current releases:

version	branch	macOS version (x86-64)	macOS version (arm64)
2.22.x	2.22.x	10.15 (self-hosted)	11 (self)
2.23.x	2.23.x	10.15 (self)	11 (self)
2.24.x	main (currently)/2.24.x (soon)	12 (GitHub-hosted)	11 (self)
2.25.x	main (soon)	13 (GH)	14 (GH)

So, it looks like only the 2.24.x branch will cause a problem, since it's the only one using the GitHub-hosted macOS-12 runners. Note, even if we were to get 2.24.0 out within the next month, we'll have problems with patch releases (2.24.1 etc.).

Some options:

1. plan on only doing 2.24.0 and then rolling on to 2.25.x immediately (i.e. no releases after 2.24.0)
2. accelerate the deprecation of macOS 12 to 2.23.x (that release is still built on 10.15 and 11 respectively, but emits deprecation warnings if running on them)
3. switch 2.24.x back to use the 10.15 self-hosted runner (but still deprecate running on macOS <= 12 (x86-64) or 13 (arm64))

I'm inclined to 3, it means we have to keep the self-hosted runners around for longer (until we close the 2.24.x milestone, this becomes encouragement to keep the releases going regularly), but is the simplest to administer and seems lowest risk.