{ci/eval,release}: migrate supported systems to top-level

[emilazy]

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

[emilazy]

Not sure if the merge group failures are blocking or not; they don’t block queue entry, but I’m not sure if they’d happen the same way on merge. If they would, then I can split the creation of release-supported-systems.json out into a separate PR that could be merged before this one, though hopefully that’s not necessary… (OTOH, maybe this would temporarily break CI on the 25.11 branch before the backport is merged, as‐is?)

[wolfgangwalther]

You can save running an extra job by just doing an API call to get that file from the right branch in the prepare jobs and then pass on the systems value the same as before.

Example here:

nixpkgs/.github/actions/checkout/action.yml

Lines 44 to 57 in 027294e

	// Getting the pinned SHA via API allows us to do one single fetch call for all commits.
	// Otherwise we would have to fetch merged/target first, read pinned, fetch again.
	// A single fetch call comes with a lot less overhead. The fetch takes essentially the
	// same time no matter whether its 1, 2 or 3 commits at once.
	async function getPinnedSha(ref) {
	if (!ref) return undefined
	const { content, encoding } = (await github.rest.repos.getContent({
	...context.repo,
	path: 'ci/pinned.json',
	ref,
	})).data
	const pinned = JSON.parse(Buffer.from(content, encoding).toString())
	return pinned.pins.nixpkgs.revision
	}

[emilazy]

Oh, I migrated this to the API but missed the part about doing it in the prepare job… I’ll fix that now. I also split that part into #493997 so that we don’t break CI on any branch with the file migration.

[emilazy]

I believe I have done this correctly now, and hopefully once this is merged and backported, pre‐merge CI on the follow‐up will succeed on a re‐run.

[mdaniels5757]

LGTM!

(This PR doesn't change ci/github-script/prepare.js to use the new file, but that doesn't matter because the ci/supportedSystems.json file still exists, and changing prepare.js to use pkgs/top-level/release-supported-systems.json in the follow-up PR will work because both files will exist on the follow-up PR's base branch once this is merged).

[nixpkgs-ci]

Successfully created backport PR for release-25.11:

• [Backport release-25.11] {ci/eval,release}: migrate supported systems to top-level #495040