ci/github-script/prepare: qualify recommendation to retarget from nixos-*

[GraysonTinker]

Currently the script unconditionally recommends that the PR be retargeted against stable if it was originally made against a stable nixos branch, which can be confusing for first-time contributors.

These PRs are always in error, and are usually made by first-time contributors who have not read CONTRIBUTING.md. Accordingly, we shouldn't expect them to know the differences between the stable and unstable branches. A recommendation of retargeting against stable is likely to cause confusion because it is presented as the absolutely correct choice.

Change the message to instead specify they should read the relevant documentation section.

Untested and done from my phone, so double-check everything's right.

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.
• Follows the automation/AI policy.

[MattSturgeon]

Currently the script unconditionally recommends that the PR be retargeted against stable

That's not the intended behaviour. The condition correctBranch = stable ? `release-${version}` : 'master' is supposed to handle that.

Are you saying that that is not working? If so, we should fix it, not remove it.

[GraysonTinker]

Currently the script unconditionally recommends that the PR be retargeted against stable

That's not the intended behaviour. The condition correctBranch = stable ? `release-${version}` : 'master' is supposed to handle that.

Are you saying that that is not working? If so, we should fix it, not remove it.

I phrased this rather confusingly, sorry for that. I've updated the original message.

[MattSturgeon]

Concept SGTM now I've re-read your updated explanation. Sorry for the confusion.

I've also not tested, but the diff LGTM.
LMK if you do test this on a fork, or using the local test harness. The changes seem fairly simple though.

Will wait a while for further input. If nothing happens after a week or so, ping me and I'll merge at a time I can monitor and react.

Thanks for the improvement!

[mdaniels5757]

If a PR targets nixos-unstable, the value of this variable is release-unstable, which of course doesn't exist.

[GraysonTinker]

It now says release-* or master when targeting nixos-unstable.

[GraysonTinker]

Here are tests:

• Unstable: Test PR against wrong branch GraysonTinker/nixpkgs#2
• Stable: Test PR against wrong branch (stable) GraysonTinker/nixpkgs#3

[mdaniels5757]

I guess these PRs could be supposed to go to a staging branch, probably would be best to allow for that?

Suggested change

	`Make sure you know the [right base branch for your changes](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md#branch-conventions), then target \`${releaseStable}\` or \`master\` instead.`,
	`Make sure you know the [right base branch for your changes](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md#branch-conventions), then target the correct branch (probably \`${releaseStable}\` or \`master\`) instead.`,