Support jj for repo root checks

[plumj-am]

Jujutsu (jj), if you are unfamiliar, is a git-compatible VCS: https://github.com/jj-vcs/jj

In jj worktrees I noticed I can't render workflows because they're independent from git unlike a lot of jj and get_git_toplevel() fails.

I've tested this in both git, jj, and git+jj scenarios and it works perfectly.

[plumj-am]

Sorry, I thought I ran the flake check. I'll fix it today.

[nialov]

I am a bit worried about the potential unwanted behavior here as I am unfamiliar with jj. get_repo_root now calls jj root first and as jj is added to runTimeInputs, it will always use jj. Will it always resolve the same as git rev-parse --show-toplevel?

I think this would be better handled by an explicit flake-parts option, such as flake.actions-nix.useJJ which enables usage of jj as input in runTimeInputs and by adding e.g. a flag to render-workflows. By default it would be false so no behavior is changed for users of actions.nix. I can provide some help to show spots where I think the code should be added if you have the time to revise?

[plumj-am]

Yes, after looking into it a bit more, I see it's a bit flawed. Sorry about that! I'm working on a better solution as you described right now.

How I would do it:

• add the option ciModule.options.useJJ
• optional pkgs.jj for runtimeInputs based on the new option
• pass useJJ through to the script via cmdLine.useJJ and then use it in the get_repo_root()

Would you add/change anything? Also, if useJJ is enabled, should it still fallback to git or should it be git OR jj only?

I'll add a bit more info about jj for you to clear some things up:

• jj repos can be colocated with git repos (so they are backed by git) which means jj root and git rev-parse --show-top-level will share the same result
• However, jj repos can also be standalone (some platforms support jj without git backing) which means git rev-parse --show-toplevel will fail but jj root will work fine
• Most of the time, people use jj git init --colocate (which gives a jj repo backed by git) but it's worth keeping in mind that it's possible to use jj alone with some providers which could cause issues if we try to fallback to git

[nialov]

Thanks a lot and sorry for delay! Merged.