Trying Jujutsu (jj) for a Week

4 min read
#jj #git #vcs

I've been using jujutsu at work for a week now, it's been a good experience so far. I wanted to try it basically because:

  • I wanted to force myself to have a clean state in my repos, I usually left many files that won't be committed
  • I don't want to name branches for PRs anymore, when making small changes, fixes, etc most of the time nobody sees the branch name in the PR so why bother to give it a proper name
  • I want to switch between changes in an easy way, I was using git stash + switching branches for this

A few concepts to keep in mind

  • jj doesn't have a stage area, every change is itself already a commit
  • @ references current change, and @- references current change's parent
  • jj undo will undo any action made by jj, it's really helpful
  • we don't have branches in jj, we use bookmarks
  • we can use jj with any git project and this won't change how other work with the repository, we just run jj git init --colocate and that is just a local change

Workflows

So let's define some common workflows I needed to fulfill with jj

I don't use git from the terminal in my regular workflow, I use magit (so much faster) from Emacs so I don't type all of the below git commands but I describe the process to clarify the idea

Make a quick fix

I'm working on some feature and then someone asks me to make a change in the same repo I'm working on, what I was doing before:

git stash
git fetch origin
git checkout main
git merge origin main # to start from a fresh main branch
# do the changes
git checkout -b a-branch-name-no-one-will-read
git commit -m "some message"
git push
# go back to work, go to previous branch
git checkout original-branch
git stash pop

Now with jj

jj git fetch
jj new main@origin
# do changes
jj describe -m "some message"
jj git push -c @
# go back to work, run jj log and search for the change-id you were at
jj edit {change-id}

jj by default will create a branch with a name push-{change-id}, for example push-zxoytvwpvmxp, we can change it by creating manually a bookmark (equivalent to a git branch) but it's not necessary

Show you current changes

This will see all the current changes using regular diff format

jj show --git

Review a Pull Request

When I need to review a PR I need to test it locally

Before

git stash
git fetch origin
git checkout -b pr_branch_name origin/pr_branch_name
# review it
git checkout -
git stash pop

Now with jj:

jj git fetch
jj new pr_branch_name@origin
# review it
jj undo
# now I'm where I was before

Building a feature

There isn't much change here, in the git side:

git fetch origin
git merge origin main
git checkout -b a-branch-name
git add -p # because we review what we're staging, we are not savages
git commit -m "this is a feature"
git push

and with jj:

jj git fetch
jj new main@origin
# do your changes
jj describe -m "this is a feature"
jj git push -c @

One difference here is that in jj we are "forced" to commit all of the work we've done at once, we use jj commit --interactive or jj split to have something like git add -p but I'm not used to that yet

Rebasing an existing pull request

Considering we are at that PR branch already and we need to update it with latest changes from main branch and push it updated

git fetch origin
git rebase origin/main
# we changed history so we need to push force
git push -f origin your-branch

In the case of jj we need to make one step extra because jj bookmarks doesn't follow changes by default, once we made the rebase we need to tell jj to move bookmark to updated change.

jj git fetch
jj rebase -d main@origin
jj bookmark set your-branch -r @
# by default jj will make a push force
jj git push

Required stuff for work

In ~/.config/jj/config.toml:

Using company email address when committing

[[--scope]]
--when.repositories = ["~/src/my-company/"]

[--scope.user]
email = "erick.navarro@mycompany.com"

Signing commits

[signing]
behavior = "own"
backend = "ssh"
key = "~/.ssh/id_ed25519.pub"

What about Emacs, are we going back to the terminal for version control?

Yes and no, first I need to get used to how jj works and doing it in the terminal is the best option, by now I'm using jj-mode.el but just to switch between changes and edit description, all of the rest commands are done in the terminal(inside Emacs obviously 😎)

Conclusion

Will I change to jj and don't use git anymore?

Nope, jj gives me more flexibility in projects where I need to make changes quickly and where I collaborate with others, for personal projects where I'm mostly the only contributor and there is no rush in making changes I'll stick to git (for now? 🤔)