Jujutsu megamerges for fun and profit

I do not understand the appeal of the workflow of working on separate things in parallel, then splitting it off into branches/commits. imo, isn't it better to fully focus on one thing at a time, even if it is "simple"?

I imagine if I follow this workflow, I might accidentally split it off in a way that branch A is dependent on some code changes in branch B, and/or vice versa. Or I might accidentally split it off in a way that makes it uncompilable (or introduce a subtle bug) in one commit/branch because I accidentally forgot there was a dependency on some code that was split off somewhere else. Of course, the CI/CD pipeline/reviewers/self-testing can catch this, but this all seems to introduce a lot of extra work when I could have just been working on things one at a time.

I'm open to changing my mind, I'm sure there are lots of benefits to this approach, since it is popular. What am I missing here?

Been trying to get into jj lately, but I rely a lot on VS Code's git gutter to review changes as I code. Doesn't look like jj has an equivalent in VS Code. Anyone got tool recommendations?

Some fantastic tricks in this article. Will definitely improve my Megamerge game. Thanks!

Though, I'd be remiss not to mention that this (and any other) jj workflow would be much easier with jjui. It's the best TUI around, not just for jj

I proposed incorporating some of this article into it. https://github.com/idursun/jjui/discussions/644

Great writeup! I've been using `jj parallelize` [1] a lot (and wrote about it here [2]) to fan out a sequence of commits to set up a megamerge, but your stack alias sounds super useful to create them on the fly, rather than at the very end of a work stream. Thanks for the tips!

[1] https://docs.jj-vcs.dev/latest/cli-reference/#jj-parallelize [2] https://blog.chay.dev/parallelized-commits

I found octopus megamerge hard to collaborate - my colleagues don't use JJ so they may introduce changes that would cause conflitcts to my megamerge. When you have a conflict on a change that has more than 2 parents, the conflict resolution becomes unmanageable very quickly. No merge tool can handle more than 3-way merge, so you have to do that manually.

Eventually I settled on a tree-like megamerge that's more practical: merge 2 branches at a time and merge the merged branch with the next branch. This way I only need to handle 2-way conflicts at a time which is more manageable.

Also you have to be very careful to decide the order when you (and your colleagues) are going to land the branches, or if you expect any new features other people are working on that's going to conflict with your branches. When using megamerger workflow, most of the problems come from coordinating with other colleagues.

Makes me happy to see the influx of jj posts as of late. Great tool. Roughly this workflow is how I convinced a few friends to finally loosen their death grip on git and try something new.

Great article, Isaac!

If anyone is JJ-curious, I also can't recommend the Discord[1] enough. The community is very helpful and welcoming.

[1]: https://discord.com/invite/dkmfj3aGQN

I love this stuff as a hobbyist, but professionally I can't help but think this is all obsolete in the age of agent-driven development. I wish jj was around a decade ago.

If this works like I think it does, it might be the missing piece I've been waiting for, for actually trying jj. Thanks!

How does the megamerge handle the case where two included branches overlap in changes and a new commit is made that applies to the overlap?

this is great stuff. I've been ad hoc building a version of this workflow, and it is quite fantastic.

I'm still not as smooth at figuring out conflicts on mega-rebase.

It's interesting to see the strange workflows that come from jujutsu users, as someone who works on git workflows.

There's some counterproductive stuff in there from my perspective but at its core you're keeping up a throwaway integration branch, which is helpful practice if you'll ever care about an integration. It's annoying with git because the interface for updating your throwaway integration branch is very clunky and easy to get wrong.

Great post. Thanks for sharing.

Finally

I saw Jujutsu on HN a few days ago and gave it a try. I picked a bunch of it up in just a couple hours and a couple days later I've completely switched to it for all my projects, it's not even close. Git is dead to me.

I just wish Jujutsu supported git tags rather than only supporting bookmarks as branches. And I also wish that Jujutsu supported preserving commit dates during rebases.

One of my absolute favorite things about Jujutsu is how easy it is to manipulate the commit graph remotely without having to manually checkout each commit first. I've been working on some pull requests to their built-in diff editor lately trying to improve the user experience enough that most conflicts will be fixable without having to use a text editor.

Also, the lack of a special staging area means you also never have to fucking stash your changes before you can do practically anything. Your changes always have a place, you can always go somewhere else and you can always come back.

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