Musings on Jujutsu VCS

As someone who feels comfortable using basically all aspects of git, I didn't really understand what jj offered the first time I played around with it. But after coming back to it and using it for a few months now, I absolutely agree with others who say jj is simpler. I also find it to be much more flexible in terms of workflow. Squashing, splitting, or just creating new changes as I go (and sometimes even describing these changes in advance). I find myself switching between these workflows throughout the day without really thinking about it, because in Jujutsu they are all just the same thing: "changes".

When using jj I don't need to stage and commit my changes, I just need to describe them (though sometimes I will jj split which feels somewhat similar). I've never had weird stuff happen with untracked files when going back to an old commit. I don't need to worry about stashing uncommitted work to check or test something on another branch. I don't have to come up with a new branch name to avoid a detached head any time I want to jump back in time and try something else (jj doesn't even have the concept of a detached head). In fact, as far as git is concerned, my local has had a detached head for 3 months!

Seriously... No stashing. No staging. No creating or switching branches. No checking out commits. No soft resets. No hard resets. No frustration that git has locked me out of using half it's features because I'm half way through a failed merge. Just... changes... Want to move to a different point in history? Just create a new change based on that commit. jj doesn't even HAVE a command for merging. A merge is just a change with multiple parents. But what about conflicts? Well yes of course merging will still have conflicts. But you aren't held hostage until you resolve them. The merge commit can just stay conflicted until you are ready to deal with it. So you can move around the history and look at the two branches you are trying to merge for more context on how to resolve the conflicts. Or you can pause it and quickly fix something else then come back and pick up where you left off.

I don't even really think that much about branches anymore. The only time branches are even relevant now is when I need to know the name of someone else's HEAD commit so I can merge their changes with mine, or when I'm giving one of my commits a name to push or create a PR.

Even if I don't stick with jj for whatever reason, the way I experience git has permanently shifted after using it. There were many things about how git operates under the hood which I intellectually understood before. Some through playing around with the git internals, and others just through reading blogposts or documentation. But when actually using git, it never really felt like it worked that way.

A branch no longer feels like a collection of commits. It's just a name which references a particular commit. By extension a merge no longer feels like merging the changes of one branch into another. It's just a (often empty) commit with two or more parent commits. When you run git merge it also happens to move the head of the active branch to that new merge commit (The branch name refers to the new commit). But the ref being updated doesn't feel like part of the merge anymore.

I guess what I'm trying to describe is the difference between thinking or knowing something, and feeling it. Because of how fundamental branches are to the git workflow and the way you work with them, it really felt like branches were quite distinct from one another. The history felt like a tree, with very linear branches which can be merged to make a fatter branch. But now it actually feels like a graph. Like a singular history comprised of a bunch of commits, some of which have names.

I also feel like jj makes it so much easier to build upon and traverse that structure, because the tools it gives you are both simpler and more powerful. The mental model is also much closer to how git works under the hood. It's shown me that the model used by the git porcelain IS more complicated than the one used by the plumbing. I might even go as far as to say that it feels like how git was supposed to work.

All this to say, jj does feel different to use and it did take a few days to get a feel for all the different workflows you can choose from. But I also think it only taking a few days of passive learning to reach a point of comfort which many git users never reach is evidence of it being simpler. Not just simpler to use, but also simpler to learn. During that learning process I was so much more confident just trying things and seeing if it did what I expected, knowing that if I messed anything up fixing it is as simple as jj undo.