The thing about jj is that it doesn't actually enable any new capabilities. I tell people to use emacs or vim or vscode or whatever instead of notepad because it gives them new capabilities, things that are simply unavailable unless you're talking to an LSP or running a full-powered scripting engine. jj doesn't make anything possible the way going from notepad to a real editor does. What jj does do is it makes everything so much easier that you can now actually use all of those features that git theoretically gave you. Rebases? No more fiddling, no more wedges, no more digging through the reflog because you fat-fingered something, you just go `jj rebase` and... that's it. And if you get it wrong, you just do `jj undo` and... that's it. And if you just had a six hour manic coding marathon without committing anything and now you want to spread its batch of changes back down through your patch stack, you just do `jj absorb` and... that's it. It's not the difference between notepad and emacs where you're going from no LSP to LSP, it's the difference between emacs@2016 where LSP support is a week-long adventure and emacs@2024 where LSP support is five lines copy-pasted out of the info page.
As a source control expert and jj's number one fan [1], I would count being able to defer merge conflict resolution as a new capability, FWIW. In general I think jj's greater than the sum of its (very good) parts because of how its features work together to create a coherent and pleasant user experience.
I guess I was thinking in terms of the patches you push up to github. `jj` is a joy to use and it absolutely enables me to implement workflows that I wouldn't even vaguely consider without it helping me; the big one I think of is the one where you work in a merged dir with like six parents and use `jj absorb` to instantly spread your changes out to the different PRs. I've been forced to do that in git. It was a nightmare and took me two days. Not impossible! Just utterly impractical. `jj` takes end results that were theoretically-possible-but-practically-infeasible and makes them usable. Which I suppose counts as a new capability from the UX perspective. :P
Absolutely! jj is a real advancement in the state of the art. I think it's the second time in the history of source control where the authors of a new system have spent a long time working on existing systems + deploying them at scale, and have brought their full expertise to bear on the design of the new system.
(The first was BitKeeper, which also was a tremendous achievement.)
> In February 2000, they contacted Karl Fogel, the author of Open Source Development with CVS (Coriolis, 1999), and asked if he'd like to work on this new project. Coincidentally, at the time Karl was already discussing a design for a new version control system with his friend Jim Blandy. In 1995, the two had started Cyclic Software, a company providing CVS support contracts, and although they later sold the business, they still used CVS every day at their jobs
You may recognize Jim as one of the authors of Programming Rust.
jj is not just a new interface for git, it has a lot of new and powerful features to offer, even when you're using the git backend with a colocated repo.
Just to name a few:
- deferred conflict resolution
- The very expressive revset language
- the op log and ability to undo any operation
Many things that you can do with the git cli are significantly easier and in some cases comparatively effortless using jj. If all you do is git add and git commit then you probably aren't missing out on much, but if you ever split or rebase commits you should definitely try jj.
