Comment by Arainach
14 hours ago
Git already won through Github, the Linux kernel, and other important projects. Even if you like Mercurial's syntax better (I do) and wish it won (I do), that battle was over many years ago.
jj's data store is git. You can use jj while other people on your project just use git. There's no migration of data or history. You can use Github and all of the various git tooling that exists today.
As such, the initial cost of switching to jj is zero for individuals, teams, or projects. That's huge.
jj's ergonomics are significantly nicer. Fewer ways to shoot yourself in the foot, much better merge resolution, etc.
It is possible to move one step further: use own store, speak git protocol. In the end, it is about the commit-tree-blob model. I think, the main headwind is the broad decay of interest in computer science topics.
Where can I read on jj merge resolution strategies? LLM links to Arch Linux man page and other random stuff.
You can speak the git protocol over the network only, but one advantage of using the same storage on disk as Git and exposing it in the same way (in a manner that keeps jj/git in sync) is that git-based tools still work. So, people still get diff markers in the gutter of their editor buffers, random scripts that do `git rev-parse` or whatnot still work out of the box, etc. This makes the experience more seamless and imposes less friction on non JJ users, eg you do not have to write a patch and add a special case for JJ because `git rev-parse` failed to run and then ask pretty please to merge it (and then keep doing that forever as you are the only user).
It doesn't sound like much, but before I started contributing to Jujutsu I was a user of https://sapling-scm.com/ -- Sapling is fantastic. It stores data on disk in git format, but back then it was not exposed to the user by default -- the .git directory is hidden away. It actually ended up causing a lot of friction that random `git` commands would not work, or tools had other various git-based behaviors. These days, sapling has a "dotgit" mode (partially inspired by jj I assume) that puts the .git directory in the root dir, so `git` commands still work.
Beyond that though, speaking Git over the network only has other complications on the client side. In particular Git clients and servers negotiate what objects each side has (given what the client requests), and from that negotiation derives a list of needed objects to give the client, and then sends a packfile for it. This is all relatively expensive to do on demand, actually, so it would make the interactivity for network operations much worse if you need to wholly translate your storage into packed objects, etc. And doing it efficiently would require you keeping a cache around that is basically a git database anyway, so you might as well just go ahead and use it. Not the end of the world in terms of downsides, but a trade-off that adds some baggage.
Using a different data store breaks compatibility and dramatically increases the friction to switching to it. jj's superpower is that my usage of it is invisible. Right now I'm working on Github projects in jj where none of the other contributors are. Nothing about my usage of jj requires them to change anything they do.
The jj tutorial is useful: https://docs.jj-vcs.dev/latest/tutorial/