IME, the only real pain point with JJ is Git integration. I love it, it's great in almost everything it does. Formalizing all the DSLs and using them consistently throughout the config and CLI is exactly how filesets, revsets, and templating should be implemented. The focus on exposing concepts as interfaces (without "directly reflecting internals"[1] in the UI) is only as good as the concepts themselves, and in JJ's case, they are powerful. The problem is that they are too flexible, so Git interop relies heavily on convention and discipline... which is fatal. The fact that (almost?) all states of JJ are representable in Git makes it easy to mess up your remote, and then you need a very solid understanding of Git to fix it.
If you can give `jj` a try on a greenfield, single-developer project, you probably should. It feels exactly like Git felt compared to Subversion (when you focus on JJ's strengths and use it in favorable conditions - it is young, after all). Get acquainted with `jj` on its terms, and if things click for you, you'll be a bit better prepared for the bumpy road that is Git interop later on.
In princple JJ has non-Git backends, but the only backend they state as being production ready is the Git backend. JJ without the Git interop is more a concept than a reality right now.
I love JJ, and the mental model of source control it presents, and I will continue to use it. However, still needing to "drop down" to Git every now and again to get something done makes it feel very much like a convenient wrapper on top of Git rather than a new SCM.
If Git adds commands to support the JJ workflow, it would be hard to justify having JJ installed any more.
The backend itself is fine, it's just trying to use JJ as a Git frontend for projects developed on Github (among 20 other devs using git, where each of them uses git through different interface and/or in different style) that's currently not ideal :(
> However, still needing to "drop down" to Git every now and again to get something done makes it feel very much like a convenient wrapper on top of Git rather than a new SCM.
Yeah, but I think that's fine. Git is a solid foundation; it's not wrong to try to build on it initially. It gets you a usable implementation faster. It is a pain point, though.
> If Git adds commands to support the JJ workflow, it would be hard to justify having JJ installed any more.
Is that a danger? I don't see Git as a fast-moving target. And among all the "convenient wrappers on top of Git", JJ seems to have the design least tied to Git, so I think it has the highest chance of breaking out of the Git dependency in the future.
If you can give `jj` a try on a greenfield, single-developer project, you probably should. It feels exactly like Git felt compared to Subversion (when you focus on JJ's strengths and use it in favorable conditions - it is young, after all). Get acquainted with `jj` on its terms, and if things click for you, you'll be a bit better prepared for the bumpy road that is Git interop later on.
[1] https://news.ycombinator.com/item?id=48903054