Cleaning up after erroneous edit instead of new

[jacg]

1. I have a commit x and its descendant y.
2. I want to create a sibling of y, but accidentally use jj edit x instead of jj new x.
3. I do lots of work, before noticing that I've messed up x rather than working in a new commit (let's call it z).

have          want

 y'           z   y
 |             \ /
 x' = z         x

I know that JJ has the three states of the working tree that I want (x, y and z) somewhere. What is a good approach to changing the DAG shown on the left (what I have) to the one on the right (what I want) ?

[tim-janik]

Here is an FAQ entry that probably matches your situation:
I accidentally changed files in the wrong commit, how do I move the recent changes into another commit?

Basically, you can jj split -i x interactively or restore a previous snapshot from the operation log (jj op log [-p]), or from the evolution log of x and/or y.

If you want a TUI for this, jj-fzf has an op log view where you can pick old snapshots and inject them as a commit before @, and it has an evolog view that you can browse for a revision like x and inject a previous snapshot of x as a historic commit before the current x. Related screencast:
jj-fzf op log

[apoelstra]

Sometimes what I'll do is write down the git commit of my accidentally-combined commit, use the evolog (or jj undo if I'm sure there's only been one snapshot since I started editing) to go back to before my commits, then jj new and jj restore -f <git commit> <edited files> to get my changes back. (I think it would be helpful for the evolog or maybe op restore to have some builtin way to do this, like a "split from op entry" flag! Unsure exactly what it would look like.)

If there have only been a few changes sometimes I'll undo/restore then manually redo things on a new commit.

If I've been editing in a single editor session, sometimes I'll hold down 'undo' to the end, save, then jj new, then hold down 'redo' til the end. Obviously I need to be a little lucky for this method to be applicable :).

Usually I find it's pretty hard to use jj split in situations like this because I can't remember exactly which changes were from the previous commit, the changes sometimes overlap or are at least very close.

[jacg]

Yes, I usually resort to jj-split and editor-undo and other such hacks, for this sort of thing. But these all become intractable when the problem becomes sufficiently complex.

Knowing that JJ does have the three commits I want, even if identifying their IDs might be nontrivial, means that there is a pure DAG-manipulation approach available, and that's what I want to explore here.

So my question is specifically about

1. finding the IDs of the commits I want
2. arranging those three commits in the DAG I want

Does it boil down to a combination of

1. inspecting jj evolog x/y/z
2. jj new ... and jj restore --from based on what is found in step 1

or are there some useful features I'm overlooking?

[PhilipMetzger]

you probably want Ilya's jj split --from- from last year (#4097)