Jj Split

Split the current jj commit into multiple focused, self-contained, easy to review commits.

Current commit

jj show --git

$ARGUMENTS

Principles

• One concern per commit: e.g. bug fix, feature, refactor, or config change
• Each commit passes all checks: format, lint, typecheck, build, test
• Tests go in the same commit as the code they test
• Never mix refactors with behavioral changes
• Prefer thin vertical slices, one complete feature end-to-end, over horizontal layers
• No orphaned code: use every added API, abstraction, or stub within the same commit. Don't split so small that a commit contains dead code

Workflow

1. Read the diff above. If the commit is already small and self-contained, tell the user and stop
2. Identify logical groupings and order them from most foundational to most dependent. When a boundary is ambiguous, keep changes together
3. Infer verification commands from project signals (e.g. package.json, Makefile, CI config). If there are none, ask the user
4. Present the plan as a numbered list:
   • Commit N: <imperative-mood description>: <file or hunk list>
   • One sentence justifying each split boundary
   • The verification commands you will run after each split
   • Ask for confirmation
5. Split each commit except the last. After each split, edit the newly created parent commit (jj edit @-) and run the verification commands
6. Give every resulting commit a description with jj describe
7. After all splits, run jj log -r 'ancestors(@, <commit count>)' and show the resulting stack

How to split

By file

Use jj split with file patterns to put specific files in the first commit:

jj split -m "<first commit description>" -- <files for first commit>

The remaining files stay in the second commit.

By hunk

When a single file contains changes that belong in different commits, edit the file directly:

1. Edit the file to contain only the changes for the first commit (remove hunks that belong later)
2. Run jj new to start the next commit
3. Re-edit the file to restore the hunks removed in step 1
4. Verify with jj log -r '@-::@' and jj diff -r @-

Fixing mistakes

Use these when verification fails because changes are in the wrong commit.

Move files between child and parent commits

# Move from child to parent
jj squash --from @+ --into @ -- <files>

# Move from parent to child
jj squash --from @ --into @+ -- <files>

Move hunks between commits

When the boundary falls inside a file, edit the file directly:

1. While on the commit that should lose the hunk, remove it from the file
2. Switch to the other commit and restore the hunk there
3. Verify both commits