jj-split

name	jj-split
description	Split the current `jj` commit into multiple focused, self-contained, easy to review commits.
argument-hint	[extra guidance on how to split]
allowed-tools	["Bash(jj show *)","Bash(jj log *)","Bash(jj diff *)","Bash(jj describe *)","Bash(jj split *)","Bash(jj new *)","Bash(jj edit *)","Bash(jj describe *)","Bash(jj squash *)"]

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 travel with the code they test
• Refactors are never mixed with behavioral changes
• Prefer thin vertical slices, one complete feature end-to-end, over horizontal layers
• No orphaned code: every added API, abstraction, or stub must be used within the same commit. Don't split so small that dead code is introduced

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 no signals are found, 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 before proceeding
5. Split each commit except the last. After each split, edit the newly created parent commit (jj edit @-) and run the verification commands
6. Ensure every resulting commit has a description using 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, use file manipulation:

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 after a split

For when verification fails because some 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