Jj:split

Split Commit by Function

Split a commit into multiple commits, grouping changes by functional purpose.

Process

1. Run jj status to check if splitting @ (has changes) or @- (working copy empty)
2. Run jj show <rev> --summary and jj diff -r <rev> --stat for overview
3. Analyze changes:
   • Small (≤5 files, ≤200 lines): run jj diff -r <rev> directly
   • Large: use /jj-context to group changes by purpose
4. Propose functional groups (implementation+tests together, config separate, migrations separate)
5. Ask user for approval via AskUserQuestion
6. Execute splits with one-line descriptions:

   jj split -r <rev> -m "<description>" file1 file2
   

7. Describe the last group (no split needed):

   jj describe -r @- -m "<description>"
   

IMPORTANT: Always use single-line commit messages. Never use multi-line descriptions or bullet points.

Common Groupings

• Core feature + its tests together
• Configuration/infrastructure separate
• Database migrations separate
• Refactoring/cleanup separate
• API changes vs UI changes

Example

# Split auth files into new commit
jj split -r @- -m "src/auth: add user authentication" src/auth.py test/test_auth.py

# Split API files
jj split -r @- -m "services/api: add rate limiting" src/api/rate_limit.py test/test_rate_limit.py

# Describe the remaining migration
jj describe -r @- -m "db/migrations: add users table"

Note: After each split, revision ID changes. Use @- for subsequent splits.