Creating Patches in a Colocated Jujutsu Repo

2 min read

Today I needed to share a couple of commits as a patch with someone outside the repo, and learned that jj covers half the job. The other half is git, right there in the colocated repo.

Say the graph looks like this and I want wmktltov and lzxnnyks combined into one patch:

@  nomryxuq dev@example.com 2026-05-11 13:21:21 a63b6073
│  (no description set)
○  lzxnnyks dev@example.com 2026-05-08 11:16:43 feature/api-backend bbea56a3
│  Complete API backend (TICKET-123 part 2)
○  wmktltov dev@example.com 2026-05-08 10:47:51 f7db1946
│  Begin API backend (TICKET-123 part 2)

A single combined patch: jj diff –git

jj diff --from "w-" --to "l" --git > backend.patch

w- is “the parent of w”: start before w’s changes and end at l’s content, producing one diff covering both commits’ work. The --git flag is what makes the output applicable: jj’s default diff format is its own human-readable “color-words” style, which git apply and patch can’t consume. --git switches it to standard git unified diff:

jj diff --from "w-" --to "l" --git > backend.patch
git apply backend.patch   # or: patch -p1 < backend.patch

One file per commit: drop into git

The git format-patch workflow produces mbox files with full From: / Subject: / Date: headers, which is what most upstream maintainers expect. It has no jj equivalent, so use the colocated Git repo directly:

git format-patch f7db1946^..bbea56a3
# produces 0001-Begin-....patch, 0002-Complete-....patch

Applying patches works the same way: there’s no jj apply, so git apply in the colocated repo, and jj snapshots the resulting changes into @ on the next command.

Anonymising before sharing

jj diff --git emits only the diff body, with no author lines or commit messages, so anonymising means scrubbing content inside the diff (paths, hostnames, project names, ticket IDs). git format-patch adds mailbox headers, so add those to the list. A quick sed pass catches the obvious stuff:

jj diff --from "w-" --to "l" --git \
  | sed -E '
      s/[A-Za-z.+-]+@example\.com/dev@example.com/g
      s/TICKET-[0-9]+/TICKET-123/g
      s/internal_service/api_backend/g
      s/internal-host/example-host/g
    ' > backend-anon.patch

Gotchas / Notes

  • Tune the sed rules to what’s actually in your diff, and eyeball the result before sending. sed won’t catch names embedded in unique strings or identifiers you didn’t anticipate.
  • This is colocated mode working as designed: jj handles the single combined diff, and git handles the mbox-per-commit case it’s still better at. Reach for whichever fits the job.