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Log

Introduction​

Change vs. Commit

jj distinguishes between change and commit. A change is a commit as it evolves over time. You can consider both to be equivalent only that the change ID will remain the same as you modify that change (as opposed to the commit ID, which is different after every amend, rebase etc.). This is very convenient if you keep modifying the same change. Commits are exactly the same thing as in Git, in fact jj relies on having an underlying Git repository.

Another way of looking at it would be to say that the change ID is a label that jj attaches to a commit. Whenever you operate on that commit, jj will notice this and after modifying the commit will move the label from the old obsolete commit to the new one. Remember that commits in Git are immutable and any modification to the parents, commit message, commit date, content etc. will cause a new commit to be created that will have a different commit ID (hash), even if the commit may look unchanged at first glance.

The jj log command shows the history of the repository. If you configured jj as recommended in the last section, you can simply run jj to get the log output.

jj

Log output

A few things to note about the above screenshot:

  • Starting at the top left, @ is the working copy, meaning all files as they currently appear in your working directory, including all modifications. jj always commits everything for you, so @ is a regular Ju Jutsu change (with an underlying commit). If you use Git directly on the repository, all modifications in @ will be displayed as uncommited changes by Git because @ is tracked internally by Ju Jutsu.
  • Next to it, you have smmzpnrn, the change ID. Every change has such an ID that never changes even as you modify, rebase etc. the change. Highlighted is the shortest unique prefix that identifies the change, s in this case. Whenever a change ID is required you can just use this prefix.
  • After the email address and commit date you have the commit ID as in Git. It is in fact exactly the same commit ID as in Git. It will change every time you modify the change. In this case cacb68cb, again with the shortest unique prefix c highlighted.
  • The next change w has a bookmark main attached to it. Bookmarks are the jj equivalent of branches. Also attached to it is the git_head() revset function which identifies the HEAD of the Git repository. You'll notice that the @ change is not included in git_head(), meaning it will not appear when for instance you execute git log. Ju Jutsu maintains a separate internal Git history inside the .jj directory.

Examples​

Try them!

Show all the history
jj -r ::
Show the ancestors of 'main' but limit to 3
jj -r ..main -n 3
Show all children of the change 'kt'
jj -r kt+
Show all changes that are ancestors of 'main' and were commited on 2024-12-05
jj -r 'committer_date(after:"2024-12-05") & committer_date(before:"2024-12-06") & ::main'

Check the Revset language for more options.

Other Commands​

Try them out!

Some more useful commands and options:

Display log with file names
jj -s
Summarize the current change
jj show
Summarize the latest change on 'main', only file names
jj show -s main

Takeaways​

Key points. As QA because of active recall. Try to come up with the answer yourself before looking 😉

  1. What is a change?
  2. What is @?