Introduction to Jujutsu ####################### Jujutsu (``jj`` on the command-line) is a modern DVCS, that uses ``git`` repositorie as its storage backend. It borrows extensively from Mercurial, but has many more features. .. contents:: Table of Contents Links and Resources ------------------- - Hope page https://jj-vcs.github.io/jj/latest/ - In-progress tutorial: https://steveklabnik.github.io/jujutsu-tutorial/ - Good introduction and context: https://v5.chriskrycho.com/essays/jj-init/ - Short introduction: https://neugierig.org/software/blog/2024/12/jujutsu.html - Introduction for Mercurial users: https://ahal.ca/blog/2024/jujutsu-mercurial-haven/ - ``:ahal``'s configuration: https://github.com/ahal/dot-files/blob/main/dot-files/jj-config.toml Quick Start ----------- To get up and running with a fresh checkout, run the following commands (line-separated) after installing ``git`` and ``jj`` (jujutsu): :: # Create a clone and enter the directory jj git clone --colocate https://github.com/mozilla-firefox/firefox cd firefox # Alternatively, if you have the Git clone already jj git init --colocate # Set up jujutsu revset aliases (which will affect e.g. the default `jj log` output) jj config edit --repo [git] fetch = ["origin"] [revset-aliases] "trunk()" = "main@origin" "immutable_heads()" = ''' builtin_immutable_heads() | remote_bookmarks('autoland') | remote_bookmarks('beta') | remote_bookmarks('esr') | remote_bookmarks('release') ''' # Track remote bookmarks (you can do this for the other bookmarks, too) jj bookmark track main@origin autoland@origin beta@origin release@origin # Move the working copy commit to bookmarks/central jj new main General Tips ------------ Changes and Commits ~~~~~~~~~~~~~~~~~~~ ``changes`` and ``commits`` are distinct concepts. While in git there’s a one-to-one record of ``changes`` *as* ``commits`` (plus, perhaps, staging), in jujutsu ``commits`` occur fairly frequently (basically any time there’s a change and you run ``jj``, which results in a snapshot). In this sense, ``commits`` can be considered literal snapshot/state commits, whereas ``changes`` are the user-friendly unit-of-work that developers are doing. ``changes`` have hashes that are alphabetic, whereas ``commits`` have hashes which are the same as their git counterparts (sha1, represented as hex characters). Thus, a particular ``change`` points to one ``commit`` at a time, however there is a history of ``commits`` recorded for each ``change`` (see ``jj evolog``, for example). You can specify either ``change`` hashes *or* ``commit`` hashes in revsets. Firefox Main Tips ----------------- Other Useful revset aliases (place in ``.jj/repo/config.toml``) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ :: [revset-aliases] # Get all changes with "Bug 12345" in the subject (can be improved with https://github.com/jj-vcs/jj/issues/5895) 'bug_all(x)' = 'mutable() & subject(glob:"Bug *") & subject(x)' # Get head change(s) with "Bug 12345" in the subject 'bug(x)' = 'heads(bug_all(x))' # Get root change(s) with "Bug 12345" in the subject 'bug_root(x)' = 'roots(bug_all(x))' ``moz-phab`` ~~~~~~~~~~~~ WIP support for Jujutsu in ``moz-phab`` is being developed at ```erichdongubler-mozilla/review``\ #1 `__. You can install this via: :: pip install MozPhab@git+https://github.com/erichdongubler-mozilla/review@refs/pull/1/head If you need to fall back to using Git with vanilla ``moz-phab``, most operations require you to not be in a detached ``HEAD`` state. However, Jujutsu frequently leaves it in one. One simple solution is to wrap the ``moz-phab`` command with a script like: :: #!/bin/sh git checkout -B moz-phab && moz-phab "$@" You could instead make this a shell alias/function, if preferred. ``mach try`` ~~~~~~~~~~~~ ``./mach try`` requires a clean working directory to push. When editing a change in Jujutsu, the changes will be moved to the index in Git. Therefore in order to push to try, you must start a new empty change on top of the change you want to push. E.g: :: $ jj new $ ./mach try ... $ jj prev --edit The following alias automates this so you can use ``jj try-push `` instead of ``./mach try `` and it will create/remove a temporary empty change: :: [aliases] try-push = ["util", "exec", "--", "bash", "-c", """ #!/usr/bin/env bash set -euo pipefail jj new --quiet ./mach try $@ || true jj prev --edit --quiet """, ""] See also `Bug 1929372 - [mozversioncontrol] Add unofficial support for Jujutsu repositories `__ ``mach lint`` ~~~~~~~~~~~~~ | ``./mach lint`` can be integrated with ``jj fix``. Follow the instructions here: | https://firefox-source-docs.mozilla.org/code-quality/lint/usage.html#jujutsu-integration (adding the config to ``jj config edit --repo``) The benefit of running ``jj fix`` over ``./mach lint --fix`` directly, is that it will step through all your mutable commits and checkout each file at that revision before running the fixers on it. So you’re guaranteed to get the fix directly in the commit that introduced the issue. Rebasing work in progress (and automatically drop changes that have landed) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You want something like: :: jj git fetch && jj rebase --skip-emptied -r 'mutable() & mine()' -d main This will: 1. Pull from the main repo 2. Rebase any mutable changesets you’ve made onto the (updated, tracked bookmark) ``main`` changeset, and drop any that become empty (because they have landed) Of course you could narrow the scope of what you want to rebase by altering the ``-r`` argument and providing specific revisions, or rebase onto autoland or beta or other bookmarks if you want. Dropping/pruning/removing obsolete commits ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (Note: you may want to look at the `previous tip <#rebasing-work-in-progress-(and-automatically-drop-changes-that-have-landed)>`__!) You can use any of: :: jj abandon x jj abandon x y jj abandon x..z jj abandon x::y To abandon individual revision ``x``, both individual revisions ``x`` and ``y``, or the range of commits from ``x`` to ``z``, respectively. When you’re dealing with temporary changes that you have not committed (“working directory changes”) this is also an easy way to revert those (a la ``hg revert --no-backup –all``). Watchman integration ~~~~~~~~~~~~~~~~~~~~ Tired of the frequent Snapshotting… message? Edit your global ``jj`` configuration by doing: :: jj config edit --user and add the following: :: [core] fsmonitor = "watchman" Instead of scanning the file system, ``jj`` will (much like ``hg``\ ’s ``fsmonitor`` extension) use file system events to be notified about file changes, resulting in much shorter operation time, without having to disable the snapshotting mechanism.