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# 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.
:::{note}
Jujutsu is an optional alternative to plain Git for managing your
patch stack. If you prefer Git, see [Working with stack of
patches Quick Reference](stack_quickref.md).
:::
```{contents} Table of Contents
```
## Links and Resources
- Short introduction:
- Introduction for Mercurial users:
## 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. Use one of the following
# (1) Fresh clone:
cd firefox
./mach vcs-setup
# (2) Or if you have a Git clone already:
./mach vcs-setup --vcs=jj
# Set up jujutsu default configuration (which will affect e.g. the default `jj log` output)
./mach vcs-setup
# Track remote bookmarks (you can do this for the other bookmarks, too)
jj bookmark track main@origin autoland@origin beta@origin release@origin
# To see the other untracked bookmarks on that remote:
jj bookmark list --remote origin -T 'if(!tracked && remote, name ++ "@" ++ remote ++ "\n")'
# 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 using the letters k..z,
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.
### Co-located Jujutsu and Git
A [co-located repository](https://jj-vcs.github.io/jj/latest/git-compatibility/#co-located-jujutsugit-repos)
allows running `jj` and `git` commands in the same repository rather than
syncing changes between `jj` and `git` repositories to switch between the
different tools. Recent versions of `jj` default to being co-located.
Git commands can be useful because some features are not yet implemented in
Jujutsu, such as `git log` and `git rebase` for [interactions with file
{ref}`Transplanting Patches To and From Mercurial Repositories
<git-mercurial-transplant>`.
## 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)'
'bug(x)' = 'heads(bug_all(x))'
'bug_root(x)' = 'roots(bug_all(x))'
```
### `moz-phab`
As of `moz-phab` 2.0.0, Jujutsu is officially supported! This applies to both
colocated Git/Jujutsu repositories, as well as standalone Jujutsu repositories
and workspaces.
If you are using a colocated repository, you can make `moz-phab` use Git
instead of Jujutsu by calling it with `--avoid-jj-vcs`. Note that if you are
using `moz-phab` with Git like that, most operations require your repo to not
be in a detached `HEAD` state, which Jujutsu frequently leaves it in. One
simple solution is to wrap the `moz-phab` command with a script like:
```
#!/bin/sh
git checkout -B moz-phab && moz-phab --avoid-jj-vcs "$@"
```
You could instead make this a shell alias/function, if preferred.
### `mach lint`
`./mach lint`
can be integrated with
`jj fix`
. Follow the
instructions here:
(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()' --onto 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 # just revision ``x``
jj abandon x y # revisions ``x`` and ``y``
jj abandon x..z # revisions leading to z that have not been merged into x
jj abandon x::y # revisions in the commit graph between x and y
```
`x::y` is similar to `x..y`. The main difference is that the former includes
`x` and the latter does not, but they are for different purposes. `x..y` has
the same meaning as in git, where `x` and `y` are used to denote entire
branches of work ending in `x`/`y`. So `main..y` for example includes
everything past the branch point from the `main` branch up to `y`. The exact
definition is "all ancestors of (aka all commits leading up to) `y`) that are
not also ancestors of `main`", or in brief: `::y ~ ::x`. This is especially
useful when `main` has advanced past the common ancestor with `y`.
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:
```
[fsmonitor]
backend = "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.
### Working with multiple workspaces
By default, `./mach vcs-setup` configures `snapshot.auto-update-stale = true`, which
causes `jj` to automatically update a workspace’s working copy when it becomes
stale. A workspace becomes stale when a commit it depends on is rewritten from
another workspace, for example by rebasing, editing, or squashing. We recommend this
default because some `mach` commands invoke `jj` and can fail, sometimes
silently, if the working copy is stale.
If you use multiple workspaces and want to control when each workspace picks up
changes, for example to avoid triggering a slow rebuild after rebasing patches
in bulk from another workspace, you can disable this per-workspace:
```
jj config set --workspace snapshot.auto-update-stale false
```
With auto-update disabled, most `jj` commands will refuse to run on a stale
workspace until you manually update with `jj workspace update-stale`. (Note
that this is only relevant when you modify one workspace's ancestor from another
workspace, which is what causes the former workspace to become stale. If you
choose to be selecting with your rebases, edits, and squashes, such that you
only touch the current workspace's ancestors, then you won't encounter stale
workspaces very often.)