jj/README.md

Jujutsu VCS

• Disclaimer
• Introduction
• Status
• Installation
• Command-line completion
• Getting started
• Related work

Disclaimer

This is not a Google product. It is an experimental version-control system (VCS). I (Martin von Zweigbergk martinvonz@google.com) started it as a hobby project in late 2019. That said, this it is now my full-time project at Google. My presentation from Git Merge 2022 has information about Google's plans. See the slides or the recording.

Introduction

Jujutsu is a Git-compatible DVCS. It combines features from Git (data model, speed), Mercurial (anonymous branching, simple CLI free from "the index", revsets, powerful history-rewriting), and Pijul/Darcs (first-class conflicts), with features not found in most of them (working-copy-as-a-commit, undo functionality, automatic rebase, safe replication via rsync, Dropbox, or distributed file system).

The command-line tool is called jj for now because it's easy to type and easy to replace (rare in English). The project is called "Jujutsu" because it matches "jj".

If you have any questions, please join us on Discord or start a GitHub Discussion. The glossary may also be helpful.

Features

Compatible with Git

Jujutsu has two backends. One of them is a Git backend (the other is a native one ¹). This lets you use Jujutsu as an alternative interface to Git. The commits you create will look like regular Git commits. You can always switch back to Git. The Git support uses the libgit2 C library.

The working copy is automatically committed

Jujutsu uses a real commit to represent the working copy. Checking out a commit results a new working-copy commit on top of the target commit. Almost all commands automatically amend the working-copy commit.

The working-copy being a commit means that commands never fail because the working copy is dirty (no "error: Your local changes to the following files..."), and there is no need for git stash. Also, because the working copy is a commit, commands work the same way on the working-copy commit as on any other commit, so you can set the commit message before you're done with the changes.

The repo is the source of truth

With Jujutsu, the working copy plays a smaller role than with Git. Commands snapshot the working copy before they start, then they update the repo, and then the working copy is updated (if the working-copy commit was modified). Almost all commands (even checkout!) operate on the commits in the repo, leaving the common functionality of snapshotting and updating of the working copy to centralized code. For example, jj restore (similar to git restore) can restore from any commit and into any commit, and jj describe can set the commit message of any commit (defaults to the working-copy commit).

Entire repo is under version control

All operations you perform in the repo are recorded, along with a snapshot of the repo state after the operation. This means that you can easily revert to an earlier repo state, or to simply undo a particular operation (which does not necessarily have to be the most recent operation).

Conflicts can be recorded in commits

If an operation results in conflicts, information about those conflicts will be recorded in the commit(s). The operation will succeed. You can then resolve the conflicts later. One consequence of this design is that there's no need to continue interrupted operations. Instead, you get a single workflow for resolving conflicts, regardless of which command caused them. This design also lets Jujutsu rebase merge commits correctly (unlike both Git and Mercurial).

Basic conflict resolution:

Juggling conflicts:

Automatic rebase

Whenever you modify a commit, any descendants of the old commit will be rebased onto the new commit. Thanks to the conflict design described above, that can be done even if there are conflicts. Branches pointing to rebased commits will be updated. So will the working copy if it points to a rebased commit.

Comprehensive support for rewriting history

Besides the usual rebase command, there's jj describe for editing the description (commit message) of an arbitrary commit. There's also jj diffedit, which lets you edit the changes in a commit without checking it out. To split a commit into two, use jj split. You can even move part of the changes in a commit to any other commit using jj move.

Status

The tool is quite feature-complete, but some important features like (the equivalent of) git blame are not yet supported. There are also several performance bugs. It's also likely that workflows and setups different from what the core developers use are not well supported.

I (Martin von Zweigbergk) have almost exclusively used jj to develop the project itself since early January 2021. I haven't had to re-clone from source (I don't think I've even had to restore from backup).

There will be changes to workflows and backward-incompatible changes to the on-disk formats before version 1.0.0. Even the binary's name may change (i.e. away from jj). For any format changes, we'll try to implement transparent upgrades (as we've done with recent changes), or provide upgrade commands or scripts if requested.

Installation

See below for how to build from source. There are also pre-built binaries for Windows, Mac, or Linux (musl).

Linux

On most distributions, you'll need to build from source using cargo directly.

Build using cargo

First make sure that you have the libssl-dev, openssl, and pkg-config packages installed by running something like this:

sudo apt-get install libssl-dev openssl pkg-config

Now run:

cargo install --git https://github.com/martinvonz/jj.git --locked --bin jj jj-cli

Nix OS

If you're on Nix OS you can use the flake for this repository. For example, if you want to run jj loaded from the flake, use:

nix run 'github:martinvonz/jj'

You can also add this flake url to your system input flakes. Or you can install the flake to your user profile:

nix profile install 'github:martinvonz/jj'

Homebrew

If you use linuxbrew, you can run:

brew install jj

Mac

Homebrew

If you use Homebrew, you can run:

brew install jj

MacPorts

You can also install jj via MacPorts (as the jujutsu port):

sudo port install jujutsu

(port page)

From Source

You may need to run some or all of these:

xcode-select --install
brew install openssl
brew install pkg-config
export PKG_CONFIG_PATH="$(brew --prefix)/opt/openssl@3/lib/pkgconfig"

Now run:

cargo install --git https://github.com/martinvonz/jj.git --locked --bin jj jj-cli

Windows

Run:

cargo install --git https://github.com/martinvonz/jj.git --locked --bin jj jj-cli --features vendored-openssl

Initial configuration

You may want to configure your name and email so commits are made in your name. Create a file at ~/.jjconfig.toml and make it look something like this:

$ cat ~/.jjconfig.toml
[user]
name = "Martin von Zweigbergk"
email = "martinvonz@google.com"

Command-line completion

To set up command-line completion, source the output of jj util completion --bash/--zsh/--fish (called jj debug completion in jj <= 0.7.0). Exactly how to source it depends on your shell.

Bash

source <(jj util completion)  # --bash is the default

Or, with jj <= 0.7.0:

source <(jj debug completion)  # --bash is the default

Zsh

autoload -U compinit
compinit
source <(jj util completion --zsh)

Or, with jj <= 0.7.0:

autoload -U compinit
compinit
source <(jj debug completion --zsh)

Fish

jj util completion --fish | source

Or, with jj <= 0.7.0:

jj debug completion --fish | source

Xonsh

source-bash $(jj util completion)

Or, with jj <= 0.7.0:

source-bash $(jj debug completion)

Getting started

The best way to get started is probably to go through the tutorial. Also see the Git comparison, which includes a table of jj vs. git commands.

Related work

There are several tools trying to solve similar problems as Jujutsu. See related work for details.

---

1. At this time, there's practically no reason to use the native backend. The backend exists mainly to make sure that it's possible to eventually add functionality that cannot easily be added to the Git backend. ↩︎