forked from mirrors/jj
283 lines
8.9 KiB
Markdown
283 lines
8.9 KiB
Markdown
# Jujutsu VCS
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<br/>
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- [Disclaimer](#disclaimer)
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- [Introduction](#introduction)
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- [Status](#status)
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- [Installation](#installation)
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- [Command-line completion](#command-line-completion)
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- [Getting started](#getting-started)
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- [Related work](#related-work)
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## Disclaimer
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This is not a Google product. It is an experimental version-control system
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(VCS). It was written by me, Martin von Zweigbergk (martinvonz@google.com). It
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is my personal hobby project and my 20% project at Google. It does not indicate
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any commitment or direction from Google.
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## Introduction
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Jujutsu is a [Git-compatible](docs/git-compatibility.md)
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[DVCS](https://en.wikipedia.org/wiki/Distributed_version_control). It combines
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features from Git (data model,
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[speed](https://github.com/martinvonz/jj/discussions/49)), Mercurial (anonymous
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branching, simple CLI [free from "the index"](docs/git-comparison.md#the-index),
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[revsets](docs/revsets.md), powerful history-rewriting), and Pijul/Darcs
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([first-class conflicts](docs/conflicts.md)), with features not found in most
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of them ([working-copy-as-a-commit](docs/working-copy.md),
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[undo functionality](docs/operation-log.md), automatic rebase,
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[safe replication via `rsync`, Dropbox, or distributed file
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system](docs/technical/concurrency.md)).
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The command-line tool is called `jj` for now because it's easy to type and easy
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to replace (rare in English). The project is called "Jujutsu" because it matches
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"jj".
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If you have any questions, please join us on Discord
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[](https://discord.gg/dkmfj3aGQN).
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## Features
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### Compatible with Git
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Jujutsu has two backends. One of them is a Git backend (the other is a native
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one [^native-backend]). This lets you use Jujutsu as an alternative interface to Git. The commits
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you create will look like regular Git commits. You can always switch back to
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Git. The Git support uses the [libgit2](https://libgit2.org/) C library.
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[^native-backend]: At this time, there's practically no reason to use the native
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backend (the only minor reason might be
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[#27](https://github.com/martinvonz/jj/issues/27)).
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The backend exists mainly to make sure that it's possible to eventually add
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functionality that cannot easily be added to the Git backend.
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<img src="demos/git_compat.png" />
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### The working copy is automatically committed
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Most Jujutsu commands automatically commit the working copy. This leads to a
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simpler and more powerful interface, since all commands work the same way on the
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working copy or any other commit. It also means that you can always check out a
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different commit without first explicitly committing the working copy changes
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(you can even check out a different commit while resolving merge conflicts).
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<img src="demos/working_copy.png" />
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### Operations update the repo first, then possibly the working copy
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The working copy is only updated at the end of an operation, after all other
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changes have already been recorded. This means that you can run any command
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(such as `jj rebase`) even if the working copy is dirty.
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### Entire repo is under version control
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All operations you perform in the repo are recorded, along with a snapshot of
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the repo state after the operation. This means that you can easily revert to an
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earlier repo state, or to simply undo a particular operation (which does not
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necessarily have to be the most recent operation).
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<img src="demos/operation_log.png" />
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### Conflicts can be recorded in commits
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If an operation results in conflicts, information about those conflicts will be
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recorded in the commit(s). The operation will succeed. You can then resolve the
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conflicts later. One consequence of this design is that there's no need to
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continue interrupted operations. Instead, you get a single workflow for
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resolving conflicts, regardless of which command caused them. This design also
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lets Jujutsu rebase merge commits correctly (unlike both Git and Mercurial).
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Basic conflict resolution:
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<img src="demos/resolve_conflicts.png" />
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Juggling conflicts:
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<img src="demos/juggle_conflicts.png" />
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### Automatic rebase
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Whenever you modify a commit, any descendants of the old commit will be rebased
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onto the new commit. Thanks to the conflict design described above, that can be
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done even if there are conflicts. Branches pointing to rebased commits will be
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updated. So will the working copy if it points to a rebased commit.
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### Comprehensive support for rewriting history
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Besides the usual rebase command, there's `jj describe` for editing the
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description (commit message) of an arbitrary commit. There's also `jj touchup`,
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which lets you edit the changes in a commit without checking it out. To split
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a commit into two, use `jj split`. You can even move part of the changes in a
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commit to any other commit using `jj move`.
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## Status
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The tool is quite feature-complete, but some important features like (the
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equivalent of) `git blame` are not yet supported. There
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are also several performance bugs. It's also likely that workflows and setups
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different from what the core developers use are not well supported.
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I (Martin von Zweigbergk) have almost exclusively used `jj` to develop the
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project itself since early January 2021. I haven't had to re-clone from source
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(I don't think I've even had to restore from backup).
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There *will* be changes to workflows and backward-incompatible changes to the
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on-disk formats before version 1.0.0. Even the binary's name may change (i.e.
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away from `jj`). For any format changes, we'll try to implement transparent
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upgrades (as we've done with recent changes), or provide upgrade commands or
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scripts if requested.
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## Installation
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See below for how to build from source. There are also
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[pre-built binaries](https://github.com/martinvonz/jj/releases) for Windows,
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Mac, or Linux (musl).
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If you're installing from source, you need to use Rust version 1.60 or higher,
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or you will get a cryptic message like this:
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```
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error: failed to select a version for the requirement `libgit2-sys = "=0.14.0"``
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candidate versions found which didn't match: 0.13.2+1.4.2, 0.13.1+1.4.2, 0.13.0+1.4.1, ...
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```
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### Linux
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On most distributions, you'll need to build from source using `cargo` directly.
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#### Build using `cargo`
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First make sure that you have the `libssl-dev` and `openssl` packages installed
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by running something like this:
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```shell script
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sudo apt-get install libssl-dev openssl
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```
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Now run:
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```shell script
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cargo install --git https://github.com/martinvonz/jj.git --bin jj
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```
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#### Nix OS
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If you're on Nix OS you can use the flake for this repository.
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For example, if you want to run `jj` loaded from the flake, use:
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```shell script
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nix run 'github:martinvonz/jj'
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```
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You can also add this flake url to your system input flakes. Or you can
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install the flake to your user profile:
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```shell script
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nix profile install 'github:martinvonz/jj'
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```
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#### Homebrew
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If you use linuxbrew, you can run:
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```shell script
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brew install jj
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```
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### Mac
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#### Homebrew
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If you use Homebrew, you can run:
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```shell script
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brew install jj
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```
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#### From Source
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You may need to run some or all of these:
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```shell script
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xcode-select --install
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brew install openssl
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brew install pkg-config
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export PKG_CONFIG_PATH="$(brew --prefix)/opt/openssl@3/lib/pkgconfig"
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```
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Now run:
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```shell script
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cargo install --git https://github.com/martinvonz/jj.git --bin jj
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```
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### Windows
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Run:
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```shell script
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cargo install --git https://github.com/martinvonz/jj.git --bin jj
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```
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## Initial configuration
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You may want to configure your name and email so commits are made in your name.
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Create a file at `~/.jjconfig.toml` and make it look something like
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this:
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```shell script
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$ cat ~/.jjconfig.toml
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[user]
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name = "Martin von Zweigbergk"
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email = "martinvonz@google.com"
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```
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## Command-line completion
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To set up command-line completion, source the output of
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`jj debug completion --bash/--zsh/--fish`. Exactly how to source it depends on
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your shell.
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### Bash
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```shell script
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source <(jj debug completion) # --bash is the default
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```
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### Zsh
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```shell script
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autoload -U compinit
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compinit
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source <(jj debug completion --zsh | sed '$d') # remove the last line
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compdef _jj jj
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```
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### Fish
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```shell script
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jj debug completion --fish | source
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```
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### Xonsh
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```shell script
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source-bash $(jj debug completion)
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```
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## Getting started
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The best way to get started is probably to go through
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[the tutorial](docs/tutorial.md). Also see the
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[Git comparison](docs/git-comparison.md), which includes a table of
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`jj` vs. `git` commands.
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## Related work
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There are several tools trying to solve similar problems as Jujutsu. See
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[related work](docs/related-work.md) for details.
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