forked from mirrors/jj
fd80dcd5ed
The link to the glossary was weirdly far from the link to the FAQ. Also, added a mention of the prerelease docs.
182 lines
8.3 KiB
Markdown
182 lines
8.3 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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- [Getting started](#getting-started)
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- [Status](#status)
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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). I (Martin von Zweigbergk <martinvonz@google.com>) started it as a hobby
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project in late 2019. That said, this is now my full-time project at Google. My
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presentation from Git Merge 2022 has information about Google's plans. See the
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[slides](https://docs.google.com/presentation/d/1F8j9_UOOSGUN9MvHxPZX_L4bQ9NMcYOp1isn17kTC_M/view)
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or the [recording](https://www.youtube.com/watch?v=bx_LGilOuE4).
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## Introduction
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Jujutsu is a
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[Git-compatible](https://martinvonz.github.io/jj/latest/git-compatibility)
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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
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index"](https://martinvonz.github.io/jj/latest/git-comparison#the-index),
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[revsets](https://martinvonz.github.io/jj/latest/revsets), powerful
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history-rewriting), and Pijul/Darcs ([first-class
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conflicts](https://martinvonz.github.io/jj/latest/conflicts)), with features not
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found in most of them
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([working-copy-as-a-commit](https://martinvonz.github.io/jj/latest/working-copy),
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[undo functionality](https://martinvonz.github.io/jj/latest/operation-log),
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automatic rebase, [safe replication via `rsync`, Dropbox, or distributed file
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system](https://martinvonz.github.io/jj/latest/technical/concurrency)).
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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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or start a [GitHub Discussion](https://github.com/martinvonz/jj/discussions).
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## Getting started
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Follow the [installation
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instructions](https://martinvonz.github.io/jj/latest/install-and-setup) to
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obtain and configure `jj`.
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The best way to get started is probably to go through [the
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tutorial](https://martinvonz.github.io/jj/latest/tutorial). Also see the [Git
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comparison](https://martinvonz.github.io/jj/latest/git-comparison), which
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includes a table of `jj` vs. `git` commands.
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As you become more familiar with Jujutsu, the following resources may be helpful:
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- The [FAQ](https://martinvonz.github.io/jj/latest/FAQ).
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- The [Glossary](https://martinvonz.github.io/jj/latest/glossary).
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- The `jj help` command (e.g. `jj help rebase`).
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If you are using a **prerelease** version of `jj`, you would want to consult
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[the docs for the prerelease (main branch)
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version](https://martinvonz.github.io/jj/prerelease/). You can also get there
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from the docs for the latest release by using the website's version switcher. The version switcher is visible in
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the header of the website when you scroll to the top of any page.
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## Features
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### Compatible with Git
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Jujutsu has two
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[backends](https://martinvonz.github.io/jj/latest/glossary#backend). One of them
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is a Git backend (the other is a native one [^native-backend]). This lets you
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use Jujutsu as an alternative interface to Git. The commits you create will look
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like regular Git commits. You can always switch back to Git. The Git support
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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 backend exists mainly to make sure that it's possible to eventually
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add functionality that cannot easily be added to the Git backend.
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<img src="demos/git_compat.png" />
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You can even have a ["co-located" local
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repository](https://martinvonz.github.io/jj/latest/git-compatibility#co-located-jujutsugit-repos)
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where you can use both `jj` and `git` commands interchangeably.
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### The working copy is automatically committed
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Jujutsu uses a real commit to represent the working copy. Checking out a commit
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results a new working-copy commit on top of the target commit. Almost all
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commands automatically amend the working-copy commit.
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The working-copy being a commit means that commands never fail because the
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working copy is dirty (no "error: Your local changes to the following
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files..."), and there is no need for `git stash`. Also, because the working copy
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is a commit, commands work the same way on the working-copy commit as on any
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other commit, so you can set the commit message before you're done with the
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changes.
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<img src="demos/working_copy.png" />
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### The repo is the source of truth
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With Jujutsu, the working copy plays a smaller role than with Git. Commands
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snapshot the working copy before they start, then they update the repo, and then
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the working copy is updated (if the working-copy commit was modified). Almost
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all commands (even checkout!) operate on the commits in the repo, leaving the
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common functionality of snapshotting and updating of the working copy to
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centralized code. For example, `jj restore` (similar to `git restore`) can
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restore from any commit and into any commit, and `jj describe` can set the
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commit message of any commit (defaults to the working-copy commit).
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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
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[conflicts](https://martinvonz.github.io/jj/latest/glossary#conflict),
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information about those conflicts will be recorded in the commit(s). The
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operation will succeed. You can then resolve the conflicts later. One
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consequence of this design is that there's no need to continue interrupted
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operations. Instead, you get a single workflow for resolving conflicts,
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regardless of which command caused them. This design also lets Jujutsu rebase
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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 diffedit`,
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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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## Related work
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There are several tools trying to solve similar problems as Jujutsu. See
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[related work](https://martinvonz.github.io/jj/latest/related-work) for details.
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