Git comparison - Jujutsu docs

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# Comparison with Git

## Introduction

This document attempts to describe how Jujutsu is different from Git. See the Git-compatibility doc for information about how the `jj` command interoperates with Git repos.

## Overview

Here is a list of conceptual differences between Jujutsu and Git, along with links to more details where applicable and available. There's a table further down explaining how to achieve various use cases.

- The working copy is automatically committed. That results in a simpler and more consistent CLI because the working copy is now treated like any other commit. Details.
- There's no index (staging area). Because the working copy is automatically committed, an index-like concept doesn't make sense. The index is very similar to an intermediate commit between `HEAD` and the working copy, so workflows that depend on it can be modeled using proper commits instead. Jujutsu has excellent support for moving changes between commits. Details.
- No need for branch names (but they are supported as bookmarks). Git lets you check out a commit without attaching a branch to it. It calls this state "detached HEAD". This is the normal state in Jujutsu (there's actually no way -- yet, at least -- to have an active branch/bookmark). However, Jujutsu keeps track of all visible heads (leaves) of the commit graph, so the commits won't get lost or garbage-collected.

- No current branch. Git lets you check out a branch, making it the 'current branch', and new commits will automatically update the branch. This is necessary in Git because Git might otherwise lose track of the new commits.

  Jujutsu does not have a corresponding concept of a 'current bookmark'; instead, you update bookmarks manually. For example, if you start work on top of a commit with a bookmark, new commits are created on top of the bookmark, then you issue a later command to update the bookmark.

- Conflicts can be committed. No commands fail because of merge conflicts. The conflicts are instead recorded in commits and you can resolve them later. Details.

- Descendant commits are automatically rebased. Whenever you rewrite a commit (e.g. by running `jj rebase`), all its descendants commits will automatically be rebased on top. Branches pointing to it will also get updated, and so will the working copy if it points to any of the rebased commits.
- Bookmarks/branches are identified by their names (across remotes). For example, if you pull from a remote that has a `main` branch, you'll get a bookmark by that name in your local repo. If you then move it and push back to the remote, the `main` branch on the remote will be updated. Details.
- The operation log replaces reflogs. The operation log is similar to reflogs, but is much more powerful. It keeps track of atomic updates to all refs at once (Jujutsu thus improves on Git's per-ref history much in the same way that Subversion improved on RCS's per-file history). The operation log powers e.g. the undo functionality. Details
- There's a single, virtual root commit. Like Mercurial, Jujutsu has a virtual commit (with a hash consisting of only zeros) called the "root commit" (called the "null revision" in Mercurial). This commit is a common ancestor of all commits. That removes the awkward state Git calls the "unborn branch" state (which is the state a newly initialized Git repo is in), and related command-line flags (e.g. `git rebase --root`, `git checkout --orphan`).

## The index

Git's "index" has multiple roles. One role is as a cache of file system information. Jujutsu has something similar. Unfortunately, Git exposes the index to the user, which makes the CLI unnecessarily complicated (learning what the different flavors of `git reset` do, especially when combined with commits and/or paths, usually takes a while). Jujutsu, like Mercurial, doesn't make that mistake.

As a Git power-user, you may think that you need the power of the index to commit only part of the working copy. However, Jujutsu provides commands for more directly achieving most use cases you're used to using Git's index for. For example, to create a commit from part of the changes in the working copy, you might be used to using `git add -p; git commit`. With Jujutsu, you'd instead use `jj split` to split the working-copy commit into two commits. To add more changes into the parent commit, which you might normally use `git add -p; git commit --amend` for, you can instead use `jj squash -i` to choose which changes to move into the parent commit, or `jj squash <file>` to move a specific file.

## Command equivalence table

Note that all `jj` commands can be run on any commit (not just the working-copy commit), but that's left out of the table to keep it simple. For example, `jj squash -r <revision>` will move the diff from that revision into its parent.

Use case | Jujutsu command | Git command
--- | --- | ---
Create a new repo | `jj git init [--colocate]` | `git init`
Clone an existing repo | `jj git clone <source> <destination> [--remote <remote name>]` (there is no support for cloning non-Git repos yet) | `git clone <source> <destination> [--origin <remote name>]`
Update the local repo with all bookmarks/branches from a remote | `jj git fetch [--remote <remote>]` (there is no support for fetching into non-Git repos yet) | `git fetch [<remote>]`
Update a remote repo with all bookmarks/branches from the local repo | `jj git push --all [--remote <remote>]` (there is no support for pushing from non-Git repos yet) | `git push --all [<remote>]`
Update a remote repo with a single bookmark from the local repo | `jj git push --bookmark <bookmark name> [--remote <remote>]` (there is no support for pushing from non-Git repos yet) | `git push <remote> <bookmark name>`
Add a remote target to the repo | `jj git remote add <remote> <url>` | `git remote add <remote> <url>`
Show summary of current work and repo status | `jj st` | `git status`
Show diff of the current change | `jj diff` | `git diff HEAD`
Show diff of another change | `jj diff -r <revision>` | `git diff <revision>^ <revision>`
Show diff from another change to the current change | `jj diff --from <revision>` | `git diff <revision>`
Show diff from change A to change B | `jj diff --from A --to B` | `git diff A B`
Show description and diff of a change | `jj show <revision>` | `git show <revision>`
Add a file to the current change | `touch filename` | `touch filename; git add filename`
Remove a file from the current change | `rm filename` | `git rm filename`
Modify a file in the current change | `echo stuff >> filename` | `echo stuff >> filename`
Finish work on the current change and start a new change | `jj commit` | `git commit -a`
See log of ancestors of the current commit | `jj log -r ::@` | `git log --oneline --graph --decorate`
See log of all reachable commits | `jj log -r 'all()'` or `jj log -r ::` | `git log --oneline --graph --decorate --branches`
Show log of commits not on the main bookmark | `jj log` | (TODO)
List versioned files in the working copy | `jj file list` | `git ls-files --cached`
Search among files versioned in the repository | `grep foo $(jj file list)`, or `rg --no-require-git foo` | `git grep foo`
Abandon the current change and start a new change | `jj abandon` | `git reset --hard` (cannot be undone)
Make the current change empty | `jj restore` | `git reset --hard` (same as abandoning a change since Git has no concept of a "change")
Abandon the parent of the working copy, but keep its diff in the working copy | `jj squash --from @-` | `git reset --soft HEAD~`
Discard working copy changes in some files | `jj restore <paths>...` | `git restore <paths>...` or `git checkout HEAD -- <paths>...`
Edit description (commit message) of the current change | `jj describe` | Not supported
Edit description (commit message) of the previous change | `jj describe @-` | `git commit --amend --only`
Temporarily put away the current change | `jj new @-` (the old working-copy commit remains as a sibling commit) (the old working-copy commit X can be restored with `jj edit X`) | `git stash`
Start working on a new change based on the <main> bookmark/branch | `jj new main` | `git switch -c topic main` or `git checkout -b topic main` (may need to stash or commit first)
Move bookmark/branch A onto bookmark/branch B | `jj rebase -b A -d B` | `git rebase B A` (may need to rebase other descendant branches separately)
Move change A and its descendants onto change B | `jj rebase -s A -d B` | `git rebase --onto B A^ <some descendant bookmark>` (may need to rebase other descendant bookmarks separately)
Reorder changes from A-B-C-D to A-C-B-D | `jj rebase -r C --before B` | `git rebase -i A`
Move the diff in the current change into the parent change | `jj squash` | `git commit --amend -a`
Interactively move part of the diff in the current change into the parent change | `jj squash -i` | `git add -p; git commit --amend`
Move the diff in the working copy into an ancestor | `jj squash --into X` | `git commit --fixup=X; git rebase -i --autosquash X^`
Interactively move part of the diff in an arbitrary change to another arbitrary change | `jj squash -i --from X --into Y` | Not supported
Interactively split the changes in the working copy in two | `jj split` | `git commit -p`
Interactively split an arbitrary change in two | `jj split -r <revision>` | Not supported (can be emulated with the "edit" action in `git rebase -i`)
Interactively edit the diff in a given change | `jj diffedit -r <revision>` | Not supported (can be emulated with the "edit" action in `git rebase -i`)
Resolve conflicts and continue interrupted operation | `echo resolved > filename; jj squash` (operations don't get interrupted, so no need to continue) | `echo resolved > filename; git add filename; git rebase/merge/cherry-pick --continue`
Create a copy of a commit on top of another commit | `jj duplicate <source> -d <destination>` | `git co <destination>; git cherry-pick <source>`
Find the root of the working copy (or check if in a repo) | `jj workspace root` | `git rev-parse --show-toplevel`
List bookmarks/branches | `jj bookmark list` or `jj b l` for short | `git branch`
Create a bookmark/branch | `jj bookmark create <name> -r <revision>` | `git branch <name> <revision>`
Move a bookmark/branch forward | `jj bookmark move <name> --to <revision>` or `jj b m <name> --to <revision>` for short | `git branch -f <name> <revision>`
Move a bookmark/branch backward or sideways | `jj bookmark move <name> --to <revision> --allow-backwards` | `git branch -f <name> <revision>`
Delete a bookmark/branch | `jj bookmark delete <name>` | `git branch --delete <name>`
See log of operations performed on the repo | `jj op log` | Not supported
Undo an earlier operation | `jj [op] undo <operation ID>` (`jj undo` is an alias for `jj op undo`) | Not supported
Create a commit that cancels out a previous commit | `jj backout -r <revision>` | `git revert <revision>`
Show what revision and author last modified each line of a file | `jj file annotate <path>` | `git blame <file>`