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jj/docs/git-compatibility.md

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Git compatibility

Jujutsu has two backends for storing commits. One of them uses a regular Git repo, which means that you can collaborate with Git users without them even knowing that you're not using the git CLI.

See jj help git for help about the jj git family of commands, and e.g. jj help git push for help about a specific command (use jj git push -h for briefer help).

Supported features

The following list describes which Git features Jujutsu is compatible with. For a comparison with Git, including how workflows are different, see the Git-comparison doc.

  • Configuration: Partial. The only configuration from Git (e.g. in ~/.gitconfig) that's respected is the following. Feel free to file a bug if you miss any particular configuration options.
    • The configuration of remotes ([remote "<name>"]).
    • core.excludesFile
  • Authentication: Partial. Only ssh-agent, a password-less key file at ~/.ssh/id_rsa (and only at exactly that path), or a credential.helper.
  • Branches: Yes. You can read more about how branches work in Jujutsu and how they interoperate with Git.
  • Tags: Partial. You can check out tagged commits by name (pointed to be either annotated or lightweight tags), but you cannot create new tags.
  • .gitignore: Yes. Ignores in .gitignore files are supported. So are ignores in .git/info/exclude or configured via Git's core.excludesfile config. The .gitignore support uses a native implementation, so please report a bug if you notice any difference compared to git.
  • .gitattributes: No. There's #53 about adding support for at least the eol attribute.
  • Hooks: No. There's #405 specifically for providing the checks from https://pre-commit.com.
  • Merge commits: Yes. Octopus merges (i.e. with more than 2 parents) are also supported.
  • Detached HEAD: Yes. Jujutsu supports anonymous branches, so this is a natural state.
  • Orphan branch: Yes. Jujutsu has a virtual root commit that appears as parent of all commits Git would call "root commits".
  • Staging area: Kind of. The staging area will be ignored. For example, jj diff will show a diff from the Git HEAD to the working copy. There are ways of fulfilling your use cases without a staging area.
  • Garbage collection: Yes. It should be safe to run git gc in the Git repo, but it's not tested, so it's probably a good idea to make a backup of the whole workspace first. There's no garbage collection and repacking of Jujutsu's own data structures yet, however.
  • Bare repositories: Yes. You can use jj init --git-repo=<path> to create a repo backed by a bare Git repo.
  • Submodules: No. They will not show up in the working copy, but they will not be lost either.
  • Partial clones: No. We use the libgit2 library, which doesn't have support for partial clones.
  • Shallow clones: No. We use the libgit2 library, which doesn't have support for shallow clones.
  • git-worktree: No. However, there's native support for multiple working copies backed by a single repo. See the jj workspace family of commands.
  • Sparse checkouts: No. However, there's native support for sparse checkouts. See the jj sparse command.
  • Signed commits: No. (#58)
  • Git LFS: No. (#80)

Creating an empty repo

To create an empty repo using the Git backend, use jj init --git <name>. Since the command creates a Jujutsu repo, it will have a .jj/ directory. The underlying Git repo will be inside of that directory (currently in .jj/repo/store/git/).

Creating a repo backed by an existing Git repo

To create a Jujutsu repo backed by a Git repo you already have on disk, use jj init --git-repo=<path to Git repo> <name>. The repo will work similar to a Git worktree, meaning that the working copies files and the record of the working-copy commit will be separate, but the commits will be accessible in both repos. Use jj git import to update the Jujutsu repo with changes made in the Git repo. Use jj git export to update the Git repo with changes made in the Jujutsu repo.

Co-located Jujutsu/Git repos

If you initialize the Jujutsu repo in the same working copy as the Git repo by running jj init --git-repo=., then the import and export will happen automatically on every command (because not doing that makes it very confusing when the working copy has changed in Git but not in Jujutsu or vice versa). We call such repos "co-located".

This mode is meant to make it easier to start using readonly jj commands in an existing Git repo. You should then be able to switch to using mutating jj commands and readonly Git commands. It's also useful when tools (e.g. build tools) expect a Git repo to be present.

The mode is new and not tested much, and interleaving mutating jj and git commands might not work well (feel free to report bugs).

Creating a repo by cloning a Git repo

To create a Jujutsu repo from a remote Git URL, use jj git clone <URL> [<destination>]. For example, jj git clone https://github.com/octocat/Hello-World will clone GitHub's "Hello-World" repo into a directory by the same name.

Branches

TODO: Describe how branches are mapped

Format mapping details

Paths are assumed to be UTF-8. I have no current plans to support paths with other encodings.

Commits created by jj have a ref starting with refs/jj/ to prevent GC.

Commit metadata that cannot be represented in Git commits (such as the Change ID) is stored outside of the Git repo (currently in .jj/store/extra/).

Paths with conflicts cannot be represented in Git. They appear as files with a .jjconflict suffix in the Git repo. They contain a JSON representation with information about the conflict. They are not meant to be human-readable.