git branchless

Motivation

Sometimes, I am working on multiple changes to a Git repository. I want to combine all of my changes in a single branch, but send them upstream in small, reviewable chunks. Refer to the related articles for some advantages of this workflow.

Git already supports this workflow via git format-patch and git send-email, however, many projects prefer to receive patches as pull requests. To make proposed changes easy to review, you'll want to submit a separate pull request for each independent change. With a branchless workflow, the sole local branch typically contains multiple independent changes. To submit those as pull requests, you need to create a separate branch for each change. Running git branchless creates the desired branches without requiring you to switch back and forth between branches. This allows you to submit small pull requests while enjoying the benefits of a branchless workflow. After making any changes to your worktree's branch you can easily update the generated branches: just re-run git branchless.

Installation

git branchless currently depends on an unreleased version of git revise.

$ pip install --user git-revise@git+https://github.com/mystor/git-revise.git@e27bc1631f5da6041c2fa7e3d1f5a9fecfb3ef57
$ pip install --user git-branchless

Usage

Create some commits with commit messages starting with [<topic>] where <topic> is a valid branch name. Then run git branchless to create a branch <topic> with the given commits.

For example, if you have created a commit history like

$ git log --graph --oneline
* 2708e12 (HEAD -> master) [my-awesome-feature] Initial support for feature
* c6dd3ab [my-awesome-feature] Some more work on feature
* 683de4b [some-unrelated-fix] Unrelated fix
* 3eee379 Local commit without topic tag
* 2ec4d51 (origin/master) Initial commit

Then this command will (re)create two branches:

$ git branchless
$ git log --graph --oneline --all
* 2708e12 (HEAD -> master) [my-awesome-feature] Initial support for feature
* c6dd3ab [my-awesome-feature] Some more work on feature
* 683de4b [some-unrelated-fix] Unrelated fix
* 3eee379 Local commit without topic tag
| * 7645890 (my-awesome-feature) Initial support for feature
| * e420fd6 Some more work on feature
|/
| * d5f4bb2 (some-unrelated-fix) Unrelated fix
|/
* 2ec4d51 (origin/master) Initial commit

By default, git branchless looks only at commits in the range @{upstream}..HEAD. It ignores commits whose subject does not start with a topic tag.

Created branches based on the common ancestor of your branch and the upstream branch, that is, git merge-base @{upstream} HEAD.

To avoid conflicts, you can specify dependencies between branches. For example use [child:parent1:parent2] to base child off both parent1 and parent2. The order here does not matter because it will be determined by which topic occurs first in the commit log.

By default, when dependencies are added to generated branches, the commit message will include their topic tags. You can turn this off for all branches with the --trim-subject option, or for a single dependency by adding the + character before a dependency specification (like [child:+parent]).

If there is a merge conflict when applying a commit, you will be shown potentially missing dependencies. You can either add the missing dependencies, or resolve the conflict. You can tell Git to remember your conflict resolution by enabling git rerere (use git config rerere.enabled true; git config rerere.autoUpdate true).

Instead of the default topic tag delimiters ([ and ]), you can set Git configuration values branchless.subjectPrefixPrefix and branchless.subjectPrefixSuffix, respectively.

Integrating Commits from Other Branches

You can use git-branchless-pick to integrate other commit ranges into your branch:

$ git branchless-pick ..some-branch 

This starts an interactive rebase, prompting you to cherry-pick all missing commits from some-branch, prefixing their commit subjects with [some-branch]. Old commits with such a subject are dropped, so this allows you to quickly update to the latest upstream version of a ref that has been force-pushed.

Here's how you would use this to cherry-pick GitHub pull requests:

$ git config --add remote.origin.fetch '+refs/pull/*/head:refs/remotes/origin/pr-*'
$ git fetch origin
$ git branchless-pick $(git merge-base origin/pr-123 HEAD)..origin/pr-123

Tips

• You can use git revise to efficiently modify your commit messages to contain the [<topic>] tags. This command lets you edit all commit messages in @{upstream}..HEAD.

  $ git revise --interactive --edit
  

  Like git revise, you can use git branchless during an interactive rebase.

• git-autofixup can eliminate some of the busywork involved in creating fixup commits.

Related Articles

• In Stacked Diffs Versus Pull Requests, Jackson Gabbard describes the advantages of a patch-based workflow (using Phabricator) over the one-branch-per-reviewable-change model; git branchless can be used to implement the first workflow, even when you have to use pull-requests.

• In My unorthodox, branchless git workflow, Drew DeVault explains some advantages of a branchless workflow.

Peer Projects

While git branchless only offers one command and relies on standard Git tools for everything else, there are some tools that offer a more comprehensive set of commands to achieve a similar workflow:

• Stacked Git
• git ps
• gh-stack

Unlike its peers, git branchless never modifies any worktree files, since it uses git revise internally. This makes it faster, and avoids invalidating builds.

Contributing

Submit feedback at https://github.com/krobelus/git-branchless/ or at the public mailing list by sending email to mailto:~krobelus/git-branchless@lists.sr.ht.