git absorb

This is a port of Facebook's hg absorb, which I first read about on mozilla.dev.version-control.

Elevator Pitch

You have a feature branch with a few commits. Your teammate reviewed the branch and pointed out a few bugs. You have fixes for the bugs, but you don't want to shove them all into an opaque commit that says fixes, because you believe in atomic commits. Instead of manually finding commit SHAs for git commit --fixup, or running a manual interactive rebase, do this:

git add $FILES_YOU_FIXED
git absorb --and-rebase
# or: git rebase -i --autosquash master

git absorb will automatically identify which commits are safe to modify, and which indexed changes belong to each of those commits. It will then write fixup! commits for each of those changes. You can check its output manually if you don't trust it, and then fold the fixups into your feature branch with git's built-in autosquash functionality.

Installing

You will need the following:

• cargo

Then cargo install git-absorb. Make sure that $CARGO_HOME/bin is on your $PATH so that git can find the command. ($CARGO_HOME defaults to ~/.cargo.)

Note that git absorb does not use the system libgit2. This means you do not need to have libgit2 installed to build or run it. However, this does mean you have to be able to build libgit2. (Due to recent changes in the git2 crate, CMake is no longer needed to build it.)

There is also a Homebrew option.

brew install git-absorb

Usage

1. git add any changes that you want to absorb. By design, git absorb will only consider content in the git index.
2. git absorb. This will create a sequence of commits on HEAD. Each commit will have a fixup! message indicating the message (if unique) or SHA of the commit it should be squashed into.
3. If you are satisfied with the output, git rebase -i --autosquash to squash the fixup! commits into their predecessors. You can set the GIT_SEQUENCE_EDITOR environment variable if you don't need to edit the rebase TODO file.
4. If you are not satisfied (or if something bad happened), git reset --soft to the pre-absorption commit to recover your old state. (You can find the commit in question with git reflog.) And if you think git absorb is at fault, please file an issue.

Configuration

Stack size

When run without --base, git-absorb will only search for candidate commits to fixup within a certain range (by default 10). If you get an error like this:

WARN stack limit reached, limit: 10

edit your local or global .gitconfig and add the following section

[absorb]
    maxStack=50 # Or any other reasonable value for your project

TODO

• implement force flag
• implement remote default branch check
• add smaller force flags to disable individual safety checks
• stop using failure::err_msg and ensure all error output is actionable by the user
• slightly more log output in the success case
• more tests (esp main module and integration tests)
• travis
• windows support and appveyor
• document stack and commute details
• more commutation cases (esp copy/rename detection)
• don't load all hunks in memory simultaneously because they could be huge
• implement some kind of index locking to protect against concurrent modifications