I’ve been working on greenfield projects for the past month. Most of my branches that have started out with a small, limited scope have tended to balloon as I’ve learned more about what the requirements really are. This has meant that I’ve needed to break down branches into smaller units. Git has tools that make this a fairly painless process.
Checking out hunks from a base branch
This is useful when a branch needs splitting up and its commit history doesn’t contain much useful information.
The commands are:
# checkout a fresh branch for the smaller scope
git checkout -b branch-with-smaller-scope master
# start checking out work from the source branch
git checkout -p the-branch-with-all-of-the-work -- src/foo/thing.clj
This command will checkout hunks from src/foo/thing.clj just as you
would if you were using git add -p. If git can’t decide how
to split up a hunk, you can manually edit the hunk in your text editor.
Rebasing
I mainly use interactive rebasing to rewrite and destroy commit history. My typical use-case is that I’ve written a large feature branch that contains work-in-progress and fixup commits. Most of the time, I’d prefer not to merge these types of throwaway commits.
The command to use is:
git rebase -i the-base-branch
This will open up an interactive prompt that allows you to select commits to alter. The prompt provides a menu allowing the user to select which commits they would like to leave unaltered, edit, squash, treat as fixup commits, or destroy. I tend to use fixup commits when a commit is simply “fixed typo in last commit” and the like. I also like to squash some commits and edit their commit message. The interactive rebase interface makes this process painless.
Cherry-picking
I use cherry-picking when a commit contains work and commit history that I would like to pull into another branch. To be honest, I use cherry-picking less frequently simply because my commit history tends to contain a fair amount of work-in-progress commits. Outside of keeping a better commit history, a solution to this would be to:
- rebase the work-in-progress commits into more meaningful commits
- cherry-pick those commits into the target branch (alternatively, rebasing could achieve the exact same thing)
Cherry-picking is a pretty simple process. It is possible to select a single commit or range of commits
# selects a single commit and apply it to the current branch
git cherry-pick hash-of-target-commit
# selects the sixth, fifth, fourth, and thrid most recent commits from target-branch
# and apply them to the current branch
git cherry-pick target-branch~5 target-branch~2
Running these commands will attempt to apply commits that were cherry-picked to the current branch. If there are any conflicts, you will need to resolve the process similarly to how you would during a merge.
For more information, here are the docs on checking out patches, rebasing, and cherry-picking