justanotherdot •

Ryan James Spencer

Newsletter

Actually Using Git Worktrees

on October 5 2019, 1:48PM

Let's say you are expected to do code review and you are also expected to code. When you do either a certain set of changes is in place. Switching because you are blocking someone means you have to do a dance with stashing changes, checking out a branch, perhaps cleaning temporary files, restarting tooling, etc. Bar changing your codebase, workflow, and job requirements, here's an approach that uses git worktrees to ease the cost of these context-switches.

git uses worktrees to track changes in a repository. git gives us the ability to make more than one worktree at a time that are checked out to potentially different sets of changes. This means we can effectively split up our codebase into review and development environments:

$ git worktree add ../foo-review --checkout master # where `foo` is the name of your project
$ cd ../foo-review
$ git clean -fddx
$ git checkout branch-name

You can tuck the change-directory code into a script if there's a slew of other steps needed to get into a good-known state. If you are using GitHub, here's an added bonus for checking out pull requests by number rather than by branch name:

[alias]
  <snip>
  copr = "!f() { git fetch origin pull/$1/head && git checkout pr/$1; }; f"
  <snip>

N.B. There are alternative ways of fetching all remote pull requests from GitHub which might be preferable to the above alias.

GitHub assigns this special remote tracking branch to your PR, but it's read-only so if you want to contribute changes you will need to know the name of the original branch.

With this setup the context-switch dance is reduced. The workflow could be like this:

  1. Someone asks for a review or perhaps you're done and want to get back to work
  2. Calling work might get you back into your development environment where you left off
  3. review branch-name will go the other direction preparing the pull-request for inspection

Git aliases are a neat way to remap the surface area of git. I actually think this is a utility for configuration I don't see more CLI tooling using that probably could to great effect. In the context of git it allows me to get around some particular ergonomic warts. Also, I don't do this workflow anymore as I leverage pull-requests largely for communicating changes more than gate-keeping these days, but I understand not all circumstances are the same. Worktrees could be used to keep a reference implementation around for quickly inspecting without having to switch branches, for example. Little things like this that help reduce toil are worth their weight in platinum so it pays to keep your eye open to automation opportunities!