Git Style Guide

This is a Git Style Guide inspired by How to Get Your Change Into the Linux Kernel, the git man pages and various practices popular among the community.

Table of contents

1. Branches
2. Commits
3. Messages
4. Merging
5. Miscellaneous

Branches

• Choose short and descriptive names:

  # good
  $ git checkout -b oauth-migration
  
  # bad - too vague
  $ git checkout -b login_fix

• Please refer to each project's Readme for specific naming conventions.

• Use hyphens (-) to separate words.

• When several people are working on the same feature, it might be convenient to have personal feature branches and a team-wide feature branch. Use the following naming convention:

  $ git checkout -b feature-a/master # team-wide branch
  $ git checkout -b feature-a/maria  # Maria's personal branch
  $ git checkout -b feature-a/nick   # Nick's personal branch

  Merge personal branches to the team-wide branch when they're done. Eventually, the team-wide branch will be merged to "master".

• Delete your branch from the upstream repository after it's merged, unless there is a specific reason not to.

  Tip: Use the following command while being on "master", to list merged branches:

  $ git branch --merged | grep -v "\*"

Commits

• Each commit should be a single logical change. Don't make several logical changes in one commit. For example, if a patch fixes a bug and optimizes the performance of a feature, split it into two separate commits.

  Tip: Use git add -p to interactively stage specific portions of the modified files.

• Don't split a single logical change into several commits. For example, the implementation of a feature and the corresponding tests should be in the same commit.

• Commit early and often. Small, self-contained commits are easier to understand and revert when something goes wrong.

• Commits should be ordered logically. For example, if commit X depends on changes done in commit Y, then commit Y should come before commit X.

Note: While working alone on a local branch that has not yet been pushed, it's fine to use commits as temporary snapshots of your work. However, it still holds true that you should apply all of the above before pushing it.

Messages

• Use the editor, not the terminal, when writing a commit message:

  # good
  $ git commit
  
  # bad
  $ git commit -m "Quick fix"

  Committing from the terminal encourages a mindset of having to fit everything in a single line which usually results in non-informative, ambiguous commit messages.

• The summary line (ie. the first line of the message) should be descriptive yet succinct. Ideally, it should be no longer than 50 characters. It should be capitalized and written in imperative present tense. It should not end with a period since it is effectively the commit title:

  # good - imperative present tense, capitalized, fewer than 50 characters
  Mark huge records as obsolete when clearing hinting faults
  
  # bad
  fixed ActiveModel::Errors deprecation messages failing when AR was used outside of Rails.

• After that should come a blank line followed by a more thorough description. It should be wrapped to 72 characters and explain why the change is needed, how it addresses the issue and what side-effects it might have.

  It should also provide any pointers to related resources (eg. link to the corresponding issue in a bug tracker):

  Short (50 chars or fewer) summary of changes
  
  More detailed explanatory text, if necessary. Wrap it to
  72 characters. In some contexts, the first
  line is treated as the subject of an email and the rest of
  the text as the body.  The blank line separating the
  summary from the body is critical (unless you omit the body
  entirely); tools like rebase can get confused if you run
  the two together.
  
  Further paragraphs come after blank lines.
  
  - Bullet points are okay, too
  
  - Use a hyphen or an asterisk for the bullet,
    followed by a single space, with blank lines in
    between
  
  Source http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html
  

  Ultimately, when writing a commit message, think about what you would need to know if you run across the commit in a year from now.

• If a commit A depends on commit B, the dependency should be stated in the message of commit A. Use the SHA1 when referring to commits.

  Similarly, if commit A solves a bug introduced by commit B, it should also be stated in the message of commit A.

• If a commit is going to be squashed to another commit use the --squash and --fixup flags respectively, in order to make the intention clear:

  $ git commit --squash f387cab2

  (Tip: Use the --autosquash flag when rebasing. The marked commits will be squashed automatically.)

Merging

• Do not rewrite published history. The repository's history is valuable in its own right and it is very important to be able to tell what actually happened. Altering published history is a common source of problems for anyone working on the project.

• However, there are cases where rewriting history is legitimate. These are when:

  • You are the only one working on the branch and it is not being reviewed.

  • You want to tidy up your branch (eg. squash commits) and/or rebase it onto the "master" in order to merge it later.

  That said, never rewrite the history of the "master" branch or any other special branches (ie. used by production or CI servers).

• Keep the history clean and simple. Just before you merge your branch:

  1. Make sure it conforms to the style guide and perform any needed actions if it doesn't (squash/reorder commits, reword messages etc.)

  2. Rebase it onto the branch it's going to be merged to:

  ```shell
  [my-branch] $ git fetch
  [my-branch] $ git rebase origin/master
  # then merge
  ```
  
  This results in a branch that can be applied directly to the end of the
  "master" branch and results in a very simple history.
  
  (Note: This strategy is better suited for projects with short-running
  branches. Otherwise it might be better to occasionally merge the
  "master" branch instead of rebasing onto it.)
  

• If your branch includes more than one commit, do not merge with a fast-forward:

  # good - ensures that a merge commit is created
  $ git merge --no-ff my-branch
  
  # bad
  $ git merge my-branch

Miscellaneous

• There are various workflows and each one has its strengths and weaknesses. Whether a workflow fits your case, depends on the team, the project and your development procedures.

  That said, it is important to actually choose a workflow and stick with it.

• Be consistent. This is related to the workflow but also expands to things like commit messages, branch names and tags. Having a consistent style throughout the repository makes it easy to understand what is going on by looking at the log, a commit message etc.

• Test before you push. Do not push half-done work.

• Use annotated tags for marking releases or other important points in the history. Prefer lightweight tags for personal use, such as to bookmark commits for future reference.

• Keep your repositories at a good shape by performing maintenance tasks occasionally:

  • git-gc(1)
  • git-prune(1)
  • git-fsck(1)

License

This work is licensed under a Creative Commons Attribution 4.0 International license.