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.

Translations are available in the following languages:

• Chinese (Simplified)
• Chinese (Traditional)
• French
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• Portuguese
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If you feel like contributing, please do so! Fork the project and open a pull
request.

Table of contents

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

Branches

• Choose short and descriptive names:

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

• Identifiers from corresponding tickets in an external service (eg. a GitHub
  issue) are also good candidates for use in branch names. For example:

  # GitHub issue #15
  $ git checkout -b issue-15
  

• Use lowercase in branch names. External ticket identifiers with uppercase
  letters are a valid exception. Use hyphens to separate words.

  $ git checkout -b new-feature      # good
  $ git checkout -b T321-new-feature # good (Phabricator task id)
  $ git checkout -b New_Feature      # bad
  

• 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 at will the personal branches to the team-wide branch (see "Merging").
  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
  
  The pointers to your related resources can serve as a footer
  for your commit message. Here is an example that is referencing
  issues in a bug tracker:
  
  Resolves: #56, #78
  See also: #12, #34
  
  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:

     [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 occassionally 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
  

Misc.

• 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.

Credits

Agis Anastasopoulos / @agisanast / http://agis.io
... and contributors!