When you're ready to commit, be sure to write a Good Commit Message™. What's in a Good Commit Message™?
We follow most general engineering best practices from other projects using Git. Some additional guidelines specific to CockroachDB apply.
General best practices:
(must) Keep in mind who reads: think of the reviewers & future maintainers, think of the release notes
(recommended) Keep the commit title concise but information-rich
(recommended) Use the imperative mood in the subject line, but not in the body
(recommended) Wrap the body at a consistent width under 100 characters
(suggested) Do not end the subject line with a period
Specific to CockroachDB:
(must) Include a release note annotation, in the right position
(recommended) Prefix the subject line with the affected package/area
Table of contents
|Table of Contents|
General structure of a commit message
docs: summarize changes in title, but be specific More detailed explanatory text, if necessary. The blank line
separating the summary from the body is critical; various tools
like `log`, `shortlog` and `rebase` can get confused if you run
the two together. Wrap the body to a fixed width consistent with the rest of the git history.
Explain how the code was, before your change. Explain the problem that this commit is solving.
Explain why the problem is important to solve.
Explain (briefly) what the new situation looks like. No need
to explain the mechanism in detail: the code and comments
should explain that already.
Are there side effects or other unintuitive consequences of this change? Here's the place to explain them. Further paragraphs come after blank lines. - Bullet points are okay, too - Typically a hyphen or asterisk is used for the bullet, preceded by a single space, with blank lines in between, but conventions vary here
Prefer imperative voice for the subject, and declarative
(descriptive) voice for the body and release note.
If there are related issues, mention them in the commit message: Resolves: #123
(this auto-closes the issue when the PR is merged)
See also: #456, #789
(this just cross-references the PR with the issues) Release note (general change): The release note should outline
what changed, how a user can see what changed, and why it was
important / what the impact is. For bug fixes, it should
also explain the symptoms of the bug pre-fix and which versions
are affected. It should remain concise. A release note can contain multiple paragraphs. This is useful to e.g. provide examples. However it does imply the release note text must appear after the detailed explanation, otherwise the detailed explanation will be considered part of the release note. Release note (general change): if there are multiple release notes, each of them should start with its own "Release note" prefix.
Tooling around git give this line a special role. The title can be at most one line. Do not break it across multiple lines. Separate it from the next paragraph with an empty line, otherwise other tools will become confused.
Prefix your commit subject line with the affected package, if one can easily be chosen. For example, the subject line of a commit mostly affecting the
serverpackage might read: "server: use net.Pipe instead of TCP HTTP/gRPC connections". Commits which affect many packages as a result of a shared dependency change should probably begin their subjects with the name of the shared dependency. Finally, some commits may need to affect many packages in a way which does not point to a specific package; those commits may begin with "
*:" or "
all:" to indicate their reach.
Since the title is prefixed with a package name, don't capitalize the title. In English, the text that follows a colon (
:) is not capitalized.
Do not end the title with a period. It's a title, not a sentence.
Not every commit requires both a title and a body. Sometimes a single line is fine, especially when the change is so simple that no further context is necessary. For example:
docs: fixed typo in introduction to user guide
Nothing more need be said; if the reader wonders what the typo was, she can simply take a look at the change itself.
Note however that at least one of the commits in a PR should include a release note annotation in a commit body, if only to state "Release note: none" to declare there are no user-facing changes. See
Make the commit title short. Other projects have a guideline of trying to keep it around 50 characters. Keeping subject lines short ensures that they are readable in
git log --pretty=oneline, and forces the author to think for a moment about the most concise way to explain what's going on.
Tip: If you’re having a hard time summarizing, you might be committing too many changes at once. Strive for atomic commits.
How to write a good commit description
Learn about how commit messages help the reviewers and future maintainers in our PR organization philosophy.
Think about the following questions:
Why should this change should be made? What is wrong with the current code? Explain how things were prior to the patch.
Why should it be done in this particular way?
Did you try a different way before? Describe alternate approaches you considered.
Can a reviewer confirm that it works as intended?
What are the consequences for further users of this code? Do they need to understand the code in a new way?
Was this discussed before? Add a link to an existing public issue if it exists, to provide context. (Note that the commit should still be self-explanatory even if there is a linked issue.)
Avoid URLs in commit messages.
Use git hashes instead of URLs to refer to other changes.
If there was external documentation or discussions, also summarize the relevant points.
Wrap the message body so that lines are less than 100 characters long. There are too many tools that cannot re-flow paragraphs, or do a miserable job at it, to afford using unwrapped paragraphs in commit messages.
Suggestion: use your editor's standard wrapping width of 72 characters so as to make commit messages uniform across the entire project. Many of your fellow developers also use the default configuration of their editor that will wrap at 72 columns.
If a URL is too long, give it its own line, but don't break or wrap it.
Pay attention to
OpenStack's chapter Information in commit messages:
Place the references to bugs or github issues after the explanation, but before the release note. For example:
This is the commit title Here's some explanation. Fixes #123. Release note (general change): the release note.