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Code Review Guidelines

This guide contains advice and best practices for performing code review, and having your code reviewed.

All merge requests for GitLab CE and EE, whether written by a GitLab team member or a volunteer contributor, must go through a code review process to ensure the code is effective, understandable, and maintainable.

Any developer can, and is encouraged to, perform code review on merge requests of colleagues and contributors. However, the final decision to accept a merge request is up to one of our merge request "endbosses", denoted on the team page.

Everyone

  • Accept that many programming decisions are opinions. Discuss tradeoffs, which you prefer, and reach a resolution quickly.
  • Ask questions; don't make demands. ("What do you think about naming this :user_id?")
  • Ask for clarification. ("I didn't understand. Can you clarify?")
  • Avoid selective ownership of code. ("mine", "not mine", "yours")
  • Avoid using terms that could be seen as referring to personal traits. ("dumb", "stupid"). Assume everyone is attractive, intelligent, and well-meaning.
  • Be explicit. Remember people don't always understand your intentions online.
  • Be humble. ("I'm not sure - let's look it up.")
  • Don't use hyperbole. ("always", "never", "endlessly", "nothing")
  • Be careful about the use of sarcasm. Everything we do is public; what seems like good-natured ribbing to you and a long-time colleague might come off as mean and unwelcoming to a person new to the project.
  • Consider one-on-one chats or video calls if there are too many "I didn't understand" or "Alternative solution:" comments. Post a follow-up comment summarizing one-on-one discussion.

Having your code reviewed

  • The first reviewer of your code is you. Before you perform that first push of your shiny new branch, read through the entire diff. Does it make sense? Did you include something unrelated to the overall purpose of the changes? Did you forget to remove any debugging code?
  • Be grateful for the reviewer's suggestions. ("Good call. I'll make that change.")
  • Don't take it personally. The review is of the code, not of you.
  • Explain why the code exists. ("It's like that because of these reasons. Would it be more clear if I rename this class/file/method/variable?")
  • Extract unrelated changes and refactorings into future merge requests/issues.
  • Seek to understand the reviewer's perspective.
  • Try to respond to every comment.
  • Push commits based on earlier rounds of feedback as isolated commits to the branch. Do not squash until the branch is ready to merge. Reviewers should be able to read individual updates based on their earlier feedback.

Reviewing code

Understand why the change is necessary (fixes a bug, improves the user experience, refactors the existing code). Then:

  • Communicate which ideas you feel strongly about and those you don't.
  • Identify ways to simplify the code while still solving the problem.
  • Offer alternative implementations, but assume the author already considered them. ("What do you think about using a custom validator here?")
  • Seek to understand the author's perspective.
  • If you don't understand a piece of code, say so. There's a good chance someone else would be confused by it as well.
  • After a round of line notes, it can be helpful to post a summary note such as "LGTM :thumbsup:", or "Just a couple things to address."
  • Avoid accepting a merge request before the build succeeds ("Merge when build succeeds" is fine).

Credits

Largely based on the thoughtbot code review guide.

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