Tips for Participating In Drake Code Reviews using reviewable.io

Introduction

Drake code reviews use https://reviewable.io. This page documents some best practices for communicating effectively in Reviewable.

GitHub Integration

Avoid using the GitHub UI to comment on code during a review. Reviewable will import comments from GitHub, but cannot reliably match them to lines of diff.

When you enter comments in Reviewable, they are saved as drafts. Use the “publish” button to send them out in a batch. Reviewable will post the comments to the GitHub PR in a single, well-formatted block, generating email to everyone else following the PR.

Every time you push to your GitHub branch under review, Reviewable will snapshot a new diff. Because it maintains an independent diff series, you can rebase freely without corrupting the review history.

Life of a Reviewable Comment

All threads in Reviewable must be resolved before you can merge your PR. The semantics of discussion resolution are a little tricky:

When a reviewer creates a new comment, the reviewer’s disposition toward the thread may be “satisfied”, “discussing”, or “blocking”. Reviewers should:

  • Use satisfied to indicate that no action is required of the author.
  • Use discussing to indicate that the author must respond, but may then close the thread without further input. However, if the author has follow-up questions, the reviewer is responsible for iterating on it. This is the default.
  • Use blocking to indicate that the author must take action on the comment. The reviewer must then review and iterate on the fix with the author. Once an acceptable resolution is achieved, the reviewer should update disposition to satisfied.

The author may respond to each comment with the same set of dispositions. Authors should:

  • Use satisfied to indicate that they believe the discussion is over. If the reviewer’s comment is not blocking, this will close the thread. This is the default disposition when the “Done” or “Acknowledged” button is clicked.
  • Use discussing to indicate that they require more input from the reviewer.
  • Use blocking to indicate that they have not yet resolved the problem. This serves as a safeguard against accidental merge.

Before commenting on a line of code, reviewers should check to see if there is already a resolved discussion addressing the same topic. Resolved discussions are indicated by a small white check-mark in a grey circle to the left of the line of code.

Reviewers should click the eye-shaped buttons to indicate that they have reviewed a file. Reviewable will remember the revisions at which the file was reviewed, and mark them with an eye icon in the file history.

Curated Commits

Each commit on Drake master should pass all unit tests and lint checks, should be logically cohesive (should not require other commits to make sense), and should have a meaningful commit message.

The label status: curate commits before merging on a PR indicates that (at the time the label was added) the commits pushed to the PR do not meet those criteria, usually because the commits contain “work-in-progress” checkpoints or scattered “fix review comments” adjustments.

When applied to a PR, this label will prevent a PR with more than one commit from being merged.

The author of a PR has three choices for how to resolve this defect:

  • Remove the label and then immediately use the “squash and merge” button to merge the PR, being careful to tweak the the commit message in the github edit box to be a sensible description of the change.
  • Locally (rebase and) squash the PR down to a single commit, and force-push that commit into the PR. This will automatically remove the merge impediment: even though the label still exists, it is a no-op when there is only one commit in the PR.
  • Locally (rebase and) squash the PR to contain more than one commit, but where each individual commit meets the above recommendations, and then remove the label.