Commit message reviewing
Reviewable now supports diffing and reviewing commit messages. This can be an important part of some workflows, but also a big UI improvement even when just figuring out how revisions map to commits.
In new reviews, Reviewable will generate a virtual Commits file that you can diff just like a normal one. This file will always be first in the list and is prefixed with a commit icon but otherwise behaves like a normal file; it will have revisions and support discussions. Note that this file doesn't affect your repository or pull request in anyway — it's generated on the fly solely for diffing and reviewing commit messages.
While the commit file is virtual, it needs to be marked as reviewed as much (or as little) as normal files, depending on your workflow. It's included in review file counters, but not counted in review status messages unless it's the only unreviewed file. It also replaces the synthetic revision commit messages in the main review discussion, which should make following comments there a lot easier.
It's also handled separately from normal files when evaluating a custom review completion condition. You can find it in review.systemFiles and easily check whether it's been reviewed via review.summary.commitsFileReviewed (as it's not included in the other summary file counters).
As always, please let us know if you experience anything undesirable or have suggestions for how we can improve the review process!