It’s equally as important to pay attention to the hidden changes during code review. Transitive dependency changes or generated code changes might bloat the resulting binary or reduce performance. Manifest changes might cause an incompatibility downstream. These problems are often found much later in the release process where an investigation is required to find the cause.

After running into a few problems with hidden changes on the Cash Android team, we decided to promote them to be more visible at the point where they change: the pull request.

APK size and method count diff on an automatic PR comment.

In every CI build, we calculate interesting pieces of data like the binary size and method count (an important metric for Android apps) and write them to shared storage. When a CI build runs for a pull request, we figure out the difference of these values from the ancestor commit on master. The numbers are sent back to the pull request in the form of a comment to ensure the author and any reviewers are notified.

These important metrics are now surfaced explicitly to ensure that the result is what you intended. Does that new dependency only add 10 methods or do we incur 10,000? Does that new hero image add only 20KB or occupy 2MB?