How do you measure the value of a PR Review?
Thinking out aloud. You employ a developer whose sole job is to review PRs submitted by other developers. How do you measure the value that developer is providing?
The time saved by not having to (1) debug issues in production plus (2) the time taken to fix the code plus (3) the time taken to review and deploy the fixes multiplied by the cost of that time.
The revenue generated by the customers who would have signed up if that bug did not exist.
The revenue that would have been maintained if those customers had not canceled their subscriptions because of the bug that got through.
The cost of the review-developer doing the PR.
The other noise created by the review-developer trying to make the value look obvious by over-commenting on the PR. (A quick aside: If you are being measured or incentivized to do PRs then you will have a tendency to comment more frequently to show value. Sometimes that will be value but sometimes it will be costly noise.)
Review Feedback and Measurement
What if the PR submitter and added value markers to each comment that the reviewer made?
Given that the submitter has to read through all the comments anyway it should be very little effort to tag the comments with a marker. In Stash there's the "like" link and in GitHub you have a collection of emojis.
An automated scripts could aggregate the tags assigned to the reviewer.
What is a valuable comment on a PR?
This brings up the question on value in comments.
"I like that you used reduce() here instead of filter() and map()" - is that a valuable comment? I think that it is. Perhaps sometimes it needs more context. The value here is that your telling the PR submitter that you (1) read through it and understood it and (2) thought that a particular section was well written.
A comment like this has even more value if the submitter has not used an optimal pattern (that you like) in the past or in another section of the PR. I have seen this where a submitter may have used a "perfect" pattern in one file and then something "messy" to solve the same type of problem in another module. Highlighting the good code as well as the "needs improvement" code has as much value.