I accidentally merged a PR from my development branch (subject-serve-image) into the main branch instead of my release branch (rc/04). I quickly reverted that PR, which created another PR. I merged the revert PR back into main. Afterward, I created a new PR from my dev branch to the release branch (rc/04), which worked fine.
As part of my regular process, I merge my release branch (rc/04) into main periodically. However, when I created and merged the PR from rc/04 to main, it did not show any changes.
What could have gone wrong? What process should I have followed to ensure that the changes from the release branch merged correctly into main?
Let's say your PR was trying to merge commit P. When you accidentally merged it, that meant that main now also contains commit P. Then you did a new PR that reverted P, call it Q and that was subsequently merged into main. So at this point, main now contains P and Q. Note that reverting here did not mean commit P never happened. It means that Q was introduced to reverse the changes in P.
Next, you created a PR to do what you originally intended, to merge P into the rc/04. Once merged, rc/04 now contains P.
When you get to the step of merging rc/04 into main, git will look at the set difference. In this case, what does rc/04 bring that I don't already have in main. Since P is present in both rc/04 and main, there are no commits to bring over. Hence, the empty diff.
You'll want to make sure that main actually represents what you want though. With Q reverting the changes, I'd bet the changes in P are not actually reflected on main.
One piece of advice is that when you end up reverting a commit and want to re-introduce the changes from that commit, it's best to create a new commit with the changes so that it gets a new ID number. You can achieve that in a couple of ways: straight-up creating a new commit, or amending the commit (git commit --amend) with no change but updates the timestamp (you might need to use --reset-author to force the timestamp to change). Once you have a new commit ID, git will no longer treat the commit as already being merged into main and you'd see the difference you expected.