Ultimately, our goal with GK is to be as helpful as possible to users without getting in the way. From time to time, we see users bring up, "hey, I want to merge X branch into Y but GK is only giving me the option to merge Y into X, what gives?". While in some rare cases this most likely is due to a bug, a majority of the time this is intentional behavior for GK. The purpose behind this, we want to help users prevent merges they don't actually want to do. Below are a few cases you can try out in this repo to better understand how the behavior in GK works.
Branch A & B: In this case, GK will offer the ability to Merge A into B or B into A. This is usually determined by how you utilized drag and drop in GK (or whichever branch you have checked out and right click on). Either way you do it, you can do A --> B or B --> A. These branches both share a common ancestor and contain commits that the other branch does not.
Branch C & D:
In this case, GK will only offer the ability to merge C into D. This is because the commit from branch-D has already been merged into branch-C and trying to merge the branch into C again, would serve
no purpose other than creating an empty merge commit. However, because branch-C has changes branch-D does not, GK is able to see that this is most likely the case a user wishes to achieve. We gain
nothing from doing D --> C but doing C --> D would actually yeild a useful merge commit (rather than an empty one).