Merge branch 'copy-mesa-gl-h' into 'master'
I think there's a setting for that, but as far as I can tell, it's not just a default. It forces every merge request to be a fast-forward.
In a lot of cases, the merge commit is useful in and of itself, because it's a place to put a reference to the merge request any discussion attached to it, which could be useful for someone reading back through old commits. A fast-forward merge would lose that.
For larger things, it also means you can have a series of small commits for easier reading, but treat them as a single unit in the commit history.
What would be really nice is if GitLab had an option to tell it merge a specific merge request as a fast-forward merge, but the only way I can find to do that is to do it manually.