"Merge failed: Something went wrong during merge: 9:not fast forward." when merged via API call
Summary
I tried to merge a merge request via the GitLab API using PUT /projects/:id/merge_requests/:merge_request_iid/merge
. The HTTP request was successful, so I assumed that the MR was merged. When I visited the MR page in the GitLab UI, however, it was not merged and displayed an error message instead:
Merge failed: Something went wrong during merge: 9:not fast forward. Please try again.
I searched the GitLab code for the error "not fast forward" but could not find any occurence. Does anybody have an idea, why this happens?
Steps to reproduce
I don't know how to reproduce it. :-/ Usually all my merge requests attempted to merge via the API either succeed or throw an HTTP error code.
What is the current bug behavior?
The HTTP request succeeds (indicating successful merge), even though the MR was not merged.
What is the expected correct behavior?
The HTTP request should return an error code.
Relevant logs and/or screenshots
Output of checks
This bug happens on GitLab.com