When reviewing a merge request that looks ready to merge but still has one or more CI builds running, you can set it to be merged automatically when the builds pipeline succeeds. This way, you don't have to wait for the builds to finish and remember to merge the request manually.
When you hit the "Merge When Pipeline Succeeds" button, the status of the merge request will be updated to represent the impending merge. If you cannot wait for the pipeline to succeed and want to merge immediately, this option is available in the dropdown menu on the right of the main button.
Both team developers and the author of the merge request have the option to cancel the automatic merge if they find a reason why it shouldn't be merged after all.
When the pipeline succeeds, the merge request will automatically be merged. When the pipeline fails, the author gets a chance to retry any failed builds, or to push new commits to fix the failure.
When the builds are retried and succeed on the second try, the merge request will automatically be merged after all. When the merge request is updated with new commits, the automatic merge is automatically canceled to allow the new changes to be reviewed.
Note: You need to have builds configured to enable this feature.
You can prevent merge requests from being merged if their pipeline did not succeed.
Navigate to your project's settings page, select the Only allow merge requests to be merged if the pipeline succeeds check box and hit Save for the changes to take effect.
From now on, every time the pipeline fails you will not be able to merge the merge request from the UI, until you make all relevant builds pass.