<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=17700) </details> <!--IssueSummary end--> ### Description * How should the merge request look when the source branch doesn't exist anymore, or there are errors. * As in https://gitlab.com/gitlab-org/gitlab-ce/issues/30368 and https://gitlab.com/gitlab-org/gitlab-ce/issues/25575. * Probably show description and discussion tab with comments. * The commits tab should probably not be visible. * Some type of error message in the merge request widget. * Remove some irrelevant UI in the merge request widget. Currently it looks like this: