Cancel Auto Merge when target branch is changed

When target branch is updated, Auto Merge should be canceled.

app/services/merge_requests/base_service.rb

@@ -68,6 +68,10 @@ module MergeRequests
         !merge_request.for_fork?
     end
 
+    def cancel_auto_merge(merge_request)
+      AutoMergeService.new(project, current_user).cancel(merge_request)
+    end
+
     # Returns all origin and fork merge requests from `@project` satisfying passed arguments.
     # rubocop: disable CodeReuse/ActiveRecord
     def merge_requests_for(source_branch, mr_states: [:opened])

app/services/merge_requests/close_service.rb

@@ -34,9 +34,5 @@ module MergeRequests
         merge_request_metrics_service(merge_request).close(close_event)
       end
     end
-
-    def cancel_auto_merge(merge_request)
-      AutoMergeService.new(project, current_user).cancel(merge_request)
-    end
   end
 end

app/services/merge_requests/refresh_service.rb

@@ -24,7 +24,7 @@ module MergeRequests
       reload_merge_requests
       outdate_suggestions
       refresh_pipelines_on_merge_requests
-      cancel_auto_merge
+      cancel_auto_merges
       mark_pending_todos_done
       cache_merge_requests_closing_issues
 
@@ -142,9 +142,9 @@ module MergeRequests
       end
     end
 
-    def cancel_auto_merge
+    def cancel_auto_merges
       merge_requests_for_source_branch.each do |merge_request|
-        AutoMergeService.new(project, current_user).cancel(merge_request)
+        cancel_auto_merge(merge_request)
       end
     end
 

app/services/merge_requests/update_service.rb

@@ -43,6 +43,8 @@ module MergeRequests
         create_branch_change_note(merge_request, 'target',
                                   merge_request.previous_changes['target_branch'].first,
                                   merge_request.target_branch)
+
+        cancel_auto_merge(merge_request)
       end
 
       if merge_request.assignees != old_assignees

changelogs/unreleased/cancel-auto-merge-when-branch-is-changed.yml

+---
+title: Cancel Auto Merge when target branch is changed
+merge_request: 29416
+author:
+type: fixed

spec/services/merge_requests/update_service_spec.rb

@@ -406,6 +406,18 @@ describe MergeRequests::UpdateService, :mailer do
           expect(pending_todo.reload).to be_done
         end
       end
+
+      context 'when auto merge is enabled and target branch changed' do
+        before do
+          AutoMergeService.new(project, user).execute(merge_request, AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
+
+          update_merge_request({ target_branch: 'target' })
+        end
+
+        it 'marks pending todos as done' do
+          expect(pending_todo.reload).to be_done
+        end
+      end
     end
 
     context 'when the merge request is relabeled' do