Display custom hook error messages when automatic merge is enabled

app/assets/javascripts/merge_request_widget.js

@@ -179,7 +179,7 @@ import MiniPipelineGraph from './mini_pipeline_graph_dropdown';
       $('.ci-widget-fetching').show();
       return $.getJSON(this.opts.ci_status_url, (function(_this) {
         return function(data) {
-          var message, status, title;
+          var message, status, title, callback;
           _this.status = data.status;
           _this.hasCi = data.has_ci;
           _this.updateMergeButton(_this.status, _this.hasCi);
@@ -201,6 +201,12 @@ import MiniPipelineGraph from './mini_pipeline_graph_dropdown';
               _this.opts.ci_sha = data.sha;
               _this.updateCommitUrls(data.sha);
             }
+            if (data.status === "success" || data.status === "failed") {
+              callback = function() {
+                return merge_request_widget.getMergeStatus();
+              };
+              return setTimeout(callback, 2000);
+            }
             if (showNotification && data.status) {
               status = _this.ciLabelForStatus(data.status);
               if (status === "preparing") {

app/services/merge_requests/refresh_service.rb

@@ -12,6 +12,7 @@ module MergeRequests
       close_merge_requests
       reload_merge_requests
       reset_merge_when_pipeline_succeeds
+      reset_merge_errors
       mark_pending_todos_done
       cache_merge_requests_closing_issues
 
@@ -99,6 +100,12 @@ module MergeRequests
       merge_requests_for_source_branch.each(&:reset_merge_when_pipeline_succeeds)
     end
 
+    def reset_merge_errors
+      merge_requests_for_source_branch.each do |merge_request|
+        merge_request.update_attribute(:merge_error, nil)
+      end
+    end
+
     def mark_pending_todos_done
       merge_requests_for_source_branch.each do |merge_request|
         todo_service.merge_request_push(merge_request, @current_user)

app/views/projects/merge_requests/widget/_open.html.haml

@@ -27,14 +27,16 @@
       = render 'projects/merge_requests/widget/open/conflicts'
     - elsif @merge_request.work_in_progress?
       = render 'projects/merge_requests/widget/open/wip'
+    - elsif @merge_request.should_be_rebased?
+      = render 'projects/merge_requests/widget/open/rebase'
+    - elsif @merge_request.merge_when_pipeline_succeeds? && @merge_request.merge_error.present?
+      = render 'projects/merge_requests/widget/open/error'
     - elsif @merge_request.merge_when_pipeline_succeeds?
       = render 'projects/merge_requests/widget/open/merge_when_pipeline_succeeds'
     - elsif !@merge_request.can_be_merged_by?(current_user)
       = render 'projects/merge_requests/widget/open/not_allowed'
     - elsif !@merge_request.mergeable_ci_state? && (@pipeline.failed? || @pipeline.canceled?)
       = render 'projects/merge_requests/widget/open/build_failed'
-    - elsif @merge_request.should_be_rebased?
-      = render 'projects/merge_requests/widget/open/rebase'
     - elsif !@merge_request.mergeable_discussions_state?
       = render 'projects/merge_requests/widget/open/unresolved_discussions'
     - elsif @pipeline&.blocked?