Merge branch 'fix/29125' into 'master'

Port of fix/29125-ee to CE

Closes #29125

See merge request !10796

app/assets/javascripts/merge_request_widget.js

@@ -157,7 +157,7 @@ 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);
@@ -179,6 +179,12 @@ 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 _this.getMergeStatus();
+              };
+              return setTimeout(callback, 2000);
+            }
             if (showNotification && data.status) {
               status = _this.ciLabelForStatus(data.status);
               if (status === "preparing") {

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

@@ -19,6 +19,8 @@
       = render 'projects/merge_requests/widget/open/conflicts'
     - elsif @merge_request.work_in_progress?
       = render 'projects/merge_requests/widget/open/wip'
+    - 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)

app/views/projects/merge_requests/widget/open/_error.html.haml

+%h4
+  = icon('exclamation-triangle')
+  This merge request failed to be merged automatically
+
+%p
+  = @merge_request.merge_error

changelogs/unreleased/fix-29125.yml

+---
+title: Display custom hook error messages when automatic merge is enabled
+merge_request:
+author:

spec/features/merge_requests/widget_spec.rb

@@ -141,6 +141,27 @@ describe 'Merge request', :feature, :js do
     end
   end
 
+  context 'view merge request with MWPS enabled but automatically merge fails' do
+    before do
+      merge_request.update(
+        merge_when_pipeline_succeeds: true,
+        merge_user: merge_request.author,
+        merge_error: 'Something went wrong'
+      )
+
+      visit namespace_project_merge_request_path(project.namespace, project, merge_request)
+    end
+
+    it 'shows information about the merge error' do
+      # Wait for the `ci_status` and `merge_check` requests
+      wait_for_ajax
+
+      page.within('.mr-widget-body') do
+        expect(page).to have_content('Something went wrong')
+      end
+    end
+  end
+
   context 'merge error' do
     before do
       allow_any_instance_of(Repository).to receive(:merge).and_return(false)