cell: display error message on ajax call failure (#29124)

combo/apps/dashboard/templates/combo/dashboardcell.html

@@ -5,6 +5,7 @@
 <div class="cell {{ cell.css_class_names }} {% if cell.slug %}{{cell.slug}}{% endif %}"
      data-ajax-cell-url="{{ site_base }}{% url 'combo-public-ajax-page-cell' page_pk=cell.page.id cell_reference=cell.get_reference %}"
      data-ajax-cell-loading-message="{{ cell.loading_message }}"
+     data-ajax-cell-error-message="{% trans "Loading error" %}"
      {% if cell.ajax_refresh %}
      data-ajax-cell-refresh="{{ cell.ajax_refresh }}"
      {% endif %}><div>{% render_cell cell %}</div></div>

combo/public/static/js/combo.public.js

@@ -28,7 +28,11 @@ function combo_load_cell(elem) {
               $(document).trigger('combo:cell-loaded', $elem);
           },
           error: function(error) {
-              $elem.find('.loading').addClass('error-loading');
+              var msg = $(elem).data('ajax-cell-error-message');
+              $elem
+                  .find('.loading')
+                  .addClass('error-loading')
+                  .html('<span class="loading-message">' + msg + '</span>');
               window.console && console.log(':(', error);
           }
   });

combo/public/templates/combo/placeholder.html

@@ -8,6 +8,7 @@
      {% if cell.slug and cell.use_slug_as_id %}id="{{ cell.slug }}"{% endif %}
      data-ajax-cell-url="{{ site_base }}{% url 'combo-public-ajax-page-cell' page_pk=cell.page.id cell_reference=cell.get_reference %}"
      data-ajax-cell-loading-message="{{ cell.loading_message }}"
+     data-ajax-cell-error-message="{% trans "Loading error" %}"
      {% if cell.ajax_refresh %}data-ajax-cell-refresh="{{ cell.ajax_refresh }}"{% endif %}
      {% if request.extra_context_data %}data-extra-context="{{ request.extra_context_data|signed|urlencode }}"{% endif %}
      ><div>{% render_cell cell %}</div></div>