ISTWCMS-6195 Remove support for nolink and button in all link fields

uw_cfg_common.module

@@ -1783,3 +1783,51 @@ function uw_cfg_common_views_query_alter(ViewExecutable $view, QueryPluginBase $
     $query->addOrderBy('redirect', 'rid');
   }
 }
+
+/**
+ * Implements hook_field_widget_single_element_WIDGET_TYPE_form_alter().
+ */
+function uw_cfg_common_field_widget_single_element_link_default_form_alter(array &$element, FormStateInterface $form_state, array $context) {
+
+  // Get field information from context.
+  $field_definition = $context['items']->getFieldDefinition();
+
+  // Set custom description only for event map field.
+  if ($field_definition->getName() == 'field_uw_event_map') {
+    $element['uri']['#description'] = t('Optional: provide a link to a map with the event location (e.g. https://uwaterloo.ca/map/). This must be an external URL such as https://example.com.');
+  }
+  else {
+    // Set custom description for all link fields except event map.
+    $element['uri']['#description'] = t('Start typing the title of a piece of content to select it. You can also enter an internal path such as /blog or an external URL such as https://example.com. Enter <front> to link to the front page.');
+
+    // Set custom description only for event host field.
+    if ($field_definition->getName() == 'field_uw_event_host') {
+      $element['uri']['#description'] .= ' ' . t('Enter <nolink> to display link text only.');
+    }
+  }
+
+  // Add link uri field element validation function.
+  $element['uri']['#element_validate'][] = '_uw_cfg_common_uw_link_validator';
+}
+
+/**
+ * Link uri field validation function.
+ */
+function _uw_cfg_common_uw_link_validator($element, &$form_state, $form) {
+  $uri = $element['#value'];
+
+  // Get the field name and set it up in the format used by setErrorByName.
+  $fieldname = rtrim($element['#name'], ']');
+  $pos = strpos($fieldname, '[');
+  $fieldname = substr_replace($fieldname, '][', $pos, 1);
+
+  // Buttons are just not allowed.
+  if ($uri == '<button>') {
+    $form_state->setErrorByName($fieldname, t('The &lt;button&gt; value is not supported for this field.'));
+  }
+
+  // Nolink is not allowed, with one exception.
+  if ($uri == '<nolink>' && $fieldname != 'field_uw_event_host][0][uri') {
+    $form_state->setErrorByName($fieldname, t('The &lt;nolink&gt; value is not supported for this field.'));
+  }
+}