term_reference_tree bug fix

web/modules/custom/materio_admin/materio_admin.module

@@ -5,33 +5,23 @@
  * Admin back-office enhancements.
  */
 
-use Drupal\term_reference_tree\Plugin\Field\FieldWidget\TermReferenceTree;
-
-/**
- * Implements hook_field_widget_single_element_form_alter().
- *
- * Attaches the widget layout library wherever the term reference tree widget
- * renders (thesaurus on materiau, etc.), so the selection tree (left) and the
- * sortable track list (right) sit side by side.
- *
- * Transposed from the retired matminimal theme CSS, which was tied to the old
- * adminimal-based admin theme. The selectors target the widget's own markup
- * classes and are admin-theme agnostic (works under Gin 4 and Gin 5).
- */
-function materio_admin_field_widget_single_element_form_alter(array &$element, \Drupal\Core\Form\FormStateInterface $form_state, array $context) {
-  if (isset($context['widget']) && $context['widget'] instanceof TermReferenceTree) {
-    $element['#attached']['library'][] = 'materio_admin/term_reference_tree';
-  }
-}
-
 /**
  * Implements hook_page_attachments().
  *
  * Loads the general admin table styling on every admin route (compact
  * paddings + constrained widths, replacing the old matminimal rules).
+ *
+ * Also loads the term reference tree widget layout (selection tree left,
+ * sortable track list right) on admin routes. Attaching it here instead of
+ * hook_field_widget_single_element_form_alter() keeps the widget element's
+ * own #attached libraries intact: setting #attached in that alter hook
+ * prevented FormBuilder's element-info defaults merge ($element += $info)
+ * from applying the checkbox_tree element #attached, which silently dropped
+ * term_reference_tree/term_reference_tree_js and _css.
  */
 function materio_admin_page_attachments(array &$attachments) {
   if (\Drupal::service('router.admin_context')->isAdminRoute()) {
     $attachments['#attached']['library'][] = 'materio_admin/admin_tables';
+    $attachments['#attached']['library'][] = 'materio_admin/term_reference_tree';
   }
 }