Issue #3284647: Respect widget collapsed property unless nested field validation fails

Closes #3284647

src/Plugin/Field/FieldWidget/InlineEntityFormComplex.php

@@ -15,7 +15,9 @@ use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Render\Element\Details;
 use Drupal\inline_entity_form\TranslationHelper;
+use Drupal\inline_entity_form\WidgetHelper;
 use Drupal\rat\v1\RenderArray;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -298,6 +300,14 @@ class InlineEntityFormComplex extends InlineEntityFormBase implements ContainerF
     if ($element['#type'] == 'details') {
       // If there's user input, keep the details open. Otherwise, use settings.
       $element['#open'] = $form_state->getUserInput() ?: !$this->getSetting('collapsed');
+
+      // Store the default state widget setting and custom #pre_render callback.
+      $element['#collapsed_setting'] = $this->getSetting('collapsed');
+      $element['#pre_render'] = [
+        [WidgetHelper::class, 'iefDetailsPreRender'],
+        [Details::class, 'preRenderDetails'],
+        [Details::class, 'preRenderGroup'],
+      ];
     }
 
     $this->prepareFormState($form_state, $items, $element['#translating']);