Issue #3311455: Support field_groups nesting

modules/ui_patterns_field_group/src/Plugin/UiPatterns/Source/FieldgroupSource.php

+<?php
+
+namespace Drupal\ui_patterns_field_group\Plugin\UiPatterns\Source;
+
+use Drupal\ui_patterns\Plugin\PatternSourceBase;
+
+/**
+ * Defines Fields API pattern source plugin.
+ *
+ * @UiPatternsSource(
+ *   id = "fieldgroup",
+ *   label = @Translation("Fieldgroups"),
+ *   provider = "field_group",
+ *   tags = {
+ *     "entity_display"
+ *   }
+ * )
+ */
+class FieldgroupSource extends PatternSourceBase {
+
+  /**
+   * Return list of source fields.
+   *
+   * @return \Drupal\ui_patterns\Definition\PatternSourceField[]
+   *   List of source fields.
+   *
+   * @throws \Drupal\Component\Plugin\Exception\PluginException
+   */
+  public function getSourceFields() {
+    $sources = [];
+    $entity_type_id = $this->getContextProperty('entity_type');
+    $bundle = $this->getContextProperty('entity_bundle');
+    $view_mode = $this->getContextProperty('entity_view_mode');
+
+    $groups = field_group_info_groups($entity_type_id, $bundle, 'view', $view_mode);
+
+    foreach ($groups as $group_name => $group) {
+      if (empty($this->getContextProperty('limit')) || in_array($group_name, $this->getContextProperty('limit'))) {
+        $sources[] = $this->getSourceField($group_name, $group->label);
+      }
+    }
+
+    return $sources;
+  }
+
+}