MC-36456: union implementation

Author: cpartica

lib/internal/Magento/Framework/GraphQl/Config/Element/Type.php

@@ -73,7 +73,15 @@ public function getFields() : array
     /**
      * Get interfaces the type implements, if any. Return an empty array if none are configured.
      *
-     * @return string[]
+     * Example return array(
+     *     array(
+     *         'interface' => 'SomeDefinedTypeInterface',
+     *         'copyFields' => true
+     *     ),
+     *     ...
+     * ),
+     *
+     * @return array
      */
     public function getInterfaces() : array
     {

lib/internal/Magento/Framework/GraphQlSchemaStitching/GraphQlReader/Reader/UnionType.php

@@ -57,18 +57,21 @@ public function read(\GraphQL\Type\Definition\Type $typeMeta): array
     {
         if ($typeMeta instanceof \GraphQL\Type\Definition\UnionType) {
             $typeName = $typeMeta->name;
-            $types = $typeMeta->getTypes();
             $result = [
                 'name' => $typeName,
                 'type' => self::GRAPHQL_UNION,
-                'types' => $types,
+                'types' => [],
             ];
 
             $unionTypeResolver = $this->getUnionTypeResolver($typeMeta);
             if (!empty($unionTypeResolver)) {
                 $result['typeResolver'] = $unionTypeResolver;
             }
 
+            foreach ($typeMeta->getTypes() as $type) {
+                $result['types'][] = $type->name;
+            }
+
             if ($this->docReader->read($typeMeta->astNode->directives)) {
                 $result['description'] = $this->docReader->read($typeMeta->astNode->directives);
             }