ACPT-978: Improve Config Save filtering

This performance improvement is in Save and Structure and totals to ~42x improvement in Magento\Config\Controller\Adminhtml\System\Config\Save::filterNodes

Author: JacobBrownAustin

app/code/Magento/Config/Controller/Adminhtml/System/Config/Save.php

@@ -335,18 +335,11 @@ private function filterPaths(string $prefix, array $groups, array $systemXmlConf
     private function filterNodes(array $configData): array
     {
         if (!empty($configData['groups'])) {
-            $systemXmlPathsFromKeys = array_keys($this->_configStructure->getFieldPaths());
-            $systemXmlPathsFromValues = array_reduce(
-                array_values($this->_configStructure->getFieldPaths()),
-                'array_merge',
-                []
-            );
             //Full list of paths defined in system.xml
-            $systemXmlConfig = array_merge($systemXmlPathsFromKeys, $systemXmlPathsFromValues);
-
+            $fieldPaths = $this->_configStructure->getFieldPaths();
+            $systemXmlConfig = array_merge(array_keys($fieldPaths), ...array_values($fieldPaths));
             $configData['groups'] = $this->filterPaths($configData['section'], $configData['groups'], $systemXmlConfig);
         }
-
         return $configData;
     }
 }

app/code/Magento/Config/Model/Config/Structure.php

@@ -384,32 +384,22 @@ public function getFieldPaths()
      * Iteration that collects config field paths recursively from config files.
      *
      * @param array $elements The elements to be parsed
+     * @param array $result used for recursive calls
      * @return array An array of config path to config structure path map
      */
-    private function getFieldsRecursively(array $elements = [])
+    private function getFieldsRecursively(array $elements = [], &$result = [])
     {
-        $result = [];
-
         foreach ($elements as $element) {
             if (isset($element['children'])) {
-                $result = array_merge_recursive(
-                    $result,
-                    $this->getFieldsRecursively($element['children'])
-                );
+                $this->getFieldsRecursively($element['children'], $result);
             } else {
                 if ($element['_elementType'] === 'field') {
                     $structurePath = (isset($element['path']) ? $element['path'] . '/' : '') . $element['id'];
                     $configPath = isset($element['config_path']) ? $element['config_path'] : $structurePath;
-
-                    if (!isset($result[$configPath])) {
-                        $result[$configPath] = [];
-                    }
-
                     $result[$configPath][] = $structurePath;
                 }
             }
         }
-
         return $result;
     }
 }