MAGETWO-61183: Fix default values not being properly loaded for ArraySerialized fields

Author: olysenko

app/code/Magento/Config/Block/System/Config/Form.php

@@ -8,6 +8,7 @@
 use Magento\Config\App\Config\Type\System;
 use Magento\Config\Model\Config\Reader\Source\Deployed\SettingChecker;
 use Magento\Config\Model\Config\Structure\ElementVisibilityInterface;
+use Magento\Framework\App\Config\Data\ProcessorInterface;
 use Magento\Framework\App\Config\ScopeConfigInterface;
 use Magento\Framework\App\DeploymentConfig;
 use Magento\Framework\App\ObjectManager;
@@ -425,23 +426,21 @@ private function getFieldData(\Magento\Config\Model\Config\Structure\Element\Fie
         if ($placeholderValue) {
             $data = $placeholderValue;
         }
-        if ($data === null) {
-            if (array_key_exists($path, $this->_configData)) {
-                $data = $this->_configData[$path];
-            } elseif ($field->getConfigPath() !== null) {
-                $data = $this->getConfigValue($field->getConfigPath());
-            } else {
-                $data = $this->getConfigValue($path);
-            }
 
+        if ($data === null) {
+            $path = $field->getConfigPath() !== null ? $field->getConfigPath() : $path;
+            $data = $this->getConfigValue($path);
             if ($field->hasBackendModel()) {
                 $backendModel = $field->getBackendModel();
-                $backendModel->setPath($path)
-                    ->setValue($data)
-                    ->setWebsite($this->getWebsiteCode())
-                    ->setStore($this->getStoreCode())
-                    ->afterLoad();
-                $data = $backendModel->getValue();
+                // Backend models which implement ProcessorInterface are processed by ScopeConfigInterface
+                if (!$backendModel instanceof ProcessorInterface) {
+                    $backendModel->setPath($path)
+                        ->setValue($data)
+                        ->setWebsite($this->getWebsiteCode())
+                        ->setStore($this->getStoreCode())
+                        ->afterLoad();
+                    $data = $backendModel->getValue();
+                }
             }
         }
 

app/code/Magento/Config/Test/Unit/Block/System/Config/FormTest.php

@@ -546,8 +546,8 @@ public function initFieldsDataProvider()
         return [
             [
                 ['section1/group1/field1' => 'some_value'],
-                false,
-                null,
+                'some_value',
+                'section1/group1/field1',
                 false,
                 'some_value',
                 null,
@@ -575,7 +575,7 @@ public function initFieldsDataProvider()
                 true,
                 'Placeholder Value',
                 'Placeholder Value',
-                0,
+                1,
                 false,
                 true,
                 true
@@ -587,7 +587,7 @@ public function initFieldsDataProvider()
                 true,
                 'Placeholder Value',
                 'Placeholder Value',
-                0,
+                1,
                 true,
                 true,
                 true

dev/tests/integration/testsuite/Magento/Config/Block/System/Config/FieldArray.php

@@ -0,0 +1,33 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+namespace Magento\Config\Block\System\Config;
+
+use Magento\Config\Block\System\Config\Form\Field\FieldArray\AbstractFieldArray;
+
+/**
+ * Backend system config array field renderer for integration test.
+ */
+class FieldArray extends AbstractFieldArray
+{
+    /**
+     * @inheritdoc
+     */
+    protected function _toHtml()
+    {
+        $value = '';
+        $element = $this->getElement();
+        if ($element->getValue() && is_array($element->getValue())) {
+            $value = implode('|', $element->getValue());
+        }
+
+        return sprintf(
+            '<input id="%s" name="%s" value="%s" />',
+            $element->getId(),
+            $element->getName(),
+            $value
+        );
+    }
+}