Issue #3269521: The 'Prevent this field from being overwritten' option does not work

migrate_override.module

@@ -5,6 +5,7 @@
  * Contains migrate_override.module.
  */
 
+use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\migrate_override\OverrideManagerServiceInterface;
@@ -46,7 +47,8 @@ function migrate_override_field_widget_multivalue_form_alter(array &$elements, F
   if (!$manager->entityBundleEnabled($entity)) {
     return;
   }
-  if ($manager->entityFieldInstanceSetting($entity, $field) === OverrideManagerServiceInterface::FIELD_IGNORED) {
+  $setting = $manager->entityFieldInstanceSetting($entity, $field);
+  if ($setting === OverrideManagerServiceInterface::FIELD_IGNORED) {
     return;
   }
   $type = $entity->getEntityTypeId();
@@ -63,30 +65,31 @@ function migrate_override_field_widget_multivalue_form_alter(array &$elements, F
 
   /** @var \Drupal\Core\Field\WidgetInterface $widget */
   $widget = $context['widget'];
+  $keys = [];
   switch ($widget->getPluginId()) {
     case 'inline_entity_form_complex':
       if (isset($elements['entities'])) {
         foreach (Element::children($elements['entities']) as $delta) {
-          $elements['entities'][$delta]['actions']['ief_entity_edit']['#states'] = $states;
-          $elements['entities'][$delta]['actions']['ief_entity_remove']['#states'] = $states;
+          $keys[] = ['entities', $delta, 'actions', 'ief_entity_edit'];
+          $keys[] = ['entities', $delta, 'actions', 'ief_entity_remove'];
         }
       }
       if (isset($elements['actions'])) {
-        $elements['actions']['#states'] = $states;
+        $keys[] = ['actions'];
       }
       break;
 
     case 'telephone_default':
     case 'email_default':
       foreach (Element::children($elements) as $key) {
-        $elements[$key]['value']['#states'] = $states;
+        $keys[] = [$key, 'value'];
       }
       break;
 
     case 'link_default':
       foreach (Element::children($elements) as $key) {
-        $elements[$key]['uri']['#states'] = $states;
-        $elements[$key]['title']['#states'] = $states;
+        $keys[] = [$key, 'uri'];
+        $keys[] = [$key, 'title'];
       }
       break;
 
@@ -97,15 +100,29 @@ function migrate_override_field_widget_multivalue_form_alter(array &$elements, F
     default:
       foreach (Element::children($elements) as $outerkey) {
         if (isset($elements[$outerkey]['#type'])) {
-          $elements[$outerkey]['#states'] = $states;
+          $keys[] = [$outerkey];
         }
         else {
           foreach (Element::children($elements[$outerkey]) as $innerkey) {
-            $elements[$outerkey][$innerkey]['#states'] = $states;
+            $keys[] = [$outerkey, $innerkey];
           }
         }
       }
   }
+
+  if ($setting === OverrideManagerServiceInterface::FIELD_OVERRIDEABLE) {
+    foreach ($keys as $key) {
+      $key[] = '#states';
+      NestedArray::setValue($elements, $key, $states);
+    }
+  }
+
+  if ($setting === OverrideManagerServiceInterface::FIELD_LOCKED) {
+    foreach ($keys as $key) {
+      $key[] = '#disabled';
+      NestedArray::setValue($elements, $key, TRUE);
+    }
+  }
 }
 
 /**