Correctly map the errors of newly created elements in CollectionTypes

Before there were just shown on the parent, now they get mapped to the right field

src/Form/CollectionTypeExtension.php

@@ -43,13 +43,16 @@ namespace App\Form;
 
 use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\Common\Collections\Collection;
+use http\Cookie;
 use ReflectionClass;
 use ReflectionException;
 use Symfony\Component\Form\AbstractTypeExtension;
+use Symfony\Component\Form\Event\PreSubmitEvent;
 use Symfony\Component\Form\Extension\Core\Type\CollectionType;
 use Symfony\Component\Form\FormBuilder;
 use Symfony\Component\Form\FormBuilderInterface;
 use Symfony\Component\Form\FormConfigBuilder;
+use Symfony\Component\Form\FormConfigInterface;
 use Symfony\Component\Form\FormEvent;
 use Symfony\Component\Form\FormEvents;
 use Symfony\Component\Form\FormInterface;
@@ -62,7 +65,7 @@ use Symfony\Component\PropertyAccess\PropertyAccessorInterface;
  * Perform a reindexing on CollectionType elements, by assigning the database id as index.
  * This prevents issues when the collection that is edited uses a OrderBy annotation and therefore the direction of the
  * elements can change during requests.
- * Must me enabled by setting reindex_enable to true in Type options.
+ * Must be enabled by setting reindex_enable to true in Type options.
  */
 class CollectionTypeExtension extends AbstractTypeExtension
 {
@@ -135,6 +138,32 @@ class CollectionTypeExtension extends AbstractTypeExtension
                 }
             }
         }, 100); //We need to have a higher priority then the PRE_SET_DATA listener on CollectionType
+
+        // This event listener fixes the error mapping for newly created elements of collection types
+        // Without this method, the errors for newly created elements are shown on the parent element, as forms
+        // can not map it to the correct element.
+        $builder->addEventListener(FormEvents::PRE_SUBMIT, function (PreSubmitEvent $event) use ($options) {
+           $data = $event->getData();
+           $form = $event->getForm();
+           $config = $form->getConfig();
+
+           if (!is_array($data) && !$data instanceof Collection) {
+               return;
+           }
+
+           if ($data instanceof Collection) {
+                $data = $data->toArray();
+           }
+
+           //The validator uses the number  of the element as index, so we have to map the errors to the correct index
+           $error_mapping = [];
+           $n = 0;
+           foreach ($data as $key => $item) {
+               $error_mapping['['.$n.']'] = $key;
+               $n++;
+           }
+            $this->setOption($config, 'error_mapping', $error_mapping);
+        });
     }
 
     /**
@@ -142,8 +171,12 @@ class CollectionTypeExtension extends AbstractTypeExtension
      * This a bit hacky cause we access private properties....
      *
      */
-    public function setOption(FormBuilder $builder, string $option, $value): void
+    public function setOption(FormConfigInterface $builder, string $option, $value): void
     {
+        if (!$builder instanceof FormConfigBuilder) {
+            throw new \RuntimeException('This method only works with FormConfigBuilder instances.');
+        }
+
         //We have to use FormConfigBuilder::class here, because options is private and not available in sub classes
         $reflection = new ReflectionClass(FormConfigBuilder::class);
         $property = $reflection->getProperty('options');