add allow_extra_fields option

src/Symfony/Component/Form/Extension/Validator/Constraints/FormValidator.php

@@ -107,7 +107,7 @@ class FormValidator extends ConstraintValidator
         }
 
         // Mark the form with an error if it contains extra fields
-        if (count($form->getExtraData()) > 0) {
+        if (!$config->getOption('allow_extra_fields') && count($form->getExtraData()) > 0) {
             $this->context->addViolation(
                 $config->getOption('extra_fields_message'),
                 array('{{ extra_fields }}' => implode('", "', array_keys($form->getExtraData()))),

src/Symfony/Component/Form/Extension/Validator/Type/FormTypeValidatorExtension.php

@@ -67,6 +67,7 @@ class FormTypeValidatorExtension extends BaseValidatorExtension
             'cascade_validation'         => false,
             'invalid_message'            => 'This value is not valid.',
             'invalid_message_parameters' => array(),
+            'allow_extra_fields'         => false,
             'extra_fields_message'       => 'This form should not contain extra fields.',
             'post_max_size_message'      => 'The uploaded file was too large. Please try to upload a smaller file.',
         ));

src/Symfony/Component/Form/Tests/Extension/Validator/Constraints/FormValidatorTest.php

@@ -615,6 +615,28 @@ class FormValidatorTest extends \PHPUnit_Framework_TestCase
         $this->validator->validate($form, new Form());
     }
 
+    public function testNoViolationIfAllowExtraData()
+    {
+        $context = $this->getMockExecutionContext();
+
+        $form = $this
+            ->getBuilder('parent', null, array('allow_extra_fields' => true))
+            ->setCompound(true)
+            ->setDataMapper($this->getDataMapper())
+            ->add($this->getBuilder('child'))
+            ->getForm();
+
+        $form->bind(array('foo' => 'bar'));
+
+        $context->expects($this->never())
+            ->method('addViolation');
+        $context->expects($this->never())
+            ->method('addViolationAt');
+
+        $this->validator->initialize($context);
+        $this->validator->validate($form, new Form());
+    }
+
     /**
      * @dataProvider getPostMaxSizeFixtures
      */