Symfony 2 Form Error Serializer. May be used for AJAX form validation. Allows tree and flat array styles for errors.

FormErrorsSerializer.php

class FormErrorsSerializer {

    public function serializeFormErrors(\Symfony\Component\Form\Form $form, $flat_array = false, $add_form_name = false, $glue_keys = '_')
    {
        $errors = array();
        $errors['global'] = array();
        $errors['fields'] = array();

        foreach ($form->getErrors() as $error) {
            $errors['global'][] = $error->getMessage();
        }

        $errors['fields'] = $this->serialize($form);

        if ($flat_array) {
            $errors['fields'] = $this->arrayFlatten($errors['fields'],
                $glue_keys, (($add_form_name) ? $form->getName() : ''));
        }


        return $errors;
    }

    private function serialize(\Symfony\Component\Form\Form $form)
    {
        $local_errors = array();
        foreach ($form->getIterator() as $key => $child) {

            foreach ($child->getErrors() as $error){
                $local_errors[$key] = $error->getMessage();
            }

            if (count($child->getIterator()) > 0) {
                $local_errors[$key] = $this->serialize($child);
            }
        }

        return $local_errors;
    }

    private function arrayFlatten($array, $separator = "_", $flattened_key = '') {
        $flattenedArray = array();
        foreach ($array as $key => $value) {

            if(is_array($value)) {

                $flattenedArray = array_merge($flattenedArray,
                    $this->arrayFlatten($value, $separator,
                        (strlen($flattened_key) > 0 ? $flattened_key . $separator : "") . $key)
                );

            } else {
                $flattenedArray[(strlen($flattened_key) > 0 ? $flattened_key . $separator : "") . $key] = $value;
            }
        }
        return $flattenedArray;
    }

}

Updated version of this to keep all the error properties intact. Added an unserializer to apply the errors back to the form if you intend to store the errors into a database or cache.

https://gist.github.com/linxlad/3ec76c181f717fba532bf43484b7c970