title: Custom single form field type ignores validation in Symfony 2?
body: <p>I've a reusable (here simplified) custom field type that inherits from <code>textarea</code> type. As default, content can't be empty, so i specified <code>validation_constraint</code> as default option:</p>
  
  <pre><code>namespace Acme\HelloBundle\Form\Type;
  
  use Symfony\Component\Form\AbstractType;
  use Symfony\Component\Validator\Constraints\NotBlank;
  
  class SmsContentType extends AbstractType
  {
  
      public function getDefaultOptions(array $options)
      {
          return $options + array(
              'label'                 =&gt; 'Testo *',
              'validation_constraint' =&gt; new NotBlank()
          );
      }
  
      public function getParent(array $options) { return 'textarea'; }
  
      public function getName() { return 'sms_content'; }
  
  }
  </code></pre>
  
  <p>But leaving the content empty doen't show any error. Not near the field itself and not as bubbled error using <code>form_errors(form)</code>.</p>
  
  <p>Where i'm wrong? Oh, i'm using this custom type inside another form:</p>
  
  <pre><code>class UserType extends AbstractType
  {
      public function buildForm(FormBuilder $builder, array $options)
      {
          $builder
              -&gt;add('sms_birthday_template', new SmsContentType(), array(
                  'label' =&gt; 'SMS compleanno',
              ))
          ;
      }
  }
  </code></pre>