The duplicated code in FormHelper (FrameworkBundle) and FormExtension (Twig bridge) should be extracted into a common base class Symfony\Component\Form\AbstractRenderer. It's interface should be extracted into a new Symfony\Component\Form\FormRendererInterface (containing the render*() methods of FormExtension).

The engine specific code should be placed in TwigRenderer (Twig bridge) and TemplatingRenderer (FrameworkBundle). FormHelper and FormExtension can then simply create such a renderer object and forward any method calls to the renderer.

@fabpot: Is the Templating component already able to load templates from components? If yes, we should definitely move FormHelper, TemplatingRenderer and the PHP templates to the Form (or Templating) component to make it self-contained (and usable without FrameworkBundle).

@vicb: Can you do this?