I've implemented the cookbook solution for dynamic generation of submitted forms across several projects. Sometimes these forms need to add/update/remove several fields, so my JavaScript replaces the entire form - not just a single, hard-coded element like in the example. My controllers typically look something like this:

public function testAction(Request $request)
{
    $entity = new Entity();
    $form = $this->createForm('foo', $entity);

    $form->handleRequest($request);

    if ($form->isValid() && !$request->isXmlHttpRequest()) {
        $em = $this->getDoctrine()->getManager();
        $em->persist($entity);
        $em->flush($entity);

        return $this->redirectToRoute('controller_index');
    }

    return ['form' => $form->createView()];
}

The problem

This works pretty well, but there's one major annoyance - AJAX submissions of incomplete forms result in lots of red errors everywhere. This occurs because Symfony validates the form by default during $form->handleRequest($request).

The cookbook recommends supressing form validation by stopping propagation of the POST_SUBMIT event. However, I have other services listening for that event, so this approach isn't feasible.

I'm currently restoring to re-building the form just prior to the return:

// ...

// Don't show any errors on partial AJAX submissions
if ($request->isXmlHttpRequest()) {
    $form = $this->createForm('foo', $entity);
}

return ['form' => $form->createView()];

This works, but it seems kinda kludgy and not like an ideal solution, which is why I've tagged this [DX]. It would be great if Symfony could provide a built-in method to prevent this common problem without weird workarounds.

Proposed solutions

Would it be possible to add a clearErrors() method to FormInterface? Ideally this would remove any previously-set validation errors (as if the form were never validated).

Alternatively, perhaps we could have some way of easily hiding/removing errors from the view? Maybe a boolean flag on the createView method, a FormView::clearErrors method, a setting on the FormRenderer, or something to that effect?