add license form crashes due to getFormDisplay() returning NULL

I've not been working on the 'add license' form lately. As its use case is an admin user creating a license by hand for another user, I figure it's not part of the MVP.

If I understand correctly, the idea is that this is a form that you get shown when you click 'Add license' in the license admin UI?

In which case, why can't it be a 2-step process, with a page to pick the bundle and then a form, the same as when you create a node? That would simplify *everything*.

If you're using Migrate, then this form shouldn't be involved, as Migrate creates entities via the API.

> In which case, why can't it be a 2-step process, with a page to pick the bundle and then a form, the same as when you create a node? That would simplify *everything*.

I am now heavily in favour of this. I don't think there's any need to have AJAX in this form, as it's admin-facing only.

For the cart form, the type of license will be dictacted by the product, and so already set. No need to AJAX there either.

So the fix here is to rip out lots of the code in the form classes and reduce them to fairly slim child classes of the ContentEntityForm class.

Thanks for the patch. Lots of things cleaned up I see!

However, I think we can do this with less code: AdminHtmlRouteProvider does a bunch of stuff such as declare routes and use a common controller if we define the link templates. See for instance getAddPageRoute():

  protected function getAddPageRoute(EntityTypeInterface $entity_type) {
    if ($entity_type->hasLinkTemplate('add-page') && $entity_type->getKey('bundle')) {
      $route = new Route($entity_type->getLinkTemplate('add-page'));
      $route->setDefault('_controller', EntityController::class . '::addPage');
      $route->setDefault('_title_callback', EntityController::class . '::addTitle');
      $route->setDefault('entity_type_id', $entity_type->id());
      $route->setRequirement('_entity_create_any_access', $entity_type->id());

      return $route;
    }
  }

And getAddFormRoute() does the same.

That removes the need for the controller and at least some of the route declarations, and the theme too -- I don't think we especially need admin UI to be themeable to that extent.

(Sorry, I feel bad for saying we should take out so much code... but it makes the module more maintainable in the long run!)

PS. As a follow-up issue, we should add validation somewhere as the product reference field must match a) a product with a license in the first place, and b) a product whose license configuration matches what the admin is trying to create. But that's not a priority -- admins should have some clue of what they're doing! ;)

Yup, a fair bit of this has been done is separate issues.