Use comment annotations to declare the typed entities

I think I can see a way to obviate the need for Typed Entity Repositories... If each wrapper annotation has entity type ID and bundle keys, the "Typed Entity Manager" service can load all the plugins/annotations that match given keys

Yeah, there is room for improvement in the DX. On one hand I like the idea of simplification. On the other hand I think the repositories should not be sidestepped because they play a crucial role. Whenever you have the temptation to have a static method in the wrapped entity, that means that you need a method in your repository.

To keep the annotations from getting too unwieldy, could we remove the conditions/variants list and just leverage an applies() method like we did for the renderers?

That is also interesting, and it definitely helps with consistency. Just to say it out loud these can be combined, see the example below:

class ThemeCloud extends Base {

  /**
   * {@inheritdoc}
   *
   * TRUE when the node should be rendered with the Acme Cloud subtheme.
   */
  public static function applies(TypedEntityRenderContext $context): bool {
    $condition = new WebSegmentThemeCondition('acme_cloud', '');
    // Add the custom requirements to evaluate the conditions.
    $condition->setContext('entity', $context->offsetGet('entity'));
    $condition->setContext('theme_manager', \Drupal::service('web_segment_companion.theme_manager'));
    return $condition->evaluate();
  }

}

Drupal core has examples of both patterns: condition objects for block visibility, and applies method in the serialization selection. The problem with any of the approaches is that today we cannot easily cache the variant selection.

----

Let's say we go with the applies() approach. We would end up with something like:

/**
 * Typed Entity Repository for a Product Page node.
 *
 * @TypedEntityRepository(
 *   entityTypeId = "node",
 *   bundle = "product_page",
 *   wrappers = @ClassWithVariants(
 *     fallback = "Drupal\custom_module\WrappedEntities\ProductPage",
 *     variants = [
 *       "Drupal\custom_module\WrappedEntities\ProductPageFoo"
 *     ]
 *   )
 *   renderers: @ClassWithVariants(
 *     fallback = "Drupal\custom_module\WrappedEntities\Render\Base",
 *     variants = [
 *       "Drupal\custom_module\WrappedEntities\Render\Teaser",
 *       "Drupal\custom_module\WrappedEntities\Render\Full",
 *     ]
 *   )
 * )
 */
final class ProductPageRepository extends TypedEntityRepositoryBase {
  // Leave empty or implement additional logic depending of your needs.
}

I think I like this one better! ☝

Go testbot!