Layout Builder/preview compatibility

I'm confused how we get to the lazy builder callback with no entity. What does this code produce for the $entity->id()?

    $build[$field_name] = [
      '#lazy_builder' => [
        'computed_field.computed_field_builder:viewField',
        [
          $entity->getEntityTypeId(),
          $entity->id(),
          $field_name,
          $display->getMode(),
        ],
      ],
      '#create_placeholder' => TRUE,
    ];

I'm not managing to reproduce this - when I went to set up the layout for my node type, I added the reverse ER field and it appeared correctly in the preview.

Could you give precise steps to reproduce please?

And also turn on error reporting, so you can see the actual error rather than just a whitescreen?

I have Commerce products that are used to purchase event registrations. Basically, the Product has an entity reference to an Event node. We want to display some information about the Product on the event automatically. In this case, it's basically a field on the Product for the maximum number of registrations allowed.

The Product has a view mode that displays this integer field, called "Capacity".

The Event has a computed field using the reverse entity reference plugin, pointing to the product.

Events have a view mode, NOT using layout builder, that includes this and some other fields, called "key_details". It renders the computed field using a the Capacity view mode.

The Event "Full" view mode uses the ctools "Entity view (Content)" block to render the event using the key_details view mode. (Yes, the event view mode renders the same event in a different view mode)"

I suspect that extra layer of abstraction is unnecessary, and you could get the same thing with the computed field in a block on the Full view mode -- but that field still isn't appearing for me.

Here's the error, which I get on my event node type's full display mode configuration's layout config page: ("/admin/structure/types/manage/event/display/full/layout")

TypeError: Drupal\computed_field\ComputedFieldBuilder::viewField(): Argument #2 ($entity_id) must be of type int, null given in Drupal\computed_field\ComputedFieldBuilder->viewField() (line 50 of modules/contrib/computed_field/src/ComputedFieldBuilder.php).
Drupal\computed_field\ComputedFieldBuilder->viewField('node', NULL, 'computed_registration_product', 'key_details')
call_user_func_array(Array, Array) (Line: 101)
Drupal\Core\Render\Renderer->doTrustedCallback(Array, Array, 'Render #lazy_builder callbacks must be methods of a class that implements \Drupal\Core\Security\TrustedCallbackInterface or be an anonymous function. The callback was %s. See https://www.drupal.org/node/2966725', 'exception', 'Drupal\Core\Render\Element\RenderCallbackInterface') (Line: 788)
Drupal\Core\Render\Renderer->doCallback('#lazy_builder', Array, Array) (Line: 353)
Drupal\Core\Render\Renderer->doRender(Array, 1) (Line: 204)
Drupal\Core\Render\Renderer->render(Array, 1) (Line: 160)
Drupal\Core\Render\Renderer->Drupal\Core\Render\{closure}() (Line: 580)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 161)
Drupal\Core\Render\Renderer->renderPlain(Array) (Line: 175)
Drupal\Core\Render\Renderer->renderPlaceholder('', Array) (Line: 665)
Drupal\Core\Render\Renderer->replacePlaceholders(Array) (Line: 550)
Drupal\Core\Render\Renderer->doRender(Array, 1) (Line: 204)
Drupal\Core\Render\Renderer->render(Array, 1) (Line: 148)
Drupal\Core\Render\Renderer->Drupal\Core\Render\{closure}() (Line: 580)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 149)
Drupal\Core\Render\Renderer->renderRoot(Array) (Line: 278)
Drupal\Core\Render\HtmlResponseAttachmentsProcessor->renderPlaceholders(Object) (Line: 127)
Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAttachments(Object) (Line: 45)
Drupal\Core\EventSubscriber\HtmlResponseSubscriber->onRespond(Object, 'kernel.response', Object)
call_user_func(Array, Object, 'kernel.response', Object) (Line: 142)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.response') (Line: 202)
Symfony\Component\HttpKernel\HttpKernel->filterResponse(Object, Object, 1) (Line: 190)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 81)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 50)
Drupal\ban\BanMiddleware->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 718)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Can you debug in computed_field_entity_view_alter() and see why $entity->id() on line 70 is NULL?

Yes -- it's what I expected. The entity is new, and doesn't have an ID. $entity->id() returns NULL. $entity->isNew() returns TRUE.

I get this all the time with layout builder and various contrib modules that aren't expecting to generate sample content for an entity generated only for the purpose of LB's preview. (If you are trying to reproduce, but editing the layout on a specific entity, you might not be able to -- I think it uses the actual entity in those cases.) This is the layout configuration at the bundle level.

There's just no entity ID to work with.

Thanks for the explanation.

So the simplest thing is just to bypass the lazy builder in that circumstance. We don't care about cacheability in preview anyway.

Can you try the new MR?

Sounds good to me, and yes this patch works great for my use case. Thanks!

Fixed.

Thanks for reporting, debugging, and testing!

I'm making a new release.

Automatically closed - issue fixed for 2 weeks with no activity.