Layout section and component information accessible during render process

While the implementation you describe above sounds particularly terrifying, it seems absolutely correct to have Section mirror SectionComponent in their toRenderArray() approaches.

+++ b/core/modules/layout_builder/src/Section.php
@@ -81,14 +82,17 @@ public function __construct($layout_id, array $layout_settings = [], array $comp
+    $this->eventDispatcher()->dispatch(LayoutBuilderEvents::SECTION_BUILD_RENDER_ARRAY, $event);
     $regions = [];
     foreach ($this->getComponents() as $component) {
       if ($output = $component->toRenderArray($contexts, $in_preview)) {
         $regions[$component->getRegion()][$component->getUuid()] = $output;
       }
     }

Similar to how \Drupal\layout_builder\SectionComponent::toRenderArray() consists solely of the dispatched event, this current implementation should be moved to an event subscriber with a priority of 100. That will allow custom event subscribers to occur before or after this default code, with the non-explicit priority code running *after* (as a sort of alter).

Note also that \Drupal\Tests\layout_builder\Unit\SectionRenderTest should be updated/adapted to reflect the changes in rendering flow. See \Drupal\Tests\layout_builder\Unit\SectionComponentTest for inspiration.

Bumping to 8.9.x, but this might be a 9.1.x issue, I'm not sure of the timing/rules with that currently.

Here's a patch that implements #4.
It still needs explicit test coverage to prove another subscriber can affect the output. The previous patch did not call $event->getBuild()

Note: The order of arguments to dispatch() changed in D9, so this will not work as-is for D8.

That's what happens when you only run the unit tests before posting...

I knew I was missing something, passing $regions to setBuild() did not feel right.

@tim.plunkett, how did you manage to get this test to pass? I am getting the following error on my site:

TypeError: Argument 2 passed to Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher::dispatch() must be an instance of Symfony\Component\EventDispatcher\Event or null, string given, called in /var/www/html/web/core/modules/layout_builder/src/Section.php on line 86 in Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch() (line 89 of core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php).

Which makes sense because your patch swapped the event name and the event.

+ $this->eventDispatcher()->dispatch($event, LayoutBuilderEvents::SECTION_BUILD_RENDER_ARRAY);

In SectionComponent.php we see this inversed:

$this->eventDispatcher()->dispatch(LayoutBuilderEvents::SECTION_COMPONENT_BUILD_RENDER_ARRAY, $event);

Manually swapping them back makes the error go away.

This works great in conjunction with #3044117: Add getter for layout object in Layout Builder's ConfigureSectionForm. Allowing one to easily set third party settings by altering the configuration form and then having access to them in this event. Many thanks for the effort.

This patch is written for 9.1, the development version of Drupal. As a feature request, it will not be backported to D8.

Ah apologies, I was under the assumption that I had spun up a 9.1 site, but it appeared to be 9.0.6 instead. I'll give it another shot later this week.

I did spin up a 9.1 instance, but patched another site in the wrong folder... It works and for me it is RTBC :)

#3062862: Third party should be allowed to alter the section render array is doing the same but it's older. Closing this as duplicate.