🇬🇧United Kingdom @rlmumford

rlmumford → created an issue.

This is the simplest fix, we could write a new version callback that starts reading lines from the bottom.

rlmumford → created an issue.

Thanks, that is updated.

This patch fixes another bug.

Rerolled to latest version.

Added a merge request.

rlmumford → created an issue.

Fixed.

smustgrave → credited rlmumford → .

Hi Eclipse and thanks for your input, hopefully I can answer both your questions.

Where the Exception Gets Thrown

So the order of calls listed is correct.

1. \Drupal\layout_builder\Section::toRenderArray() is responsible for getting the render array of all the blocks and regions representative of a given section.
2. \Drupal\layout_builder\Section::toRenderArray() calls: \Drupal\layout_builder\SectionComponent::toRenderArray()
3. \Drupal\layout_builder\SectionComponent::toRenderArray() dispatches the Event in question.
4. Contexts are already provided to the event object which is capable of getting a block plugin via: \Drupal\layout_builder\Event\SectionComponentBuildRenderArrayEvent::getPlugin()
5. The event's __construct() method delegates all the instantiation and context setting bits of the block to: \Drupal\layout_builder\SectionComponent::getPlugin()
6. Event subscribers are free to get the plugin or configuration details and make use of it as necessary.
7. \Drupal\layout_builder\EventSubscriber\BlockComponentRenderArray actually calls the build() method of the block. This event has a priority of 100.

The MissingValueContextExecption gets thrown in point 3. SectionComponent::toRenderArray() creates a new SectionComponentBuildRenderArrayEvent. SectionComponentBuildRenderArrayEvent::__construct() calls $component->getPlugin(), which calls ContextHandler::applyContextMapping() which throws MissingValueContextException. All before the event gets dispatched.

How the situation arises

I'm not sure whether this is possible to do in core, but it might be if you have a block that requires the node route context and then place it on a layout that doesn't have a node route context when its displayed. In my case, I'm using the patch in https://www.drupal.org/project/drupal/issues/3001188 ✨ Make it possible to add relationships to layout builder Needs work to add extra contexts to entity view displays, for example a particular profile related to a user account. If the profile doesn't exist for that particular user then the error gets thrown.

I've changed approach slightly in this patch. As noted in https://www.drupal.org/project/drupal/issues/3056907 ✨ Allow layout builder blocks to be optional depending on whether the required context exists Needs work , using an EventSubscriber is too late to avoid throwing MissingValueContextExceptions and it seems like conditions should be able to prevent that (if user X doesn't have the "staff" role then don't should the staff profile, if entity x doesn't exist then don't render it etc)

This change moves the condition evaluation directly into Section::toRenderArray() so that the component is never touched unless conditions pass.

I also changed the urls to include the {region} to match all the other routes (I also couldn't get the contextual links to appear unless I did this?)