--- /dev/null
+<?php
+
+namespace Drupal\layout_builder\Plugin\Block;
+
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Entity\EntityFieldManagerInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Plugin\ContextAwarePluginInterface;
+use Drupal\Core\Render\Element;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a block that renders an extra field from an entity.
+ *
+ * This block handles fields that are provided by implementations of
+ * hook_entity_extra_field_info().
+ *
+ * @see \Drupal\layout_builder\Plugin\Block\FieldBlock
+ * This block plugin handles all other field entities not provided by
+ * hook_entity_extra_field_info().
+ *
+ * @Block(
+ * id = "extra_field_block",
+ * deriver = "\Drupal\layout_builder\Plugin\Derivative\ExtraFieldBlockDeriver",
+ * )
+ *
+ * @internal
+ * Plugin classes are internal.
+ */
+class ExtraFieldBlock extends BlockBase implements ContextAwarePluginInterface, ContainerFactoryPluginInterface {
+
+ /**
+ * The entity field manager.
+ *
+ * @var \Drupal\Core\Entity\EntityFieldManagerInterface
+ */
+ protected $entityFieldManager;
+
+ /**
+ * The field name.
+ *
+ * @var string
+ */
+ protected $fieldName;
+
+ /**
+ * The entity type manager.
+ *
+ * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+ */
+ protected $entityTypeManager;
+
+ /**
+ * Constructs a new ExtraFieldBlock.
+ *
+ * @param array $configuration
+ * A configuration array containing information about the plugin instance.
+ * @param string $plugin_id
+ * The plugin ID for the plugin instance.
+ * @param mixed $plugin_definition
+ * The plugin implementation definition.
+ * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+ * The entity type manager.
+ * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager
+ * The entity field manager.
+ */
+ public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager, EntityFieldManagerInterface $entity_field_manager) {
+ $this->entityTypeManager = $entity_type_manager;
+ $this->entityFieldManager = $entity_field_manager;
+ // Get field name from the plugin ID.
+ list (, , , $field_name) = explode(static::DERIVATIVE_SEPARATOR, $plugin_id, 4);
+ assert(!empty($field_name));
+ $this->fieldName = $field_name;
+
+ parent::__construct($configuration, $plugin_id, $plugin_definition);
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function defaultConfiguration() {
+ return [
+ 'label_display' => FALSE,
+ ];
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+ return new static(
+ $configuration,
+ $plugin_id,
+ $plugin_definition,
+ $container->get('entity_type.manager'),
+ $container->get('entity_field.manager')
+ );
+ }
+
+ /**
+ * Gets the entity that has the field.
+ *
+ * @return \Drupal\Core\Entity\FieldableEntityInterface
+ * The entity.
+ */
+ protected function getEntity() {
+ return $this->getContextValue('entity');
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function build() {
+ $entity = $this->getEntity();
+ // Add a placeholder to replace after the entity view is built.
+ // @see layout_builder_entity_view_alter().
+ $extra_fields = $this->entityFieldManager->getExtraFields($entity->getEntityTypeId(), $entity->bundle());
+ if (!isset($extra_fields['display'][$this->fieldName])) {
+ $build = [];
+ }
+ else {
+ $build = [
+ '#extra_field_placeholder_field_name' => $this->fieldName,
+ // Always provide a placeholder. The Layout Builder will NOT invoke
+ // hook_entity_view_alter() so extra fields will not be added to the
+ // render array. If the hook is invoked the placeholder will be
+ // replaced.
+ // @see ::replaceFieldPlaceholder()
+ '#markup' => new TranslatableMarkup('Placeholder for the "@field" field', ['@field' => $extra_fields['display'][$this->fieldName]['label']]),
+ ];
+ }
+ CacheableMetadata::createFromObject($this)->applyTo($build);
+ return $build;
+ }
+
+ /**
+ * Replaces all placeholders for a given field.
+ *
+ * @param array $build
+ * The built render array for the elements.
+ * @param array $built_field
+ * The render array to replace the placeholder.
+ * @param string $field_name
+ * The field name.
+ *
+ * @see ::build()
+ */
+ public static function replaceFieldPlaceholder(array &$build, array $built_field, $field_name) {
+ foreach (Element::children($build) as $child) {
+ if (isset($build[$child]['#extra_field_placeholder_field_name']) && $build[$child]['#extra_field_placeholder_field_name'] === $field_name) {
+ $placeholder_cache = CacheableMetadata::createFromRenderArray($build[$child]);
+ $built_cache = CacheableMetadata::createFromRenderArray($built_field);
+ $merged_cache = $placeholder_cache->merge($built_cache);
+ $build[$child] = $built_field;
+ $merged_cache->applyTo($build);
+ }
+ else {
+ static::replaceFieldPlaceholder($build[$child], $built_field, $field_name);
+ }
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ protected function blockAccess(AccountInterface $account) {
+ return $this->getEntity()->access('view', $account, TRUE);
+ }
+
+}