class EntityReferenceEntityFormatter

class EntityReferenceEntityFormatter extends EntityReferenceFormatterBase {
    
    /**
     * The number of times this formatter allows rendering the same entity.
     *
     * @var int
     */
    const RECURSIVE_RENDER_LIMIT = 20;
    
    /**
     * The logger factory.
     *
     * @var \Drupal\Core\Logger\LoggerChannelFactoryInterface
     */
    protected $loggerFactory;
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The entity display repository.
     *
     * @var \Drupal\Core\Entity\EntityDisplayRepositoryInterface
     */
    protected $entityDisplayRepository;
    
    /**
     * An array of counters for the recursive rendering protection.
     *
     * Each counter takes into account all the relevant information about the
     * field and the referenced entity that is being rendered.
     *
     * @see \Drupal\Core\Field\Plugin\Field\FieldFormatter\EntityReferenceEntityFormatter::viewElements()
     *
     * @var array
     */
    protected static $recursiveRenderDepth = [];
    
    /**
     * Constructs an EntityReferenceEntityFormatter instance.
     *
     * @param string $plugin_id
     *   The plugin ID for the formatter.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
     *   The definition of the field to which the formatter is associated.
     * @param array $settings
     *   The formatter settings.
     * @param string $label
     *   The formatter label display setting.
     * @param string $view_mode
     *   The view mode.
     * @param array $third_party_settings
     *   Any third party settings.
     * @param \Drupal\Core\Logger\LoggerChannelFactoryInterface $logger_factory
     *   The logger factory.
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Entity\EntityDisplayRepositoryInterface $entity_display_repository
     *   The entity display repository.
     */
    public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, LoggerChannelFactoryInterface $logger_factory, EntityTypeManagerInterface $entity_type_manager, EntityDisplayRepositoryInterface $entity_display_repository) {
        parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
        $this->loggerFactory = $logger_factory;
        $this->entityTypeManager = $entity_type_manager;
        $this->entityDisplayRepository = $entity_display_repository;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($plugin_id, $plugin_definition, $configuration['field_definition'], $configuration['settings'], $configuration['label'], $configuration['view_mode'], $configuration['third_party_settings'], $container->get('logger.factory'), $container->get('entity_type.manager'), $container->get('entity_display.repository'));
    }
    
    /**
     * {@inheritdoc}
     */
    public static function defaultSettings() {
        return [
            'view_mode' => 'default',
            'link' => FALSE,
        ] + parent::defaultSettings();
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $elements['view_mode'] = [
            '#type' => 'select',
            '#options' => $this->entityDisplayRepository
                ->getViewModeOptions($this->getFieldSetting('target_type')),
            '#title' => $this->t('View mode'),
            '#default_value' => $this->getSetting('view_mode'),
            '#required' => TRUE,
        ];
        return $elements;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsSummary() {
        $summary = [];
        $view_modes = $this->entityDisplayRepository
            ->getViewModeOptions($this->getFieldSetting('target_type'));
        $view_mode = $this->getSetting('view_mode');
        $summary[] = $this->t('Rendered as @mode', [
            '@mode' => $view_modes[$view_mode] ?? $view_mode,
        ]);
        return $summary;
    }
    
    /**
     * {@inheritdoc}
     */
    public function viewElements(FieldItemListInterface $items, $langcode) {
        $view_mode = $this->getSetting('view_mode');
        $elements = [];
        foreach ($this->getEntitiesToView($items, $langcode) as $delta => $entity) {
            // Due to render caching and delayed calls, the viewElements() method
            // will be called later in the rendering process through a '#pre_render'
            // callback, so we need to generate a counter that takes into account
            // all the relevant information about this field and the referenced
            // entity that is being rendered.
            $recursive_render_id = $items->getFieldDefinition()
                ->getTargetEntityTypeId() . $items->getFieldDefinition()
                ->getTargetBundle() . $items->getName() . $items->getEntity()
                ->id() . $entity->getEntityTypeId() . $entity->id();
            if (isset(static::$recursiveRenderDepth[$recursive_render_id])) {
                static::$recursiveRenderDepth[$recursive_render_id]++;
            }
            else {
                static::$recursiveRenderDepth[$recursive_render_id] = 1;
            }
            // Protect ourselves from recursive rendering.
            if (static::$recursiveRenderDepth[$recursive_render_id] > static::RECURSIVE_RENDER_LIMIT) {
                $this->loggerFactory
                    ->get('entity')
                    ->error('Recursive rendering detected when rendering entity %entity_type: %entity_id, using the %field_name field on the %parent_entity_type:%parent_bundle %parent_entity_id entity. Aborting rendering.', [
                    '%entity_type' => $entity->getEntityTypeId(),
                    '%entity_id' => $entity->id(),
                    '%field_name' => $items->getName(),
                    '%parent_entity_type' => $items->getFieldDefinition()
                        ->getTargetEntityTypeId(),
                    '%parent_bundle' => $items->getFieldDefinition()
                        ->getTargetBundle(),
                    '%parent_entity_id' => $items->getEntity()
                        ->id(),
                ]);
                return $elements;
            }
            $view_builder = $this->entityTypeManager
                ->getViewBuilder($entity->getEntityTypeId());
            $elements[$delta] = $view_builder->view($entity, $view_mode, $entity->language()
                ->getId());
            // Add a resource attribute to set the mapping property's value to the
            // entity's URL. Since we don't know what the markup of the entity will
            // be, we shouldn't rely on it for structured data.
            if (!empty($items[$delta]->_attributes) && !$entity->isNew() && $entity->hasLinkTemplate('canonical')) {
                $items[$delta]->_attributes += [
                    'resource' => $entity->toUrl()
                        ->toString(),
                ];
            }
        }
        return $elements;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function isApplicable(FieldDefinitionInterface $field_definition) {
        // This formatter is only available for entity types that have a view
        // builder.
        $target_type = $field_definition->getFieldStorageDefinition()
            ->getSetting('target_type');
        return \Drupal::entityTypeManager()->getDefinition($target_type)
            ->hasViewBuilderClass();
    }

}