class EntityReferenceLabelFormatter

class EntityReferenceLabelFormatter extends EntityReferenceFormatterBase {
    
    /**
     * {@inheritdoc}
     */
    public static function defaultSettings() {
        return [
            'link' => TRUE,
        ] + parent::defaultSettings();
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $elements['link'] = [
            '#title' => $this->t('Link label to the referenced entity'),
            '#type' => 'checkbox',
            '#default_value' => $this->getSetting('link'),
        ];
        return $elements;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsSummary() {
        $summary = [];
        $summary[] = $this->getSetting('link') ? $this->t('Link to the referenced entity') : $this->t('No link');
        return $summary;
    }
    
    /**
     * {@inheritdoc}
     */
    public function viewElements(FieldItemListInterface $items, $langcode) {
        $elements = [];
        $output_as_link = $this->getSetting('link');
        foreach ($this->getEntitiesToView($items, $langcode) as $delta => $entity) {
            $label = $entity->label();
            // If the link is to be displayed and the entity has a uri, display a
            // link.
            if ($output_as_link && !$entity->isNew()) {
                try {
                    $uri = $entity->toUrl();
                } catch (UndefinedLinkTemplateException $e) {
                    // This exception is thrown by \Drupal\Core\Entity\Entity::urlInfo()
                    // and it means that the entity type doesn't have a link template nor
                    // a valid "uri_callback", so don't bother trying to output a link for
                    // the rest of the referenced entities.
                    $output_as_link = FALSE;
                }
            }
            if ($output_as_link && isset($uri) && !$entity->isNew()) {
                $elements[$delta] = [
                    '#type' => 'link',
                    '#title' => $label,
                    '#url' => $uri,
                    '#options' => $uri->getOptions(),
                ];
                if (!empty($items[$delta]->_attributes)) {
                    $elements[$delta]['#options'] += [
                        'attributes' => [],
                    ];
                    $elements[$delta]['#options']['attributes'] += $items[$delta]->_attributes;
                    // Unset field item attributes since they have been included in the
                    // formatter output and shouldn't be rendered in the field template.
                    unset($items[$delta]->_attributes);
                }
            }
            else {
                $elements[$delta] = [
                    '#plain_text' => $label,
                ];
            }
            $elements[$delta]['#entity'] = $entity;
            $elements[$delta]['#cache']['tags'] = $entity->getCacheTags();
        }
        return $elements;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function checkAccess(EntityInterface $entity) {
        return $entity->access('view label', NULL, TRUE);
    }

}