class ContextualLinksPlaceholder

class ContextualLinksPlaceholder extends RenderElement {
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        $class = static::class;
        return [
            '#pre_render' => [
                [
                    $class,
                    'preRenderPlaceholder',
                ],
            ],
            '#id' => NULL,
        ];
    }
    
    /**
     * Pre-render callback: Renders a contextual links placeholder into #markup.
     *
     * Renders an empty (hence invisible) placeholder div with a data-attribute
     * that contains an identifier ("contextual id"), which allows the JavaScript
     * of the drupal.contextual-links library to dynamically render contextual
     * links.
     *
     * @param array $element
     *   A structured array with #id containing a "contextual id".
     *
     * @return array
     *   The passed-in element with a contextual link placeholder in '#markup'.
     *
     * @see _contextual_links_to_id()
     */
    public static function preRenderPlaceholder(array $element) {
        $token = Crypt::hmacBase64($element['#id'], Settings::getHashSalt() . \Drupal::service('private_key')->get());
        $attribute = new Attribute([
            'data-contextual-id' => $element['#id'],
            'data-contextual-token' => $token,
        ]);
        $element['#markup'] = new FormattableMarkup('<div@attributes></div>', [
            '@attributes' => $attribute,
        ]);
        return $element;
    }

}