class SystemCompactLink

class SystemCompactLink extends Link {

  /**
   * {@inheritdoc}
   */
  public function getInfo() {
    $class = static::class;
    return [
      '#pre_render' => [
        [
          $class,
          'preRenderCompactLink',
        ],
        [
          $class,
          'preRenderLink',
        ],
      ],
      '#theme_wrappers' => [
        'container' => [
          '#attributes' => [
            'class' => [
              'compact-link',
            ],
          ],
        ],
      ],
    ];
  }

  /**
   * Pre-render callback: Renders a link into #markup.
   *
   * Doing so during pre_render gives modules a chance to alter the link parts.
   *
   * @param array $element
   *   A structured array whose keys form the arguments to Drupal::l():
   *   - #title: The link text to pass as argument to Drupal::l().
   *   - One of the following:
   *     - #route_name and (optionally) a #route_parameters array; The route
   *       name and route parameters which will be passed into the link
   *       generator.
   *     - #href: The system path or URL to pass as argument to Drupal::l().
   *   - #options: (optional) An array of options to pass to Drupal::l() or the
   *     link generator.
   *
   * @return array
   *   The passed-in element containing the system compact link default values.
   */
  public static function preRenderCompactLink($element) {

    // By default, link options to pass to l() are normally set in #options.
    $element += [
      '#options' => [],
    ];
    if (system_admin_compact_mode()) {
      $element['#title'] = t('Show descriptions');
      $element['#url'] = BaseUrl::fromRoute('system.admin_compact_page', [
        'mode' => 'off',
      ]);
      $element['#options'] = [
        'attributes' => [
          'title' => t('Expand layout to include descriptions.'),
        ],
        'query' => \Drupal::destination()
          ->getAsArray(),
      ];
    }
    else {
      $element['#title'] = t('Hide descriptions');
      $element['#url'] = BaseUrl::fromRoute('system.admin_compact_page', [
        'mode' => 'on',
      ]);
      $element['#options'] = [
        'attributes' => [
          'title' => t('Compress layout by hiding descriptions.'),
        ],
        'query' => \Drupal::destination()
          ->getAsArray(),
      ];
    }
    $options = NestedArray::mergeDeep($element['#url']
      ->getOptions(), $element['#options']);
    $element['#markup'] = BaseLink::fromTextAndUrl($element['#title'], $element['#url']
      ->setOptions($options))
      ->toString();
    return $element;
  }

}