Tag: module

I’m trying to find what is the proper way to override the template_preprocess_book_navigation function from the Drupal 8’s core Book module. I want to add only two lines (bolded), but don’t know how this should be done in “Drupal 8 way”. Should I create a custom module or add something in the mytheme.theme file?

Thank you and be healthy!

function template_preprocess_book_navigation(&$variables) {
  $book_link = $variables('book_link');

  // Provide extra variables for themers. Not needed by default.
  $variables('book_id') = $book_link('bid');
  $variables('book_title') = $book_link('link_title');
  $variables('book_url') = Url::fromRoute('entity.node.canonical', ('node' => $book_link('bid')))->toString();
  $variables('current_depth') = $book_link('depth');
  $variables('tree') = '';

  /** @var DrupalbookBookOutline $book_outline */
  $book_outline = Drupal::service('book.outline');

  if ($book_link('nid')) {
    $variables('tree') = $book_outline->childrenLinks($book_link);

    $build = ();

    if ($prev = $book_outline->prevLink($book_link)) {
      $prev_href = Url::fromRoute('entity.node.canonical', ('node' => $prev('nid')))->toString();
      $build('#attached')('html_head_link')()() = (
        'rel' => 'prev',
        'href' => $prev_href,
      );
      $variables('prev_url') = $prev_href;
      $variables('prev_title') = $prev('title');
    }

    /** @var DrupalbookBookManagerInterface $book_manager */
    $book_manager = Drupal::service('book.manager');
    if ($book_link('pid') && $parent = $book_manager->loadBookLink($book_link('pid'))) {
      $parent_href = Url::fromRoute('entity.node.canonical', ('node' => $book_link('pid')))->toString();
      $build('#attached')('html_head_link')()() = (
        'rel' => 'up',
        'href' => $parent_href,
      );
      $variables('parent_url') = $parent_href;
      $variables('parent_title') = $parent('title');
      $variables('prev_depth') = $prev('depth');
    }

    if ($next = $book_outline->nextLink($book_link)) {
      $next_href = Url::fromRoute('entity.node.canonical', ('node' => $next('nid')))->toString();
      $build('#attached')('html_head_link')()() = (
        'rel' => 'next',
        'href' => $next_href,
      );
      $variables('next_url') = $next_href;
      $variables('next_title') = $next('title');
      $variables('next_depth') = $next('depth');
    }
  }

  if (!empty($build)) {
    Drupal::service('renderer')->render($build);
  }

  $variables('has_links') = FALSE;
  // Link variables to filter for values and set state of the flag variable.
  $links = ('prev_url', 'prev_title', 'parent_url', 'parent_title', 'next_url', 'next_title');
  foreach ($links as $link) {
    if (isset($variables($link))) {
      // Flag when there is a value.
      $variables('has_links') = TRUE;
    }
    else {
      // Set empty to prevent notices.
      $variables($link) = '';
    }
  }
}