class Link

class Link extends RenderElement {
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        $class = get_class($this);
        return [
            '#pre_render' => [
                [
                    $class,
                    'preRenderLink',
                ],
            ],
        ];
    }
    
    /**
     * Pre-render callback: Renders a link into #markup.
     *
     * Doing so during pre_render gives modules a chance to alter the link parts.
     *
     * @param array $element
     *   A structured array whose keys form the arguments to
     *   \Drupal\Core\Utility\LinkGeneratorInterface::generate():
     *   - #title: The link text.
     *   - #url: The URL info either pointing to a route or a non routed path.
     *   - #options: (optional) An array of options to pass to the link generator.
     *
     * @return array
     *   The passed-in element containing a rendered link in '#markup'.
     */
    public static function preRenderLink($element) {
        // By default, link options to pass to the link generator are normally set
        // in #options.
        $element += [
            '#options' => [],
        ];
        // However, within the scope of renderable elements, #attributes is a valid
        // way to specify attributes, too. Take them into account, but do not override
        // attributes from #options.
        if (isset($element['#attributes'])) {
            $element['#options'] += [
                'attributes' => [],
            ];
            $element['#options']['attributes'] += $element['#attributes'];
        }
        // This #pre_render callback can be invoked from inside or outside of a Form
        // API context, and depending on that, a HTML ID may be already set in
        // different locations. #options should have precedence over Form API's #id.
        // #attributes have been taken over into #options above already.
        if (isset($element['#options']['attributes']['id'])) {
            $element['#id'] = $element['#options']['attributes']['id'];
        }
        elseif (isset($element['#id'])) {
            $element['#options']['attributes']['id'] = $element['#id'];
        }
        // Conditionally invoke self::preRenderAjaxForm(), if #ajax is set.
        if (isset($element['#ajax']) && !isset($element['#ajax_processed'])) {
            // If no HTML ID was found above, automatically create one.
            if (!isset($element['#id'])) {
                $element['#id'] = $element['#options']['attributes']['id'] = HtmlUtility::getUniqueId('ajax-link');
            }
            $element = static::preRenderAjaxForm($element);
        }
        if (!empty($element['#url']) && $element['#url'] instanceof CoreUrl) {
            $options = NestedArray::mergeDeep($element['#url']->getOptions(), $element['#options']);
            
            /** @var \Drupal\Core\Utility\LinkGenerator $link_generator */
            $link_generator = \Drupal::service('link_generator');
            $generated_link = $link_generator->generate($element['#title'], $element['#url']->setOptions($options));
            $element['#markup'] = $generated_link;
            $generated_link->merge(BubbleableMetadata::createFromRenderArray($element))
                ->applyTo($element);
        }
        return $element;
    }
    
    /**
     * Pre-render callback: Collects child links into a single array.
     *
     * This method can be added as a pre_render callback for a renderable array,
     * usually one which will be themed by links.html.twig. It iterates through
     * all unrendered children of the element, collects any #links properties it
     * finds, merges them into the parent element's #links array, and prevents
     * those children from being rendered separately.
     *
     * The purpose of this is to allow links to be logically grouped into related
     * categories, so that each child group can be rendered as its own list of
     * links if drupal_render() is called on it, but calling drupal_render() on
     * the parent element will still produce a single list containing all the
     * remaining links, regardless of what group they were in.
     *
     * A typical example comes from node links, which are stored in a renderable
     * array similar to this:
     * @code
     * $build['links'] = array(
     *   '#theme' => 'links__node',
     *   '#pre_render' => array(Link::class, 'preRenderLinks'),
     *   'comment' => array(
     *     '#theme' => 'links__node__comment',
     *     '#links' => array(
     *       // An array of links associated with node comments, suitable for
     *       // passing in to links.html.twig.
     *     ),
     *   ),
     *   'statistics' => array(
     *     '#theme' => 'links__node__statistics',
     *     '#links' => array(
     *       // An array of links associated with node statistics, suitable for
     *       // passing in to links.html.twig.
     *     ),
     *   ),
     *   'translation' => array(
     *     '#theme' => 'links__node__translation',
     *     '#links' => array(
     *       // An array of links associated with node translation, suitable for
     *       // passing in to links.html.twig.
     *     ),
     *   ),
     * );
     * @endcode
     *
     * In this example, the links are grouped by functionality, which can be
     * helpful to themers who want to display certain kinds of links
     * independently. For example, adding this code to node.html.twig will result
     * in the comment links being rendered as a single list:
     * @code
     * {{ content.links.comment }}
     * @endcode
     *
     * (where a node's content has been transformed into $content before handing
     * control to the node.html.twig template).
     *
     * The preRenderLinks method defined here allows the above flexibility, but
     * also allows the following code to be used to render all remaining links
     * into a single list, regardless of their group:
     * @code
     * {{ content.links }}
     * @endcode
     *
     * In the above example, this will result in the statistics and translation
     * links being rendered together in a single list (but not the comment links,
     * which were rendered previously on their own).
     *
     * Because of the way this method works, the individual properties of each
     * group (for example, a group-specific #theme property such as
     * 'links__node__comment' in the example above, or any other property such as
     * #attributes or #pre_render that is attached to it) are only used when that
     * group is rendered on its own. When the group is rendered together with
     * other children, these child-specific properties are ignored, and only the
     * overall properties of the parent are used.
     *
     * @param array $element
     *   Render array containing child links to group.
     *
     * @return array
     *   Render array containing child links grouped into a single array.
     */
    public static function preRenderLinks($element) {
        $element += [
            '#links' => [],
            '#attached' => [],
        ];
        foreach (Element::children($element) as $key) {
            $child =& $element[$key];
            // If the child has links which have not been printed yet and the user has
            // access to it, merge its links in to the parent.
            if (isset($child['#links']) && empty($child['#printed']) && Element::isVisibleElement($child)) {
                $element['#links'] += $child['#links'];
                // Mark the child as having been printed already (so that its links
                // cannot be mistakenly rendered twice).
                $child['#printed'] = TRUE;
            }
            // Merge attachments.
            if (isset($child['#attached'])) {
                $element['#attached'] = BubbleableMetadata::mergeAttachments($element['#attached'], $child['#attached']);
            }
        }
        return $element;
    }

}