html_title.module

<?php

/**
 * @file
 * This module enables limited HTML to be used in node titles. It strips title
 * markup from RSS feeds to eliminate unsightly markup in feed readers.
 */

use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
use Drupal\Core\Render\Element;
use Drupal\node\Entity\Node;
use Drupal\Component\Utility\SafeMarkup;

/**
 * Implementation of hook_theme_registry_alter()
 */
function html_title_theme_registry_alter(&$theme_registry) {
  // Re-order search result pre-processing so ours always runs last
  if ( \Drupal::moduleHandler()->moduleExists('search') && is_array($theme_registry['search_result']['preprocess functions'])) {
    foreach($theme_registry['search_result']['preprocess functions'] as $value) {
      if ($value != 'html_title_preprocess_search_result') {
        $callbacks[] = $value;
      }
    }
    $callbacks[] = 'html_title_preprocess_search_result';
    $theme_registry['search_result']['preprocess functions'] = $callbacks;
  }
}

/**
 * Implementation of hook_preprocess_page_title()
 */
function html_title_preprocess_page_title(&$variables) {
  if ($node = \Drupal::routeMatch()->getParameter('node')) {
    $variables['node'] = $node;
    /** @var \Drupal\node\NodeInterface $node */
    $node = $variables['node'];
    $config = \Drupal::config('html_title.settings');
    $elements = $config->get('html_title_allowed_elements');
    $elements = array_unique($elements);
    $variables['title'] = SafeMarkup::format($node->getTitle(), $elements);
  }
}
/**
 * Implementation of template_preprocess_node()
 */
function html_title_preprocess_node(&$variables) {
  $variables['node'] = $variables['elements']['#node'];
  /** @var \Drupal\node\NodeInterface $node */
  $node = $variables['node'];
  switch ($variables['view_mode']) {
    case 'search_index':
    case 'rss':
      return;
    default:
      $config = \Drupal::config('html_title.settings');
      $elements = $config->get('html_title_allowed_elements');
      if ($variables['view_mode'] == 'full' && isset($variables['content']['title'])) {
        // @todo, find a way to deal with titles on full page views now that
        // the title is in a block.
        // $variables['content']['title']['#printed'] = FALSE;
      }
      $elements = array_unique($elements);
      $variables['label'] = SafeMarkup::format($node->getTitle(), $elements);
      unset($variables['elements']['title']);
  }
}

/**
 * Implementation of hook_preprocess_search_result()
 */
function html_title_preprocess_search_result(&$vars) {
  $config = \Drupal::config('html_title.settings');
  $elements = $config->get('html_title_allowed_elements');
  $elements = array_values(array_unique($elements));
  if (isset($vars['result']['title'])) {
    $vars['title'] = SafeMarkup::format($vars['result']['title'], $elements);
  }
  if (isset($vars['result']['snippet'])) {
    $vars['snippet'] = SafeMarkup::format($vars['result']['snippet']['#markup'], $elements);
  }
}

/**
 * Implements hook_ENTITY_TYPE_view().
 */
function html_title_node_view(array &$build, \Drupal\Node\Entity\Node $node, EntityViewDisplayInterface $display, $view_mode) {
  switch ($view_mode) {
    case 'rss':
      $title = strip_tags($node->getTitle());
      // @todo: Change title of node when there is RSS display type.
      break;
  }
}

/**
 * Implements hook_entity_prepare_view().
 */
function html_title_entity_prepare_view($entity_type_id, array $entities, array $displays, $view_mode) {
  if ($entity_type_id !== 'node') {
    return;
  }
  // @todo, this is only required because template_preprocess_node assumes there
  // is a key inside the renderable array inside the elements array:
  // $variables['label'] = $variables['elements']['title'];
  // Since it can be display configured to be removed, it disappaers from the
  // elements list. We must reinstate if it has been hidden from display.
  // The alternative is a core patch or an alt implementation, perhaps involving
  // a new extra field?
  foreach ($entities as $entity) {
    $display = $displays[$entity->bundle()];
    if (!$display->getComponent('title')) {
      $fields = \Drupal::entityManager()->getFieldDefinitions($entity_type_id, $entity->bundle());
      $options = $fields['title']->getDisplayOptions('view');
      $built_title = \Drupal::service('plugin.manager.field.formatter')->prepareConfiguration($fields['title']->getType(), $options);
      $display->setComponent('title', $built_title);
    }
  }
}