Useful preprocess theme functions (may use deprecated php)

drupal-preprocess.theme

<?php

use Drupal\Core\Cache\CacheableMetadata;
use Drupal\Core\Template\Attribute;
use Drupal\Core\Url;
use Drupal\node\NodeInterface;
use Drupal\Core\Link;

/**
 * Implements hook_preprocess_page() for page.html.twig.
 */
function THEME_preprocess_page(array &$vars): void {
  // Add sitename and slogan to page.
  $vars['site_name'] = \Drupal::config('system.site')->get('name');
  $vars['site_slogan'] = \Drupal::config('system.site')->get('slogan');

  // Do things based on route.
  $route_match = \Drupal::routeMatch();
  $current_route = $route_match->getRouteName();
  $current_path = \Drupal::service('path.current')->getPath();

  switch ($current_route) {
    case 'system.401':
    case 'system.403':
      $vars['title'] = t('Access denied');
      break;

    case 'system.404':
      $vars['title'] = t('Page not found');
      break;
  }

  // Do things based on the node.
  if (($node = $route_match->getParameter('node')) && $node instanceof NodeInterface) {

    // Set a global var we can use when viewing a node.
    $vars['is_node'] = TRUE;
    $vars['type_class'] = 'page-type--' . strtr($node->getType(), '_', '-');

    if ($node->getType() === 'article') {
      // Add created date when viewing an article node.
      $vars['created_date'] = \Drupal::service('date.formatter')->format($node->getCreatedTime(), 'medium'),

      // Add the author when viewing an article node.
      $uid = $node->getOwnerId();
      $vars['author'] = \Drupal::entityTypeManager()->getViewBuilder('user')->view($uid, 'compact');
      // Or just their name.
      $user = \Drupal\user\Entity\User::load($uid);
      $vars['author'] = $user->getDisplayName();

      // Render node header_image.
      $vars['header_image'] = \Drupal::entityTypeManager()->getViewBuilder('node')->view($node, 'header_image');
    }
  }
}

/**
 * Implements hook_preprocess_node().
 */
function THEME_preprocess_node(array &$vars): void {
  $node = $vars['elements']['#node'];
  $view_mode = $vars['elements']['#view_mode'];
  $type = $node->getType();

  // Check if field has value.
  if ($node->hasField('field_suburb') && !$node->field_suburb->isEmpty()) {
    $vars['attributes']['class'][] = 'has-suburb';

    // Get field value (if normal field)
    $vars['suburb'] = $node->get('field_suburb')->value;

    // Get referenced entity (if entity ref field)
    $vars['suburb'] = $node->get('field_suburb')->entity;
  }

  // Make a new link from an entity reference and plain text field.
  // So the editor can customise the link text.
  if ($node->hasField('field_reference') && $node->hasField('field_link_label')) {
    // Get the URL of the referenced node.
    $referenced_url = $node->get('field_reference')->entity->toUrl()->getInternalPath();
    // Get the value of the label field.
    $label = $node->get('field_link_label')->value;
    // Create the link.
    $link = Link::fromTextAndUrl($label,
      Url::fromUserInput(base_path() . $referenced_url, [
        'attributes' => [
          'class' => ['button'],
        ]
      ]));
    // Create a var to use in the template.
    $vars['link'] = $link->toString();
  }
}

/**
 * Implements hook_preprocess_field().
 */
function THEME_preprocess_field(array &$vars): void {
  $name = $vars['element']['#field_name'];
  $bundle = $vars['element']['#bundle'];
  $entity_type = $vars['element']['#entity_type'];
  $field_type = $vars['element']['#field_type'];

  // Ds overrides '#view_mode' to '_custom' but keeps the original in '#ds_view_mode'.
  $view_mode = isset($vars['element']['#ds_view_mode']) ? $vars['element']['#ds_view_mode'] : $vars['element']['#view_mode'];

  if ($name === 'field_suburb') {
    // Add a custom variable to a field
    $vars['items'][0]['icon_id'] = 'location';

    // Add a class to a field
    $vars['attributes']['class'][] = 'is-suburb';

    // Change it's rendered label
    $vars['label'] = t('My suburb');

    // Add a class to each item in a field
    foreach ($vars['items'] as $delta => $item) {
      if ($vars['items'][$delta]['attributes'] instanceof Attribute) {
        $vars['items'][$delta]['attributes']->addClass('meta__type');
      }
    }
  }
}

/**
 * Implements hook_preprocess_HOOK() for Block document templates.
 */
function THEME_preprocess_block(array &$vars): void {
  $vars['block_content'] = $vars['elements']['content']['#block_content'] ?? NULL;
  // These variables are set in HOOK_theme_suggestions_block_alter().
  // @see https://gist.github.com/rikki-iki/6fe41e11ac59b3e1d07e#file-drupal-8-theme-suggestions-theme-L7

  // Pass the block_id through to the content.
  $block_id = $vars['attributes']['id'] ?? NULL;
  $vars['content']['#attributes']['block_id'] = $block_id;
  
  // Pass the region through to the content.
  $region = $vars['elements']['#region'] ?? NULL;
  $vars['content']['#attributes']['region'] = $region;
  
  $provider = $vars['elements']['#configuration']['provider'] ?? NULL;
  $bundle =  $vars['elements']['#bundle'] ?? NULL;
}

/**
 * Implements hook_preprocess_maintenance_page().
 */
function THEME_preprocess_maintenance_page(array &$vars): void {
  $vars['title'] = t('Temporarily down for maintenance');
}

/**
 * Implements hook_form_alter().
 */
function THEME_form_alter(&$form, $form_state, $form_id): void {
  // Add search placeholder for keywords field.
  if ('views_exposed_form' === $form_id) {
    $view = $form_state->get('view');
    if ($view->id() === 'search') {
      $form['#attributes']['class'][] = 'form__search';
      $form['query']['#attributes']['placeholder'] = t("How can we help you today?");
    }
  }
}

/**
 * Implements hook_preprocess_breadcrumb().
 */
function THEME_preprocess_breadcrumb(array &$vars): void {
  $route = \Drupal::routeMatch()->getRouteObject();
  $title = NULL;
  if ($route) {
    $title = \Drupal::service('title_resolver')->getTitle(\Drupal::request(), $route);
  }

  $vars['breadcrumb'][] = [
    'text' => $title,
  ];

  // Adding a dependency on the route actually disables caching for this block
  // but that's what we want, to prevent caching issues.
  CacheableMetadata::createFromRenderArray($vars)
    ->addCacheContexts(['route'])
    ->applyTo($vars);
}

/**
 * Implements hook_preprocess_HOOK() for menu.html.twig.
 */
function THEME_preprocess_menu(array &$vars): void {
  // Add the menu label as a variable.
  $vars['menu_label'] = \Drupal::entityTypeManager()->getStorage('menu')->load($vars['menu_name'])->label();
}

/**
 * Implements hook_preprocess_HOOK() for pager.html.twig.
 */
function THEME_preprocess_pager(array &$vars): void {
  // Remove html characters for Previous/Next buttons.
  if (isset($vars['items']['previous']['text'])) {
    $vars['items']['previous']['text'] = t('Previous');
  }
  if (isset($vars['items']['next']['text'])) {
    $vars['items']['next']['text'] = t('Next');
  }
  $pager = \Drupal::service('pager.manager')->getPager($vars['pager']['#element']);
  $vars['total'] = $pager->getTotalPages();
}