custom token

llnl_site_settings.tokens.inc

<?php

/**
 * @file
 * Token related hook implementations.
 */

use Drupal\Core\Render\BubbleableMetadata;

/**
 * Implements hook_token_info().
 */
function llnl_site_settings_token_info() {
  $types['search'] = [
    'name' => t('Search'),
    'description' => t('Tokens for search bar placement'),
  ];
  $search['search-bar'] = [
    'name' => t('Header search bar'),
    'description' => t('The search bar form element'),
  ];

  return [
    'types' => $types,
    'tokens' => [
      'search' => $search,
    ],
  ];
}

/**
 * Implements hook_tokens().
 */
function llnl_site_settings_tokens($type, $tokens, $data, $options, BubbleableMetadata $bubbleable_metadata) {
  $replacements = [];

  switch ($type) {
    case 'search':
      foreach ($tokens as $name => $original) {
        switch ($name) {
          case 'search-bar':
            $replacements[$original] = \Drupal::formBuilder()->getForm('Drupal\llnl_search\Form\HeaderSearchForm');
            break;
        }
      }
  }
  return $replacements;
}