class UserAutocomplete

UserAutocompleteController.php in drupal/core/modules/user/lib/Drupal/user/Controller/UserAutocompleteController.php

Contains \Drupal\user\Controller\UserAutocompleteController.

user.services.yml in drupal/core/modules/user/user.services.yml

drupal/core/modules/user/user.services.yml

user.autocomplete in drupal/core/modules/user/user.services.yml

Drupal\user\UserAutocomplete

class UserAutocomplete {

  /**
   * The database connection to query for the user names.
   *
   * @var \Drupal\Core\Database\Connection
   */
  protected $connection;

  /**
   * The config factory to get the anonymous user name.
   *
   * @var \Drupal\Core\Config\ConfigFactory
   */
  protected $configFactory;

  /**
   * Constructs a UserAutocomplete object.
   *
   * @param \Drupal\Core\Database\Connection $connection
   *   The database connection to query for the user names.
   * @param \Drupal\Core\Config\ConfigFactory $config_factory
   *   The config factory.
   */
  public function __construct(Connection $connection, ConfigFactory $config_factory) {
    $this->connection = $connection;
    $this->configFactory = $config_factory;
  }

  /**
   * Get matches for the autocompletion of user names.
   *
   * @param string $string
   *   The string to match for usernames.
   *
   * @param bool $include_anonymous
   *   (optional) TRUE if the the name used to indicate anonymous users (e.g.
   *   "Anonymous") should be autocompleted. Defaults to FALSE.
   *
   * @return array
   *   An array containing the matching usernames.
   */
  public function getMatches($string, $include_anonymous = FALSE) {
    $matches = array();
    if ($string) {
      if ($include_anonymous) {
        $anonymous_name = $this->configFactory
          ->get('user.settings')
          ->get('anonymous');

        // Allow autocompletion for the anonymous user.
        if (stripos($anonymous_name, $string) !== FALSE) {
          $matches[$anonymous_name] = check_plain($anonymous_name);
        }
      }
      $result = $this->connection
        ->select('users')
        ->fields('users', array(
        'name',
      ))
        ->condition('name', db_like($string) . '%', 'LIKE')
        ->range(0, 10)
        ->execute();
      foreach ($result as $account) {
        $matches[$account->name] = check_plain($account->name);
      }
    }
    return $matches;
  }

}