debug-method.php

<?php  
  /**
   * Helper function to log info.
   */
  public static function _bc_filelog($message) {
    error_log(print_r($message, 1) . PHP_EOL, 3, '../checkout-session-info.log');
  }
  
  /**
   * {@inheritdoc}
   */
  public function addCartId($cart_id, $type = self::ACTIVE) {
    $key = $this->getSessionKey($type);
    $ids = $this->session->get($key, []);
    $ids[] = $cart_id;
    $this->session->set($key, array_unique($ids));
    self::_bc_filelog(date('Y-m-d H:i:s', strtotime('now')) . ' ' . __FUNCTION__);
    self::_bc_filelog($_SESSION);
  }