class-wc-cart.php

/**
* Get the cart data from the PHP session and store it in class variables.
*/
public function get_cart_from_session() {
	// Load cart session data from session
	foreach ( $this->cart_session_data as $key => $default ) {
      $this->$key = WC()->session->get( $key, $default );
  }

  $update_cart_session         = false;
  $this->removed_cart_contents = array_filter( WC()->session->get( 'removed_cart_contents', array() ) );
  $this->applied_coupons       = array_filter( WC()->session->get( 'applied_coupons', array() ) );

  /**
   * Load the cart object. This defaults to the persistent cart if null.
   */
  $cart = WC()->session->get( 'cart', null );

  if ( is_null( $cart ) && ( $saved_cart = get_user_meta( get_current_user_id(), '_woocommerce_persistent_cart', true ) ) ) {
    $cart                = $saved_cart['cart'];
    $update_cart_session = true;
  } elseif ( is_null( $cart ) ) {
    $cart = array();
  }

/* rest of code */
}