presto-main/src/main/java/io/prestosql/operator/scalar/SessionFunctions.java/SessionFunctions/currentPath
class SessionFunctions:    @ScalarFunction(value = "$current_path", hidden = true)
    @Description("retrieve current path")
    @SqlType(StandardTypes.VARCHAR)
    public static Slice currentPath(ConnectorSession session)
    {
        // this function is a language construct and has special access to internals
        return utf8Slice(((FullConnectorSession) session).getSession().getPath().toString());
    }