presto-parser/src/main/java/io/prestosql/sql/SqlFormatter.java/SqlFormatter/formatPrincipal
class SqlFormatter:        private static String formatPrincipal(PrincipalSpecification principal)
        {
            PrincipalSpecification.Type type = principal.getType();
            switch (type) {
                case UNSPECIFIED:
                    return principal.getName().toString();
                case USER:
                case ROLE:
                    return format("%s %s", type.name(), principal.getName().toString());
                default:
                    throw new IllegalArgumentException("Unsupported principal type: " + type);
            }
        }