presto-main/src/main/java/io/prestosql/operator/scalar/DateTimeFunctions.java/DateTimeFunctions/dateFormat
class DateTimeFunctions:    @ScalarFunction
    @LiteralParameters("x")
    @SqlType(StandardTypes.VARCHAR)
    public static Slice dateFormat(ConnectorSession session, @SqlType(StandardTypes.TIMESTAMP) long timestamp, @SqlType("varchar(x)") Slice formatString)
    {
        if (session.isLegacyTimestamp()) {
            return dateFormat(getChronology(session.getTimeZoneKey()), session.getLocale(), timestamp, formatString);
        }
        else {
            return dateFormat(UTC_CHRONOLOGY, session.getLocale(), timestamp, formatString);
        }
    }