presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitSpecialDateTimeFunction
class AstBuilder:    @Override
    public Node visitSpecialDateTimeFunction(SqlBaseParser.SpecialDateTimeFunctionContext context)
    {
        CurrentTime.Function function = getDateTimeFunctionType(context.name);

        if (context.precision != null) {
            return new CurrentTime(getLocation(context), function, Integer.parseInt(context.precision.getText()));
        }

        return new CurrentTime(getLocation(context), function);
    }