presto-parser/src/main/java/io/prestosql/sql/ExpressionFormatter.java/ExpressionFormatter/formatGroupingSet
class ExpressionFormatter:    private static String formatGroupingSet(List<Expression> groupingSet)
    {
        return format("(%s)", Joiner.on(", ").join(groupingSet.stream()
                .map(ExpressionFormatter::formatExpression)
                .iterator()));
    }