tochar: implement roman numerals for to_char

For ~shits and giggles~ completeness!

This commit implements the roman numeral commands for to_char.

Release note: None

pkg/util/tochar/constants.go

@@ -271,6 +271,14 @@ var dchKeywords = []keyWord{
 	//{"", 0, false, 0},
 }
 
+// Months in roman-numeral
+// (Must be in reverse order for seq_search (in FROM_CHAR), because
+// 'VIII' must have higher precedence than 'V')
+var (
+	ucMonthRomanNumerals = []string{"XII", "XI", "X", "IX", "VIII", "VII", "VI", "V", "IV", "III", "II", "I"}
+	lcMonthRomanNumerals = []string{"xii", "xi", "x", "ix", "viii", "vii", "vi", "v", "iv", "iii", "ii", "i"}
+)
+
 // From https://github.com/postgres/postgres/blob/b0b72c64a0ce7bf5dd78a80b33d85c89c943ad0d/src/backend/utils/adt/formatting.c#L194-L198.
 type formatNodeType int
 

pkg/util/tochar/testdata/ymd.ddt

@@ -546,3 +546,38 @@ J
 3 years 6 months 01:02:03
 ----
 3 years 6 months 01:02:03: 1722306
+
+# RM
+timestamp
+RM"x"
+2020-02-01 BC 01:02:03
+2020-12-01 01:02:03
+2020-01-01 01:02:03
+----
+2020-02-01 BC 01:02:03: II  x
+2020-12-01 01:02:03: XII x
+2020-01-01 01:02:03: I   x
+
+timestamp
+rm"< spaces here"
+2020-02-01 BC 01:02:03
+2020-12-01 01:02:03
+2020-01-01 01:02:03
+----
+2020-02-01 BC 01:02:03: ii  < spaces here
+2020-12-01 01:02:03: xii < spaces here
+2020-01-01 01:02:03: i   < spaces here
+
+interval
+FMRM" < no spaces here"
+1 day
+1 month 1 day
+-1 month 1 day
+-13 months
+13 months
+----
+1 day:  < no spaces here
+1 month 1 day: I < no spaces here
+-1 month 1 day: XI < no spaces here
+-13 months: XI < no spaces here
+13 months: I < no spaces here

pkg/util/tochar/tochar.go

@@ -494,12 +494,30 @@ func timeToChar(t timeInterface, formatNodes []formatNode) (string, error) {
 			sb.WriteString(fmt.Sprintf("%0*d", zeroPad, val))
 			sb.WriteString(fn.suffix.thVal(val))
 		case DCH_RM, DCH_rm:
-			// Roman numerals, not supporting this for now...
-			return "", pgerror.Newf(
-				pgcode.FeatureNotSupported,
-				"to_char format %s not supported",
-				fn.key.name,
-			)
+			if t.Month() == 0 && t.Year() == 0 {
+				continue
+			}
+			// Roman numerals are in reverse order, which is why the indexes
+			// are reversed.
+			var idx int
+			if t.Month() == 0 {
+				if t.Year() >= 0 {
+					idx = 0
+				} else {
+					idx = 11
+				}
+			} else if t.Month() < 0 {
+				idx = -1 * int(t.Month())
+			} else {
+				idx = 12 - int(t.Month())
+			}
+			var str string
+			if fn.key.id == DCH_RM {
+				str = ucMonthRomanNumerals[idx]
+			} else {
+				str = lcMonthRomanNumerals[idx]
+			}
+			sb.WriteString(fmt.Sprintf("%*s", fn.suffix.zeroPad(-4), str))
 		case DCH_W:
 			val := (t.Day()-1)/7 + 1
 			sb.WriteString(fmt.Sprintf("%d", val))