time: add support for day-of-year in Format and Parse

Day of year is 002 or __2, in contrast to day-in-month 2 or 02 or _2.
This means there is no way to print a variable-width day-of-year,
but that's probably OK.

Fixes #25689.

Change-Id: I1425d412cb7d2d360e9b3bf74e89566714e2477a
Reviewed-on: https://go-review.googlesource.com/c/go/+/122876
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

1 files changed, 96 insertions, 9 deletions

diff --git a/src/time/format.go b/src/time/format.go
index 2adbbe0770..d8e295f696 100644
--- a/src/time/format.go
+++ b/src/time/format.go
@@ -48,6 +48,10 @@ import "errors"
 // The recognized day of week formats are "Mon" and "Monday".
 // The recognized month formats are "Jan" and "January".
 //
+// The formats 2, _2, and 02 are unpadded, space-padded, and zero-padded
+// day of month. The formats __2 and 002 are space-padded and zero-padded
+// three-character day of year; there is no unpadded day of year format.
+//
 // Text in the format string that is not recognized as part of the reference
 // time is echoed verbatim during Format and expected to appear verbatim
 // in the input to Parse.
@@ -96,6 +100,8 @@ const (
 	stdDay                                         // "2"
 	stdUnderDay                                    // "_2"
 	stdZeroDay                                     // "02"
+	stdUnderYearDay                                // "__2"
+	stdZeroYearDay                                 // "002"
 	stdHour                  = iota + stdNeedClock // "15"
 	stdHour12                                      // "3"
 	stdZeroHour12                                  // "03"
@@ -170,10 +176,13 @@ func nextStdChunk(layout string) (prefix string, std int, suffix string) {
 				}
 			}
 
-		case '0': // 01, 02, 03, 04, 05, 06
+		case '0': // 01, 02, 03, 04, 05, 06, 002
 			if len(layout) >= i+2 && '1' <= layout[i+1] && layout[i+1] <= '6' {
 				return layout[0:i], std0x[layout[i+1]-'1'], layout[i+2:]
 			}
+			if len(layout) >= i+3 && layout[i+1] == '0' && layout[i+2] == '2' {
+				return layout[0:i], stdZeroYearDay, layout[i+3:]
+			}
 
 		case '1': // 15, 1
 			if len(layout) >= i+2 && layout[i+1] == '5' {
@@ -187,7 +196,7 @@ func nextStdChunk(layout string) (prefix string, std int, suffix string) {
 			}
 			return layout[0:i], stdDay, layout[i+1:]
 
-		case '_': // _2, _2006
+		case '_': // _2, _2006, __2
 			if len(layout) >= i+2 && layout[i+1] == '2' {
 				//_2006 is really a literal _, followed by stdLongYear
 				if len(layout) >= i+5 && layout[i+1:i+5] == "2006" {
@@ -195,6 +204,9 @@ func nextStdChunk(layout string) (prefix string, std int, suffix string) {
 				}
 				return layout[0:i], stdUnderDay, layout[i+2:]
 			}
+			if len(layout) >= i+3 && layout[i+1] == '_' && layout[i+2] == '2' {
+				return layout[0:i], stdUnderYearDay, layout[i+3:]
+			}
 
 		case '3':
 			return layout[0:i], stdHour12, layout[i+1:]
@@ -503,6 +515,7 @@ func (t Time) AppendFormat(b []byte, layout string) []byte {
 		year  int = -1
 		month Month
 		day   int
+		yday  int
 		hour  int = -1
 		min   int
 		sec   int
@@ -520,7 +533,8 @@ func (t Time) AppendFormat(b []byte, layout string) []byte {
 
 		// Compute year, month, day if needed.
 		if year < 0 && std&stdNeedDate != 0 {
-			year, month, day, _ = absDate(abs, true)
+			year, month, day, yday = absDate(abs, true)
+			yday++
 		}
 
 		// Compute hour, minute, second if needed.
@@ -560,6 +574,16 @@ func (t Time) AppendFormat(b []byte, layout string) []byte {
 			b = appendInt(b, day, 0)
 		case stdZeroDay:
 			b = appendInt(b, day, 2)
+		case stdUnderYearDay:
+			if yday < 100 {
+				b = append(b, ' ')
+				if yday < 10 {
+					b = append(b, ' ')
+				}
+			}
+			b = appendInt(b, yday, 0)
+		case stdZeroYearDay:
+			b = appendInt(b, yday, 3)
 		case stdHour:
 			b = appendInt(b, hour, 2)
 		case stdHour12:
@@ -688,7 +712,7 @@ func isDigit(s string, i int) bool {
 	return '0' <= c && c <= '9'
 }
 
-// getnum parses s[0:1] or s[0:2] (fixed forces the latter)
+// getnum parses s[0:1] or s[0:2] (fixed forces s[0:2])
 // as a decimal integer and returns the integer and the
 // remainder of the string.
 func getnum(s string, fixed bool) (int, string, error) {
@@ -704,6 +728,20 @@ func getnum(s string, fixed bool) (int, string, error) {
 	return int(s[0]-'0')*10 + int(s[1]-'0'), s[2:], nil
 }
 
+// getnum3 parses s[0:1], s[0:2], or s[0:3] (fixed forces s[0:3])
+// as a decimal integer and returns the integer and the remainder
+// of the string.
+func getnum3(s string, fixed bool) (int, string, error) {
+	var n, i int
+	for i = 0; i < 3 && isDigit(s, i); i++ {
+		n = n*10 + int(s[i]-'0')
+	}
+	if i == 0 || fixed && i != 3 {
+		return 0, s, errBad
+	}
+	return n, s[i:], nil
+}
+
 func cutspace(s string) string {
 	for len(s) > 0 && s[0] == ' ' {
 		s = s[1:]
@@ -792,8 +830,9 @@ func parse(layout, value string, defaultLocation, local *Location) (Time, error)
 	// Time being constructed.
 	var (
 		year       int
-		month      int = 1 // January
-		day        int = 1
+		month      int = -1
+		day        int = -1
+		yday       int = -1
 		hour       int
 		min        int
 		sec        int
@@ -861,10 +900,17 @@ func parse(layout, value string, defaultLocation, local *Location) (Time, error)
 				value = value[1:]
 			}
 			day, value, err = getnum(value, std == stdZeroDay)
-			if day < 0 {
-				// Note that we allow any one- or two-digit day here.
-				rangeErrString = "day"
+			// Note that we allow any one- or two-digit day here.
+			// The month, day, year combination is validated after we've completed parsing.
+		case stdUnderYearDay, stdZeroYearDay:
+			for i := 0; i < 2; i++ {
+				if std == stdUnderYearDay && len(value) > 0 && value[0] == ' ' {
+					value = value[1:]
+				}
 			}
+			yday, value, err = getnum3(value, std == stdZeroYearDay)
+			// Note that we allow any one-, two-, or three-digit year-day here.
+			// The year-day, year combination is validated after we've completed parsing.
 		case stdHour:
 			hour, value, err = getnum(value, false)
 			if hour < 0 || 24 <= hour {
@@ -1044,6 +1090,47 @@ func parse(layout, value string, defaultLocation, local *Location) (Time, error)
 		hour = 0
 	}
 
+	// Convert yday to day, month.
+	if yday >= 0 {
+		var d int
+		var m int
+		if isLeap(year) {
+			if yday == 31+29 {
+				m = int(February)
+				d = 29
+			} else if yday > 31+29 {
+				yday--
+			}
+		}
+		if yday < 1 || yday > 365 {
+			return Time{}, &ParseError{alayout, avalue, "", value, ": day-of-year out of range"}
+		}
+		if m == 0 {
+			m = yday/31 + 1
+			if int(daysBefore[m]) < yday {
+				m++
+			}
+			d = yday - int(daysBefore[m-1])
+		}
+		// If month, day already seen, yday's m, d must match.
+		// Otherwise, set them from m, d.
+		if month >= 0 && month != m {
+			return Time{}, &ParseError{alayout, avalue, "", value, ": day-of-year does not match month"}
+		}
+		month = m
+		if day >= 0 && day != d {
+			return Time{}, &ParseError{alayout, avalue, "", value, ": day-of-year does not match day"}
+		}
+		day = d
+	} else {
+		if month < 0 {
+			month = int(January)
+		}
+		if day < 0 {
+			day = 1
+		}
+	}
+
 	// Validate the day of the month.
 	if day < 1 || day > daysIn(Month(month), year) {
 		return Time{}, &ParseError{alayout, avalue, "", value, ": day out of range"}