[PATCH v5 0/4] More ISO-8601 support

This series aims to extend support for ISO-8601 datetime format to allow compact version, and fractional part of ISO-8601.

Change in v5 from v4:
* cleanup [3/4] following Junio's suggestion.

Changes in v4 from v3:
* s/is_date/set_date/ the function's name suggest it only does validation,
  but it does more than that. Junio suggested to me to use it for validation,
  When I looked more into it, I think it's better to not use it, and rename
  the function to reduce the confusion
* Extract the validate and set time to its own function
* Correct a check for time in compact ISO-8601

Changes in v3 from v2:
* Add example for fractional parts of second in documentation
* Add/Fix regression test on 12:34:56.7.days.ago

Đoàn Trần Công Danh (4):
  date.c: s/is_date/set_date/
  date.c: validate and set time in a helper function
  date.c: skip fractional second part of ISO-8601
  date.c: allow compact version of ISO-8601 datetime

Đoàn Trần Công Danh (4):
  date.c: s/is_date/set_date/
  date.c: validate and set time in a helper function
  date.c: skip fractional second part of ISO-8601
  date.c: allow compact version of ISO-8601 datetime

 Documentation/date-formats.txt |  5 ++-
 date.c                         | 67 ++++++++++++++++++++++++++--------
 t/t0006-date.sh                |  6 +++
 3 files changed, 62 insertions(+), 16 deletions(-)

Range-diff against v4:
1:  1fe69008fc = 1:  1fe69008fc date.c: s/is_date/set_date/
2:  0d0e4d8edc ! 2:  a6b97b19f2 date.c: validate and set time in a helper function
    @@ Commit message
     
         Signed-off-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
     
    +
    + ## Notes ##
    +    I intentionally leave a pair of bracket around if (set_time(...))
    +    to reduce the noise in next patch
    +
      ## date.c ##
     @@ date.c: static int set_date(int year, int month, int day, struct tm *now_tm, time_t now,
      	return -1;
    @@ date.c: static int set_date(int year, int month, int day, struct tm *now_tm, tim
      
     +static int set_time(long hour, long minute, long second, struct tm *tm)
     +{
    -+	/* C90 and old POSIX accepts 2 leap seconds, it's a defect,
    -+	 * ignore second number 61
    -+	 */
    ++	/* We accept 61st second because of leap second */
     +	if (0 <= hour && hour <= 24 &&
     +	    0 <= minute && minute < 60 &&
     +	    0 <= second && second <= 60) {
    @@ date.c: static int match_multi_number(timestamp_t num, char c, const char *date,
     -			tm->tm_hour = num;
     -			tm->tm_min = num2;
     -			tm->tm_sec = num3;
    -+		if (set_time(num, num2, num3, tm) == 0)
    ++		if (set_time(num, num2, num3, tm) == 0) {
      			break;
    --		}
    + 		}
      		return 0;
    - 
    - 	case '-':
3:  8b18d0ee5d ! 3:  f21aa2dcf5 date.c: skip fractional second part of ISO-8601
    @@ Commit message
         relative to current time.
     
         Reported-by: Brian M. Carlson <sandals@crustytoothpaste.net>
    +    Helped-by: Junio C Hamano <gitster@pobox.com>
         Signed-off-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
     
      ## Documentation/date-formats.txt ##
    @@ Documentation/date-formats.txt: RFC 2822::
      `YYYY.MM.DD`, `MM/DD/YYYY` and `DD.MM.YYYY`.
     
      ## date.c ##
    +@@ date.c: static int set_time(long hour, long minute, long second, struct tm *tm)
    + 	return -1;
    + }
    + 
    ++static int is_date_known(struct tm *tm)
    ++{
    ++	return tm->tm_year != -1 && tm->tm_mon != -1 && tm->tm_mday != -1;
    ++}
    ++
    + static int match_multi_number(timestamp_t num, char c, const char *date,
    + 			      char *end, struct tm *tm, time_t now)
    + {
     @@ date.c: static int match_multi_number(timestamp_t num, char c, const char *date,
    - 	/* Time? Date? */
    - 	switch (c) {
    - 	case ':':
    --		if (num3 < 0)
    -+		if (num3 < 0) {
    + 		if (num3 < 0)
      			num3 = 0;
    -+		} else if (*end == '.' && isdigit(end[1]) &&
    -+			   tm->tm_year != -1 && tm->tm_mon != -1 && tm->tm_mday != -1 &&
    -+			   set_time(num, num2, num3, tm) == 0) {
    -+			/* %Y%m%d is known, ignore fractional <num4> in HHMMSS.<num4> */
    -+			strtol(end + 1, &end, 10);
    -+		}
    - 		if (set_time(num, num2, num3, tm) == 0)
    + 		if (set_time(num, num2, num3, tm) == 0) {
    ++			/*
    ++			 * If %H:%M:%S was just parsed followed by: .<num4>
    ++			 * Consider (& discard) it as fractional second
    ++			 * if %Y%m%d is parsed before.
    ++			 */
    ++			if (*end == '.' && isdigit(end[1]) && is_date_known(tm))
    ++				strtol(end + 1, &end, 10);
      			break;
    + 		}
      		return 0;
     
      ## t/t0006-date.sh ##
4:  2812439a26 = 4:  51aa60c069 date.c: allow compact version of ISO-8601 datetime