date.c: Support iso8601 timezone formats

Timezone designators in the following formats are all valid according to
ISO8601:2004, section 4.3.2:

    [+-]hh, [+-]hhmm, [+-]hh:mm

but we have ignored the ones with colon so far.

Signed-off-by: Haitao Li <[email protected]>
Helped-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

date.c

@@ -552,23 +552,35 @@ static int match_digit(const char *date, struct tm *tm, int *offset, int *tm_gmt
 static int match_tz(const char *date, int *offp)
 {
 	char *end;
-	int offset = strtoul(date+1, &end, 10);
-	int min, hour;
-	int n = end - date - 1;
+	int hour = strtoul(date + 1, &end, 10);
+	int n = end - (date + 1);
+	int min = 0;
 
-	min = offset % 100;
-	hour = offset / 100;
+	if (n == 4) {
+		/* hhmm */
+		min = hour % 100;
+		hour = hour / 100;
+	} else if (n != 2) {
+		min = 99; /* random crap */
+	} else if (*end == ':') {
+		/* hh:mm? */
+		min = strtoul(end + 1, &end, 10);
+		if (end - (date + 1) != 5)
+			min = 99; /* random crap */
+	} /* otherwise we parsed "hh" */
 
 	/*
-	 * Don't accept any random crap.. At least 3 digits, and
-	 * a valid minute. We might want to check that the minutes
-	 * are divisible by 30 or something too.
+	 * Don't accept any random crap. Even though some places have
+	 * offset larger than 12 hours (e.g. Pacific/Kiritimati is at
+	 * UTC+14), there is something wrong if hour part is much
+	 * larger than that. We might also want to check that the
+	 * minutes are divisible by 15 or something too. (Offset of
+	 * Kathmandu, Nepal is UTC+5:45)
 	 */
-	if (min < 60 && n > 2) {
-		offset = hour*60+min;
+	if (min < 60 && hour < 24) {
+		int offset = hour * 60 + min;
 		if (*date == '-')
 			offset = -offset;
-
 		*offp = offset;
 	}
 	return end - date;

t/t0006-date.sh

@@ -40,6 +40,12 @@ check_parse 2008-02 bad
 check_parse 2008-02-14 bad
 check_parse '2008-02-14 20:30:45' '2008-02-14 20:30:45 +0000'
 check_parse '2008-02-14 20:30:45 -0500' '2008-02-14 20:30:45 -0500'
+check_parse '2008-02-14 20:30:45 -0015' '2008-02-14 20:30:45 -0015'
+check_parse '2008-02-14 20:30:45 -5' '2008-02-14 20:30:45 +0000'
+check_parse '2008-02-14 20:30:45 -5:' '2008-02-14 20:30:45 +0000'
+check_parse '2008-02-14 20:30:45 -05' '2008-02-14 20:30:45 -0500'
+check_parse '2008-02-14 20:30:45 -:30' '2008-02-14 20:30:45 +0000'
+check_parse '2008-02-14 20:30:45 -05:00' '2008-02-14 20:30:45 -0500'
 check_parse '2008-02-14 20:30:45' '2008-02-14 20:30:45 -0500' EST5
 
 check_approxidate() {