Support output ISO 8601 format dates

Support output of full ISO 8601 style dates in e.g. git log
and other places that use interpolation for formatting.

Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/pretty-formats.txt

@@ -106,12 +106,14 @@ The placeholders are:
 - '%aD': author date, RFC2822 style
 - '%ar': author date, relative
 - '%at': author date, UNIX timestamp
+- '%ai': author date, ISO 8601 format
 - '%cn': committer name
 - '%ce': committer email
 - '%cd': committer date
 - '%cD': committer date, RFC2822 style
 - '%cr': committer date, relative
 - '%ct': committer date, UNIX timestamp
+- '%ci': committer date, ISO 8601 format
 - '%e': encoding
 - '%s': subject
 - '%b': body

cache.h

@@ -409,7 +409,7 @@ extern void *read_object_with_reference(const unsigned char *sha1,
 					unsigned long *size,
 					unsigned char *sha1_ret);
 
-enum date_mode { DATE_NORMAL = 0, DATE_RELATIVE, DATE_SHORT, DATE_LOCAL };
+enum date_mode { DATE_NORMAL = 0, DATE_RELATIVE, DATE_SHORT, DATE_LOCAL, DATE_ISO8601 };
 const char *show_date(unsigned long time, int timezone, enum date_mode mode);
 const char *show_rfc2822_date(unsigned long time, int timezone);
 int parse_date(const char *date, char *buf, int bufsize);

commit.c

@@ -781,6 +781,7 @@ static void fill_person(struct interp *table, const char *msg, int len)
 	interp_set_entry(table, 2, show_date(date, tz, 0));
 	interp_set_entry(table, 3, show_rfc2822_date(date, tz));
 	interp_set_entry(table, 4, show_date(date, tz, 1));
+	interp_set_entry(table, 6, show_date(date, tz, DATE_ISO8601));
 }
 
 static long format_commit_message(const struct commit *commit,
@@ -799,12 +800,14 @@ static long format_commit_message(const struct commit *commit,
 		{ "%aD" },	/* author date, RFC2822 style */
 		{ "%ar" },	/* author date, relative */
 		{ "%at" },	/* author date, UNIX timestamp */
+		{ "%ai" },	/* author date, ISO 8601 */
 		{ "%cn" },	/* committer name */
 		{ "%ce" },	/* committer email */
 		{ "%cd" },	/* committer date */
 		{ "%cD" },	/* committer date, RFC2822 style */
 		{ "%cr" },	/* committer date, relative */
 		{ "%ct" },	/* committer date, UNIX timestamp */
+		{ "%ci" },	/* committer date, ISO 8601 */
 		{ "%e" },	/* encoding */
 		{ "%s" },	/* subject */
 		{ "%b" },	/* body */
@@ -821,10 +824,11 @@ static long format_commit_message(const struct commit *commit,
 		IPARENTS, IPARENTS_ABBREV,
 		IAUTHOR_NAME, IAUTHOR_EMAIL,
 		IAUTHOR_DATE, IAUTHOR_DATE_RFC2822, IAUTHOR_DATE_RELATIVE,
-		IAUTHOR_TIMESTAMP,
+		IAUTHOR_TIMESTAMP, IAUTHOR_ISO8601,
 		ICOMMITTER_NAME, ICOMMITTER_EMAIL,
 		ICOMMITTER_DATE, ICOMMITTER_DATE_RFC2822,
 		ICOMMITTER_DATE_RELATIVE, ICOMMITTER_TIMESTAMP,
+		ICOMMITTER_ISO8601,
 		IENCODING,
 		ISUBJECT,
 		IBODY,

date.c

@@ -137,6 +137,13 @@ const char *show_date(unsigned long time, int tz, enum date_mode mode)
 	if (mode == DATE_SHORT)
 		sprintf(timebuf, "%04d-%02d-%02d", tm->tm_year + 1900,
 				tm->tm_mon + 1, tm->tm_mday);
+	else if (mode == DATE_ISO8601)
+		sprintf(timebuf, "%04d-%02d-%02d %02d:%02d:%02d %+05d",
+				tm->tm_year + 1900,
+				tm->tm_mon + 1,
+				tm->tm_mday,
+				tm->tm_hour, tm->tm_min, tm->tm_sec,
+				tz);
 	else
 		sprintf(timebuf, "%.3s %.3s %d %02d:%02d:%02d %d%c%+05d",
 				weekday_names[tm->tm_wday],