date: add "unix" format

We already have "--date=raw", which is a Unix epoch
timestamp plus a contextual timezone (either the author's or
the local). But one may not care about the timezone and just
want the epoch timestamp by itself. It's not hard to parse
the two apart, but if you are using a pretty-print format,
you may want git to show the "finished" form that the user
will see.

We can accomodate this by adding a new date format, "unix",
which is basically "raw" without the timezone.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -751,6 +751,10 @@ Note that the `-local` option does not affect the seconds-since-epoch
 value (which is always measured in UTC), but does switch the accompanying
 timezone value.
 +
+`--date=unix` shows the date as a Unix epoch timestamp (seconds since
+1970).  As with `--raw`, this is always in UTC and therefore `-local`
+has no effect.
++
 `--date=format:...` feeds the format `...` to your system `strftime`.
 Use `--date=format:%c` to show the date in your system locale's
 preferred format.  See the `strftime` manual for a complete list of

builtin/blame.c

@@ -2626,6 +2626,9 @@ parse_done:
 	case DATE_RAW:
 		blame_date_width = sizeof("1161298804 -0700");
 		break;
+	case DATE_UNIX:
+		blame_date_width = sizeof("1161298804");
+		break;
 	case DATE_SHORT:
 		blame_date_width = sizeof("2006-10-19");
 		break;

cache.h

@@ -1223,7 +1223,8 @@ struct date_mode {
 		DATE_ISO8601_STRICT,
 		DATE_RFC2822,
 		DATE_STRFTIME,
-		DATE_RAW
+		DATE_RAW,
+		DATE_UNIX
 	} type;
 	const char *strftime_fmt;
 	int local;

date.c

@@ -177,6 +177,12 @@ const char *show_date(unsigned long time, int tz, const struct date_mode *mode)
 	struct tm *tm;
 	static struct strbuf timebuf = STRBUF_INIT;
 
+	if (mode->type == DATE_UNIX) {
+		strbuf_reset(&timebuf);
+		strbuf_addf(&timebuf, "%lu", time);
+		return timebuf.buf;
+	}
+
 	if (mode->local)
 		tz = local_tzoffset(time);
 
@@ -792,6 +798,8 @@ static enum date_mode_type parse_date_type(const char *format, const char **end)
 		return DATE_NORMAL;
 	if (skip_prefix(format, "raw", end))
 		return DATE_RAW;
+	if (skip_prefix(format, "unix", end))
+		return DATE_UNIX;
 	if (skip_prefix(format, "format", end))
 		return DATE_STRFTIME;
 

t/t0006-date.sh

@@ -46,8 +46,10 @@ check_show rfc2822 "$TIME" 'Wed, 15 Jun 2016 16:13:20 +0200'
 check_show short "$TIME" '2016-06-15'
 check_show default "$TIME" 'Wed Jun 15 16:13:20 2016 +0200'
 check_show raw "$TIME" '1466000000 +0200'
+check_show unix "$TIME" '1466000000'
 check_show iso-local "$TIME" '2016-06-15 14:13:20 +0000'
 check_show raw-local "$TIME" '1466000000 +0000'
+check_show unix-local "$TIME" '1466000000'
 
 # arbitrary time absurdly far in the future
 FUTURE="5758122296 -0400"