date.c: s/is_date/set_date/

The function is_date, confusingly also set tm_year. tm_mon, and tm_mday
after validating input.

Rename to set_date to reflect its real usage.

Also, change return value is 0 on success and -1 on failure following
our convention on function do some real work.

Signed-off-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

date.c

@@ -497,7 +497,7 @@ static int match_alpha(const char *date, struct tm *tm, int *offset)
 	return skip_alpha(date);
 }
 
-static int is_date(int year, int month, int day, struct tm *now_tm, time_t now, struct tm *tm)
+static int set_date(int year, int month, int day, struct tm *now_tm, time_t now, struct tm *tm)
 {
 	if (month > 0 && month < 13 && day > 0 && day < 32) {
 		struct tm check = *tm;
@@ -518,9 +518,9 @@ static int is_date(int year, int month, int day, struct tm *now_tm, time_t now,
 		else if (year < 38)
 			r->tm_year = year + 100;
 		else
-			return 0;
+			return -1;
 		if (!now_tm)
-			return 1;
+			return 0;
 
 		specified = tm_to_time_t(r);
 
@@ -529,14 +529,14 @@ static int is_date(int year, int month, int day, struct tm *now_tm, time_t now,
 		 * sure it is not later than ten days from now...
 		 */
 		if ((specified != -1) && (now + 10*24*3600 < specified))
-			return 0;
+			return -1;
 		tm->tm_mon = r->tm_mon;
 		tm->tm_mday = r->tm_mday;
 		if (year != -1)
 			tm->tm_year = r->tm_year;
-		return 1;
+		return 0;
 	}
-	return 0;
+	return -1;
 }
 
 static int match_multi_number(timestamp_t num, char c, const char *date,
@@ -575,10 +575,10 @@ static int match_multi_number(timestamp_t num, char c, const char *date,
 
 		if (num > 70) {
 			/* yyyy-mm-dd? */
-			if (is_date(num, num2, num3, NULL, now, tm))
+			if (set_date(num, num2, num3, NULL, now, tm) == 0)
 				break;
 			/* yyyy-dd-mm? */
-			if (is_date(num, num3, num2, NULL, now, tm))
+			if (set_date(num, num3, num2, NULL, now, tm) == 0)
 				break;
 		}
 		/* Our eastern European friends say dd.mm.yy[yy]
@@ -586,14 +586,14 @@ static int match_multi_number(timestamp_t num, char c, const char *date,
 		 * mm/dd/yy[yy] form only when separator is not '.'
 		 */
 		if (c != '.' &&
-		    is_date(num3, num, num2, refuse_future, now, tm))
+		    set_date(num3, num, num2, refuse_future, now, tm) == 0)
 			break;
 		/* European dd.mm.yy[yy] or funny US dd/mm/yy[yy] */
-		if (is_date(num3, num2, num, refuse_future, now, tm))
+		if (set_date(num3, num2, num, refuse_future, now, tm) == 0)
 			break;
 		/* Funny European mm.dd.yy */
 		if (c == '.' &&
-		    is_date(num3, num, num2, refuse_future, now, tm))
+		    set_date(num3, num, num2, refuse_future, now, tm) == 0)
 			break;
 		return 0;
 	}