date.c: add parse_expiry_date()

"git reflog --expire=all" tries to expire reflog entries up to the
current second, because the approxidate() parser gives the current
timestamp for anything it does not understand (and it does not know
what time "all" means).  When the user tells us to expire "all" (or
set the expiration time to "now"), the user wants to remove all the
reflog entries (no reflog entry should record future time).

Just set it to ULONG_MAX and to let everything that is older that
timestamp expire.

While at it, allow "now" to be treated the same way for callers that
parse expiry date timestamp with this function.  Also use an error
reporting version of approxidate() to report misspelled date.  When
the user says e.g. "--expire=mnoday" to delete entries two days or
older on Wednesday, we wouldn't want the "unknown, default to now"
logic to kick in.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/reflog.c

@@ -496,11 +496,9 @@ static int parse_expire_cfg_value(const char *var, const char *value, unsigned l
 {
 	if (!value)
 		return config_error_nonbool(var);
-	if (!strcmp(value, "never") || !strcmp(value, "false")) {
-		*expire = 0;
-		return 0;
-	}
-	*expire = approxidate(value);
+	if (parse_expiry_date(value, expire))
+		return error(_("%s' for '%s' is not a valid timestamp"),
+			     value, var);
 	return 0;
 }
 
@@ -613,11 +611,13 @@ static int cmd_reflog_expire(int argc, const char **argv, const char *prefix)
 		if (!strcmp(arg, "--dry-run") || !strcmp(arg, "-n"))
 			cb.dry_run = 1;
 		else if (!prefixcmp(arg, "--expire=")) {
-			cb.expire_total = approxidate(arg + 9);
+			if (parse_expiry_date(arg + 9, &cb.expire_total))
+				die(_("'%s' is not a valid timestamp"), arg);
 			explicit_expiry |= EXPIRE_TOTAL;
 		}
 		else if (!prefixcmp(arg, "--expire-unreachable=")) {
-			cb.expire_unreachable = approxidate(arg + 21);
+			if (parse_expiry_date(arg + 21, &cb.expire_unreachable))
+				die(_("'%s' is not a valid timestamp"), arg);
 			explicit_expiry |= EXPIRE_UNREACH;
 		}
 		else if (!strcmp(arg, "--stale-fix"))

cache.h

@@ -878,6 +878,7 @@ void show_date_relative(unsigned long time, int tz, const struct timeval *now,
 			struct strbuf *timebuf);
 int parse_date(const char *date, char *buf, int bufsize);
 int parse_date_basic(const char *date, unsigned long *timestamp, int *offset);
+int parse_expiry_date(const char *date, unsigned long *timestamp);
 void datestamp(char *buf, int bufsize);
 #define approxidate(s) approxidate_careful((s), NULL)
 unsigned long approxidate_careful(const char *, int *);

date.c

@@ -705,6 +705,28 @@ int parse_date_basic(const char *date, unsigned long *timestamp, int *offset)
 	return 0; /* success */
 }
 
+int parse_expiry_date(const char *date, unsigned long *timestamp)
+{
+	int errors = 0;
+
+	if (!strcmp(date, "never") || !strcmp(date, "false"))
+		*timestamp = 0;
+	else if (!strcmp(date, "all") || !strcmp(date, "now"))
+		/*
+		 * We take over "now" here, which usually translates
+		 * to the current timestamp.  This is because the user
+		 * really means to expire everything she has done in
+		 * the past, and by definition reflogs are the record
+		 * of the past, and there is nothing from the future
+		 * to be kept.
+		 */
+		*timestamp = ULONG_MAX;
+	else
+		*timestamp = approxidate_careful(date, &errors);
+
+	return errors;
+}
+
 int parse_date(const char *date, char *result, int maxlen)
 {
 	unsigned long timestamp;