[PATCH 2/2] read-cache: use time_t instead of unsigned long

["Carlo Marcelo Arenas Belón" <carenas@gmail.com>]

There are still some more possible improvements around this code but
they are orthogonal to this change :

* migrate to approxidate_careful or parse_expiry_date
* maybe make sure only approxidate are used for expiration

Changes in v2:
* improved commit message as suggested by Eric
* failsafe against time_t truncation as suggested by Junio

-- >8 --
Subject: [PATCH v2 2/2] read-cache: use time specific types instead of
 unsigned long

b968372279 ("read-cache: unlink old sharedindex files", 2017-03-06)
introduced get_shared_index_expire_date using unsigned long to track
the modification times of a shared index.

dddbad728c ("timestamp_t: a new data type for timestamps", 2017-04-26)
shows why that might be problematic so move to timestamp_t/time_t.

if time_t can't represent a valid time keep the indexes for failsafe

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
---
 read-cache.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/read-cache.c b/read-cache.c
index 7b1354d759..7d322f11c8 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2625,9 +2625,9 @@ static int write_split_index(struct index_state *istate,
 
 static const char *shared_index_expire = "2.weeks.ago";
 
-static unsigned long get_shared_index_expire_date(void)
+static timestamp_t get_shared_index_expire_date(void)
 {
-	static unsigned long shared_index_expire_date;
+	static timestamp_t shared_index_expire_date;
 	static int shared_index_expire_date_prepared;
 
 	if (!shared_index_expire_date_prepared) {
@@ -2643,12 +2643,12 @@ static unsigned long get_shared_index_expire_date(void)
 static int should_delete_shared_index(const char *shared_index_path)
 {
 	struct stat st;
-	unsigned long expiration;
+	time_t expiration;
+	timestamp_t t = get_shared_index_expire_date();
 
-	/* Check timestamp */
-	expiration = get_shared_index_expire_date();
-	if (!expiration)
+	if (!t || date_overflows(t))
 		return 0;
+	expiration = t;
 	if (stat(shared_index_path, &st))
 		return error_errno(_("could not stat '%s'"), shared_index_path);
 	if (st.st_mtime > expiration)
-- 
2.19.1.856.g8858448bb