Incr expired_keys if the unix-time is already expired for EXPIREAT and other commands(#1517)

Some commands that use unix-time, such as `EXPIREAT` and `SET EXAT`, should include the deleted keys in the `expired_keys` statistics if the specified time has already expired, and notifications should be sent in the manner of expired.

---------

Signed-off-by: Ray Cao <zisong.cw@alibaba-inc.com>

src/db.c

@@ -1850,7 +1850,8 @@ void deleteExpiredKeyFromOverwriteAndPropagate(client *c, robj *keyobj) {
     robj *aux = server.lazyfree_lazy_expire ? shared.unlink : shared.del;
     rewriteClientCommandVector(c, 2, aux, keyobj);
     signalModifiedKey(c, c->db, keyobj);
-    notifyKeyspaceEvent(NOTIFY_GENERIC, "del", keyobj, c->db->id);
+    notifyKeyspaceEvent(NOTIFY_EXPIRED, "expired", keyobj, c->db->id);
+    server.stat_expiredkeys++;
 }
 
 /* Propagate an implicit key deletion into replicas and the AOF file.

tests/unit/expire.tcl

@@ -142,6 +142,31 @@ start_server {tags {"expire"}} {
         list $e $f
     } {somevalue {}}
 
+    test {EXPIRE / EXPIREAT / PEXPIRE / PEXPIREAT Expiration time is already expired} {
+        r flushall
+        r config resetstat
+
+        r set x somevalue
+        r expire x -1
+        assert_equal {0} [r exists x]
+        assert_equal {1} [s expired_keys]
+
+        r set x somevalue
+        r expireat x [expr [clock seconds] - 1]
+        assert_equal {0} [r exists x]
+        assert_equal {2}  [s expired_keys]
+
+        r set x somevalue
+        r pexpire x -1000
+        assert_equal {0} [r exists x]
+        assert_equal {3} [s expired_keys]
+
+        r set x somevalue
+        r pexpireat x [expr [clock milliseconds] - 1000]
+        assert_equal {0} [r exists x]
+        assert_equal {4} [s expired_keys]
+    }
+
     test {TTL returns time to live in seconds} {
         r del x
         r setex x 10 somevalue

tests/unit/pubsub.tcl

@@ -425,6 +425,17 @@ start_server {tags {"pubsub network"}} {
         $rd1 close
     }
 
+    test "Keyspace notification: expired event (Expiration time is already expired)" {
+        r config set notify-keyspace-events Ex
+        r del foo
+        set rd1 [valkey_deferring_client]
+        assert_equal {1} [psubscribe $rd1 *]
+        r set foo 1
+        r expire foo -1
+        assert_equal "pmessage * __keyevent@${db}__:expired foo" [$rd1 read]
+        $rd1 close
+    }
+
     test "Keyspace notifications: evicted events" {
         r config set notify-keyspace-events Ee
         r config set maxmemory-policy allkeys-lru