Description:
------------
It appears that you can construct a DateTime object, that, upon serialize/unserialize cycle will have *different* data or will fail to unserialize.

Granted, these dates are outside the range people will typically use, but if DateTime can't work with them reliably it should reject them in constructor.



Test script:
---------------
<?php
var_dump('PHP version', PHP_VERSION);

foreach ([PHP_INT_MIN, PHP_INT_MAX] as $extreme) {
    $i = 64;
    while ($i --> 0) {
        $d = new DateTime('@' . ($extreme >> $i));
        $s = serialize($d);
        try {
            $u = unserialize($s);
        } catch (Error $e) {
            $u = "failed unserialization: " . $e->getMessage() . ' : ' . $s;
        }
        $original = $d->format('Y-m-d H:i:s');
        $serializedUnserialized = is_string($u) ? $u : $u->format('Y-m-d H:i:s');
        if ($original !== $serializedUnserialized) {
            var_dump('[' . ($extreme >> $i) . '] ' . $original . ' => ' . $serializedUnserialized);
        }
    }
}


Expected result:
----------------
string(11) "PHP version"
string(5) "7.1.8"

Actual result:
--------------
string(11) "PHP version"
string(5) "7.1.8"
string(60) "[-549755813888] -15452-12-06 11:41:52 => 2002-12-06 11:41:52"
string(61) "[-1099511627776] -32873-11-12 23:23:44 => 1973-11-12 23:23:44"
string(61) "[-2199023255552] -67715-09-22 22:47:28 => 0715-09-22 22:47:28"
string(62) "[-4398046511104] -137399-06-15 21:34:56 => 0399-06-15 21:34:56"
string(62) "[-8796093022208] -276768-11-27 19:09:52 => 6768-11-27 19:09:52"
string(63) "[-17592186044416] -555505-10-25 14:19:44 => 0505-10-25 14:19:44"
string(64) "[-35184372088832] -1112979-08-20 04:39:28 => 0979-08-20 04:39:28"
string(64) "[-70368744177664] -2227927-04-07 09:18:56 => 0927-04-07 09:18:56"
string(65) "[-140737488355328] -4457824-07-13 18:37:52 => 7824-07-13 18:37:52"
string(65) "[-281474976710656] -8917617-01-25 13:15:44 => 2007-01-25 13:15:44"
string(66) "[-562949953421312] -17837204-02-19 02:31:28 => 2004-02-19 02:31:28"
string(67) "[-1125899906842624] -35676378-04-08 05:02:56 => 2008-04-08 05:02:56"
string(67) "[-2251799813685248] -71354726-07-14 10:05:52 => 2006-07-14 10:05:52"
string(245) "[-4503599627370496] -142711421-01-25 20:11:44 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:32:"-142711421-01-25 20:11:44.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(68) "[-9007199254740992] -285424812-02-20 16:23:28 => 0812-02-20 16:23:28"
string(246) "[-18014398509481984] -570851594-04-11 08:46:56 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:32:"-570851594-04-11 08:46:56.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(70) "[-36028797018963968] -1141705158-07-20 17:33:52 => 2058-07-20 17:33:52"
string(248) "[-72057594037927936] -2283412285-02-07 11:07:44 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:33:"-2283412285-02-07 11:07:44.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(71) "[-144115188075855872] -4566826540-03-15 22:15:28 => 0540-03-15 22:15:28"
string(249) "[-288230376151711744] -9133655050-05-29 20:30:56 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:33:"-9133655050-05-29 20:30:56.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(251) "[-576460752303423488] -18267312070-10-26 17:01:52 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:34:"-18267312070-10-26 17:01:52.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(252) "[-1152921504606846976] -36534626109-08-20 10:03:44 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:34:"-36534626109-08-20 10:03:44.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(73) "[-2305843009213693952] -73069254187-04-08 20:07:28 => 4187-04-08 20:07:28"
string(254) "[-4611686018427387904] -146138510344-07-14 16:14:56 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:35:"-146138510344-07-14 16:14:56.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(254) "[-9223372036854775808] -292277022657-01-27 08:29:53 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:35:"-292277022657-01-27 08:29:53.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(58) "[274877906943] 10680-07-14 06:09:03 => 2000-07-14 06:09:03"
string(230) "[549755813887] 19391-01-25 12:18:07 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:27:"19391-01-25 12:18:07.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(59) "[1099511627775] 36812-02-20 00:36:15 => 2002-02-20 00:36:15"
string(59) "[2199023255551] 71654-04-10 01:12:31 => 2004-04-10 01:12:31"
string(233) "[4398046511103] 141338-07-19 02:25:03 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:{s:4:"date";s:28:"141338-07-19 02:25:03.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(60) "[8796093022207] 280707-02-04 04:50:07 => 2007-02-04 04:50:07"
string(61) "[17592186044415] 559444-03-08 09:40:15 => 2044-03-08 09:40:15"
string(236) "[35184372088831] 1116918-05-14 19:20:31 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:29:"1116918-05-14 19:20:31.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(236) "[70368744177663] 2231866-09-25 14:41:03 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:29:"2231866-09-25 14:41:03.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(63) "[140737488355327] 4461763-06-20 05:22:07 => 0763-06-20 05:22:07"
string(63) "[281474976710655] 8921556-12-07 10:44:15 => 0556-12-07 10:44:15"
string(239) "[562949953421311] 17841143-11-13 21:28:31 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:30:"17841143-11-13 21:28:31.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(240) "[1125899906842623] 35680317-09-25 18:57:03 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:30:"35680317-09-25 18:57:03.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(65) "[2251799813685247] 71358665-06-19 13:54:07 => 8665-06-19 13:54:07"
string(242) "[4503599627370495] 142715360-12-06 03:48:15 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:31:"142715360-12-06 03:48:15.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(242) "[9007199254740991] 285428751-11-12 07:36:31 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:31:"285428751-11-12 07:36:31.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(67) "[18014398509481983] 570855533-09-22 15:13:03 => 2003-09-22 15:13:03"
string(245) "[36028797018963967] 1141709097-06-13 06:26:07 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:32:"1141709097-06-13 06:26:07.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(68) "[72057594037927935] 2283416224-11-24 12:52:15 => 2024-11-24 12:52:15"
string(69) "[144115188075855871] 4566830479-10-18 01:44:31 => 1979-10-18 01:44:31"
string(69) "[288230376151711743] 9133658989-08-04 03:29:03 => 1989-08-04 03:29:03"
string(248) "[576460752303423487] 18267316009-03-08 06:58:07 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:33:"18267316009-03-08 06:58:07.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(249) "[1152921504606846975] 36534630048-05-13 13:56:15 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:33:"36534630048-05-13 13:56:15.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(249) "[2305843009213693951] 73069258126-09-25 03:52:31 => failed unserialization: Invalid serialization data for DateTime object : O:8:"DateTime":3:s:4:"date";s:33:"73069258126-09-25 03:52:31.000000";s:13:"timezone_type";i:1;s:8:"timezone";s:6:"+00:00";}"
string(72) "[4611686018427387903] 146138514283-06-19 07:45:03 => 4283-06-19 07:45:03"
string(72) "[9223372036854775807] 292277026596-12-04 15:30:07 => 6596-12-04 15:30:07"