Fix GH-9891: DateTime modify with unixtimestamp (@) must work like setTimestamp

Author: derickr

NEWS

@@ -5,6 +5,10 @@ PHP                                                                        NEWS
 - Apache:
   . Fixed bug GH-9949 (Partial content on incomplete POST request). (cmb)
 
+- Date:
+  . Fixed bug GH-9891 (DateTime modify with unixtimestamp (@) must work like
+    setTimestamp). (Derick)
+
 - LDAP:
   . Fixed bug GH-10112 (LDAP\Connection::__construct() refers to ldap_create()).
     (cmb)

ext/date/php_date.c

@@ -2897,6 +2897,10 @@ static int php_date_modify(zval *object, char *modify, size_t modify_len) /* {{{
 		dateobj->time->us = tmp_time->us;
 	}
 
+	if (tmp_time->have_zone && tmp_time->zone_type == TIMELIB_ZONETYPE_OFFSET) {
+		timelib_set_timezone_from_offset(dateobj->time, tmp_time->z);
+	}
+
 	timelib_time_dtor(tmp_time);
 
 	timelib_update_ts(dateobj->time, NULL);

ext/date/tests/gh9891.phpt

@@ -0,0 +1,30 @@
+--TEST--
+Bug GH-9891 (DateTime modify with unixtimestamp (@) must work like setTimestamp)
+--FILE--
+<?php
+$m = new DateTime('2022-12-20 14:30:25', new DateTimeZone('Europe/Paris'));
+$m->modify('@1234567890');
+var_dump($m->getTimeStamp());
+
+echo "=======\n";
+
+$a = new DateTime('2022-11-01 13:30:00', new DateTimezone('America/Lima'));
+$b = clone $a;
+echo '$a: ', $a->format(DateTime::ATOM), "\n";
+echo '$b: ', $b->format(DateTime::ATOM), "\n";
+echo '$a: @', $a->getTimestamp(), "\n";
+echo '$b: setTimestamp(', $b->getTimestamp(), ")\n";
+$a->modify('@' . $a->getTimestamp());
+$b->setTimestamp($b->getTimestamp());
+echo '$a: ', $a->format(DateTime::ATOM), "\n";
+echo '$b: ', $b->format(DateTime::ATOM), "\n";
+?>
+--EXPECT--
+int(1234567890)
+=======
+$a: 2022-11-01T13:30:00-05:00
+$b: 2022-11-01T13:30:00-05:00
+$a: @1667327400
+$b: setTimestamp(1667327400)
+$a: 2022-11-01T18:30:00+00:00
+$b: 2022-11-01T13:30:00-05:00