Fix GH-10583: DateTime modify with tz pattern should not update linked timezone

Author: derickr

NEWS

@@ -16,6 +16,10 @@ PHP                                                                        NEWS
   . Fixed bug GH-10810 (Fix NUL byte terminating Exception::__toString()).
     (ilutov)
 
+- Date:
+  . Fixed bug GH-10583 (DateTime modify with tz pattern should not update
+    linked timezone). (Derick)
+
 - FPM:
   . Fixed bug GH-10611 (fpm_env_init_main leaks environ). (nielsdos)
   . Destroy file_handle in fpm_main. (Jakub Zelenka, nielsdos)

ext/date/php_date.c

@@ -2897,8 +2897,14 @@ 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);
+	/* Reset timezone to UTC if we detect a "@<ts>" modification */
+	if (
+		tmp_time->y == 1970 && tmp_time->m == 1 && tmp_time->d == 1 &&
+		tmp_time->h == 0 && tmp_time->i == 0 && tmp_time->s == 0 && tmp_time->us == 0 &&
+		tmp_time->have_zone && tmp_time->zone_type == TIMELIB_ZONETYPE_OFFSET &&
+		tmp_time->z == 0 && tmp_time->dst == 0
+	) {
+		timelib_set_timezone_from_offset(dateobj->time, 0);
 	}
 
 	timelib_time_dtor(tmp_time);

ext/date/tests/gh10583.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Bug GH-10583 (DateTime modify with tz pattern should not update linked timezone)
+--FILE--
+<?php
+
+$dt = new DateTime('2015-01-01 00:00:00+00:00');
+var_dump($dt->format('c'));
+var_dump($dt->modify('+1 s')->format('c'));
+
+$dt = new DateTimeImmutable('2015-01-01 00:00:00+00:00');
+var_dump($dt->format('c'));
+var_dump($dt->modify('+1 s')->format('c'));
+?>
+--EXPECT--
+string(25) "2015-01-01T00:00:00+00:00"
+string(25) "2015-01-01T00:00:00+00:00"
+string(25) "2015-01-01T00:00:00+00:00"
+string(25) "2015-01-01T00:00:00+00:00"