From e9fc71bbbe8bb5353dbc874e0496ae52e09681b3 Mon Sep 17 00:00:00 2001
From: Sergey Biryukov <sergeybiryukov@git.wordpress.org>
Date: Thu, 20 Jun 2019 14:10:44 +0000
Subject: [PATCH] Date/Time: Eliminate use of `date_default_timezone_set()` for
 determining DST status on General Options screen.

Time calculations should not need to rely on manipulating global PHP configuration state.

Props Rarst.
Fixes #46483.

git-svn-id: https://develop.svn.wordpress.org/trunk@45556 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-admin/options-general.php | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/src/wp-admin/options-general.php b/src/wp-admin/options-general.php
index dad6f94f3f..ff50e6fbd4 100644
--- a/src/wp-admin/options-general.php
+++ b/src/wp-admin/options-general.php
@@ -252,10 +252,10 @@ if ( empty( $tzstring ) ) { // Create a UTC+- zone if no timezone string exists
 <p class="timezone-info">
 <span>
 	<?php
-	// Set TZ so localtime works.
-	date_default_timezone_set( $tzstring );
-	$now = localtime( time(), true );
-	if ( $now['tm_isdst'] ) {
+	$now = new DateTime( 'now', new DateTimeZone( $tzstring ) );
+	$dst = (bool) $now->format( 'I' );
+
+	if ( $dst ) {
 		_e( 'This timezone is currently in daylight saving time.' );
 	} else {
 		_e( 'This timezone is currently in standard time.' );
@@ -296,8 +296,6 @@ if ( empty( $tzstring ) ) { // Create a UTC+- zone if no timezone string exists
 			_e( 'This timezone does not observe daylight saving time.' );
 		}
 	}
-	// Set back to UTC.
-	date_default_timezone_set( 'UTC' );
 	?>
 	</span>
 </p>