Added support DateTimeInterface (PHP 5.5) if available

lib/Twig/Extension/Core.php

@@ -485,13 +485,15 @@ function twig_date_converter(Twig_Environment $env, $date = null, $timezone = nu
         $defaultTimezone = $timezone;
     }
 
-    if ($date instanceof DateTime) {
+    if ($date instanceof DateTime || $date instanceof DateTimeInterface) {
-        $date = clone $date;
+        $returningDate = new DateTime($date->format('c'));
         if (false !== $timezone) {
-            $date->setTimezone($defaultTimezone);
+            $returningDate->setTimezone($defaultTimezone);
+        } else {
+            $returningDate->setTimezone($date->getTimezone());
         }
 
-        return $date;
+        return $returningDate;
     }
 
     $asString = (string) $date;

test/Twig/Tests/Fixtures/filters/date_immutable.test

@@ -0,0 +1,35 @@
+--TEST--
+"date" filter
+--CONDITION--
+version_compare(phpversion(), '5.5.0', '>=')
+--TEMPLATE--
+{{ date1|date }}
+{{ date1|date('d/m/Y') }}
+{{ date1|date('d/m/Y H:i:s', 'Asia/Hong_Kong') }}
+{{ date1|date('d/m/Y H:i:s', timezone1) }}
+{{ date1|date('d/m/Y H:i:s') }}
+
+{{ date2|date('d/m/Y H:i:s P', 'Europe/Paris') }}
+{{ date2|date('d/m/Y H:i:s P', 'Asia/Hong_Kong') }}
+{{ date2|date('d/m/Y H:i:s P', false) }}
+{{ date2|date('e', 'Europe/Paris') }}
+{{ date2|date('e', false) }}
+--DATA--
+date_default_timezone_set('Europe/Paris');
+return array(
+    'date1' => new DateTimeImmutable('2010-10-04 13:45'),
+    'date2' => new DateTimeImmutable('2010-10-04 13:45', new DateTimeZone('America/New_York')),
+    'timezone1' => new DateTimeZone('America/New_York'),
+)
+--EXPECT--
+October 4, 2010 13:45
+04/10/2010
+04/10/2010 19:45:00
+04/10/2010 07:45:00
+04/10/2010 13:45:00
+
+04/10/2010 19:45:00 +02:00
+05/10/2010 01:45:00 +08:00
+04/10/2010 13:45:00 -04:00
+Europe/Paris
+America/New_York