Ticket #28636: 28636-handle-zero-timestamp.patch

src/wp-includes/functions.php

@@ -176 +176 @@
          */
         if ( 'U' === $format ) {
                 $date = $timestamp;
-        } elseif ( $gmt && ! $timestamp_with_offset ) { // Current time in UTC.
+        } elseif ( $gmt && ( false === $timestamp_with_offset ) ) { // Current time in UTC.
                 $date = wp_date( $format, null, new DateTimeZone( 'UTC' ) );
-        } elseif ( ! $timestamp_with_offset ) { // Current time in site's timezone.
+        } elseif ( false === $timestamp_with_offset ) { // Current time in site's timezone.
                 $date = wp_date( $format );
         } else {
                 /*

tests/phpunit/tests/date/dateI18n.php

@@ -19 +19 @@
                 $this->assertEquals( $wp_timestamp, date_i18n( 'U', 'invalid' ), '', 5 );
         }
 
+        public function test_should_handle_zero_timestamp() {
+                $timezone = 'Europe/Kiev';
+                update_option( 'timezone_string', $timezone );
+
+                $datetime = DateTimeImmutable::createFromFormat(
+                        'Y-m-d H:i:s',
+                        '1970-01-01 00:00:00',
+                        new DateTimeZone( $timezone )
+                );
+                $rfc3339  = $datetime->format( DATE_RFC3339 );
+
+                $this->assertEquals( 0, date_i18n( 'U', 0 ) );
+                $this->assertEquals( $rfc3339, date_i18n( DATE_RFC3339, 0 ) );
+        }
+
         public function test_should_format_date() {
                 $this->assertEquals( strtotime( gmdate( 'Y-m-d H:i:s' ) ), strtotime( date_i18n( 'Y-m-d H:i:s' ) ), 'The dates should be equal', 2 );
         }