Date/Time: Make sure `get_post_time()` keeps UTC time on timezone change.

Add `$source` parameter to `get_post_datetime()` to instantiate from local or UTC time in database.

Props Rarst, david.binda.
Reviewed by azaozz, SergeyBiryukov.
Fixes #48384.
Built from https://develop.svn.wordpress.org/trunk@46580


git-svn-id: http://core.svn.wordpress.org/trunk@46377 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/general-template.php

@@ -2565,7 +2565,8 @@ function get_post_time( $d = 'U', $gmt = false, $post = null, $translate = false
 		return false;
 	}
 
-	$datetime = get_post_datetime( $post );
+	$source   = ( $gmt ) ? 'gmt' : 'local';
+	$datetime = get_post_datetime( $post, 'date', $source );
 
 	if ( false === $datetime ) {
 		return false;
@@ -2606,26 +2607,48 @@ function get_post_time( $d = 'U', $gmt = false, $post = null, $translate = false
  *
  * The object will be set to the timezone from WordPress settings.
  *
+ * For legacy reasons, this function allows to choose to instantiate from local or UTC time in database.
+ * Normally this should make no difference to the result. However, the values might get out of sync in database,
+ * typically because of timezone setting changes. The parameter ensures the ability to reproduce backwards
+ * compatible behaviors in such cases.
+ *
  * @since 5.3.0
  *
  * @param int|WP_Post $post   Optional. WP_Post object or ID. Default is global `$post` object.
- * @param string      $field Optional. Post field to use. Accepts 'date' or 'modified'.
+ * @param string      $field  Optional. Published or modified time to use from database. Accepts 'date' or 'modified'.
+ *                            Default 'date'.
+ * @param string      $source Optional. Local or UTC time to use from database. Accepts 'local' or 'gmt'.
+ *                            Default 'local'.
  * @return DateTimeImmutable|false Time object on success, false on failure.
  */
-function get_post_datetime( $post = null, $field = 'date' ) {
+function get_post_datetime( $post = null, $field = 'date', $source = 'local' ) {
 	$post = get_post( $post );
 
 	if ( ! $post ) {
 		return false;
 	}
 
+	$wp_timezone = wp_timezone();
+
+	if ( 'gmt' === $source ) {
+		$time     = ( 'modified' === $field ) ? $post->post_modified_gmt : $post->post_date_gmt;
+		$timezone = new DateTimeZone( 'UTC' );
+	} else {
 		$time     = ( 'modified' === $field ) ? $post->post_modified : $post->post_date;
+		$timezone = $wp_timezone;
+	}
 
 	if ( empty( $time ) || '0000-00-00 00:00:00' === $time ) {
 		return false;
 	}
 
-	return date_create_immutable_from_format( 'Y-m-d H:i:s', $time, wp_timezone() );
+	$datetime = date_create_immutable_from_format( 'Y-m-d H:i:s', $time, $timezone );
+
+	if ( false === $datetime ) {
+		return false;
+	}
+
+	return $datetime->setTimezone( $wp_timezone );
 }
 
 /**
@@ -2637,7 +2660,8 @@ function get_post_datetime( $post = null, $field = 'date' ) {
  * @since 5.3.0
  *
  * @param int|WP_Post $post  Optional. WP_Post object or ID. Default is global `$post` object.
- * @param string      $field Optional. Post field to use. Accepts 'date' or 'modified'.
+ * @param string      $field Optional. Published or modified time to use from database. Accepts 'date' or 'modified'.
+ *                           Default 'date'.
  * @return int|false Unix timestamp on success, false on failure.
  */
 function get_post_timestamp( $post = null, $field = 'date' ) {
@@ -2729,7 +2753,8 @@ function get_post_modified_time( $d = 'U', $gmt = false, $post = null, $translat
 		return false;
 	}
 
-	$datetime = get_post_datetime( $post, 'modified' );
+	$source   = ( $gmt ) ? 'gmt' : 'local';
+	$datetime = get_post_datetime( $post, 'modified', $source );
 
 	if ( false === $datetime ) {
 		return false;

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-RC2-46579';
+$wp_version = '5.3-RC2-46580';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.