Ticket #48358: 48358.2.diff

src/wp-includes/post.php

@@ -7436 +7436 @@
  *
  * @since 3.1.0
  *
- * @param int|WP_Post $post Post ID or post object.
+ * @param int|WP_Post|null $post Optional. Post ID or post object.
  * @return int|false Post parent ID (which can be 0 if there is no parent),
  *                   or false if the post does not exist.
  */
-function wp_get_post_parent_id( $post ) {
+function wp_get_post_parent_id( $post = null ) {
         $post = get_post( $post );
         if ( ! $post || is_wp_error( $post ) ) {
                 return false;

tests/phpunit/tests/post/wpGetPostParentId.php

@@ -33 +33 @@
                 $this->assertSame( self::$parent_post_id, wp_get_post_parent_id( self::$post_id ) );
         }
 
+        /**
+         * @ticket 48358
+         */
+        public function test_wp_get_post_parent_id_with_no_post_argument_default_to_global_post_id() {
+                $GLOBALS['post'] = get_post( self::$post_id );
+                $this->assertSame( self::$parent_post_id, wp_get_post_parent_id() );
+        }
+
         public function test_wp_get_post_parent_id_with_non_existing_id_default_to_global_post_id() {
                 $GLOBALS['post'] = get_post( self::$post_id );
                 $this->assertSame( self::$parent_post_id, wp_get_post_parent_id( 0 ) );