Ticket #45882: 45882.patch

src/wp-includes/class-wp-block-type.php

@@ -198 +198 @@
          * @return array Array of attributes.
          */
         public function get_attributes() {
-                return is_array( $this->attributes ) ?
+                $attributes = is_array( $this->attributes ) ?
                         array_merge(
                                 $this->attributes,
                                 array(
+                                        'className' => array(
+                                                'type' => 'string',
+                                        ),
                                         'layout' => array(
                                                 'type' => 'string',
                                         ),
@@ -208 +211 @@
                                 )
                         ) :
                         array(
+                                'className' => array(
+                                        'type' => 'string',
+                                ),
                                 'layout' => array(
                                         'type' => 'string',
                                 ),
                         );
+                return apply_filters( 'block_attributes', $attributes, $this );
         }
 }