Ticket #36163: 36163.diff

src/wp-includes/class-walker-nav-menu.php

@@ -57 +57 @@
                         $t = "\t";
                         $n = "\n";
                 }
-                $indent = str_repeat( $t, $depth );
-                $output .= "{$n}{$indent}<ul class=\"sub-menu\">{$n}";
+                $indent  = str_repeat( $t, $depth );
+                $classes = array( 'sub-menu' );
+
+                /**
+                 * Filters the CSS class(es) applied to a submenu container element.
+                 *
+                 * @since 4.8.0
+                 *
+                 * @param array    $classes The CSS classes that are applied to the submenu item's `<ul>` element.
+                 * @param stdClass $args    An object of wp_nav_menu() arguments.
+                 * @param int      $depth   Depth of menu item. Used for padding.
+                 */
+                $class_names = join( ' ', apply_filters( 'nav_menu_submenu_css_class', array_filter( $classes ), $args, $depth ) );
+                $class_names = $class_names ? ' class="' . esc_attr( $class_names ) . '"' : '';
+
+                $output .= "{$n}{$indent}<ul" . $class_names . ">{$n}";
         }
 
         /**