Ticket #22401: 22401.diff

src/wp-includes/theme.php

@@ -746 +746 @@
          *
          * @param string   $new_name  Name of the new theme.
          * @param WP_Theme $new_theme WP_Theme instance of the new theme.
+         * @param WP_Theme $old_theme WP_Theme instance of the old theme.
          */
-        do_action( 'switch_theme', $new_name, $new_theme );
+        do_action( 'switch_theme', $new_name, $new_theme, $old_theme );
 }
 
 /**