[wp-trac] [WordPress Trac] #49332: method Walker_Nav_Menu::start_el should not call filter the_title on non post menu items

[WordPress Trac]

#49332: method Walker_Nav_Menu::start_el should not call filter the_title on non
post menu items
--------------------------+-----------------------------
 Reporter:  erwinbr       |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  General       |    Version:  5.3.2
 Severity:  normal        |   Keywords:
  Focuses:                |
--------------------------+-----------------------------
 I am working on a site with a.o:
 - WP 5.3.2
 - WPML 4.3.6
 - Estatik-pro 3.8.1
 - Divi 3.29.1

 And am seeing the following notices in the debug log:

 PHP Notice:  Trying to get property 'post_type' of non-object in .\wp-
 content\plugins\estatik-pro_3.8.1\functions.php on line 386
 PHP Stack trace:
 PHP   1. {main}() .\index.php:0
 PHP   2. require() .\index.php:17
 PHP   3. require_once() .\wp-blog-header.php:19
 PHP   4. include() .\wp-includes\template-loader.php:98
 PHP   5. get_header() .\wp-content\themes\Divi\single.php:3
 PHP   6. locate_template() .\wp-includes\general-template.php:41
 PHP   7. load_template() .\wp-includes\template.php:671
 PHP   8. require_once() .\wp-includes\template.php:722
 PHP   9. wp_nav_menu() .\wp-content\themes\Divi\header.php:263
 PHP  10. walk_nav_menu_tree() .\wp-includes\nav-menu-template.php:217
 PHP  11. Walker_Nav_Menu->walk() .\wp-includes\nav-menu-template.php:583
 PHP  12. Walker_Nav_Menu->display_element() .\wp-includes\class-wp-
 walker.php:244
 PHP  13. Walker_Nav_Menu->display_element() .\wp-includes\class-wp-
 walker.php:156
 PHP  14. Walker_Nav_Menu->start_el() .\wp-includes\class-wp-walker.php:144
 PHP  15. apply_filters() .\wp-includes\class-walker-nav-menu.php:213
 PHP  16. WP_Hook->apply_filters() .\wp-includes\plugin.php:206
 PHP  17. es_the_title_filter() .\wp-includes\class-wp-hook.php:288
 (If you want, I can post a stack trace with variable info.)

 Diving into this problem I noticed that:
 - The main nav menu does not only contain items that are a post, but also
 the language switcher flags (added by WPML)
 - On line 213 of file wp-includes/class-walker-nav-menu.php,
 Walker_Nav_Menu->start_el() calls
 {{{
 apply_filters( 'the_title', $item->title, $item->ID );
 }}}
   for all items in the menu, be it posts or other items.
 - Estatik-pro hooks into this filter and calls get_post() on the given ID
 which is not a post ID:
 {{{#!php
 <?php
 function es_the_title_filter( $title, $id = null ) {
         global $es_settings;
         $post = get_post( $id );
         if ( is_single() && $post->post_type ==
 Es_Property::get_post_type_name() ) {
                 ...
         }

         return $title;
 }
 add_filter( 'the_title', 'es_the_title_filter', 10, 2 );
 }}}

 Who is wrong?
 - WPML: by adding non-posts to menu's.
 - Estatik-pro for not checking that the filter is called for non-posts?
 - Walker_Nav_Menu->start_el() for unconditionally calling the filter
 'the_title' on all menu-items?

 IMO:
 - Menu-items can be other things than posts, and WPML shows that this is
 indeed possible.
 - The filter 'the_title' seems to be explicitly for altering a post title,
 not titles of images, non-post menu-items, or whatever. So Estatik-pro
 should not have to check that the given ID is indeed from a post.
 - Walker_Nav_Menu->start_el() calls its own filter 'nav_menu_item_title'
 directly after calling the 'the_title' filter (though still documenting
 $item as a WP_Post).

 Based on the above, my conclusion is: Walker_Nav_Menu->start_el() should
 check if the item is a WP_Post before calling the 'the_title' filter.

 If you agree, solving this should be easy, surround line 213 with
 {{{
 if ( $item instanceof WP_Post ) { ... }
 }}}
 However, in a lot of places it is documented that a menu-item is a WP_Post
 and changing that may take considerably more work.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/49332>
WordPress Trac <https://core.trac.wordpress.org/>
WordPress publishing platform