Calling wp_update_nav_menu_item() with an invalid taxonomy causes a fatal error

[dd32]

For background, please see ​https://github.com/WordPress/wordpress-importer/issues/164

When attempting to import a WXR which contains a Nav menu item that references a taxonomy that doesn't exist on the site, wp_update_nav_menu_item() will hit a fatal error.

PHP Fatal error:  Uncaught Error: Object of class WP_Error could not be converted to string in /wordpress/wp-includes/formatting.php:2
Stack trace:
#0 /wordpress/wp-includes/nav-menu.php(2): wp_specialchars_decode(Object(WP_Error))
#1 /wordpress/wp-content/plugins/wordpress-importer/class-wp-import.php(996): wp_update_nav_menu_item(3, 0, Array)
#2 /wordpress/wp-content/plugins/wordpress-importer/class-wp-import.php(653): WP_Import->process_menu_item(Array)
#3 /wordpress/wp-content/plugins/wordpress-importer/class-wp-import.php(89): WP_Import->process_posts()
#4 /wordpress/wp-content/plugins/wordpress-importer/class-wp-import.php(65): WP_Import->import('/wordpress/wp-c...')
#5 /wordpress/wp-admin/admin.php(2): WP_Import->dispatch()
#6 {main}
  thrown in /wordpress/wp-includes/formatting.php on line 2

It appears that invalid post type archives are handled, just not missing taxonomies.

Relevant lines:
https://core.trac.wordpress.org/browser/tags/6.6/src/wp-includes/nav-menu.php?marks=496,509#L484
$original_title will be a WP_Error for a non-existent taxonomy in $args['menu-item-object'].

[dd32]

Untested, but it might be enough to simply avoid the fatal on update and leave the menu code to resolve the issue elsewhere:

nav-menu.php

@@ -491 +491 @@
                 $args['menu-item-url'] = '';
 
                 $original_title = '';
-                if ( 'taxonomy' === $args['menu-item-type'] ) {
+                if ( 'taxonomy' === $args['menu-item-type'] && taxonomy_exists( $args['menu-item-object'] ) ) {
                         $original_parent = get_term_field( 'parent', $args['menu-item-object-id'], $args['menu-item-object'], 'raw' );
                         $original_title  = get_term_field( 'name', $args['menu-item-object-id'], $args['menu-item-object'], 'raw' );
                 } elseif ( 'post_type' === $args['menu-item-type'] ) {

[mukesh27]

The changes you suggest works but the get_term_field return $term here ​https://github.com/WordPress/wordpress-develop/blob/6.6/src/wp-includes/taxonomy.php#L1221-L1236, If it return error then it should return null instead of $term

what do you think?

Trac ticket: https://core.trac.wordpress.org/ticket/61799

[dd32]

Replying to mukesh27:

If it return error then it should return null instead of $term

It is 'weird' that it returns an empty string in other cases of error, but not this one.
But given it's documented as returning an empty string, and has done so since [5726] it's not worth changing IMHO.

[SergeyBiryukov]

In 58854:

Menus: Check if taxonomy term exists in wp_update_nav_menu_item().

When inserting a term from a non-existing taxonomy as a nav item, the post_title property should be empty, and the function should not throw a fatal error for wp_specialchars_decode().

Includes bringing some consistency to similar checks for post types and post type archives in the same code fragment.

Follow-up to [14283], [14450], [35382], [36095].

Props dd32, narenin, mukesh27, SergeyBiryukov.
Fixes #61799.

Thanks for the PR! Merged in r58854.