get_coauthors() and is_coauthor_for_post() with faulty condition

[biophonc]

Environment: PHP 8.0, WP 5.9+

Hi, my PHP log is flooded with these entries for a while:

[08-Jun-2022 10:10:10] WARNING: [pool foo] child 32581 said into stderr: "NOTICE: PHP message: PHP Warning: Attempt to read property "ID" on int in /var/www/foo/wp-content/plugins/co-authors-plus/template-tags.php on line 13"

• same issue on line 94

Basically, it's this condition:

if ( ! $post_id && $post ) { 
    $post_id = $post->ID;
}

Both $post_id and $post are integers. This means, that in get_coauthors() the $post_id will always be 0, resulting in, that the final filter will always be called with these values:

$coauthors = apply_filters( 'get_coauthors', [], 0);

The function is_coauthor_for_post() will permanently return early, with the value false because of this.

[lschuyler]

Hi @biophonc,

If this is still happening on your site, could you try outputting the global post object before the get_coauthors function is called to check its value?

It sounds like the post object has been inadvertently set to an integer, maybe in your theme or by another plugin or with something you're testing? Or possibly, could be calling get_coauthors from outside the loop where the post object doesn't exist?

[biophonc]

Hi @lschuyler,

Unfortunately I'm currently using a patched version of co authors (using this repo as upstream) but I'll prepare a test to see whether it's most likely caused by a 3rd party plugin, my theme or the co authors plugin.

[biophonc]

Hi @lschuyler,

I finally have found the time to investigate the issue further, and you were right, it was caused by my theme that:

1. uses global $post in one template, without being encapsulated (haven't noticed it earlier)
2. included template parts then inherit the object/variable
3. and in one template was a foreach loop for a SearchWP result set, that simplified did this:

   foreach ($related_content as $post) { // note: $post is still global here and thus gets overwritten
   setup_postdata($post); 
   }
   wp_reset_postdata(); 

I've also tested it with a fresh installation of WP 6.0 on PHP 8, with the twentyone theme and everything works fine as expected :-) This means it's not a Co-Authors-Plus bug.

I feel so stupid right now, because the cause was so obvious :facepalm:. This probably happens only, when you work on a codebase for 5 years+ and it's your own ^^

Thanks!