check if exists before accessing object properties of $post->comment_count

[Presskopp]

I got a

Warning: Attempt to read property "comment_count" on null in [...]\wp-includes\general-template.php on line 3352

let's check if the object exists and the property is not empty.

Original line:

if ( $show_post_comments_feed && ( comments_open() || pings_open() || $post->comment_count > 0 ) ) {

possible patch, something like:

if ( $show_post_comments_feed 
     && isset( $post ) 
     && $post instanceof WP_Post 
     && ( comments_open() || pings_open() || $post->comment_count > 0 ) 
) {

[abcd95]

Hi, @Presskopp. Thanks for raising this.

Can you please sketch out the steps to reproduce the warning that you are observing?

Additional information, like the WP version or the theme version that you are using, will be helpful.

[Presskopp]

Hi @abcd95

I only get the warning when I provoke it. This happens during testing, not in productive operation. Nevertheless, I think the line should be changed.

You can provoke it by opening the Posts page and add a non existing page query like ?p=12345 to it.

Sorry, I should have mentioned it.

[dilipbheda]

@Presskopp I can't reproduce the issue. When I visit a page that doesn't exist, it shows a 404 page.

[Presskopp]

Did you define('WP_DEBUG', true); ?

[dilipbheda]

@Presskopp Yes

[Presskopp]

Interesting. I tried with Twenty Twenty-Five and Twenty Seventeen and I see the warning in both cases. Maybe it's because you have no posts at all or something!?

Please set permalinks to /%postname%/

[sabernhardt]

(Line 3352 is inside the feed_links_extra() function)

[Presskopp]

FYI: there's a function get_comments_number( $post = 0 ), which could be helpful here. Also there are more instances of $post->comment_count in 3 more core files.

[abcd95]

@Presskopp I followed everything you said, and I still don't see any warnings anywhere.

I did the following things -

Ensured I have enough posts in the system
Changed permalinks to /%postname%/
Accessed an invalid post ID (like localhost/blog/?p=12345 and even localhost/?p=12345)

However, I was only able to see the standard 404 Not Found page without any PHP warnings appearing. This matches the experience reported by @dilipbheda earlier.

Is there anything more to be done?

[Presskopp]

Weird. All I do after a fresh installation is

• define('WP_DEBUG', true);
• change permalinks to anything but 'Plain'
• set a Posts page
• open that Posts page and add a non existing page parameter like ?p=12345.
• reload the page
• see the warning

It makes no difference which theme is active (talking about standard themes)

[Presskopp]

As you can see on the screenshot, there's also an issue with the property "ID" using the Twenty Ten Theme. So we could open the scope of this ticket to a general check if objects and their properties exists, before assigning a value.

[indirabiswas27]

I have carefully followed all the steps outlined, but I was only presented with the default 404 Not Found page, and no warnings appeared.

[awetz583]

I see this error as well on the custom classic/hybrid theme I'm working on.

To reproduce I:

1. Go to a page that really does result in a 404 (like /nopenopenopenope/thisnomatch so it doesn't attempt to redirect to another post in the DB)
2. The Page loads fine, but I see the PHP warning Attempt to read property "comment_count" on null

I think this is because there is now way to get a comment_count on a 404 page.
if ( $show_post_comments_feed && ( comments_open() || pings_open() || $post->comment_count > 0 ) ) { ...

Here is the error stack trace for WP 6.8.2:

wp-includes/general-template.php:3352

feed_links_extra()
wp-includes/class-wp-hook.php:324

do_action('wp_head')
wp-includes/general-template.php:3192

wp_head()
wp-content/themes/my-theme/header.php:7

[awetz583]

For now, I can add this to our theme as a workaround to remove the warning:

<?php
add_action( 'template_redirect', function() {
    if ( is_404() ) {
        add_filter( 'feed_links_extra_show_post_comments_feed', '__return_false' );
    }
});

Replying to awetz583:

I see this error as well on the custom classic/hybrid theme I'm working on.

To reproduce I:

1. Go to a page that really does result in a 404 (like /nopenopenopenope/thisnomatch so it doesn't attempt to redirect to another post in the DB)
2. The Page loads fine, but I see the PHP warning Attempt to read property "comment_count" on null

I think this is because there is now way to get a comment_count on a 404 page.
if ( $show_post_comments_feed && ( comments_open() || pings_open() || $post->comment_count > 0 ) ) { ...

Here is the error stack trace for WP 6.8.2:

wp-includes/general-template.php:3352

feed_links_extra()
wp-includes/class-wp-hook.php:324

do_action('wp_head')
wp-includes/general-template.php:3192

wp_head()
wp-content/themes/my-theme/header.php:7

[Presskopp]

related: #64104

[johnjamesjacoby]

This happens specifically when show_on_front is set, because the "Queried Object" is the Page ID of the Posts landing page, which makes is_singular() return true.

Patch incoming.

[westonruter]

It wouldn't hurt to also include a $post instanceof WP_Post check as well, even though it is most likely that the global will have been set. There're no guarantees!

[johnjamesjacoby]

Replying to westonruter:

It wouldn't hurt to also include a $post instanceof WP_Post check as well, even though it is most likely that the global will have been set. There're no guarantees!

The surrounding code attempts to guarantee it here by mocking an empty WP_Post object:

https://core.trac.wordpress.org/browser/trunk/src/wp-includes/general-template.php#L3330

It just did not factor in the situation where a Singular queried object (home page) would simultaneously result in “no posts”. 🤣

[westonruter]

@johnjamesjacoby Here?

<?php
$id   = 0;
$post = get_post( $id );

That's not mocking an empty WP_Post object, is it? That seems to be just another way of doing $post = get_post() since an ID of 0 will result in the global $post being used. But if that global doesn't exist, then $post->comment_count would still issue a warning.

[westonruter]

This code originates in r19094 to work around the fact that get_post() used to pass the first arg by reference (​ref):

function &get_post(&$post, $output = OBJECT, $filter = 'raw')

The use of $post->comment_count originates in r10377 (​19577d0).

Trac ticket: https://core.trac.wordpress.org/ticket/63263

[johnjamesjacoby]

PR looks OK to me.

[westonruter]

In 61056:

General: Improve resilience of feed_links_extra() when global $post is not set.

This obtains the global post via get_queried_object() when is_singular().

Developed in ​https://github.com/WordPress/wordpress-develop/pull/10401

Props westonruter, johnjamesjacoby, Presskopp, abcd95, dilipbheda, sabernhardt, awetz583, indirabiswas27.
Fixes #63263.

Trac ticket: https://core.trac.wordpress.org/ticket/63263

[westonruter]

In 61058:

General: Add comment explaining use of queried object in feed_links_extra() instead of global $post.

Follow-up to [61056].

Props mukesh27, westonruter.
See #63263.

Committed in r61058.