PHP deprecation notice in wp_title()

[nexbridge]

I'm getting the following warning on what is currently the latest version of WordPress:

PHP Deprecated:  explode(): Passing null to parameter #2 ($string) of type string is deprecated in /wp-includes/general-template.php on line 1425

This is the line in question:

$title_array = apply_filters( 'wp_title_parts', explode( $t_sep, $title ) );

The PHP version is 8.2.

[Tussendoor]

We are experiencing the same problem. It occurs on a dynamic post which we are creating on runtime.

Ways to reproduce:

1. Add a rewrite tag to be able to catch a custom query

   <?php
   add_rewrite_tag('%rewrite_tag_example%', '([^&]+)');
   

2. Add a rewrite rule for the rewrite tag

   <?php
   add_rewrite_rule('basepage/([^/]*)/?', 'index.php?rewrite_tag_example=$matches[1]', 'top');
   

3. Register a template with template_include

   <?php
   add_filter('template_include', 'registerFrontendTemplate', 9999);
   

4. Add the registerFrontendTemplate function with a custom query to dynamically populate a template

   <?php
   /**
    * Register the template file
    *
    * @param string $template
    * @return string
    */
   function registerFrontendTemplate(string $template)
   {
       if (empty(get_query_var('rewrite_tag_example'))) {
           return $template;
       }
   
       // Add custom query here. To get data from a custom database table for 
       // example. Use the custom query variable to get postdata dynamically 
       // based on the request
   
       return locate_template('template/single.php');
   }
   

5. Refresh the permalinks by navigating to the permalinks settings in the WordPress admin.

6. Go to the generated frontend page: https:/example.com/basepage/test. With that URL the "rewrite_tag_example" query variable is filled with "test".

7. On this page the <title> HTML-element will show the deprecation warning. This is because in wp-includes/general-template.php the wp_title function call the single_post_title function via:

   <?php
   // If there is a post.
   if ( is_single() || ( is_home() && ! is_front_page() ) || ( is_page() && ! is_front_page() ) ) {
       $title = single_post_title( '', false );
   }
   

And the single_post_title function returns null because of:

<?php
if ( ! isset( $_post->post_title ) ) {
   return;
}

Possible solution
We could make the single_post_title function return a string value. But this does not solve the problem for other possible occurances of this error that are possibly triggered by the wp_title function. So that requires changing the functions below to always return a string instead of string|void:

• single_post_title
• post_type_archive_title
• single_term_title
• single_term_title
• post_type_archive_title

As the default value of $title is already an empty string (and not null) in the wp_title function we could try this for each occurance of those functions in wp_title:

<?php
// If there is a post.
if ( is_single() || ( is_home() && ! is_front_page() ) || ( is_page() && ! is_front_page() ) ) {
    $title ??= single_post_title( '', false );
}

The Null Coalescing Assignment operator (??=) does require PHP 7.4 tho.

Hope this helps! :)

[michaelreetz]

Perhaps it would be better to just do the Null coalescing operator inside the explode.

<?php
/**
 * Filters the parts of the page title.
 *
 * @since 4.0.0
 *
 * @param string[] $title_array Array of parts of the page title.
 */
$title_array = apply_filters( 'wp_title_parts', explode( $t_sep, $title ?? '') ); 

This feels to me like what the code would have done in previous versions. And it would be compatible to php7.0.

[Tussendoor]

Replying to michaelreetz:

Yes that seems like a good approach!

[nexbridge]

Just to say that this is still happening in the latest version (6.5.5). I notice that the ticket status is currently "awaiting review" - how long does it normally take for a ticket to be reviewed?

[nexbridge]

Just to say that this is still happening in 6.6.1, however the line number has now changed to 1440.

[nexbridge]

I've now added a as per the suggestion by @michaelreetz.

[o----o]

Same here.
The problem occurs at least in my case when on custom route where there is no "title" parameter as it is on default WP views.

WP Version 6.6.2

[Beee]

Still happening in 6.7.

When will this fix be applied ? This error is kind of annoying.

[nexbridge]

Confirmed that this is still happening in 6.7.1, and the line number is now 1439.

[sabernhardt]

#63333 was marked as a duplicate.

[neo2k23]

@sabernhardt

Setting a static blog page leaving the homepage set to --select-- instantly creates the issue and is easier to reproduce the issue than by recoding or adding code as mentioned above as "steps to recreate it".

I wonder why resolving this issue in the core code takes that long (more than 11 months) as the fix is easy and simple to apply and would have saved me a lot of time today.

Any theme using the wptitle function with a static blog page trigger the deprecated message.

Thank you

[SirLouen]

Replying to neo2k23:

I wonder why resolving this issue in the core code takes that long (more than 11 months) as the fix is easy and simple to apply and would have saved me a lot of time today.

Long story short

[sabernhardt]

PR 8729 removes the deprecation notice and passes the tests.

I'll also suggest an alternative in case it might be better:

	// If there is a post.
	if ( is_single() || ( is_home() && ! is_front_page() ) || ( is_page() && ! is_front_page() ) ) {
		$title = single_post_title( '', false );
		if ( empty( $title ) ) {
			$title = '';
		}
	}

[neo2k23]

@sabernhardt This is all about wordpress being php compatible. Why checking for a empty($title) in above code as the cause of the problem is the filter with the explode call in general-template.php on line 1439.

The only logical fix would be checking $title before the filter is called or in that explode call on line 1439 and if $title is empty make sure its a empty string.

There are many cases why one can land on that line with $title == null.

The given solution in https://core.trac.wordpress.org/attachment/ticket/61352/general-template.diff

requires at least php 7.4 and i am not sure if the latest minimum requirement for php in wordpress already has been set to 7.4 or still is on 7.2

​https://make.wordpress.org/core/handbook/references/php-compatibility-and-wordpress-versions/

[sabernhardt]

My alternative suggestion, whether it includes empty() or null === $title, would only be a good idea if some situation should give an error (that is, if it ever indicates doing something wrong). I did not create a because I am not convinced my direction is better than PR 8729.

If this function's deprecation notice should be silenced in all cases,
wp_resolve_block_style_variation_ref_values() already established a precedent with
explode( '.', $value['ref'] ?? '' ) and comment:2 says that syntax is compatible with PHP 7.0.

[neo2k23]

@sabernhardt you are right it was introduced in php 7.0 ​https://www.php.net/manual/en/migration70.new-features.php

I doubt if one is interested in false doing it wrongs which also could be the case and as we have now when f.e. one sets a static blog page.

I rather see it silenced for all than getting these false incorrect deprecated messages. Moreover even if the title is empty the correct one is still presented after the filter has ran. Which was the case with the static blog page.