[wp-trac] [WordPress Trac] #62407: PHP Notice: Undefined offset in WordPress core when using template registered in a plugin via register_block_template() in WordPress 6.7

[WordPress Trac]

#62407: PHP Notice: Undefined offset in WordPress core when using template
registered in a plugin via register_block_template() in WordPress 6.7
------------------------------+--------------------------------------
 Reporter:  Grigory Volochiy  |      Owner:  (none)
     Type:  defect (bug)      |     Status:  new
 Priority:  normal            |  Milestone:  Awaiting Review
Component:  General           |    Version:  6.7
 Severity:  normal            |   Keywords:  needs-patch has-dev-note
  Focuses:  template          |
------------------------------+--------------------------------------
 Issue Description \\
 With the release of WordPress 6.7, the register_block_template() function
 allows plugins to register block templates. While this functionality
 operates as intended, it triggers a PHP notice about an undefined offset
 within the WordPress core. \\ \\

 Affected file: wp-includes/block-editor.php \\
 Line: 467 \\
 Code snippet: {{{#!php
 <?php
 $template_blocks    = parse_blocks( $current_template[0]->content );
 }}} \\ \\

 Cause of the Issue \\
 The get_block_templates() function now returns an array with a mix of
 numerical keys and associative keys where the associative keys are the
 registered template IDs via plugin (e.g., 'my-plugin//my-template')
 instead of numerical keys.
 The core code at block-editor.php line 467 expects $current_template to be
 a numerically indexed array.
 When an associative key is encountered, it leads to a PHP notice: Notice:
 Undefined offset: 0 in /wp-includes/block-editor.php on line 467. \\
 \\

 Impact \\
 PHP Notice: \\
 Notice: Undefined offset: 0 in /wp-includes/block-editor.php on line 467
 \\
 \\ \\

 Compatibility Issues: \\
 Existing plugin code that relies on numerical keys within the templates
 array does not anticipate associative keys, potentially causing further
 functional discrepancies beyond the PHP notice.\\
 \\
 \\
 Steps to Reproduce\\
 \\
 Environment Setup:\\
 WordPress Version: 6.7\\
 PHP Version: [PHP 7.4.33 (or higher)]\\
 Active Theme: [Twenty Twenty-Five (the notice appears with other themes
 too)]\\
 \\
 Procedure:\\
 Create a plugin that registers a block template using
 register_block_template().\\
 {{{#!php
 <?php
 function add_template() {

         $template_id = 'my-plugin//my-template';
         $existing_template = get_block_template( $template_id );

         if ( $existing_template || is_wp_error( $existing_template ) ) {
                 return;
         }

         $template_content =
                 '<!-- wp:template-part {"slug":"header"} /-->
                 <!-- wp:post-content {"lock":{"remove":true}} /-->
                 <!-- wp:template-part {"slug":"footer"} /-->';

         register_block_template( $template_id, [
                 'title' => __( 'Template title', 'my-plugin' ),
                 'description' => __( 'Template description', 'my-plugin'
 ),
                 'content' => $template_content,
                 'post_types'  => array( 'page' ),
         ] );
 }
 }}}
 \\\\
 Ensure DEBUG is set to true in wp-config.php to see the notice printed in
 HTML.\\
 Navigate to Pages -> Add New Page. Assign newly created template to the
 page. Publish the page. Reload the editor page.\\
 \\\\

 Observation:\\
 A PHP notice appears in the page HTML (it appears briefly in the editor
 and is better visible in browser developer tools when viewing the source
 HTML of the current page)\\

 Notice: Undefined offset: 0 in /wp-includes/block-editor.php on line 467\\
 And as additional result next PHP notice:\\
 Trying to get property 'content' of non-object in /wp-includes/block-
 editor.php on line 467\\
 \\
 Expected Behavior\\
 The WordPress core should handle templates registered via
 register_block_template() without triggering any PHP notices or errors.
 Specifically, the get_block_templates() function should return a
 numerically indexed array compatible with existing code expectations.\\
 \\
 Actual Behavior\\
 A PHP notice about an undefined offset is displayed, indicating that
 get_block_templates() returns an associative array with template IDs as
 keys instead of a numerically indexed array. This discrepancy leads to
 compatibility issues with existing code that expects numerical keys.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/62407>
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