[wp-trac] [WordPress Trac] #64216: Undefined array key 0 in wp-includes/block-editor.php on line 468

[WordPress Trac]

#64216: Undefined array key 0 in wp-includes/block-editor.php on line 468
--------------------------+-----------------------------
 Reporter:  d4z_c0nf      |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Editor        |    Version:  6.8.3
 Severity:  normal        |   Keywords:
  Focuses:                |
--------------------------+-----------------------------
 Hi there,
 I'm using `register_block_template` (with WordPress version 6.8.3) to
 register a custom template from within a plugin for a specific custom post
 type (the template slug I chose isn't in the `single-{cpt_name}` form, not
 sure it matters...).

 The new template shows up in the template picker (select) on the cpt
 **block editor screen**, but as soon as I choose it, I get the following
 PHP warning logged:

 {{{
 [07-Nov-2025 13:55:18 UTC] PHP Warning:  Undefined array key 0 in
 /shared/httpd/wptest/wordpress/wp-includes/block-editor.php on line 468
 }}}
 https://github.com/WordPress/WordPress/blob/ba9e7f97f08a7fbb88fbfa35641bcc230500b37a
 /wp-includes/block-editor.php#L468

 I've found the issue being here:
 https://github.com/WordPress/WordPress/blob/bc7f6b462ddd8cfb4a095da8a9af9311e4bca3ab
 /wp-includes/block-template-utils.php#L1243

 where {{{$query_result}}}, a standard array (of `WP_Template`), is merged
 with `$matching_registered_templates`, which is basically the associative
 array in the form
 `$template_name => $template pairs`
 resulting from
 https://github.com/WordPress/WordPress/blob/bc7f6b462ddd8cfb4a095da8a9af9311e4bca3ab
 /wp-includes/block-template-utils.php#L1218

 see:
 https://developer.wordpress.org/reference/classes/wp_block_templates_registry/get_by_query/#return


 The issue (warning) could be easily fixed by turning
 https://github.com/WordPress/WordPress/blob/bc7f6b462ddd8cfb4a095da8a9af9311e4bca3ab
 /wp-includes/block-template-utils.php#L1243

 Into:
 {{{#!php
 $query_result = array_merge( $query_result, array_values(
 $matching_registered_templates ) );
 }}}


 This only happens in the **block editor** but I'm not sure I should open
 the issue on https://github.com/WordPress/gutenberg/issues/new/choose as
 suggested, because the code generating the issue is in wp core, right?

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/64216>
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