gutenberg_locate_block_template slicing template slugs

[shramee]

Description

TLDR

Check if specificity $index of the located php $template is not false before clearing out the template candidates $templates in gutenberg_locate_block_template

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Function gutenberg_locate_block_template trims $templates (template candidates) even when located php template doesn't match php candidates. This breaks template lookups for custom post types (product in my case) on lib/compat/wordpress-5.9/block-template.php:61.

The comment line says,

// If the template hiearchy algorithm has successfully located a PHP template file,
// we will only consider block templates with higher or equal specificity.

for product post type $template is ./wp-includes/template-canvas.php, which doesn't seem specific to me at all.

Possible Solution

Just check if the $index is not false before splicing the array.

Step-by-step reproduction instructions

1. Create an FSE theme.
2. Add single-product.html template.
3. Notice it doesn't work.

Screenshots, screen recording, code snippet

Environment info

Gutenberg Version 12.2.0
WordPress Version 5.8.2

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

No