Block hooks are not applied to templates loaded via the Template registration API

[Aljullu]

Description

Apparently, block hooks are not being applied to templates registered by plugins using the Template registration API.

Step-by-step reproduction instructions

1. Install the Dynamic Copyright Date plugin, to have a block as an example.
2. Add this snippet to your site that (1) creates a template for posts, where only the Separator block is rendered and (2) hooks the Dynamic Copyright Date block to the Separator block:

register_block_template(
	'my-plugin//plugin-template',
	array(
		'title'       => 'Test Template',
		'description' => 'This is a test template',
		'content'     => '<!-- wp:separator {className":"is-style-dots"} --><hr class="wp-block-separator has-alpha-channel-opacity is-style-dots"/><!-- /wp:separator -->',
	)
);

add_action(
	'single_template_hierarchy',
	function () {
		return array( 'plugin-template' );
	}
);

add_filter(
	'hooked_block_types',
	function ( $hooked_block_types, $relative_position, $anchor_block_type, $context ) {
		if ( 'after' === $relative_position && 'core/separator' === $anchor_block_type ) {
			$hooked_block_types[] = 'dynamic-copyright-date/copyright-date-block';
		}
		return $hooked_block_types;
	},
	10,
	4
);

3. Create a new page and add the Separator block.
4. Now, in the frontend, visit a page (using the theme template) and a post (using the plugin template):
5. Notice the page correctly applies the block hook (adds the Dynamic Copyright Date block after the Separator block), while the post, doesn't.

Screenshots, screen recording, code snippet

Page	Post

Environment info

• WordPress 6.8.2.
• Plugins: Code Snippets and Dynamic Copyright Date Block.
• Themes used for testing: TT4 and TT5.

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

• Yes

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

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[Aljullu]

I think this issue could be solved by making templates loaded from the Template registration API go through insert_hooked_blocks_and_set_ignored_hooked_blocks_metadata. In other words, modifying this line as follows:

+			$matching_registered_templates = array_map(
+				function( $template ) {
+					$template->content = apply_block_hooks_to_content(
+						$template->content,
+						$template,
+						'insert_hooked_blocks_and_set_ignored_hooked_blocks_metadata'
+					);
+					return $template;
+				},
+				$matching_registered_templates
+			);
			$query_result = array_merge( $query_result, $matching_registered_templates );

[ockham]

Good spot, thank you for reporting! I was unaware of register_block_template (and WP_Block_Templates_Registry), which seem to have been added in WP 6.7. You're right that Block Hooks don't seem to be applied to block templates registered through this new feature (as opposed to the ones that are "automatically" loaded from theme files, or the DB objects created from the latter).

The fix you're suggesting looks good; it seems to be consistent with how we're applying Block Hooks to block templates provided by the theme, which is also at get_block_templates time (via _build_block_template_result_from_file and _build_block_template_result_from_post). For theme-provided block templates, the Block Hooks injection logic also had to be added to the get_block_template (singular!) function; at first glance, I don't see that function look for block templates in WP_Block_Templates_Registry 🤔 Maybe that's another bug.

[Adi-ty]

I have opened a corresponding ticket in Core Trac and referenced this issue for context https://core.trac.wordpress.org/ticket/63808 and opened a PR with suggested fix

[Aljullu]

For theme-provided block templates, the Block Hooks injection logic also had to be added to the get_block_template (singular!) function; at first glance, I don't see that function look for block templates in WP_Block_Templates_Registry 🤔 Maybe that's another bug.

Thanks for checking this, @ockham! From what I see, get_block_template() calls get_block_file_template() when the template can't be found in the database. That function ultimately calls _build_block_template_result_from_file() in theme templates which add the hooks. For plugin templates we aren't doing so, so hooks aren't added. Is that what you meant?

I guess it could be solved with something like:

	$block_template = WP_Block_Templates_Registry::get_instance()->get_by_slug( $slug );

+	$block_template->content = apply_block_hooks_to_content(
+		$block_template->content,
+		$block_template,
+		'insert_hooked_blocks_and_set_ignored_hooked_blocks_metadata'
+	);

I tested making a rest request to /wp-json/wp/v2/templates/twentytwentyfour//plugin-template and it seems to work. From a user perspective, I don't know if there is any way to test it other than making a request, though. 🤔

I have opened a corresponding ticket in Core Trac and referenced this issue for context https://core.trac.wordpress.org/ticket/63808 and opened a PR with suggested fix

Thanks for creating the ticket and the PR, @Adi-ty! I tested it and it's working well on my end. But let's see if we need to add it to get_block_file_template() as well before doing a full review.

[ockham]

For plugin templates we aren't doing so, so hooks aren't added. Is that what you meant?

More or less! I thought that plugin templates weren't taken into account at all by get_block_template() -- I didn't realize they were included one level down, by get_block_file_template(). So your suggested solution makes sense.

---

(More of a note to self, get_block_file_template() doesn't seem like the right place for getting the plugin template, as that function was meant to fetch a template from a file. We should consider moving the fetching of the plugin template -- and subsequent application of Block Hooks -- to get_block_template(), which is the high-level function to fetch a block template from either a file, the DB -- or, arguably, the template registry that was introduced in 6.7.)

[Aljullu]

Good points, @ockham! To be honest, I didn't think about that too much when working on the Template registration API.

IMO, plugin templates are more similar to theme templates than to templates saved in the database, that's why I added the logic that reads from the template registry in get_block_file_template(). But I also see the point that they could be considered a different type and be in get_block_template() instead.

Whatever we decide, the get_block_file_template() doc block will need to be updated. Because right now it's a bit confusing.

Just to make sure we move this discussion forward, as next steps I suggest:

1. For now, we add apply_block_hooks_to_content() to plugin templates in get_block_file_template(), as described in my previous comment. This could be added to @Adi-ty's PR, if that's fine for him.
2. We make a decision on whether plugin templates should be loaded directly in get_block_template() or from inside get_block_file_template(). We should make sure moving the code doesn't have unintended consequences.
3. Based on the decision in (2), we update the get_block_file_template() docblock.

How does it sound?

[ockham]

That sounds good to me!

[Adi-ty]

Thanks for the suggestions. I have updated the PR to include the fix for get_block_file_template() as well.

[Aljullu]

I think we can close this issue now that WordPress/wordpress-develop#9418 has been merged. Thank you both! 🙌