Duplicated <title> tag

[rufus87]

Description

There is a great possibility to overwrite templates in FSE mod. But as soon as any template is overwritten and it content is served from database, <title> tag rendered in is duplicated, because there are 2 actions callbacks wit different names attached to 'wp_head' action:

1. add_action( 'wp_head', '_block_template_render_title_tag', 1 ); in wp-includes/block-template.php line 84
2. add_action( 'wp_head', 'gutenberg_render_title_tag', 1 ); in wp-content/plugins/gutenberg/lib/full-site-editing/template-loader.php line 100

this happens only if FSE theme template is edited and saved in FSE mod in database.

Step-by-step reproduction instructions

1. Enable any FSE theme
2. Overwrite any page/post template in FSE
3. Render page/post

Screenshots, screen recording, code snippet

Environment info

No response

Pre-checks

• I have searched the existing issues.
• I have tested with all plugins deactivated except Gutenberg.

[fwazeter]

EDIT: Seems another member was able to remove / comment the lines and the issue went away - I tested across multiple browsers, but I'm going to assume that my experiment below is caused by caching or local being weird.

Referencing conversation happening in #core-editor slack about this.

TT1 Blocks Testing
Gutenberg File Linked (template-loader.php).

The viewport meta tag is also being repeated when a wp_template CPT is loaded, not just the title tag.

<meta name="viewport" content="width=device-width, initial-scale=1">

Removed lines 94-100 in GB template-loader.php:

	// Add hooks for template canvas.
	// Add viewport meta tag.
	add_action( 'wp_head', 'gutenberg_viewport_meta_tag', 0 );

	// Render title tag with content, regardless of whether theme has title-tag support.
	remove_action( 'wp_head', '_wp_render_title_tag', 1 );    // Remove conditional title tag rendering...
	add_action( 'wp_head', 'gutenberg_render_title_tag', 1 ); // ...and make it unconditional.

Reloaded plugin, the same error occurs when saving a brand new template (saved a new one in case the old edited file did not re-render on plugin code change).

It appears like there is another file / call somewhere that is causing the duplication.

[gziolo]

It looks like it's an issue with how the same functionality is handled in the plugin to bridge older versions of WordPress. Related part here that uses gutenberg_render_title_tag callback:

gutenberg/lib/full-site-editing/template-loader.php

Lines 98 to 100 in 0028d20

	// Render title tag with content, regardless of whether theme has title-tag support.
	remove_action( 'wp_head', '_wp_render_title_tag', 1 ); // Remove conditional title tag rendering...
	add_action( 'wp_head', 'gutenberg_render_title_tag', 1 ); // ...and make it unconditional.

In the WordPress core it's handled with _block_template_render_title_tag :

https://github.com/WordPress/wordpress-develop/blob/b97fe776da274ed6349c795d495dcb72968e698f/src/wp-includes/block-template.php#L82-L84

The simplest approach would be to remove the wp_head action with _block_template_render_title_tag callback in the Gutenberg plugin. There might be also room for improvements in how we polyfill older versions of WordPress that don't have the functionality added in WP 5.8.

[fwazeter]

Technically, couldn't the polyfill be as simple as a WP Version check in the template loader in GB?

[gziolo]

Technically, couldn't the polyfill be as simple as a WP Version check in the template loader in GB?

Sure, the usual approach used in the plugin is to check if the function is defined, so here if there is no _block_template_render_title_tag then you either define the same function or define a different one and register in a hook

[fwazeter]

That makes sense, at scale version tracking for different functions would become a nightmare over updates.

[jdevalk]

@gziolo @mtias this is a very dangerous issue, so please make sure the proposed fixes work with SEO plugins like Yoast SEO and others too. Currently it doesn’t seem to.