Iframe: Stylesheet was not properly added error

[renatho]

Description

In the latest version of Gutenberg, I started receiving an error in the console. It was introduced here: https://github.com/WordPress/gutenberg/pull/31870/files#diff-ab17abd38e687edd56573694ae3017e105e96b319571c190e9d4705c1872bc9cR58

Basically, the error is happening every time I select a block that contains the iframe to the sidebar, and this block enqueues styles through the following hooks: enqueue_block_assets / enqueue_block_editor_assets.

Since it's something new and we need backward compatibility in plugins, I wonder if it should be just a deprecation warning instead of an error. Or is there any other approach we could use for older WP versions along with the new approach?

Also, if we have styles shared between different blocks, how could we do that? Should editorStyle and style support arrays?

Step-by-step reproduction instructions

1. Add a hook (enqueue_block_assets or enqueue_block_editor_assets) to enqueue styles.
2. Go to the editor.
3. Open the browser console.
4. Select a block which contains styles (to have the iframe in the sidebar with the thumbnail for the different styles).

Screenshots, screen recording, code snippet

Environment info

• WordPress 5.8 / Gutenberg 11.3.0 / Chrome or Firefox

Pre-checks

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

[CreativeDive]

I can confirm, I get the same error messages by using the "enqueue_block_editor_assets" action.

In my case I have global block styles, which are not block specific.

Why this error messages are added with the latest release?

[richtabor]

I've run into this as well.

[CreativeDive]

@bph is this issue only related to "Backwards Compatibility" and "CSS Styling"? For me it sounds like wrong error messages.

This error message are also fired by styles which are included by admin_enqueue_scripts. But this styles are only related to the admin screen, not block related. It seems there is something wrong with this block styles check.

And on the other hand, the block style check should not fire on styles which are included with enqueue_block_editor_assets, because this action is allowed to load block editor styles.

[ellatrix]

Is this still an issue after WP 6.3? For more info on styles in the iframe, see https://make.wordpress.org/core/2023/07/18/miscellaneous-editor-changes-in-wordpress-6-3/#post-editor-iframed.

[renatho]

Hi @ellatrix! I just checked it on a site with WP 6.3, and I couldn't see the error anymore. So I'm closing this issue.
Thank you!