Registering block styles via JSON no longer works without extra styles

[coreyworrell]

Description

JSON files in theme styles folder used to register if you only had a title and slug property (along with blockTypes), this would add the CSS class to the block and allow you to style externally or hook into with JavaScript, etc.

Now it seems those files are ignored unless you specify an external stylesheet in the JSON or you use some kind of style in the schema.

Step-by-step reproduction instructions

1. Create theme/styles/blocks/gallery-1.json

   {
     "$schema": "https://schemas.wp.org/trunk/theme.json",
     "version": 3,
     "title": "Slideshow",
     "slug": "slider",
     "blockTypes": [
       "core/gallery"
     ]
   }

2. Load admin, insert Gallery block, notice there is no style option for "Slideshow"
3. Add styles to JSON

   "styles": {
     "spacing": {
       "padding": {
         "top": "0"
       }
     }
   }

4. Reload admin, you'll see "Slideshow" as option for style

Screenshots, screen recording, code snippet

No response

Environment info

• WordPress 6.8.3

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

[SirLouen]

Reproduction Report

Description

⚠️ This report validates that the issue can be reproduced with some caveats

Environment

• WordPress: 6.9-beta2-61080-src
• PHP: 8.2.29
• Server: nginx/1.29.3
• Database: mysqli (Server: 8.4.7 / Client: mysqlnd 8.2.29)
• Browser: Chrome 141.0.0.0
• OS: Windows 10/11
• Theme: Twenty Twenty-Five 1.3
• MU Plugins: None activated
• Plugins:
  • Test Reports 1.2.0

Actual Results

1. ⚠️ Error condition occurs (reproduced).

Additional Notes

This is not something new by any means. Almost one year and a half when these changes happened
It all started here #62686

Which brought into core this change:
https://github.com/wordpress/wordpress-develop/blob/bafd51b8ff87c8f51357e01def21489dc38e2474/src/wp-includes/block-supports/block-style-variations.php#L273

More specifically, in this change [58466]

So this is not a bug, this was intended, partials should have a style to register. Any style will do as long as its not empty.

[coreyworrell]

@SirLouen appreciate the background. I don't see any reasoning on why that was decided though. Just because there are no styles or stylesheets to register does not mean it should be skipped as a variation. And having to add random style properties just to make it appear makes little sense.