Theme.json: __experimentalSelector not working for blocks newly adopting it

[aaronrobertshaw]

Description

Adding an __experimentalSelector to a server-side registered block's supports within its block.json file has no effect.

What I expected

I expected that adding __experimentalSelector to a block's supports config would override the default .wp-block-<name> selector generated by theme.json.

What happens instead

Nothing.

Extra information

• Encountered this while attempting to add __experimentalSelector to the Image block
• Image block is registered server-side. I also tried moving its registration to blocks.php for testing purposes.
• Adding logging to the theme.json determination of block selectors shows that core blocks haven't yet been reregistered with Gutenberg's so the theme.json function only has the block's metadata from core i.e. the outdated block.json from core.

Step-by-step reproduction instructions

1. Add supports.__experimentalSelector to the image block.json file and set it to ".wp-block-image img"
2. Via global styles or your theme's theme.json, configure a border radius
3. Reload the block editor
4. Inspect the image block or the theme.json generated stylesheet and notice that the block's selector is still .wp-block-image not the selector you set i.e. .wp-block-image img

Screenshots, screen recording, code snippet

No response

Environment info

• WP 5.9 and WP 6.0
• Gutenberg latest from trunk

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