Warnings and invalid HTML generated from gutenberg_render_elements_support() for empty block

[bobbingwide]

Description

After updating to Gutenberg 11.0.0 I noticed a number of Warnings being produced.
I analysed the problem in bobbingwide/thisis#34
and eventually determined that the problem occurs when the block being rendered has produced no output
but has a style attribute for the link color.

• For my block this happened because the user was not logged in.
• For the scenario to reproduce the problem below it occurs because the block is not registered.
• The filter function is still being run against blank output.
• This causes the Warnings to be displayed and the invalid output is generated.

Step-by-step reproduction instructions

1. Add a new post.
2. Enter Code edit
3. Paste this content.

<!-- wp:paragraph --><p>Apart from this paragraph the only content in the post is another block with a style attribute. The template only displays the post-content. What could possibly go wrong?</p><!-- /wp:paragraph -->
<!-- wp:reproduce/issue34 {"style":{"elements":{"link":{"color":{"text":"var:preset|color|dark-grey"}}}}} /-->

4. Save the post.
5. View the post on the front end. See the unexpected output.
6. Re edit the post
7. Change style to smyle
8. Save and view again
9. The problem goes away.

Expected behaviour

The block should not appear on the front end.
There shouldn't be any attempt to generate a <style> tag.

Actual behaviour

Warning messages and invalid HTML generated

Warning: Undefined array key 0 in C:\apache\htdocs\wp55\wp-content\plugins\gutenberg\lib\block-supports\elements.php on line 51

Warning: Trying to access array offset on value of type null in C:\apache\htdocs\wp55\wp-content\plugins\gutenberg\lib\block-supports\elements.php on line 51

Warning: Undefined array key 0 in C:\apache\htdocs\wp55\wp-content\plugins\gutenberg\lib\block-supports\elements.php on line 63

Warning: Trying to access array offset on value of type null in C:\apache\htdocs\wp55\wp-content\plugins\gutenberg\lib\block-supports\elements.php on line 63

Apart from this paragraph the only content in the post is another block with a style attribute. The template only displays the post-content. What could possibly go wrong?

class=”wp-elements-60edf9307a0c3″

Screenshots or screen recording (optional)

This is what I got:

This is what @annezazu got

Code snippet (optional)

Proposed fix:
Return early when the block content is empty

function gutenberg_render_elements_support( $block_content, $block )
{
    if ( empty( $block_content ) ) {
        return $block_content;
    }

WordPress information

• WordPress version: 5.7.2 | 5.8-RC2
• Gutenberg version: 11.0.0
• Are all plugins except Gutenberg deactivated? No ( @bobbingwide )
• Are you using a default theme (e.g. Twenty Twenty-One)? No ( @bobbingwide )

Device information

For @bobbingwide

• Device: Desktop
• Operating system: Windows 10
• Browser:

[Mamaduka]

Hi, @bobbingwide

I believe this was resolved via #35836.

[talldan]

Sounds like it is resolved, so I'll close this.