PHP notice in class-wp-block-supports.php

[petitphp]

On Core trunk with the TwentyTwentyThree theme with debug mode, a notice is visible on the frontend :

 Notice: Undefined index: attrs in /var/www/src/wp-includes/class-wp-block-supports.php on line 97

This come from the WP_Block_Supports::apply_block_supports method which expect the block data to contain an attrs key :

public function apply_block_supports() {
    $block_attributes = self::$block_to_render['attrs'];
    $block_type       = WP_Block_Type_Registry::get_instance()->get_registered(
			self::$block_to_render['blockName']
    );
    ...

[desrosj]

Moving to the milestone for investigation.

Trac ticket: https://core.trac.wordpress.org/ticket/56799

[spacedmonkey]

Maybe related: #56801

[petitphp]

To add more context, this seem to come from the core/page-list block which doesn't declare any attributes. That seem to cause the self::$block_to_render to not contain a key attrs in the PHP side.

This in turn was causing a warning in wp-includes/block-supports/custom-classname.php, reported in #56801

[hellofromTonya]

I am able to reproduce the reported issue. The PR resolves the issue and is ready for commit. Self-assigning. Will commit shortly.

[hellofromTonya]

In 54498:

Editor: Fix PHP notice in WP_Block_Supports when no attributes declared.

A check is added to verify if the block's 'attrs' key exists before accessing it. If no, it defaults to an empty array.

How was this found?
WP 6.1 removed the attributes from the core/page-list block. When this block is being processed by WP_Block_Supports::apply_block_supports(), the key 'attrs' does not exist in self::$block_to_render.

This commit includes a tiny micro-optimization by moving this line of code after the existing guard clause. Why? If the guard clause is triggered, the method bails out early, meaning the attributes code is not used. By moving it after the guard clause, it saves a tiny bit of memory and processing if this happens.

Follow-up to [49310], [54399].

Props petitphp, spacedmonkey, hellofromTonya.
Fixes #56799.

Committed via changeset https://core.trac.wordpress.org/changeset/54498. Thank you @petitphp for your contribution!