register_block_type_from_metadata fails to register style attribute when using $args

[mreishus]

Summary

The register_block_type_from_metadata function fails to properly register a block's style attribute when the block is registered using the $args parameter instead of reading from a block.json file.

Steps to Reproduce

1. Call register_block_type_from_metadata and pass the block configuration in the $args array instead of reading from block.json. The first argument should be an empty string to specify a block.json file is not used.
2. Include a style attribute in $args specifying an array of style handles.
3. Observe a PHP warning about an undefined index 'name' when it attempts to call register_block_style_handle.

Expected Result

The block should register successfully with the specified style attribute. No PHP warnings should be generated.

Actual Result

A PHP warning is emitted:

Warning: Undefined array key "name" in .../wp-includes/blocks.php on line 294

The style attribute is not properly registered for the block.

Relevant Code

The issue lies in this part of register_block_type_from_metadata:

foreach ( $style_fields as $metadata_field_name => $settings_field_name ) {
    if ( ! empty( $settings[ $metadata_field_name ] ) ) {
        $metadata[ $metadata_field_name ] = $settings[ $metadata_field_name ];
    }
    if ( ! empty( $metadata[ $metadata_field_name ] ) ) {
        $styles           = $metadata[ $metadata_field_name ];
        $processed_styles = array();
        if ( is_array( $styles ) ) {
            for ( $index = 0; $index < count( $styles ); $index++ ) {
                $result = register_block_style_handle(
                    $metadata,
                    $metadata_field_name, 
                    $index
                );
                if ( $result ) {
                    $processed_styles[] = $result;
                }
            }
        } else {
            $result = register_block_style_handle(
                $metadata,
                $metadata_field_name
            );
            if ( $result ) {
                $processed_styles[] = $result;
            }
        }
        $settings[ $settings_field_name ] = $processed_styles;
    }
}

When calling register_block_style_handle, it passes the $metadata array. However, when registering via $args, the block name is not present in $metadata. It only exists in $args/$settings at this point.

Unit Test

Here is a failing unit test that demonstrates the issue: (see attached)

The test currently fails due to the PHP warning.

Related

#56865, [57026] - Original change allowing register_block_type_from_metadata() to be used without a block.json file.

[mreishus]

Failing Unit Test