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Fix performance regression in the block-level custom CSS feature #11686

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Fix performance regression in the block-level custom CSS feature #11686

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79df64b
Update BASE_TAG default version to 6.8.0
mukeshpanchal27 Apr 16, 2026
57bd3b6
Merge branch 'WordPress:trunk' into trunk
mukeshpanchal27 Apr 30, 2026
98aa939
Return early if no custom CSS class is provided
mukeshpanchal27 Apr 30, 2026
391f5b7
Update default BASE_TAG version to 6.7.0
mukeshpanchal27 Apr 30, 2026
ac2597e
Merge branch 'trunk' into perf/10777
mukeshpanchal27 Apr 30, 2026
7e5a7d0
Merge branch 'trunk' into perf/10777
mukeshpanchal27 May 1, 2026
a331593
Refactor custom CSS support validation logic
mukeshpanchal27 May 1, 2026
68c4f7e
Merge branch 'trunk' into perf/10777
mukeshpanchal27 May 6, 2026
439b39f
Apply suggestions from code review
mukeshpanchal27 May 6, 2026
87d952c
Merge branch 'trunk' into perf/10777
westonruter May 10, 2026
a291f83
Guard against malformed attrs from parsed block
westonruter May 10, 2026
d637df3
Guard against non-string className in attrs
westonruter May 10, 2026
fba41c3
Harden types for wp_render_custom_css_class_name()
westonruter May 10, 2026
62781ae
Omit irrelevant types from phpdoc for wp_render_custom_css_support_st…
westonruter May 10, 2026
0bbcfe2
Merge branch 'trunk' into perf/10777
mukeshpanchal27 May 11, 2026
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45 changes: 35 additions & 10 deletions src/wp-includes/block-supports/custom-css.php
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Original file line number Diff line number Diff line change
Expand Up @@ -12,17 +12,28 @@
*
* @param array $parsed_block The parsed block.
* @return array The same parsed block with custom CSS class name added if appropriate.
*
* @phpstan-param array{
* blockName: string|null,
* attrs: array{
* className?: string,
* style?: array{
* css?: string,
* ...
* },
* ...
* },
* ...
* } $parsed_block
*/
function wp_render_custom_css_support_styles( $parsed_block ) {
$block_type = WP_Block_Type_Registry::get_instance()->get_registered( $parsed_block['blockName'] );

if ( ! block_has_support( $block_type, 'customCSS', true ) ) {
$custom_css = $parsed_block['attrs']['style']['css'] ?? null;
if ( ! is_string( $custom_css ) || '' === trim( $custom_css ) ) {
return $parsed_block;
}

$custom_css = trim( $parsed_block['attrs']['style']['css'] ?? '' );

if ( empty( $custom_css ) ) {
$block_type = WP_Block_Type_Registry::get_instance()->get_registered( $parsed_block['blockName'] );
if ( ! block_has_support( $block_type, 'customCSS', true ) ) {
return $parsed_block;
}

Expand All @@ -32,9 +43,10 @@ function wp_render_custom_css_support_styles( $parsed_block ) {
}

// Generate a unique class name for this block instance.
$class_name = wp_unique_id_from_values( $parsed_block, 'wp-custom-css-' );
$updated_class_name = isset( $parsed_block['attrs']['className'] )
? $parsed_block['attrs']['className'] . " $class_name"
$class_name = wp_unique_id_from_values( $parsed_block, 'wp-custom-css-' );
$existing_class_name = $parsed_block['attrs']['className'] ?? null;
$updated_class_name = is_string( $existing_class_name )
? "$existing_class_name $class_name"
: $class_name;

_wp_array_set( $parsed_block, array( 'attrs', 'className' ), $updated_class_name );
Expand Down Expand Up @@ -76,9 +88,22 @@ function wp_enqueue_block_custom_css() {
* @param string $block_content Rendered block content.
* @param array $block Block object.
* @return string Filtered block content.
*
* @phpstan-param array{
* attrs: array{
* className?: string,
* ...
* },
* ...
* } $block
*/
function wp_render_custom_css_class_name( $block_content, $block ) {
$class_string = $block['attrs']['className'] ?? '';
$class_string = $block['attrs']['className'] ?? null;

if ( ! is_string( $class_string ) || '' === $class_string ) {
return $block_content;
}

preg_match( '/\bwp-custom-css-\S+\b/', $class_string, $matches );

if ( empty( $matches ) ) {
Expand Down
6 changes: 3 additions & 3 deletions src/wp-includes/blocks.php
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Original file line number Diff line number Diff line change
Expand Up @@ -2604,9 +2604,9 @@ function unregister_block_style( $block_name, $block_style_name ) {
* @since 5.8.0
* @since 6.4.0 The `$feature` parameter now supports a string.
*
* @param WP_Block_Type $block_type Block type to check for support.
* @param string|array $feature Feature slug, or path to a specific feature to check support for.
* @param mixed $default_value Optional. Fallback value for feature support. Default false.
* @param WP_Block_Type|null $block_type Block type to check for support.
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@westonruter westonruter May 11, 2026

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This change is because the return value of WP_Block_Type_Registry::get_instance()->get_registered() is often passed right into block_has_support(). And the function specifically is checking for whether the arg is a WP_Block_Type.

* @param string|array $feature Feature slug, or path to a specific feature to check support for.
* @param mixed $default_value Optional. Fallback value for feature support. Default false.
* @return bool Whether the feature is supported.
*/
function block_has_support( $block_type, $feature, $default_value = false ) {
Expand Down
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