elements.php

<?php
/**
 * Elements styles block support.
 *
 * @package gutenberg
 */

/**
 * Get the elements class names.
 *
 * @param array $block Block object.
 * @return string      The unique class name.
 */
function gutenberg_get_elements_class_name( $block ) {
	return 'wp-elements-' . md5( serialize( $block ) );
}

/**
 * Update the block content with elements class names.
 *
 * @param  string $block_content Rendered block content.
 * @param  array  $block         Block object.
 * @return string                Filtered block content.
 */
function gutenberg_render_elements_support( $block_content, $block ) {
	if ( ! $block_content ) {
		return $block_content;
	}

	$block_type                    = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );
	$skip_link_color_serialization = wp_should_skip_block_supports_serialization( $block_type, 'color', 'link' );

	if ( $skip_link_color_serialization ) {
		return $block_content;
	}

	$link_color = null;
	if ( ! empty( $block['attrs'] ) ) {
		$link_color = _wp_array_get( $block['attrs'], array( 'style', 'elements', 'link', 'color', 'text' ), null );
	}

	/*
	* For now we only care about link color.
	* This code in the future when we have a public API
	* should take advantage of WP_Theme_JSON_Gutenberg::compute_style_properties
	* and work for any element and style.
	*/
	if ( null === $link_color ) {
		return $block_content;
	}

	// Like the layout hook this assumes the hook only applies to blocks with a single wrapper.
	// Add the class name to the first element, presuming it's the wrapper, if it exists.
	$tags = new WP_HTML_Tag_Processor( $block_content );
	if ( $tags->next_tag() ) {
		$tags->add_class( gutenberg_get_elements_class_name( $block ) );
	}

	return $tags->get_updated_html();
}

/**
 * Render the elements stylesheet.
 *
 * In the case of nested blocks we want the parent element styles to be rendered before their descendants.
 * This solves the issue of an element (e.g.: link color) being styled in both the parent and a descendant:
 * we want the descendant style to take priority, and this is done by loading it after, in DOM order.
 *
 * @param string|null $pre_render   The pre-rendered content. Default null.
 * @param array       $block The block being rendered.
 *
 * @return null
 */
function gutenberg_render_elements_support_styles( $pre_render, $block ) {
	$block_type           = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );
	$element_block_styles = isset( $block['attrs']['style']['elements'] ) ? $block['attrs']['style']['elements'] : null;

	/*
	* For now we only care about link color.
	*/
	$skip_link_color_serialization = wp_should_skip_block_supports_serialization( $block_type, 'color', 'link' );

	if ( $skip_link_color_serialization ) {
		return null;
	}
	$class_name        = gutenberg_get_elements_class_name( $block );
	$link_block_styles = isset( $element_block_styles['link'] ) ? $element_block_styles['link'] : null;

	gutenberg_style_engine_get_styles(
		$link_block_styles,
		array(
			'selector' => ".$class_name a",
			'context'  => 'block-supports',
		)
	);

	return null;
}

// Remove WordPress core filters to avoid rendering duplicate elements stylesheet & attaching classes twice.
remove_filter( 'render_block', 'wp_render_elements_support', 10, 2 );
remove_filter( 'pre_render_block', 'wp_render_elements_support_styles', 10, 2 );
add_filter( 'render_block', 'gutenberg_render_elements_support', 10, 2 );
add_filter( 'pre_render_block', 'gutenberg_render_elements_support_styles', 10, 2 );