Block Bindings API についてしらべる

add_action( 'init', 'chiilog_register_meta_fields' );

function chiilog_register_meta_fields() {
	register_meta(
		'post',
		'company_name',
		array(
			'show_in_rest'      => true,
			'single'            => true,
			'type'              => 'string',
			'sanitize_callback' => 'wp_strip_all_tags'
		)
	);
}

<!-- wp:paragraph {
	"metadata":{
		"bindings":{
			"content":{
				"source":"core/post-meta",
				"args":{
					"key":"company_name"
				}
			}
		}
	}
} -->
<p></p>
<!-- /wp:paragraph -->

<!-- wp:buttons {"style":{"spacing":{"blockGap":"var:preset|spacing|30"}}} -->
<div class="wp-block-buttons"><!-- wp:button {"metadata":{"bindings":{"url":{"source":"chiilog/share-button","args":{"key":"x"}}}}} -->
<div class="wp-block-button"><a class="wp-block-button__link wp-element-button">X</a></div>
<!-- /wp:button -->

<!-- wp:button {"metadata":{"bindings":{"url":{"source":"chiilog/share-button","args":{"key":"facebook"}}}}} -->
<div class="wp-block-button"><a class="wp-block-button__link wp-element-button">Facebook</a></div>
<!-- /wp:button -->

<!-- wp:button {"metadata":{"bindings":{"url":{"source":"chiilog/share-button","args":{"key":"line"}}}}} -->
<div class="wp-block-button"><a class="wp-block-button__link wp-element-button">LINE</a></div>
<!-- /wp:button -->

<!-- wp:button {"metadata":{"bindings":{"url":{"source":"chiilog/share-button","args":{"key":"hatena"}}}}} -->
<div class="wp-block-button"><a class="wp-block-button__link wp-element-button">はてな</a></div>
<!-- /wp:button --></div>
<!-- /wp:buttons -->

add_action( 'init', 'chiilog_register_block_bindings' );

function chiilog_register_block_bindings() {
	register_block_bindings_source( 'chiilog/share-button', array(
		'label'              => __( 'SNS', 'chiilog-share-button' ),
		'get_value_callback' => 'chiilog_sns_data_bindings',
		'uses_context'       => [ 'postId' ]
	) );
}

function chiilog_sns_data_bindings( $source_args, $block_instance ) {
	$current_post_id = $block_instance->context['postId'];

	// キーがない場合はなにもしない
	if ( ! isset( $source_args['key'] ) ) {
		return null;
	}
}

/**
 * SNSのシェアリンクを返す
 *
 * @param array $source_args
 * @param WP_Block $block_instance
 *
 * @return string|null
 */
function chiilog_sns_data_bindings( $source_args, $block_instance ) {
	$current_post_id = $block_instance->context['postId'];

	// キーがない場合はなにもしない
	if ( ! isset( $source_args['key'] ) ) {
		return null;
	}

	switch ( $source_args['key'] ) {
		case 'x':
			return 'https://twitter.com/intent/tweet?url=' . esc_url( get_permalink( $current_post_id ) ) . '&text=' . esc_attr( get_the_title( $current_post_id ) );
		case 'facebook':
			return 'https://www.facebook.com/sharer/sharer.php?u=' . esc_url( get_permalink( $current_post_id ) );
		case 'line':
			return 'https://social-plugins.line.me/lineit/share?url=' . esc_url( get_permalink( $current_post_id ) ) . '&text=' . esc_attr( get_the_title( $current_post_id ) );
		default:
			return null;
	}
}

add_filter( 'render_block_core/button', 'add_link_target_for_binding_button', 10, 2 );

function add_link_target_for_binding_button( $block_content, $block ) {
	$processor = new WP_HTML_Tag_Processor( $block_content );

	if ( isset( $block['attrs']['metadata']['bindings']['url']['source'] ) ) {
		$binding_source = $block['attrs']['metadata']['bindings']['url']['source'];
		if ( $binding_source === 'chiilog/share-button' ) {
			$processor->next_tag( array( 'class_name' => 'wp-block-button__link' ) );
			$processor->set_attribute( 'target', '_blank' );
		}
	}

	return $processor->get_updated_html();
}