Adding column count class to Gutenberg columns block

functions.php

<?php
/**
 * inject_class_column_count
 *
 * @param string 	$content 		The block content about to be appended.
 * @param array 	$block 			The full block, including name and attributes
 * @return $content;
 */
function inject_class_column_count( $content, $block ) {
	if ( ! is_block_type( $block, "core/columns" ) ) {
		return $content;
	} else {
		$column_count = array_column($block['innerBlocks'],'blockName');
		$modified_content = str_replace('wp-block-columns','wp-block-columns has-'.count($column_count).'-columns',$content);
		return $modified_content;
	}
}
add_filter( 'render_block', 'inject_class_column_count', 10, 2 );

/**
 * is_block_type
 *
 * @param array $block 		A WordPress block array
 * @param string $type 		The block name being queried
 * @return bool;
 */
function is_block_type( $block, $type ) {
	if ( $type === $block['blockName'] ) {
		return true;
	}
	return false;
}

?>