Fix add to cart URL/text for external products that don't have an external URL

wc-mnm-external-grouping.php

<?php
/**
 * Plugin Name: Mix and Match external product parents
 * Plugin URI: https://gist.github.com/helgatheviking/af72435b3cf729886b852c61c0f2d38c
 * Description: Fix add to cart URL/text for external products that don't have an external URL. Like when using a product table to group products together.
 * Version: 1.0.0
 * Author: Kathy Darling
 * Author URI: https://kathyisawesome.com
 * Text Domain: mnm-external-parent
 * Domain Path: /i18n/languages/
 * Requires at least: 5.2
 * Requires PHP: 7.0
 *
 * @package WooCommerce
 */

defined( 'ABSPATH' ) || exit;


/**
 * Set a flag on external products that do not have an external link.
 */
function kia_set_external_pseudo_parent() {
	global $product;
	$product->is_parent_container = $product->is_type( 'external' ) && '' === $product->get_product_url() ? true : false;
}
add_action( 'woocommerce_before_shop_loop_item', 'kia_set_external_pseudo_parent' );

/**
 * Link to product page for external products with no product URL
 * 
 * @param  str $url
 * @param  obj WC_Product_Mix_and_Match $product
 * @return string
 */
function kia_external_product_add_to_cart_url( $url, $product ) {

	if ( ! is_product() && $product->is_parent_container ) {
		$url = $product->get_permalink();
	}

    return $url;
}
add_filter( 'woocommerce_product_add_to_cart_url', 'kia_external_product_add_to_cart_url', 10, 2 );


/**
 * Link to product page for external products with no product URL
 * 
 * @param  str $text
 * @param  obj WC_Product_Mix_and_Match $product
 * @return string
 */
function kia_external_product_add_to_cart_text( $text, $product ) {

	if ( $product->is_parent_container ) {
		$text = $product->get_button_text() ? $product->get_button_text() : __( 'Select options', 'your-textdomain' );
	}

    return $text;
}
add_filter( 'woocommerce_product_add_to_cart_text', 'kia_external_product_add_to_cart_text', 10, 2 );


/**
 * Link to product page for external products with no product URL
 * 
 * @param  str $description
 * @param  obj WC_Product_Mix_and_Match $product
 * @return string
 */
function kia_external_product_add_to_cart_description( $description, $product ) {

	if ( $product->is_parent_container ) {
		$description = $product->get_button_text() ? $product->get_button_text() : sprintf( __( 'Select options for %s', 'your-textdomain' ), $product->get_name() );
	}

    return $description;
}
add_filter( 'woocommerce_product_add_to_cart_description', 'kia_external_product_add_to_cart_description', 10, 2 );