以编程方式将产品添加到购物车时出现的问题

Question

I'm not well-versed with wordpress, but I'm facing a weird issue when trying to programmatically add a product to the cart.

The flow is like this:
Customer views a product
Customer can add an additional product to their cart by selecting a checkbox option
The item and an additional item should get added to the cart if the checkbox is confirmed checked

// product_extra_item_checkbox.php
add_action('woocommerce_before_add_to_cart_button', 'product_extra_item_checkbox');
add_action('woocommerce_add_to_cart', 'add_additional_item_to_cart');

function product_extra_item_checkbox () {
    echo "
        <input id='_add_additional_item' type='checkbox' class='checkbox add_item' value='1' name='_add_additional_item' />
    ";
}

function add_additional_item_to_cart () {
    global $woocommerce;
    if (isset($_POST['_add_additional_item'])) {
        $productId = 59;
        $woocommerce->cart->add_to_cart($productId);
        echo "<script>alert('ADDED ADDITIONAL PRODUCT TO CART!!!');</script>"; // debug
    }
}

I did get some complaints from xdebug saying the call stack was exceeded, so I guess it is relating to that, but I can't for the life of me figure out why the entire site crashes when I'm just trying to do something millions have done before (I've found examples as Wordpress is not my strong side).

Is it a limitation with my dev-environment, or am I doing something really wrong?

Edit: I have disabled xdebug in my development environment, but the site crashes.

I've tested some more and got another error message:

Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 20480 bytes) in .../wp-includes/taxonomy.php on line 1989

seems to only be related to $woocommerce->cart->add_to_cart($productId); .

Answer 1

Solution?

Well, logical errors happen, and it was actually just my own stupidity which resulted in the stack overflow ;) .

Infinite loop caused because the system kept firing woocommerce_add_to_cart action (which is to be expected) and $_POST['_add_additional_item'] was never cleaned up.

function add_additional_item_to_cart () {
    global $woocommerce;
    if (isset($_POST['_add_additional_item'])) {
        unset($_POST['_add_additional_item']); // this fixed it
        $productId = 59;
        $woocommerce->cart->add_to_cart($productId);
    }
}