wc-cart-checkout-classic

WooCommerce classic cart and checkout

Use this for the PHP/classic cart and shortcode checkout flow. It covers product add-to-cart customization, cart item data, calculated prices/fees, checkout fields, checkout validation, and copying cart data to orders.

It is not a Checkout Block UI skill. Some low-level cart hooks also run during Store API requests, but woocommerce_checkout_fields does not make fields appear in the Checkout Block.

Misconception this skill corrects

"I added custom cart item data, so WooCommerce will automatically show it on the order."

Cart item data affects the cart key and lives in the cart/session. It is not automatically saved as order line-item meta. Display it with woocommerce_get_item_data, and copy it to the order line with woocommerce_checkout_create_order_line_item.

When to use this skill

Trigger when ANY of the following is true:

• Adding a product option from an add-to-cart form.
• Storing custom data on a cart item.
• Showing custom data in cart/checkout/order line items.
• Changing cart item price dynamically.
• Adding a handling, insurance, gift-wrap, or payment-related fee.
• Adding fields to classic checkout.
• Validating checkout data server-side.
• The diff contains woocommerce_add_cart_item_data, woocommerce_get_item_data, woocommerce_before_calculate_totals, woocommerce_cart_calculate_fees, woocommerce_checkout_fields, woocommerce_after_checkout_validation, or woocommerce_checkout_create_order_line_item.

Cart item identity

WC_Cart::add_to_cart() applies woocommerce_add_cart_item_data before generating the cart ID. WC_Cart::generate_cart_id() includes product ID, variation ID, variation attributes, and every value in $cart_item_data.

That means:

• If two cart additions have the same product, variation, and cart item data, Woo merges quantities into one cart line.
• If cart item data differs, Woo creates a different cart line.
• Do not add a random unique value unless you intentionally want every add-to-cart click to be a separate line.