WordPress at a glance
filter is not described

woocommerce_add_cart_item filter-hook . WC 1.0

Add item after merging with $cart_item_data - hook to allow plugins to modify cart item.

Usage

add_filter( 'woocommerce_add_cart_item', 'filter_function_name_1355', 10, 2 );
function filter_function_name_1355( $array_merge, $cart_item_key ){
	// filter...

	return $array_merge;
}
$array_merge
-
$cart_item_key
-

Where the hook is called

WC_Cart::add_to_cart()
woocommerce_add_cart_item
CartController::add_to_cart()
woocommerce_add_cart_item
woocommerce/includes/class-wc-cart.php 1227-1242
$this->cart_contents[ $cart_item_key ] = apply_filters(
	'woocommerce_add_cart_item',
	array_merge(
		$cart_item_data,
		array(
			'key'          => $cart_item_key,
			'product_id'   => $product_id,
			'variation_id' => $variation_id,
			'variation'    => $variation,
			'quantity'     => $quantity,
			'data'         => $product_data,
			'data_hash'    => wc_get_cart_item_data_hash( $product_data ),
		)
	),
	$cart_item_key
);
woocommerce/packages/woocommerce-blocks/src/StoreApi/Utilities/CartController.php 71-86
$cart->cart_contents[ $cart_id ] = apply_filters(
	'woocommerce_add_cart_item',
	array_merge(
		$request['cart_item_data'],
		array(
			'key'          => $cart_id,
			'product_id'   => $this->get_product_id( $product ),
			'variation_id' => $this->get_variation_id( $product ),
			'variation'    => $request['variation'],
			'quantity'     => $request['quantity'],
			'data'         => $product,
			'data_hash'    => wc_get_cart_item_data_hash( $product ),
		)
	),
	$cart_id
);

Where in WP core the hook is used WooCommerce

Usage not found.