Adding an item to the cart with an invalid merchandiseId is not popullating the error field from the useCart hook (hydrogen-react)

[luispcosta]

Hello everyone. I am trying to make it so that adding an item that does not exist to a cart throws an error (when calling linesAdd from useCart).

The useCart hook has a property called error which states:

If an error occurred on the previous cart action, then error will exist and cart will be put back into the last valid status it was in.

But if I try to render that error field after calling linesAdd, it is always undefined. And I know that this should fail because if I replicate this request using raw graphql queries to the shopify storefront API, here's the response I get back:

{
    "data": {
        "cartLinesAdd": {
            "userErrors": [
                {
                    "field": [
                        "lines",
                        "0",
                        "merchandiseId"
                    ],
                    "message": "The merchandise with id gid://shopify/ProductVariant/xxxx does not exist.",
                    "code": "INVALID"
                }
            ]
        }
    }
}

However, looking at the query that hydrogen-react is doing when adding that same product with the invalid id, the response I get back is:

{
  "data": {
    "cartLinesAdd": {
      "cart": null
    }
  },
  "extensions": {
    "context": {
      "country": "US",
      "language": "EN"
    }
  }
}

So my question is, how can we test that the error property is properly populated?

For reference, the way I'm trying to print the value for this variable is:

const { linesAdd, error } = useCart();

useEffect(() => {
  console.log("cart error", error);
}, [error]};

// calling linesAdd(..)

Hydrogen react version: @shopify/[email protected]
React version: 19

Thank you!