stripe.Error does not work with errors.As()

[ffigiel]

Hello!

I have a shop package with a Client type that wraps a Stripe client in a focused, higher-level interface. I am adding support for coupon codes and need to check if the error I get from Stripe means "that coupon code is invalid" or something else.

I have this

package shop

func IsNotFound(err error) bool {
        var stripeErr stripe.Error
        if errors.As(err, &stripeErr) {
                return stripeErr.Type == stripe.ErrorTypeInvalidRequest &&
                        stripeErr.Code == stripe.ErrorCodeResourceMissing
        }
        return false
}

but I get this warning in my editor, and executing this code results in a panic

second argument to errors.As must be a non-nil pointer to either a type that implements error, or to any interface type

Which is weird, as in the docs I clearly see that stripe.Error implements the error interface. I'm not sure if this is a bug in stripe-go package, the built-in errors package, or maybe I'm too tired to think. By the way, is this the correct way for checking for such an error? Please advise 🙂

---

Additional note: I can't just do a type assertion, because my shop.Client wraps the error with fmt.Errorf. For now I will just type-assert Unwrap()pable interface, and then type-assert stripe.Error the inner error.

---

My environment:

$ go version
go version go1.15.2 linux/amd64
$ grep stripe go.mod
	github.com/stripe/stripe-go/v72 v72.35.0

[brandur-stripe]

The docs for errors.As are shockingly awful in that as far as I can tell, this is never explicitly mentioned, but it actually wants a pointer to a pointer. Make stripeErr in your code a pointer type:

var stripeErr *stripe.Error

[ffigiel]

Right, because that Error method actually takes *stripe.Error and errors.As needs a pointer to that receiver. Thank you for responding so quickly!