Duplicate shippingOptions lead to inconsistent updateWith() - should throw!

[marcoscaceres]

If given:

const methods = [{ supportedMethods: ["basic-card"] }];
const details = {
  total: {
    label: "Total due",
    amount: { currency: "USD", value: "1.0" },
  },
};
const options = {
  requestShipping: true,
};

const request = new PaymentRequest(methods, detailsNoShippingOptions, options);
// See below
const response = await request.show();

And we do:

response.onshippingaddresschange =  ev =>{
  const shippingOptions = [
    {
      id: "duplicate",
      label: "Option",
      amount: { currency: "USD", value: "5.00" },
      selected: true,
    },
    {
      id: "duplicate",
      label: "Option",
      amount: { currency: "USD", value: "5.00" },
    },
    {
      id: "not a duplicate",
      label: "Option",
      amount: { currency: "USD", value: "5.00" },
    },
 ];
 const newDetails = {...details, shippingOptions};
 ev.updateWith(newDetails);
}

The API says that because there are duplicates, all the shippingOptions become invalid and essentially this becomes an error in the payment sheet.

However, the above is developer error, not a user error! This leads to somewhat frustrating user experience where the user is told the merchant can't ship to that address (when in fact, the merchant can!):

I think we should throw on duplicate IDs instead, because the developer screwed up.

[marcoscaceres]

Note also in the above, that the use can keep trying/modifying/adding addresses but they will all continue to fail. But neither the user or the developer will know why!!!!