Re: [w3c/browser-payment-api] Reject acceptedPromise if converting method data fails (#536)

adrianhopebailie commented on this pull request.



> -              <a>payment method identifiers</a> given <var>identifiers</var>.
-              For each resulting payment handler, if payment method specific
-              capabilities supplied by the payment handler match those provided
-              by <var>data</var>, the payment handler matches.
+              <li>Let <var>data</var> be the result of <a data-cite=
+              "!ECMA-262-2015#sec-json.parse">JSON-parsing</a> the second
+              element in <var>paymentMethod</var> tuple.
+              </li>
+              <li>If required by the specification that defines the
+              <var>identifer</var>, then <a data-cite=
+              "!WEBIDL#dfn-convert-ecmascript-to-idl-value">convert</a>
+              <var>data</var> to an IDL value. Otherwise, <a data-cite=
+              "!WEBIDL#dfn-convert-ecmascript-to-idl-value">convert</a> to
+              <a data-cite="!WEBIDL#idl-object">object</a>.
+              </li>
+              <li>If conversion results in an error, reject

Per @adrianba 's comment below, I understand the editors to have decided to take a fail fast approach to this API, therefor a payment request with bad data in one of the provided payment methods will fail entirely rather than simply logging an error.

For consistency, I recommend that the payment method identifier is also validated as part of this algorithm. It should either be a recognised short-string identifier or a valid URL form identifier (per the validity rules in the PMI spec).

Also, I wonder if this sentence in the PMI spec should be revised:
"User agents MUST NOT enforce validity or well-formedness of standardized payment method identifiers. "

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