fix(ext/webidl): follow GetIterator semantics in async iterable converter#34872
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…rter The async iterable converter used by ReadableStream.from() rejected non-Object values and only treated an `undefined` (not `null`) @@asynciterator / @@iterator as an absent method. Per the GetIterator(obj, async) abstract operation, the iterator methods are looked up with GetMethod semantics, which (1) performs ToObject on the value, so primitives such as strings are accepted, and (2) treats both `undefined` and `null` as an absent method. Fixes two WPT subtests in streams/readable-streams/from.any: - ReadableStream.from accepts a string - ReadableStream.from ignores a null @@asynciterator
The unit test asserted ReadableStream.from(string) throws, which was the pre-spec behavior. Per the Streams spec it accepts any iterable, including strings; update the test to assert characters are yielded.
The ReadableStream.from type signature requires an object, so passing a string primitive is a static type error even though it is iterable at runtime. Add a @ts-expect-error directive (matching the prior test).
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This is incorrect, see whatwg/webidl#1397, whatwg/streams#1372 |
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The WebIDL async iterable converter (used by
ReadableStream.from()and anyoperation taking an
async iterable<T>argument) did not follow theGetIterator(obj, async)abstract operation:Objectvalue up front (type(V) !== "Object"throws),so primitives such as strings could never be converted, even though
GetIteratorperformsToObject(V)and strings are iterable.@@asyncIterator/@@iteratormethods it only treatedundefinedas "method absent". PerGetMethod, anullvalue must also betreated as absent, so a
null@@asyncIteratorshould fall back to the sync@@iteratorrather than being called.This fix narrows the early rejection to only
undefined/null(the values thatToObjectwould reject) and treats bothundefinedandnullmethod values asabsent, matching
GetIterator/GetMethod.Spec
GetIterator/GetMethodReadableStream.from(asyncIterable)WPT
Flips the following subtests from failing to passing under
streams/readable-streams/from.any.{html,worker.html}(+4 total):ReadableStream.from accepts a stringReadableStream.from ignores a null @@asyncIteratorExpectations in
tests/wpt/runner/expectations/streams.jsonupdatedaccordingly (both
from.any.htmlandfrom.any.worker.htmlnow fully pass).