Re: [whatwg/streams] ReadableStream.from(asyncIterable) (#1083)

@domenic commented on this pull request.



> +  }
+  if (typeof func !== 'function') {
+    throw new TypeError();
+  }
+  return func;
+};
+
+exports.GetIterator = (obj, hint = 'sync', method) => {
+  assert(hint === 'sync' || hint === 'async');
+  if (method === undefined) {
+    if (hint === 'async') {
+      method = exports.GetMethod(obj, Symbol.asyncIterator);
+      if (method === undefined) {
+        const syncMethod = exports.GetMethod(obj, Symbol.iterator);
+        const syncIterator = exports.GetIterator(obj, 'sync', syncMethod);
+        return syncIterator; // TODO sync to async iterator

No, wait. The issue is what happens if you have a sync iterator of promises. With AsyncFromSyncIterator, you get the promises unwrapped. Without it, you get the promises.

So I think omitting this step would break test cases like `ReadableStream.from([promiseFor1, promiseFor2])`. That should be equivalent to `ReadableStream.from([1, 2])` but without the AsyncFromSyncIterator, it would give you a stream where `(await reader.read()).value` was a promise.

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