Await promises from sync iterators with for-await

packages/babel-helpers/src/helpers-generated.ts

@@ -9,7 +9,7 @@ export const asyncIterator = {
   minVersion: "7.15.9",
   ast: () =>
     template.program.ast(
-      '\nexport default function _asyncIterator(iterable) {\n  var method;\n  if (typeof Symbol !== "undefined") {\n    if (Symbol.asyncIterator) method = iterable[Symbol.asyncIterator];\n    if (method == null && Symbol.iterator) {\n      method = iterable[Symbol.iterator];\n      if (method != null) {\n        return new AsyncFromSyncIterator(method.call(iterable));\n      }\n    }\n  }\n  if (method == null) method = iterable["@@asyncIterator"];\n  if (method == null) {\n    method = iterable["@@iterator"];\n    if (method != null) return new AsyncFromSyncIterator(method.call(iterable));\n  }\n  if (method == null) throw new TypeError("Object is not async iterable");\n  return method.call(iterable);\n}\nfunction AsyncFromSyncIterator(s) {\n  AsyncFromSyncIterator = function (s) {\n    this.s = s;\n    this.n = s.next;\n  };\n  AsyncFromSyncIterator.prototype = {\n     s: null,\n     n: null,\n    next: function () {\n      return AsyncFromSyncIteratorContinuation(this.n.apply(this.s, arguments));\n    },\n    return: function (value) {\n      var ret = this.s.return;\n      if (ret === undefined) {\n        return Promise.resolve({ value: value, done: true });\n      }\n      return AsyncFromSyncIteratorContinuation(ret.apply(this.s, arguments));\n    },\n    throw: function (value) {\n      var thr = this.s.return;\n      if (thr === undefined) return Promise.reject(value);\n      return AsyncFromSyncIteratorContinuation(thr.apply(this.s, arguments));\n    },\n  };\n  function AsyncFromSyncIteratorContinuation(r) {\n    \n    if (Object(r) !== r) {\n      return Promise.reject(new TypeError(r + " is not an object."));\n    }\n    var done = r.done;\n    return Promise.resolve(r.value).then(function (value) {\n      return { value: value, done: done };\n    });\n  }\n  return new AsyncFromSyncIterator(s);\n}\n',
+      '\nexport default function _asyncIterator(iterable) {\n  var method, async, sync;\n  if (typeof Symbol !== "undefined") {\n    async = Symbol.asyncIterator;\n    sync = Symbol.iterator;\n  }\n  do {\n    if (!sync) {\n      async = "@@asyncIterator";\n      sync = "@@iterator";\n    }\n    if (async && (method = iterable[async]) != null) {\n      return method.call(iterable);\n    }\n    if ((method = iterable[sync]) != null) {\n      return new AsyncFromSyncIterator(method.call(iterable));\n    }\n  } while (!(sync === "@@iterator" || (sync = null)));\n  throw new TypeError("Object is not async iterable");\n}\nfunction AsyncFromSyncIterator(s) {\n  AsyncFromSyncIterator = function (s) {\n    this.s = s;\n    this.n = s.next;\n  };\n  AsyncFromSyncIterator.prototype = {\n     s: null,\n     n: null,\n    next: function () {\n      return AsyncFromSyncIteratorContinuation(this.n.apply(this.s, arguments));\n    },\n    return: function (value) {\n      var ret = this.s.return;\n      if (ret === undefined) {\n        return Promise.resolve({ value: value, done: true });\n      }\n      return AsyncFromSyncIteratorContinuation(ret.apply(this.s, arguments));\n    },\n    throw: function (value) {\n      var thr = this.s.return;\n      if (thr === undefined) return Promise.reject(value);\n      return AsyncFromSyncIteratorContinuation(thr.apply(this.s, arguments));\n    },\n  };\n  function AsyncFromSyncIteratorContinuation(r) {\n    \n    if (Object(r) !== r) {\n      return Promise.reject(new TypeError(r + " is not an object."));\n    }\n    var done = r.done;\n    return Promise.resolve(r.value).then(function (value) {\n      return { value: value, done: done };\n    });\n  }\n  return new AsyncFromSyncIterator(s);\n}\n',
     ),
 };
 

packages/babel-helpers/src/helpers/asyncIterator.js

@@ -1,23 +1,24 @@
 /* @minVersion 7.15.9 */
 
 export default function _asyncIterator(iterable) {
-  var method;
+  var method, async, sync;
   if (typeof Symbol !== "undefined") {
-    if (Symbol.asyncIterator) method = iterable[Symbol.asyncIterator];
-    if (method == null && Symbol.iterator) {
-      method = iterable[Symbol.iterator];
-      if (method != null) {
-        return new AsyncFromSyncIterator(method.call(iterable));
-      }
-    }
-  }
-  if (method == null) method = iterable["@@asyncIterator"];
-  if (method == null) {
-    method = iterable["@@iterator"];
-    if (method != null) return new AsyncFromSyncIterator(method.call(iterable));
+    async = Symbol.asyncIterator;
+    sync = Symbol.iterator;
   }
-  if (method == null) throw new TypeError("Object is not async iterable");
-  return method.call(iterable);
+  do {
+    if (!sync) {
+      async = "@@asyncIterator";
+      sync = "@@iterator";
+    }
+    if (async && (method = iterable[async]) != null) {
+      return method.call(iterable);
+    }
+    if ((method = iterable[sync]) != null) {
+      return new AsyncFromSyncIterator(method.call(iterable));
+    }
+  } while (!(sync === "@@iterator" || (sync = null)));
+  throw new TypeError("Object is not async iterable");
 }
 
 function AsyncFromSyncIterator(s) {