Await promises from sync iterators with for-await (#13824)

Co-authored-by: Mickey Rose <lightmare@users.noreply.github.com>

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

@@ -5,6 +5,14 @@
 
 import template from "@babel/template";
 
+export const asyncIterator = {
+  minVersion: "7.15.9",
+  ast: () =>
+    template.program.ast(
+      '\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',
+    ),
+};
+
 export const jsx = {
   minVersion: "7.0.0-beta.0",
   ast: () =>

packages/babel-helpers/src/helpers.ts

@@ -16,20 +16,6 @@ const helper = (minVersion: string) => (tpl: TemplateStringsArray) => ({
   ast: () => template.program.ast(tpl),
 });
 
-helpers.asyncIterator = helper("7.0.0-beta.0")`
-  export default function _asyncIterator(iterable) {
-    var method;
-    if (typeof Symbol !== "undefined") {
-      if (Symbol.asyncIterator) method = iterable[Symbol.asyncIterator];
-      if (method == null && Symbol.iterator) method = iterable[Symbol.iterator];
-    }
-    if (method == null) method = iterable["@@asyncIterator"];
-    if (method == null) method = iterable["@@iterator"]
-    if (method == null) throw new TypeError("Object is not async iterable");
-    return method.call(iterable);
-  }
-`;
-
 helpers.AwaitValue = helper("7.0.0-beta.0")`
   export default function _AwaitValue(value) {
     this.wrapped = value;

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

@@ -0,0 +1,67 @@
+/* @minVersion 7.15.9 */
+
+export default function _asyncIterator(iterable) {
+  var method,
+    async,
+    sync,
+    retry = 2;
+
+  if (typeof Symbol !== "undefined") {
+    async = Symbol.asyncIterator;
+    sync = Symbol.iterator;
+  }
+
+  while (retry--) {
+    if (async && (method = iterable[async]) != null) {
+      return method.call(iterable);
+    }
+    if (sync && (method = iterable[sync]) != null) {
+      return new AsyncFromSyncIterator(method.call(iterable));
+    }
+
+    async = "@@asyncIterator";
+    sync = "@@iterator";
+  }
+
+  throw new TypeError("Object is not async iterable");
+}
+
+function AsyncFromSyncIterator(s) {
+  AsyncFromSyncIterator = function (s) {
+    this.s = s;
+    this.n = s.next;
+  };
+  AsyncFromSyncIterator.prototype = {
+    /* SyncIterator */ s: null,
+    /* SyncIterator.[[Next]] */ n: null,
+    next: function () {
+      return AsyncFromSyncIteratorContinuation(this.n.apply(this.s, arguments));
+    },
+    return: function (value) {
+      var ret = this.s.return;
+      if (ret === undefined) {
+        return Promise.resolve({ value: value, done: true });
+      }
+      return AsyncFromSyncIteratorContinuation(ret.apply(this.s, arguments));
+    },
+    throw: function (value) {
+      var thr = this.s.return;
+      if (thr === undefined) return Promise.reject(value);
+      return AsyncFromSyncIteratorContinuation(thr.apply(this.s, arguments));
+    },
+  };
+
+  function AsyncFromSyncIteratorContinuation(r) {
+    // This step is _before_ calling AsyncFromSyncIteratorContinuation in the spec.
+    if (Object(r) !== r) {
+      return Promise.reject(new TypeError(r + " is not an object."));
+    }
+
+    var done = r.done;
+    return Promise.resolve(r.value).then(function (value) {
+      return { value: value, done: done };
+    });
+  }
+
+  return new AsyncFromSyncIterator(s);
+}

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/for-await/create-async-from-sync-iterator/exec.js

@@ -0,0 +1,12 @@
+async function* fn() {
+  for await (const result of [Promise.resolve("ok")]) {
+    return { result };
+  }
+}
+
+return fn().next().then(result => {
+  expect(result).toEqual({
+    done: true,
+    value: { result: "ok" }
+  });
+});

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/for-await/create-async-from-sync-iterator/input.js

@@ -0,0 +1,5 @@
+async function* fn() {
+  for await (const result of [Promise.resolve("ok")]) {
+    return { result };
+  }
+}

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/for-await/create-async-from-sync-iterator/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": ["proposal-async-generator-functions"],
+  "parserOpts": {
+    "allowReturnOutsideFunction": true
+  }
+}

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/for-await/create-async-from-sync-iterator/output.js

@@ -0,0 +1,35 @@
+function fn() {
+  return _fn.apply(this, arguments);
+}
+
+function _fn() {
+  _fn = babelHelpers.wrapAsyncGenerator(function* () {
+    var _iteratorAbruptCompletion = false;
+    var _didIteratorError = false;
+
+    var _iteratorError;
+
+    try {
+      for (var _iterator = babelHelpers.asyncIterator([Promise.resolve("ok")]), _step; _iteratorAbruptCompletion = !(_step = yield babelHelpers.awaitAsyncGenerator(_iterator.next())).done; _iteratorAbruptCompletion = false) {
+        const result = _step.value;
+        return {
+          result
+        };
+      }
+    } catch (err) {
+      _didIteratorError = true;
+      _iteratorError = err;
+    } finally {
+      try {
+        if (_iteratorAbruptCompletion && _iterator.return != null) {
+          yield babelHelpers.awaitAsyncGenerator(_iterator.return());
+        }
+      } finally {
+        if (_didIteratorError) {
+          throw _iteratorError;
+        }
+      }
+    }
+  });
+  return _fn.apply(this, arguments);
+}

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/yield-star/create-async-from-sync-iterator/exec.js

@@ -0,0 +1,7 @@
+async function* fn() {
+  yield* [Promise.resolve("ok")] // CreateAsyncFromSyncIterator
+}
+
+return fn().next().then(result => {
+  expect(result).toEqual({ value: "ok", done: false });
+});

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/yield-star/create-async-from-sync-iterator/input.js

@@ -0,0 +1,3 @@
+async function* fn() {
+  yield* [Promise.resolve("ok")] // CreateAsyncFromSyncIterator
+}

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/yield-star/create-async-from-sync-iterator/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": ["proposal-async-generator-functions"],
+  "parserOpts": {
+    "allowReturnOutsideFunction": true
+  }
+}

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/yield-star/create-async-from-sync-iterator/output.js

@@ -0,0 +1,10 @@
+function fn() {
+  return _fn.apply(this, arguments);
+}
+
+function _fn() {
+  _fn = babelHelpers.wrapAsyncGenerator(function* () {
+    yield* babelHelpers.asyncGeneratorDelegate(babelHelpers.asyncIterator([Promise.resolve("ok")]), babelHelpers.awaitAsyncGenerator); // CreateAsyncFromSyncIterator
+  });
+  return _fn.apply(this, arguments);
+}

packages/babel-runtime-corejs2/package.json

@@ -18,6 +18,15 @@
     "regenerator-runtime": "^0.13.4"
   },
   "exports": {
+    "./helpers/asyncIterator": [
+      {
+        "node": "./helpers/asyncIterator.js",
+        "import": "./helpers/esm/asyncIterator.js",
+        "default": "./helpers/asyncIterator.js"
+      },
+      "./helpers/asyncIterator.js"
+    ],
+    "./helpers/esm/asyncIterator": "./helpers/esm/asyncIterator.js",
     "./helpers/jsx": [
       {
         "node": "./helpers/jsx.js",
@@ -54,15 +63,6 @@
       "./helpers/wrapRegExp.js"
     ],
     "./helpers/esm/wrapRegExp": "./helpers/esm/wrapRegExp.js",
-    "./helpers/asyncIterator": [
-      {
-        "node": "./helpers/asyncIterator.js",
-        "import": "./helpers/esm/asyncIterator.js",
-        "default": "./helpers/asyncIterator.js"
-      },
-      "./helpers/asyncIterator.js"
-    ],
-    "./helpers/esm/asyncIterator": "./helpers/esm/asyncIterator.js",
     "./helpers/AwaitValue": [
       {
         "node": "./helpers/AwaitValue.js",

packages/babel-runtime-corejs3/package.json

@@ -17,6 +17,15 @@
     "regenerator-runtime": "^0.13.4"
   },
   "exports": {
+    "./helpers/asyncIterator": [
+      {
+        "node": "./helpers/asyncIterator.js",
+        "import": "./helpers/esm/asyncIterator.js",
+        "default": "./helpers/asyncIterator.js"
+      },
+      "./helpers/asyncIterator.js"
+    ],
+    "./helpers/esm/asyncIterator": "./helpers/esm/asyncIterator.js",
     "./helpers/jsx": [
       {
         "node": "./helpers/jsx.js",
@@ -53,15 +62,6 @@
       "./helpers/wrapRegExp.js"
     ],
     "./helpers/esm/wrapRegExp": "./helpers/esm/wrapRegExp.js",
-    "./helpers/asyncIterator": [
-      {
-        "node": "./helpers/asyncIterator.js",
-        "import": "./helpers/esm/asyncIterator.js",
-        "default": "./helpers/asyncIterator.js"
-      },
-      "./helpers/asyncIterator.js"
-    ],
-    "./helpers/esm/asyncIterator": "./helpers/esm/asyncIterator.js",
     "./helpers/AwaitValue": [
       {
         "node": "./helpers/AwaitValue.js",

packages/babel-runtime/package.json

@@ -17,6 +17,15 @@
     "regenerator-runtime": "^0.13.4"
   },
   "exports": {
+    "./helpers/asyncIterator": [
+      {
+        "node": "./helpers/asyncIterator.js",
+        "import": "./helpers/esm/asyncIterator.js",
+        "default": "./helpers/asyncIterator.js"
+      },
+      "./helpers/asyncIterator.js"
+    ],
+    "./helpers/esm/asyncIterator": "./helpers/esm/asyncIterator.js",
     "./helpers/jsx": [
       {
         "node": "./helpers/jsx.js",
@@ -53,15 +62,6 @@
       "./helpers/wrapRegExp.js"
     ],
     "./helpers/esm/wrapRegExp": "./helpers/esm/wrapRegExp.js",
-    "./helpers/asyncIterator": [
-      {
-        "node": "./helpers/asyncIterator.js",
-        "import": "./helpers/esm/asyncIterator.js",
-        "default": "./helpers/asyncIterator.js"
-      },
-      "./helpers/asyncIterator.js"
-    ],
-    "./helpers/esm/asyncIterator": "./helpers/esm/asyncIterator.js",
     "./helpers/AwaitValue": [
       {
         "node": "./helpers/AwaitValue.js",