Use global Iterator.prototype for down-level generators (#59514)

Author: rbuckton

src/compiler/factory/emitHelpers.ts

@@ -836,7 +836,7 @@ const asyncGeneratorHelper: UnscopedEmitHelper = {
         var __asyncGenerator = (this && this.__asyncGenerator) || function (thisArg, _arguments, generator) {
             if (!Symbol.asyncIterator) throw new TypeError("Symbol.asyncIterator is not defined.");
             var g = generator.apply(thisArg, _arguments || []), i, q = [];
-            return i = {}, verb("next"), verb("throw"), verb("return", awaitReturn), i[Symbol.asyncIterator] = function () { return this; }, i;
+            return i = Object.create((typeof AsyncIterator === "function" ? AsyncIterator : Object).prototype), verb("next"), verb("throw"), verb("return", awaitReturn), i[Symbol.asyncIterator] = function () { return this; }, i;
             function awaitReturn(f) { return function (v) { return Promise.resolve(v).then(f, reject); }; }
             function verb(n, f) { if (g[n]) { i[n] = function (v) { return new Promise(function (a, b) { q.push([n, v, a, b]) > 1 || resume(n, v); }); }; if (f) i[n] = f(i[n]); } }
             function resume(n, v) { try { step(g[n](v)); } catch (e) { settle(q[0][3], e); } }
@@ -1102,8 +1102,8 @@ const generatorHelper: UnscopedEmitHelper = {
     priority: 6,
     text: `
             var __generator = (this && this.__generator) || function (thisArg, body) {
-                var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
-                return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
+                var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g = Object.create((typeof Iterator === "function" ? Iterator : Object).prototype);
+                return g.next = verb(0), g["throw"] = verb(1), g["return"] = verb(2), typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
                 function verb(n) { return function (v) { return step([n, v]); }; }
                 function step(op) {
                     if (f) throw new TypeError("Generator is already executing.");

src/testRunner/unittests/evaluation/asyncGenerator.ts

@@ -83,4 +83,26 @@ describe("unittests:: evaluation:: asyncGeneratorEvaluation", () => {
             { done: true, value: 2 },
         ]);
     });
+    it("Supports global `AsyncIterator.prototype` if present", () => {
+        class AsyncIterator {}
+        const { gen } = evaluator.evaluateTypeScript(
+            `
+            export async function * gen() {}
+            `,
+            { target: ts.ScriptTarget.ES5 },
+            { AsyncIterator },
+        );
+        const g = gen();
+        assert.instanceOf(g, AsyncIterator);
+    });
+    it("Ignores global `AsyncIterator.prototype` if missing", () => {
+        const { gen } = evaluator.evaluateTypeScript(
+            `
+            export async function * gen() {}
+            `,
+            { target: ts.ScriptTarget.ES5 },
+            { AsyncIterator: undefined },
+        );
+        gen();
+    });
 });

src/testRunner/unittests/evaluation/generator.ts

@@ -39,4 +39,26 @@ describe("unittests:: evaluation:: generatorEvaluation", () => {
         assert.deepEqual(g.next(), { value: undefined, done: true });
         assert.deepEqual(output, []);
     });
+    it("Supports global `Iterator.prototype` if present", () => {
+        class Iterator {}
+        const { gen } = evaluator.evaluateTypeScript(
+            `
+            export function * gen() {}
+            `,
+            { target: ts.ScriptTarget.ES5 },
+            { Iterator },
+        );
+        const g = gen();
+        assert.instanceOf(g, Iterator);
+    });
+    it("Ignores global `Iterator.prototype` if missing", () => {
+        const { gen } = evaluator.evaluateTypeScript(
+            `
+            export function * gen() {}
+            `,
+            { target: ts.ScriptTarget.ES5 },
+            { Iterator: undefined },
+        );
+        gen();
+    });
 });

tests/baselines/reference/asyncArrowFunction11_es5.js

@@ -20,8 +20,8 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
     });
 };
 var __generator = (this && this.__generator) || function (thisArg, body) {
-    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
-    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
+    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g = Object.create((typeof Iterator === "function" ? Iterator : Object).prototype);
+    return g.next = verb(0), g["throw"] = verb(1), g["return"] = verb(2), typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
     function verb(n) { return function (v) { return step([n, v]); }; }
     function step(op) {
         if (f) throw new TypeError("Generator is already executing.");

tests/baselines/reference/asyncAwaitIsolatedModules_es5.js

@@ -53,8 +53,8 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
     });
 };
 var __generator = (this && this.__generator) || function (thisArg, body) {
-    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
-    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
+    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g = Object.create((typeof Iterator === "function" ? Iterator : Object).prototype);
+    return g.next = verb(0), g["throw"] = verb(1), g["return"] = verb(2), typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
     function verb(n) { return function (v) { return step([n, v]); }; }
     function step(op) {
         if (f) throw new TypeError("Generator is already executing.");

tests/baselines/reference/asyncAwait_es5.js

@@ -59,8 +59,8 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
     });
 };
 var __generator = (this && this.__generator) || function (thisArg, body) {
-    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
-    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
+    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g = Object.create((typeof Iterator === "function" ? Iterator : Object).prototype);
+    return g.next = verb(0), g["throw"] = verb(1), g["return"] = verb(2), typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
     function verb(n) { return function (v) { return step([n, v]); }; }
     function step(op) {
         if (f) throw new TypeError("Generator is already executing.");

tests/baselines/reference/asyncFunctionNoReturnType.js

@@ -18,8 +18,8 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
     });
 };
 var __generator = (this && this.__generator) || function (thisArg, body) {
-    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
-    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
+    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g = Object.create((typeof Iterator === "function" ? Iterator : Object).prototype);
+    return g.next = verb(0), g["throw"] = verb(1), g["return"] = verb(2), typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
     function verb(n) { return function (v) { return step([n, v]); }; }
     function step(op) {
         if (f) throw new TypeError("Generator is already executing.");

tests/baselines/reference/asyncFunctionReturnExpressionErrorSpans.js

@@ -34,8 +34,8 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
     });
 };
 var __generator = (this && this.__generator) || function (thisArg, body) {
-    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
-    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
+    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g = Object.create((typeof Iterator === "function" ? Iterator : Object).prototype);
+    return g.next = verb(0), g["throw"] = verb(1), g["return"] = verb(2), typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
     function verb(n) { return function (v) { return step([n, v]); }; }
     function step(op) {
         if (f) throw new TypeError("Generator is already executing.");

tests/baselines/reference/asyncFunctionTempVariableScoping.js

@@ -17,8 +17,8 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
     });
 };
 var __generator = (this && this.__generator) || function (thisArg, body) {
-    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
-    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
+    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g = Object.create((typeof Iterator === "function" ? Iterator : Object).prototype);
+    return g.next = verb(0), g["throw"] = verb(1), g["return"] = verb(2), typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
     function verb(n) { return function (v) { return step([n, v]); }; }
     function step(op) {
         if (f) throw new TypeError("Generator is already executing.");

tests/baselines/reference/asyncFunctionWithForStatementNoInitializer.js

@@ -37,8 +37,8 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
     });
 };
 var __generator = (this && this.__generator) || function (thisArg, body) {
-    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
-    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
+    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g = Object.create((typeof Iterator === "function" ? Iterator : Object).prototype);
+    return g.next = verb(0), g["throw"] = verb(1), g["return"] = verb(2), typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
     function verb(n) { return function (v) { return step([n, v]); }; }
     function step(op) {
         if (f) throw new TypeError("Generator is already executing.");