microsoft · rbuckton · Jun 6, 2017 · Jun 5, 2017
diff --git a/src/compiler/transformers/esnext.ts b/src/compiler/transformers/esnext.ts
@@ -351,8 +351,10 @@ namespace ts {
             );
         }
 
-        function awaitAsYield(expression: Expression) {
-            return createYield(/*asteriskToken*/ undefined, enclosingFunctionFlags & FunctionFlags.Generator ? createAwaitHelper(context, expression) : expression);
+        function createDownlevelAwait(expression: Expression) {
+            return enclosingFunctionFlags & FunctionFlags.Generator
+                ? createYield(/*asteriskToken*/ undefined, createAwaitHelper(context, expression))
+                : createAwait(expression);
         }
 
         function transformForAwaitOfStatement(node: ForOfStatement, outermostLabeledStatement: LabeledStatement) {
@@ -385,11 +387,11 @@ namespace ts {
                             EmitFlags.NoHoisting
                         ),
                         /*condition*/ createComma(
-                            createAssignment(result, awaitAsYield(callNext)),
+                            createAssignment(result, createDownlevelAwait(callNext)),
                             createLogicalNot(getDone)
                         ),
                         /*incrementor*/ undefined,
-                        /*statement*/ convertForOfStatementHead(node, awaitAsYield(getValue))
+                        /*statement*/ convertForOfStatementHead(node, createDownlevelAwait(getValue))
                     ),
                     /*location*/ node
                 ),
@@ -434,7 +436,7 @@ namespace ts {
                                             createPropertyAccess(iterator, "return")
                                         )
                                     ),
-                                    createStatement(awaitAsYield(callReturn))
+                                    createStatement(createDownlevelAwait(callReturn))
                                 ),
                                 EmitFlags.SingleLine
                             )

diff --git a/tests/baselines/reference/emitter.forAwait.es2017.js b/tests/baselines/reference/emitter.forAwait.es2017.js
@@ -0,0 +1,143 @@
+//// [tests/cases/conformance/emitter/es2017/forAwait/emitter.forAwait.es2017.ts] ////
+
+//// [file1.ts]
+async function f1() {
+    let y: any;
+    for await (const x of y) {
+    }
+}
+//// [file2.ts]
+async function f2() {
+    let x: any, y: any;
+    for await (x of y) {
+    }
+}
+//// [file3.ts]
+async function* f3() {
+    let y: any;
+    for await (const x of y) {
+    }
+}
+//// [file4.ts]
+async function* f4() {
+    let x: any, y: any;
+    for await (x of y) {
+    }
+}
+
+//// [file1.js]
+var __asyncValues = (this && this.__asyncIterator) || function (o) {
+    if (!Symbol.asyncIterator) throw new TypeError("Symbol.asyncIterator is not defined.");
+    var m = o[Symbol.asyncIterator];
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+};
+async function f1() {
+    let y;
+    try {
+        for (var y_1 = __asyncValues(y), y_1_1; y_1_1 = await y_1.next(), !y_1_1.done;) {
+            const x = await y_1_1.value;
+        }
+    }
+    catch (e_1_1) { e_1 = { error: e_1_1 }; }
+    finally {
+        try {
+            if (y_1_1 && !y_1_1.done && (_a = y_1.return)) await _a.call(y_1);
+        }
+        finally { if (e_1) throw e_1.error; }
+    }
+    var e_1, _a;
+}
+//// [file2.js]
+var __asyncValues = (this && this.__asyncIterator) || function (o) {
+    if (!Symbol.asyncIterator) throw new TypeError("Symbol.asyncIterator is not defined.");
+    var m = o[Symbol.asyncIterator];
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+};
+async function f2() {
+    let x, y;
+    try {
+        for (var y_1 = __asyncValues(y), y_1_1; y_1_1 = await y_1.next(), !y_1_1.done;) {
+            x = await y_1_1.value;
+        }
+    }
+    catch (e_1_1) { e_1 = { error: e_1_1 }; }
+    finally {
+        try {
+            if (y_1_1 && !y_1_1.done && (_a = y_1.return)) await _a.call(y_1);
+        }
+        finally { if (e_1) throw e_1.error; }
+    }
+    var e_1, _a;
+}
+//// [file3.js]
+var __asyncValues = (this && this.__asyncIterator) || function (o) {
+    if (!Symbol.asyncIterator) throw new TypeError("Symbol.asyncIterator is not defined.");
+    var m = o[Symbol.asyncIterator];
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+};
+var __await = (this && this.__await) || function (v) { return this instanceof __await ? (this.v = v, this) : new __await(v); }
+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"), i[Symbol.asyncIterator] = function () { return this; }, i;
+    function verb(n) { if (g[n]) i[n] = function (v) { return new Promise(function (a, b) { q.push([n, v, a, b]) > 1 || resume(n, v); }); }; }
+    function resume(n, v) { try { step(g[n](v)); } catch (e) { settle(q[0][3], e); } }
+    function step(r) { r.value instanceof __await ? Promise.resolve(r.value.v).then(fulfill, reject) : settle(q[0][2], r);  }
+    function fulfill(value) { resume("next", value); }
+    function reject(value) { resume("throw", value); }
+    function settle(f, v) { if (f(v), q.shift(), q.length) resume(q[0][0], q[0][1]); }
+};
+function f3() {
+    return __asyncGenerator(this, arguments, function* f3_1() {
+        let y;
+        try {
+            for (var y_1 = __asyncValues(y), y_1_1; y_1_1 = yield __await(y_1.next()), !y_1_1.done;) {
+                const x = yield __await(y_1_1.value);
+            }
+        }
+        catch (e_1_1) { e_1 = { error: e_1_1 }; }
+        finally {
+            try {
+                if (y_1_1 && !y_1_1.done && (_a = y_1.return)) yield __await(_a.call(y_1));
+            }
+            finally { if (e_1) throw e_1.error; }
+        }
+        var e_1, _a;
+    });
+}
+//// [file4.js]
+var __asyncValues = (this && this.__asyncIterator) || function (o) {
+    if (!Symbol.asyncIterator) throw new TypeError("Symbol.asyncIterator is not defined.");
+    var m = o[Symbol.asyncIterator];
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+};
+var __await = (this && this.__await) || function (v) { return this instanceof __await ? (this.v = v, this) : new __await(v); }
+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"), i[Symbol.asyncIterator] = function () { return this; }, i;
+    function verb(n) { if (g[n]) i[n] = function (v) { return new Promise(function (a, b) { q.push([n, v, a, b]) > 1 || resume(n, v); }); }; }
+    function resume(n, v) { try { step(g[n](v)); } catch (e) { settle(q[0][3], e); } }
+    function step(r) { r.value instanceof __await ? Promise.resolve(r.value.v).then(fulfill, reject) : settle(q[0][2], r);  }
+    function fulfill(value) { resume("next", value); }
+    function reject(value) { resume("throw", value); }
+    function settle(f, v) { if (f(v), q.shift(), q.length) resume(q[0][0], q[0][1]); }
+};
+function f4() {
+    return __asyncGenerator(this, arguments, function* f4_1() {
+        let x, y;
+        try {
+            for (var y_1 = __asyncValues(y), y_1_1; y_1_1 = yield __await(y_1.next()), !y_1_1.done;) {
+                x = yield __await(y_1_1.value);
+            }
+        }
+        catch (e_1_1) { e_1 = { error: e_1_1 }; }
+        finally {
+            try {
+                if (y_1_1 && !y_1_1.done && (_a = y_1.return)) yield __await(_a.call(y_1));
+            }
+            finally { if (e_1) throw e_1.error; }
+        }
+        var e_1, _a;
+    });
+}
diff --git a/tests/baselines/reference/emitter.forAwait.es2017.symbols b/tests/baselines/reference/emitter.forAwait.es2017.symbols
@@ -0,0 +1,50 @@
+=== tests/cases/conformance/emitter/es2017/forAwait/file1.ts ===
+async function f1() {
+>f1 : Symbol(f1, Decl(file1.ts, 0, 0))
+
+    let y: any;
+>y : Symbol(y, Decl(file1.ts, 1, 7))
+
+    for await (const x of y) {
+>x : Symbol(x, Decl(file1.ts, 2, 20))
+>y : Symbol(y, Decl(file1.ts, 1, 7))
+    }
+}
+=== tests/cases/conformance/emitter/es2017/forAwait/file2.ts ===
+async function f2() {
+>f2 : Symbol(f2, Decl(file2.ts, 0, 0))
+
+    let x: any, y: any;
+>x : Symbol(x, Decl(file2.ts, 1, 7))
+>y : Symbol(y, Decl(file2.ts, 1, 15))
+
+    for await (x of y) {
+>x : Symbol(x, Decl(file2.ts, 1, 7))
+>y : Symbol(y, Decl(file2.ts, 1, 15))
+    }
+}
+=== tests/cases/conformance/emitter/es2017/forAwait/file3.ts ===
+async function* f3() {
+>f3 : Symbol(f3, Decl(file3.ts, 0, 0))
+
+    let y: any;
+>y : Symbol(y, Decl(file3.ts, 1, 7))
+
+    for await (const x of y) {
+>x : Symbol(x, Decl(file3.ts, 2, 20))
+>y : Symbol(y, Decl(file3.ts, 1, 7))
+    }
+}
+=== tests/cases/conformance/emitter/es2017/forAwait/file4.ts ===
+async function* f4() {
+>f4 : Symbol(f4, Decl(file4.ts, 0, 0))
+
+    let x: any, y: any;
+>x : Symbol(x, Decl(file4.ts, 1, 7))
+>y : Symbol(y, Decl(file4.ts, 1, 15))
+
+    for await (x of y) {
+>x : Symbol(x, Decl(file4.ts, 1, 7))
+>y : Symbol(y, Decl(file4.ts, 1, 15))
+    }
+}
diff --git a/tests/baselines/reference/emitter.forAwait.es2017.types b/tests/baselines/reference/emitter.forAwait.es2017.types
@@ -0,0 +1,50 @@
+=== tests/cases/conformance/emitter/es2017/forAwait/file1.ts ===
+async function f1() {
+>f1 : () => Promise<void>
+
+    let y: any;
+>y : any
+
+    for await (const x of y) {
+>x : any
+>y : any
+    }
+}
+=== tests/cases/conformance/emitter/es2017/forAwait/file2.ts ===
+async function f2() {
+>f2 : () => Promise<void>
+
+    let x: any, y: any;
+>x : any
+>y : any
+
+    for await (x of y) {
+>x : any
+>y : any
+    }
+}
+=== tests/cases/conformance/emitter/es2017/forAwait/file3.ts ===
+async function* f3() {
+>f3 : () => AsyncIterableIterator<any>
+
+    let y: any;
+>y : any
+
+    for await (const x of y) {
+>x : any
+>y : any
+    }
+}
+=== tests/cases/conformance/emitter/es2017/forAwait/file4.ts ===
+async function* f4() {
+>f4 : () => AsyncIterableIterator<any>
+
+    let x: any, y: any;
+>x : any
+>y : any
+
+    for await (x of y) {
+>x : any
+>y : any
+    }
+}
diff --git a/tests/cases/conformance/emitter/es2017/forAwait/emitter.forAwait.es2017.ts b/tests/cases/conformance/emitter/es2017/forAwait/emitter.forAwait.es2017.ts
@@ -0,0 +1,26 @@
+// @target: es2017
+// @lib: esnext
+// @filename: file1.ts
+async function f1() {
+    let y: any;
+    for await (const x of y) {
+    }
+}
+// @filename: file2.ts
+async function f2() {
+    let x: any, y: any;
+    for await (x of y) {
+    }
+}
+// @filename: file3.ts
+async function* f3() {
+    let y: any;
+    for await (const x of y) {
+    }
+}
+// @filename: file4.ts
+async function* f4() {
+    let x: any, y: any;
+    for await (x of y) {
+    }
+}