Fix generated name scope when emitting async functions

src/compiler/transformers/es2017.ts

@@ -463,7 +463,7 @@ namespace ts {
         );
 
         // Mark this node as originally an async function
-        (generatorFunc.emitNode || (generatorFunc.emitNode = {})).flags |= EmitFlags.AsyncFunctionBody;
+        (generatorFunc.emitNode || (generatorFunc.emitNode = {})).flags |= EmitFlags.AsyncFunctionBody | EmitFlags.ReuseTempVariableScope;
 
         return createCall(
             getHelperName("__awaiter"),

tests/baselines/reference/asyncFunctionTempVariableScoping.js

@@ -0,0 +1,64 @@
+//// [asyncFunctionTempVariableScoping.ts]
+// https://github.com/Microsoft/TypeScript/issues/19187
+
+async ({ foo, bar, ...rest }) => bar(await foo);
+
+//// [asyncFunctionTempVariableScoping.js]
+// https://github.com/Microsoft/TypeScript/issues/19187
+var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
+    return new (P || (P = Promise))(function (resolve, reject) {
+        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
+        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
+        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
+        step((generator = generator.apply(thisArg, _arguments || [])).next());
+    });
+};
+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;
+    function verb(n) { return function (v) { return step([n, v]); }; }
+    function step(op) {
+        if (f) throw new TypeError("Generator is already executing.");
+        while (_) try {
+            if (f = 1, y && (t = y[op[0] & 2 ? "return" : op[0] ? "throw" : "next"]) && !(t = t.call(y, op[1])).done) return t;
+            if (y = 0, t) op = [0, t.value];
+            switch (op[0]) {
+                case 0: case 1: t = op; break;
+                case 4: _.label++; return { value: op[1], done: false };
+                case 5: _.label++; y = op[1]; op = [0]; continue;
+                case 7: op = _.ops.pop(); _.trys.pop(); continue;
+                default:
+                    if (!(t = _.trys, t = t.length > 0 && t[t.length - 1]) && (op[0] === 6 || op[0] === 2)) { _ = 0; continue; }
+                    if (op[0] === 3 && (!t || (op[1] > t[0] && op[1] < t[3]))) { _.label = op[1]; break; }
+                    if (op[0] === 6 && _.label < t[1]) { _.label = t[1]; t = op; break; }
+                    if (t && _.label < t[2]) { _.label = t[2]; _.ops.push(op); break; }
+                    if (t[2]) _.ops.pop();
+                    _.trys.pop(); continue;
+            }
+            op = body.call(thisArg, _);
+        } catch (e) { op = [6, e]; y = 0; } finally { f = t = 0; }
+        if (op[0] & 5) throw op[1]; return { value: op[0] ? op[1] : void 0, done: true };
+    }
+};
+var __rest = (this && this.__rest) || function (s, e) {
+    var t = {};
+    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
+        t[p] = s[p];
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
+        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
+            t[p[i]] = s[p[i]];
+    return t;
+};
+var _this = this;
+(function (_a) { return __awaiter(_this, void 0, void 0, function () {
+    var foo = _a.foo, bar = _a.bar, rest = __rest(_a, ["foo", "bar"]);
+    var _b;
+    return __generator(this, function (_c) {
+        switch (_c.label) {
+            case 0:
+                _b = bar;
+                return [4 /*yield*/, foo];
+            case 1: return [2 /*return*/, _b.apply(void 0, [_c.sent()])];
+        }
+    });
+}); });

tests/baselines/reference/asyncFunctionTempVariableScoping.symbols

@@ -0,0 +1,10 @@
+=== tests/cases/compiler/asyncFunctionTempVariableScoping.ts ===
+// https://github.com/Microsoft/TypeScript/issues/19187
+
+async ({ foo, bar, ...rest }) => bar(await foo);
+>foo : Symbol(foo, Decl(asyncFunctionTempVariableScoping.ts, 2, 8))
+>bar : Symbol(bar, Decl(asyncFunctionTempVariableScoping.ts, 2, 13))
+>rest : Symbol(rest, Decl(asyncFunctionTempVariableScoping.ts, 2, 18))
+>bar : Symbol(bar, Decl(asyncFunctionTempVariableScoping.ts, 2, 13))
+>foo : Symbol(foo, Decl(asyncFunctionTempVariableScoping.ts, 2, 8))
+

tests/baselines/reference/asyncFunctionTempVariableScoping.types

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/asyncFunctionTempVariableScoping.ts ===
+// https://github.com/Microsoft/TypeScript/issues/19187
+
+async ({ foo, bar, ...rest }) => bar(await foo);
+>async ({ foo, bar, ...rest }) => bar(await foo) : ({ foo, bar, ...rest }: { [x: string]: any; foo: any; bar: any; }) => Promise<any>
+>foo : any
+>bar : any
+>rest : { [x: string]: any; }
+>bar(await foo) : any
+>bar : any
+>await foo : any
+>foo : any
+

tests/cases/compiler/asyncFunctionTempVariableScoping.ts

@@ -0,0 +1,5 @@
+// @target: es5
+// @lib: es2015
+// https://github.com/Microsoft/TypeScript/issues/19187
+
+async ({ foo, bar, ...rest }) => bar(await foo);