Fixed an issue with broken await using declarations in for of loo…

…ps (#56466)

Co-authored-by: Jake Bailey <[email protected]>

src/compiler/checker.ts

@@ -50935,7 +50935,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                         return true;
                     }
                 }
-                return false;
             }
         }
 

src/compiler/transformers/esnext.ts

@@ -14,6 +14,7 @@ import {
     ExportAssignment,
     ExportSpecifier,
     Expression,
+    firstOrUndefined,
     ForOfStatement,
     ForStatement,
     GeneratedIdentifierFlags,
@@ -305,11 +306,7 @@ export function transformESNext(context: TransformationContext): (x: SourceFile
             //
             // before handing the shallow transformation back to the visitor for an in-depth transformation.
             const forInitializer = node.initializer;
-            Debug.assertNode(forInitializer, isUsingVariableDeclarationList);
-            Debug.assert(forInitializer.declarations.length === 1, "ForInitializer may only have one declaration");
-
-            const forDecl = forInitializer.declarations[0];
-            Debug.assert(!forDecl.initializer, "ForInitializer may not have an initializer");
+            const forDecl = firstOrUndefined(forInitializer.declarations) || factory.createVariableDeclaration(factory.createTempVariable(/*recordTempVariable*/ undefined));
 
             const isAwaitUsing = getUsingKindOfVariableDeclarationList(forInitializer) === UsingKind.Async;
             const temp = factory.getGeneratedNameForNode(forDecl.name);

tests/baselines/reference/awaitUsingDeclarationsInForAwaitOf.3(target=es5).errors.txt

@@ -0,0 +1,22 @@
+awaitUsingDeclarationsInForAwaitOf.3.ts(5,5): error TS1432: Top-level 'for await' loops are only allowed when the 'module' option is set to 'es2022', 'esnext', 'system', 'node16', 'nodenext', or 'preserve', and the 'target' option is set to 'es2017' or higher.
+awaitUsingDeclarationsInForAwaitOf.3.ts(5,23): error TS1123: Variable declaration list cannot be empty.
+awaitUsingDeclarationsInForAwaitOf.3.ts(8,25): error TS1123: Variable declaration list cannot be empty.
+
+
+==== awaitUsingDeclarationsInForAwaitOf.3.ts (3 errors) ====
+    // https://github.com/microsoft/TypeScript/pull/55558#issuecomment-1817595357
+
+    declare const x: any[]
+
+    for await (await using of x);
+        ~~~~~
+!!! error TS1432: Top-level 'for await' loops are only allowed when the 'module' option is set to 'es2022', 'esnext', 'system', 'node16', 'nodenext', or 'preserve', and the 'target' option is set to 'es2017' or higher.
+
+!!! error TS1123: Variable declaration list cannot be empty.
+
+    export async function test() {
+      for await (await using of x);
+
+!!! error TS1123: Variable declaration list cannot be empty.
+    }
+

tests/baselines/reference/awaitUsingDeclarationsInForAwaitOf.3(target=es5).js

@@ -0,0 +1,196 @@
+//// [tests/cases/conformance/statements/VariableStatements/usingDeclarations/awaitUsingDeclarationsInForAwaitOf.3.ts] ////
+
+//// [awaitUsingDeclarationsInForAwaitOf.3.ts]
+// https://github.com/microsoft/TypeScript/pull/55558#issuecomment-1817595357
+
+declare const x: any[]
+
+for await (await using of x);
+
+export async function test() {
+  for await (await using of x);
+}
+
+
+//// [awaitUsingDeclarationsInForAwaitOf.3.js]
+// https://github.com/microsoft/TypeScript/pull/55558#issuecomment-1817595357
+var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
+    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
+    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) : adopt(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 (g && (g = 0, op[0] && (_ = 0)), _) try {
+            if (f = 1, y && (t = op[0] & 2 ? y["return"] : op[0] ? y["throw"] || ((t = y["return"]) && t.call(y), 0) : y.next) && !(t = t.call(y, op[1])).done) return t;
+            if (y = 0, t) op = [op[0] & 2, 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 __addDisposableResource = (this && this.__addDisposableResource) || function (env, value, async) {
+    if (value !== null && value !== void 0) {
+        if (typeof value !== "object" && typeof value !== "function") throw new TypeError("Object expected.");
+        var dispose, inner;
+        if (async) {
+            if (!Symbol.asyncDispose) throw new TypeError("Symbol.asyncDispose is not defined.");
+            dispose = value[Symbol.asyncDispose];
+        }
+        if (dispose === void 0) {
+            if (!Symbol.dispose) throw new TypeError("Symbol.dispose is not defined.");
+            dispose = value[Symbol.dispose];
+            if (async) inner = dispose;
+        }
+        if (typeof dispose !== "function") throw new TypeError("Object not disposable.");
+        if (inner) dispose = function() { try { inner.call(this); } catch (e) { return Promise.reject(e); } };
+        env.stack.push({ value: value, dispose: dispose, async: async });
+    }
+    else if (async) {
+        env.stack.push({ async: true });
+    }
+    return value;
+};
+var __disposeResources = (this && this.__disposeResources) || (function (SuppressedError) {
+    return function (env) {
+        function fail(e) {
+            env.error = env.hasError ? new SuppressedError(e, env.error, "An error was suppressed during disposal.") : e;
+            env.hasError = true;
+        }
+        function next() {
+            while (env.stack.length) {
+                var rec = env.stack.pop();
+                try {
+                    var result = rec.dispose && rec.dispose.call(rec.value);
+                    if (rec.async) return Promise.resolve(result).then(next, function(e) { fail(e); return next(); });
+                }
+                catch (e) {
+                    fail(e);
+                }
+            }
+            if (env.hasError) throw env.error;
+        }
+        return next();
+    };
+})(typeof SuppressedError === "function" ? SuppressedError : function (error, suppressed, message) {
+    var e = new Error(message);
+    return e.name = "SuppressedError", e.error = error, e.suppressed = suppressed, e;
+});
+var __asyncValues = (this && this.__asyncValues) || function (o) {
+    if (!Symbol.asyncIterator) throw new TypeError("Symbol.asyncIterator is not defined.");
+    var m = o[Symbol.asyncIterator], i;
+    return m ? m.call(o) : (o = typeof __values === "function" ? __values(o) : o[Symbol.iterator](), i = {}, verb("next"), verb("throw"), verb("return"), i[Symbol.asyncIterator] = function () { return this; }, i);
+    function verb(n) { i[n] = o[n] && function (v) { return new Promise(function (resolve, reject) { v = o[n](v), settle(resolve, reject, v.done, v.value); }); }; }
+    function settle(resolve, reject, d, v) { Promise.resolve(v).then(function(v) { resolve({ value: v, done: d }); }, reject); }
+};
+var _a, e_1, _b, _c;
+try {
+    for (var _d = true, x_1 = __asyncValues(x), x_1_1; x_1_1 = await x_1.next(), _a = x_1_1.done, !_a; _d = true) {
+        _c = x_1_1.value;
+        _d = false;
+        var _e_1 = _c;
+        var env_1 = { stack: [], error: void 0, hasError: false };
+        try {
+            var _e = __addDisposableResource(env_1, _e_1, true);
+            ;
+        }
+        catch (e_2) {
+            env_1.error = e_2;
+            env_1.hasError = true;
+        }
+        finally {
+            var result_1 = __disposeResources(env_1);
+            if (result_1)
+                await result_1;
+        }
+    }
+}
+catch (e_1_1) { e_1 = { error: e_1_1 }; }
+finally {
+    try {
+        if (!_d && !_a && (_b = x_1.return)) await _b.call(x_1);
+    }
+    finally { if (e_1) throw e_1.error; }
+}
+export function test() {
+    return __awaiter(this, void 0, void 0, function () {
+        var _a, x_2, x_2_1, _b_1, env_2, _b, e_3, result_2, e_4_1;
+        var _c, e_4, _d, _e;
+        return __generator(this, function (_f) {
+            switch (_f.label) {
+                case 0:
+                    _f.trys.push([0, 10, 11, 16]);
+                    _a = true, x_2 = __asyncValues(x);
+                    _f.label = 1;
+                case 1: return [4 /*yield*/, x_2.next()];
+                case 2:
+                    if (!(x_2_1 = _f.sent(), _c = x_2_1.done, !_c)) return [3 /*break*/, 9];
+                    _e = x_2_1.value;
+                    _a = false;
+                    _b_1 = _e;
+                    env_2 = { stack: [], error: void 0, hasError: false };
+                    _f.label = 3;
+                case 3:
+                    _f.trys.push([3, 4, 5, 8]);
+                    _b = __addDisposableResource(env_2, _b_1, true);
+                    ;
+                    return [3 /*break*/, 8];
+                case 4:
+                    e_3 = _f.sent();
+                    env_2.error = e_3;
+                    env_2.hasError = true;
+                    return [3 /*break*/, 8];
+                case 5:
+                    result_2 = __disposeResources(env_2);
+                    if (!result_2) return [3 /*break*/, 7];
+                    return [4 /*yield*/, result_2];
+                case 6:
+                    _f.sent();
+                    _f.label = 7;
+                case 7: return [7 /*endfinally*/];
+                case 8:
+                    _a = true;
+                    return [3 /*break*/, 1];
+                case 9: return [3 /*break*/, 16];
+                case 10:
+                    e_4_1 = _f.sent();
+                    e_4 = { error: e_4_1 };
+                    return [3 /*break*/, 16];
+                case 11:
+                    _f.trys.push([11, , 14, 15]);
+                    if (!(!_a && !_c && (_d = x_2.return))) return [3 /*break*/, 13];
+                    return [4 /*yield*/, _d.call(x_2)];
+                case 12:
+                    _f.sent();
+                    _f.label = 13;
+                case 13: return [3 /*break*/, 15];
+                case 14:
+                    if (e_4) throw e_4.error;
+                    return [7 /*endfinally*/];
+                case 15: return [7 /*endfinally*/];
+                case 16: return [2 /*return*/];
+            }
+        });
+    });
+}

tests/baselines/reference/awaitUsingDeclarationsInForAwaitOf.3(target=esnext).errors.txt

@@ -0,0 +1,19 @@
+awaitUsingDeclarationsInForAwaitOf.3.ts(5,23): error TS1123: Variable declaration list cannot be empty.
+awaitUsingDeclarationsInForAwaitOf.3.ts(8,25): error TS1123: Variable declaration list cannot be empty.
+
+
+==== awaitUsingDeclarationsInForAwaitOf.3.ts (2 errors) ====
+    // https://github.com/microsoft/TypeScript/pull/55558#issuecomment-1817595357
+
+    declare const x: any[]
+
+    for await (await using of x);
+
+!!! error TS1123: Variable declaration list cannot be empty.
+
+    export async function test() {
+      for await (await using of x);
+
+!!! error TS1123: Variable declaration list cannot be empty.
+    }
+

tests/baselines/reference/awaitUsingDeclarationsInForAwaitOf.3(target=esnext).js

@@ -0,0 +1,22 @@
+//// [tests/cases/conformance/statements/VariableStatements/usingDeclarations/awaitUsingDeclarationsInForAwaitOf.3.ts] ////
+
+//// [awaitUsingDeclarationsInForAwaitOf.3.ts]
+// https://github.com/microsoft/TypeScript/pull/55558#issuecomment-1817595357
+
+declare const x: any[]
+
+for await (await using of x);
+
+export async function test() {
+  for await (await using of x);
+}
+
+
+//// [awaitUsingDeclarationsInForAwaitOf.3.js]
+// https://github.com/microsoft/TypeScript/pull/55558#issuecomment-1817595357
+for await (await using  of x)
+    ;
+export async function test() {
+    for await (await using  of x)
+        ;
+}

tests/baselines/reference/awaitUsingDeclarationsInForOf.5(target=es5).errors.txt

@@ -0,0 +1,19 @@
+awaitUsingDeclarationsInForOf.5.ts(5,17): error TS1123: Variable declaration list cannot be empty.
+awaitUsingDeclarationsInForOf.5.ts(8,19): error TS1123: Variable declaration list cannot be empty.
+
+
+==== awaitUsingDeclarationsInForOf.5.ts (2 errors) ====
+    // https://github.com/microsoft/TypeScript/pull/55558#issuecomment-1817595357
+
+    declare const x: any[]
+
+    for (await using of x);
+
+!!! error TS1123: Variable declaration list cannot be empty.
+
+    export async function test() {
+      for (await using of x);
+
+!!! error TS1123: Variable declaration list cannot be empty.
+    }
+