Merge pull request #24474 from Microsoft/fix21115.2

Do not await iterated value in for-await-of

src/compiler/transformers/esnext.ts

@@ -416,7 +416,7 @@ namespace ts {
                             createLogicalNot(getDone)
                         ),
                         /*incrementor*/ undefined,
-                        /*statement*/ convertForOfStatementHead(node, createDownlevelAwait(getValue))
+                        /*statement*/ convertForOfStatementHead(node, getValue)
                     ),
                     /*location*/ node
                 ),

src/harness/unittests/forAwaitOfEvaluation.ts

@@ -0,0 +1,148 @@
+/// <reference path="..\harness.ts" />
+
+namespace ts {
+    declare var Symbol: SymbolConstructor;
+
+    describe("forAwaitOfEvaluation", () => {
+        const sourceFile = vpath.combine(vfs.srcFolder, "source.ts");
+
+        function compile(sourceText: string, options?: CompilerOptions) {
+            const fs = vfs.createFromFileSystem(Harness.IO, /*ignoreCase*/ false);
+            fs.writeFileSync(sourceFile, sourceText);
+            const compilerOptions: CompilerOptions = { target: ScriptTarget.ES5, module: ModuleKind.CommonJS, lib: ["lib.esnext.d.ts"], ...options };
+            const host = new fakes.CompilerHost(fs, compilerOptions);
+            return compiler.compileFiles(host, [sourceFile], compilerOptions);
+        }
+
+        function noRequire(id: string) {
+            throw new Error(`Module '${id}' could not be found.`);
+        }
+
+        // Define a custom "Symbol" constructor to attach missing built-in symbols without
+        // modifying the global "Symbol" constructor
+        // tslint:disable-next-line:variable-name
+        const FakeSymbol: SymbolConstructor = ((description?: string) => Symbol(description)) as any;
+        (<any>FakeSymbol).prototype = Symbol.prototype;
+        for (const key of Object.getOwnPropertyNames(Symbol)) {
+            Object.defineProperty(FakeSymbol, key, Object.getOwnPropertyDescriptor(Symbol, key)!);
+        }
+
+        // Add "asyncIterator" if missing
+        if (!hasProperty(FakeSymbol, "asyncIterator")) Object.defineProperty(FakeSymbol, "asyncIterator", { value: Symbol.for("Symbol.asyncIterator"), configurable: true });
+
+        function evaluate(result: compiler.CompilationResult) {
+            const output = result.getOutput(sourceFile, "js")!;
+            assert.isDefined(output);
+
+            const evaluateText = `(function (module, exports, require, __dirname, __filename, Symbol) { ${output.text} })`;
+            const evaluateThunk = eval(evaluateText) as (module: any, exports: any, require: (id: string) => any, dirname: string, filename: string, symbolConstructor: SymbolConstructor) => void;
+            const module: { exports: any; } = { exports: {} };
+            evaluateThunk(module, module.exports, noRequire, vpath.dirname(output.file), output.file, FakeSymbol);
+            return module;
+        }
+
+        it("sync (es5)", async () => {
+            const module = evaluate(compile(`
+            let i = 0;
+            const iterator = {
+                [Symbol.iterator]() { return this; },
+                next() {
+                    switch (i++) {
+                        case 0: return { value: 1, done: false };
+                        case 1: return { value: Promise.resolve(2), done: false };
+                        case 2: return { value: new Promise<number>(resolve => setTimeout(resolve, 100, 3)), done: false };
+                        default: return { value: undefined: done: true };
+                    }
+                }
+            };
+            export const output: any[] = [];
+            export async function main() {
+                for await (const item of iterator) {
+                    output.push(item);
+                }
+            }`));
+            await module.exports.main();
+            assert.strictEqual(module.exports.output[0], 1);
+            assert.strictEqual(module.exports.output[1], 2);
+            assert.strictEqual(module.exports.output[2], 3);
+        });
+
+        it("sync (es2015)", async () => {
+            const module = evaluate(compile(`
+            let i = 0;
+            const iterator = {
+                [Symbol.iterator]() { return this; },
+                next() {
+                    switch (i++) {
+                        case 0: return { value: 1, done: false };
+                        case 1: return { value: Promise.resolve(2), done: false };
+                        case 2: return { value: new Promise<number>(resolve => setTimeout(resolve, 100, 3)), done: false };
+                        default: return { value: undefined: done: true };
+                    }
+                }
+            };
+            export const output: any[] = [];
+            export async function main() {
+                for await (const item of iterator) {
+                    output.push(item);
+                }
+            }`, { target: ScriptTarget.ES2015 }));
+            await module.exports.main();
+            assert.strictEqual(module.exports.output[0], 1);
+            assert.strictEqual(module.exports.output[1], 2);
+            assert.strictEqual(module.exports.output[2], 3);
+        });
+
+        it("async (es5)", async () => {
+            const module = evaluate(compile(`
+            let i = 0;
+            const iterator = {
+                [Symbol.asyncIterator]() { return this; },
+                async next() {
+                    switch (i++) {
+                        case 0: return { value: 1, done: false };
+                        case 1: return { value: Promise.resolve(2), done: false };
+                        case 2: return { value: new Promise<number>(resolve => setTimeout(resolve, 100, 3)), done: false };
+                        default: return { value: undefined: done: true };
+                    }
+                }
+            };
+            export const output: any[] = [];
+            export async function main() {
+                for await (const item of iterator) {
+                    output.push(item);
+                }
+            }`));
+            await module.exports.main();
+            assert.strictEqual(module.exports.output[0], 1);
+            assert.instanceOf(module.exports.output[1], Promise);
+            assert.instanceOf(module.exports.output[2], Promise);
+        });
+
+        it("async (es2015)", async () => {
+            const module = evaluate(compile(`
+            let i = 0;
+            const iterator = {
+                [Symbol.asyncIterator]() { return this; },
+                async next() {
+                    switch (i++) {
+                        case 0: return { value: 1, done: false };
+                        case 1: return { value: Promise.resolve(2), done: false };
+                        case 2: return { value: new Promise<number>(resolve => setTimeout(resolve, 100, 3)), done: false };
+                        default: return { value: undefined: done: true };
+                    }
+                }
+            };
+            export const output: any[] = [];
+            export async function main() {
+                for await (const item of iterator) {
+                    output.push(item);
+                }
+            }`, { target: ScriptTarget.ES2015 }));
+            await module.exports.main();
+            assert.strictEqual(module.exports.output[0], 1);
+            assert.instanceOf(module.exports.output[1], Promise);
+            assert.instanceOf(module.exports.output[2], Promise);
+        });
+    });
+}