Support top level "for await of"

src/compiler/checker.ts

@@ -40104,19 +40104,33 @@ namespace ts {
             }
 
             if (forInOrOfStatement.kind === SyntaxKind.ForOfStatement && forInOrOfStatement.awaitModifier) {
-                if ((forInOrOfStatement.flags & NodeFlags.AwaitContext) === NodeFlags.None) {
-                    // use of 'for-await-of' in non-async function
+                if (!(forInOrOfStatement.flags & NodeFlags.AwaitContext)) {
                     const sourceFile = getSourceFileOfNode(forInOrOfStatement);
-                    if (!hasParseDiagnostics(sourceFile)) {
-                        const diagnostic = createDiagnosticForNode(forInOrOfStatement.awaitModifier, Diagnostics.A_for_await_of_statement_is_only_allowed_within_an_async_function_or_async_generator);
-                        const func = getContainingFunction(forInOrOfStatement);
-                        if (func && func.kind !== SyntaxKind.Constructor) {
-                            Debug.assert((getFunctionFlags(func) & FunctionFlags.Async) === 0, "Enclosing function should never be an async function.");
-                            const relatedInfo = createDiagnosticForNode(func, Diagnostics.Did_you_mean_to_mark_this_function_as_async);
-                            addRelatedInfo(diagnostic, relatedInfo);
-                        }
-                        diagnostics.add(diagnostic);
-                        return true;
+                    if (isInTopLevelContext(forInOrOfStatement)) {
+                        if (!hasParseDiagnostics(sourceFile)) {
+                            if (!isEffectiveExternalModule(sourceFile, compilerOptions)) {
+                                diagnostics.add(createDiagnosticForNode(forInOrOfStatement.awaitModifier,
+                                    Diagnostics.await_expressions_are_only_allowed_at_the_top_level_of_a_file_when_that_file_is_a_module_but_this_file_has_no_imports_or_exports_Consider_adding_an_empty_export_to_make_this_file_a_module));
+                            }
+                            if ((moduleKind !== ModuleKind.ESNext && moduleKind !== ModuleKind.System) || languageVersion < ScriptTarget.ES2017) {
+                                diagnostics.add(createDiagnosticForNode(forInOrOfStatement.awaitModifier,
+                                    Diagnostics.Top_level_await_expressions_are_only_allowed_when_the_module_option_is_set_to_esnext_or_system_and_the_target_option_is_set_to_es2017_or_higher));
+                            }
+                        }
+                    }
+                    else {
+                        // use of 'for-await-of' in non-async function
+                        if (!hasParseDiagnostics(sourceFile)) {
+                            const diagnostic = createDiagnosticForNode(forInOrOfStatement.awaitModifier, Diagnostics.A_for_await_of_statement_is_only_allowed_within_an_async_function_or_async_generator);
+                            const func = getContainingFunction(forInOrOfStatement);
+                            if (func && func.kind !== SyntaxKind.Constructor) {
+                                Debug.assert((getFunctionFlags(func) & FunctionFlags.Async) === 0, "Enclosing function should never be an async function.");
+                                const relatedInfo = createDiagnosticForNode(func, Diagnostics.Did_you_mean_to_mark_this_function_as_async);
+                                addRelatedInfo(diagnostic, relatedInfo);
+                            }
+                            diagnostics.add(diagnostic);
+                            return true;
+                        }
                     }
                     return false;
                 }

tests/baselines/reference/awaitInNonAsyncFunction.errors.txt

@@ -12,7 +12,7 @@ tests/cases/compiler/awaitInNonAsyncFunction.ts(30,9): error TS1103: A 'for-awai
 tests/cases/compiler/awaitInNonAsyncFunction.ts(31,5): error TS1308: 'await' expressions are only allowed within async functions and at the top levels of modules.
 tests/cases/compiler/awaitInNonAsyncFunction.ts(34,7): error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
 tests/cases/compiler/awaitInNonAsyncFunction.ts(35,5): error TS1308: 'await' expressions are only allowed within async functions and at the top levels of modules.
-tests/cases/compiler/awaitInNonAsyncFunction.ts(39,5): error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
+tests/cases/compiler/awaitInNonAsyncFunction.ts(39,5): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
 tests/cases/compiler/awaitInNonAsyncFunction.ts(40,1): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
 
 
@@ -97,7 +97,7 @@ tests/cases/compiler/awaitInNonAsyncFunction.ts(40,1): error TS1378: Top-level '
 
     for await (const _ of []);
         ~~~~~
-!!! error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
+!!! error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
     await null;
     ~~~~~
 !!! error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.

tests/baselines/reference/parser.forAwait.es2018.errors.txt

@@ -7,24 +7,30 @@ tests/cases/conformance/parser/ecmascript2018/forAwait/inFunctionDeclWithDeclIsE
 tests/cases/conformance/parser/ecmascript2018/forAwait/inFunctionDeclWithExprIsError.ts(3,9): error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
 tests/cases/conformance/parser/ecmascript2018/forAwait/inGeneratorWithDeclIsError.ts(3,9): error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
 tests/cases/conformance/parser/ecmascript2018/forAwait/inGeneratorWithExprIsError.ts(3,9): error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
-tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithDeclIsError.ts(1,5): error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
+tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithDeclIsError.ts(1,5): error TS1375: 'await' expressions are only allowed at the top level of a file when that file is a module, but this file has no imports or exports. Consider adding an empty 'export {}' to make this file a module.
+tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithDeclIsError.ts(1,5): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
 tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithDeclIsError.ts(1,23): error TS2304: Cannot find name 'y'.
-tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithExprIsError.ts(1,5): error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
+tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithExprIsError.ts(1,5): error TS1375: 'await' expressions are only allowed at the top level of a file when that file is a module, but this file has no imports or exports. Consider adding an empty 'export {}' to make this file a module.
+tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithExprIsError.ts(1,5): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
 tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithExprIsError.ts(1,12): error TS2304: Cannot find name 'x'.
 tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithExprIsError.ts(1,17): error TS2304: Cannot find name 'y'.
 
 
-==== tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithDeclIsError.ts (2 errors) ====
+==== tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithDeclIsError.ts (3 errors) ====
     for await (const x of y) {
         ~~~~~
-!!! error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
+!!! error TS1375: 'await' expressions are only allowed at the top level of a file when that file is a module, but this file has no imports or exports. Consider adding an empty 'export {}' to make this file a module.
+        ~~~~~
+!!! error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
                           ~
 !!! error TS2304: Cannot find name 'y'.
     }
-==== tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithExprIsError.ts (3 errors) ====
+==== tests/cases/conformance/parser/ecmascript2018/forAwait/topLevelWithExprIsError.ts (4 errors) ====
     for await (x of y) {
         ~~~~~
-!!! error TS1103: A 'for-await-of' statement is only allowed within an async function or async generator.
+!!! error TS1375: 'await' expressions are only allowed at the top level of a file when that file is a module, but this file has no imports or exports. Consider adding an empty 'export {}' to make this file a module.
+        ~~~~~
+!!! error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
                ~
 !!! error TS2304: Cannot find name 'x'.
                     ~

tests/baselines/reference/topLevelAwait.1(module=esnext,target=es2015).errors.txt

@@ -1,5 +1,6 @@
 tests/cases/conformance/externalModules/index.ts(2,1): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
 tests/cases/conformance/externalModules/index.ts(46,3): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
+tests/cases/conformance/externalModules/other.ts(9,5): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
 
 
 ==== tests/cases/conformance/externalModules/index.ts (2 errors) ====
@@ -72,8 +73,18 @@ tests/cases/conformance/externalModules/index.ts(46,3): error TS1378: Top-level
     await
         1;
 
-==== tests/cases/conformance/externalModules/other.ts (0 errors) ====
+==== tests/cases/conformance/externalModules/other.ts (1 errors) ====
     const _await = 1;
 
     // await allowed in aliased export
-    export { _await as await };
+    export { _await as await };
+
+    // for-await-of
+    const arr = [Promise.resolve()];
+
+    for await (const item of arr) {
+        ~~~~~
+!!! error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
+      item;
+    }
+

tests/baselines/reference/topLevelAwait.1(module=esnext,target=es2015).js

@@ -70,12 +70,36 @@ await
 const _await = 1;
 
 // await allowed in aliased export
-export { _await as await };
+export { _await as await };
+
+// for-await-of
+const arr = [Promise.resolve()];
+
+for await (const item of arr) {
+  item;
+}
+
 
 //// [other.js]
+var e_1, _a;
 const _await = 1;
 // await allowed in aliased export
 export { _await as await };
+// for-await-of
+const arr = [Promise.resolve()];
+try {
+    for (var arr_1 = __asyncValues(arr), arr_1_1; arr_1_1 = await arr_1.next(), !arr_1_1.done;) {
+        const item = arr_1_1.value;
+        item;
+    }
+}
+catch (e_1_1) { e_1 = { error: e_1_1 }; }
+finally {
+    try {
+        if (arr_1_1 && !arr_1_1.done && (_a = arr_1.return)) await _a.call(arr_1);
+    }
+    finally { if (e_1) throw e_1.error; }
+}
 //// [index.js]
 export const x = 1;
 await x;

tests/baselines/reference/topLevelAwait.1(module=esnext,target=es2015).symbols

@@ -126,3 +126,18 @@ export { _await as await };
 >_await : Symbol(_await, Decl(other.ts, 0, 5))
 >await : Symbol(await, Decl(other.ts, 3, 8))
 
+// for-await-of
+const arr = [Promise.resolve()];
+>arr : Symbol(arr, Decl(other.ts, 6, 5))
+>Promise.resolve : Symbol(PromiseConstructor.resolve, Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>resolve : Symbol(PromiseConstructor.resolve, Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --))
+
+for await (const item of arr) {
+>item : Symbol(item, Decl(other.ts, 8, 16))
+>arr : Symbol(arr, Decl(other.ts, 6, 5))
+
+  item;
+>item : Symbol(item, Decl(other.ts, 8, 16))
+}
+

tests/baselines/reference/topLevelAwait.1(module=esnext,target=es2015).types

@@ -176,3 +176,20 @@ export { _await as await };
 >_await : 1
 >await : 1
 
+// for-await-of
+const arr = [Promise.resolve()];
+>arr : Promise<void>[]
+>[Promise.resolve()] : Promise<void>[]
+>Promise.resolve() : Promise<void>
+>Promise.resolve : { (): Promise<void>; <T>(value: T | PromiseLike<T>): Promise<T>; }
+>Promise : PromiseConstructor
+>resolve : { (): Promise<void>; <T>(value: T | PromiseLike<T>): Promise<T>; }
+
+for await (const item of arr) {
+>item : void
+>arr : Promise<void>[]
+
+  item;
+>item : void
+}
+

tests/baselines/reference/topLevelAwait.1(module=esnext,target=es2017).js

@@ -70,12 +70,36 @@ await
 const _await = 1;
 
 // await allowed in aliased export
-export { _await as await };
+export { _await as await };
+
+// for-await-of
+const arr = [Promise.resolve()];
+
+for await (const item of arr) {
+  item;
+}
+
 
 //// [other.js]
+var e_1, _a;
 const _await = 1;
 // await allowed in aliased export
 export { _await as await };
+// for-await-of
+const arr = [Promise.resolve()];
+try {
+    for (var arr_1 = __asyncValues(arr), arr_1_1; arr_1_1 = await arr_1.next(), !arr_1_1.done;) {
+        const item = arr_1_1.value;
+        item;
+    }
+}
+catch (e_1_1) { e_1 = { error: e_1_1 }; }
+finally {
+    try {
+        if (arr_1_1 && !arr_1_1.done && (_a = arr_1.return)) await _a.call(arr_1);
+    }
+    finally { if (e_1) throw e_1.error; }
+}
 //// [index.js]
 export const x = 1;
 await x;

tests/baselines/reference/topLevelAwait.1(module=esnext,target=es2017).symbols

@@ -126,3 +126,18 @@ export { _await as await };
 >_await : Symbol(_await, Decl(other.ts, 0, 5))
 >await : Symbol(await, Decl(other.ts, 3, 8))
 
+// for-await-of
+const arr = [Promise.resolve()];
+>arr : Symbol(arr, Decl(other.ts, 6, 5))
+>Promise.resolve : Symbol(PromiseConstructor.resolve, Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>resolve : Symbol(PromiseConstructor.resolve, Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --))
+
+for await (const item of arr) {
+>item : Symbol(item, Decl(other.ts, 8, 16))
+>arr : Symbol(arr, Decl(other.ts, 6, 5))
+
+  item;
+>item : Symbol(item, Decl(other.ts, 8, 16))
+}
+

tests/baselines/reference/topLevelAwait.1(module=esnext,target=es2017).types

@@ -176,3 +176,20 @@ export { _await as await };
 >_await : 1
 >await : 1
 
+// for-await-of
+const arr = [Promise.resolve()];
+>arr : Promise<void>[]
+>[Promise.resolve()] : Promise<void>[]
+>Promise.resolve() : Promise<void>
+>Promise.resolve : { (): Promise<void>; <T>(value: T | PromiseLike<T>): Promise<T>; }
+>Promise : PromiseConstructor
+>resolve : { (): Promise<void>; <T>(value: T | PromiseLike<T>): Promise<T>; }
+
+for await (const item of arr) {
+>item : void
+>arr : Promise<void>[]
+
+  item;
+>item : void
+}
+

tests/baselines/reference/topLevelAwait.1(module=system,target=es2015).errors.txt

@@ -1,5 +1,6 @@
 tests/cases/conformance/externalModules/index.ts(2,1): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
 tests/cases/conformance/externalModules/index.ts(46,3): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
+tests/cases/conformance/externalModules/other.ts(9,5): error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
 
 
 ==== tests/cases/conformance/externalModules/index.ts (2 errors) ====
@@ -72,8 +73,18 @@ tests/cases/conformance/externalModules/index.ts(46,3): error TS1378: Top-level
     await
         1;
 
-==== tests/cases/conformance/externalModules/other.ts (0 errors) ====
+==== tests/cases/conformance/externalModules/other.ts (1 errors) ====
     const _await = 1;
 
     // await allowed in aliased export
-    export { _await as await };
+    export { _await as await };
+
+    // for-await-of
+    const arr = [Promise.resolve()];
+
+    for await (const item of arr) {
+        ~~~~~
+!!! error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.
+      item;
+    }
+

tests/baselines/reference/topLevelAwait.1(module=system,target=es2015).js

@@ -70,18 +70,41 @@ await
 const _await = 1;
 
 // await allowed in aliased export
-export { _await as await };
+export { _await as await };
+
+// for-await-of
+const arr = [Promise.resolve()];
+
+for await (const item of arr) {
+  item;
+}
+
 
 //// [other.js]
 System.register([], function (exports_1, context_1) {
     "use strict";
-    var _await;
+    var e_1, _a, _await, arr;
     var __moduleName = context_1 && context_1.id;
     return {
         setters: [],
-        execute: function () {
+        execute: async function () {
             _await = 1;
             exports_1("await", _await);
+            // for-await-of
+            arr = [Promise.resolve()];
+            try {
+                for (var arr_1 = __asyncValues(arr), arr_1_1; arr_1_1 = await arr_1.next(), !arr_1_1.done;) {
+                    const item = arr_1_1.value;
+                    item;
+                }
+            }
+            catch (e_1_1) { e_1 = { error: e_1_1 }; }
+            finally {
+                try {
+                    if (arr_1_1 && !arr_1_1.done && (_a = arr_1.return)) await _a.call(arr_1);
+                }
+                finally { if (e_1) throw e_1.error; }
+            }
         }
     };
 });

tests/baselines/reference/topLevelAwait.1(module=system,target=es2015).symbols

@@ -126,3 +126,18 @@ export { _await as await };
 >_await : Symbol(_await, Decl(other.ts, 0, 5))
 >await : Symbol(await, Decl(other.ts, 3, 8))
 
+// for-await-of
+const arr = [Promise.resolve()];
+>arr : Symbol(arr, Decl(other.ts, 6, 5))
+>Promise.resolve : Symbol(PromiseConstructor.resolve, Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>resolve : Symbol(PromiseConstructor.resolve, Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --))
+
+for await (const item of arr) {
+>item : Symbol(item, Decl(other.ts, 8, 16))
+>arr : Symbol(arr, Decl(other.ts, 6, 5))
+
+  item;
+>item : Symbol(item, Decl(other.ts, 8, 16))
+}
+