Moved async functions for ES6 behind experimental flag

Author: rbuckton

src/compiler/checker.ts

@@ -9863,6 +9863,10 @@ namespace ts {
             checkSignatureDeclaration(node);
             let isAsync = isAsyncFunctionLike(node);
             if (isAsync) {
+                if (!compilerOptions.experimentalAsyncFunctions) {
+                    error(node, Diagnostics.Experimental_support_for_async_functions_is_a_feature_that_is_subject_to_change_in_a_future_release_Specify_experimentalAsyncFunctions_to_remove_this_warning);
+                }
+                
                 emitAwaiter = true;
             } 
 

src/compiler/commandLineParser.ts

@@ -192,6 +192,11 @@ namespace ts {
             type: "boolean",
             description: Diagnostics.Watch_input_files,
         },
+        {
+            name: "experimentalAsyncFunctions",
+            type: "boolean",
+            description: Diagnostics.Enables_experimental_support_for_ES7_async_functions
+        },
         {
             name: "experimentalDecorators",
             type: "boolean",

src/compiler/diagnosticInformationMap.generated.ts

@@ -201,6 +201,7 @@ namespace ts {
         An_export_declaration_can_only_be_used_in_a_module: { code: 1233, category: DiagnosticCategory.Error, key: "An export declaration can only be used in a module." },
         An_ambient_module_declaration_is_only_allowed_at_the_top_level_in_a_file: { code: 1234, category: DiagnosticCategory.Error, key: "An ambient module declaration is only allowed at the top level in a file." },
         A_namespace_declaration_is_only_allowed_in_a_namespace_or_module: { code: 1235, category: DiagnosticCategory.Error, key: "A namespace declaration is only allowed in a namespace or module." },
+        Experimental_support_for_async_functions_is_a_feature_that_is_subject_to_change_in_a_future_release_Specify_experimentalAsyncFunctions_to_remove_this_warning: { code: 1236, category: DiagnosticCategory.Error, key: "Experimental support for async functions is a feature that is subject to change in a future release. Specify '--experimentalAsyncFunctions' to remove this warning." },
         with_statements_are_not_allowed_in_an_async_function_block: { code: 1300, category: DiagnosticCategory.Error, key: "'with' statements are not allowed in an async function block." },
         await_expression_is_only_allowed_within_an_async_function: { code: 1308, category: DiagnosticCategory.Error, key: "'await' expression is only allowed within an async function." },
         Async_functions_are_only_available_when_targeting_ECMAScript_6_and_higher: { code: 1311, category: DiagnosticCategory.Error, key: "Async functions are only available when targeting ECMAScript 6 and higher." },
@@ -547,6 +548,8 @@ namespace ts {
         Option_experimentalDecorators_must_also_be_specified_when_option_emitDecoratorMetadata_is_specified: { code: 6064, category: DiagnosticCategory.Error, key: "Option 'experimentalDecorators' must also be specified when option 'emitDecoratorMetadata' is specified." },
         Enables_experimental_support_for_ES7_decorators: { code: 6065, category: DiagnosticCategory.Message, key: "Enables experimental support for ES7 decorators." },
         Enables_experimental_support_for_emitting_type_metadata_for_decorators: { code: 6066, category: DiagnosticCategory.Message, key: "Enables experimental support for emitting type metadata for decorators." },
+        Option_experimentalAsyncFunctions_cannot_be_specified_when_targeting_ES5_or_lower: { code: 6067, category: DiagnosticCategory.Message, key: "Option 'experimentalAsyncFunctions' cannot be specified when targeting ES5 or lower." },
+        Enables_experimental_support_for_ES7_async_functions: { code: 6068, category: DiagnosticCategory.Message, key: "Enables experimental support for ES7 async functions." },
         Variable_0_implicitly_has_an_1_type: { code: 7005, category: DiagnosticCategory.Error, key: "Variable '{0}' implicitly has an '{1}' type." },
         Parameter_0_implicitly_has_an_1_type: { code: 7006, category: DiagnosticCategory.Error, key: "Parameter '{0}' implicitly has an '{1}' type." },
         Member_0_implicitly_has_an_1_type: { code: 7008, category: DiagnosticCategory.Error, key: "Member '{0}' implicitly has an '{1}' type." },

src/compiler/diagnosticMessages.json

@@ -791,6 +791,10 @@
         "category": "Error",
         "code": 1235
     },
+    "Experimental support for async functions is a feature that is subject to change in a future release. Specify '--experimentalAsyncFunctions' to remove this warning.": {
+        "category": "Error",
+        "code": 1236
+    },
 
 
     "'with' statements are not allowed in an async function block.": {
@@ -2180,6 +2184,14 @@
         "category": "Message",
         "code": 6066
     },
+    "Option 'experimentalAsyncFunctions' cannot be specified when targeting ES5 or lower.": {
+        "category": "Message",
+        "code": 6067
+    },
+    "Enables experimental support for ES7 async functions.": {
+        "category": "Message",
+        "code": 6068
+    },
 
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",

src/compiler/program.ts

@@ -144,7 +144,7 @@ namespace ts {
         let program: Program;
         let files: SourceFile[] = [];
         let diagnostics = createDiagnosticCollection();
-
+
         let commonSourceDirectory: string;
         let diagnosticsProducingTypeChecker: TypeChecker;
         let noDiagnosticsTypeChecker: TypeChecker;
@@ -676,6 +676,11 @@ namespace ts {
                 !options.experimentalDecorators) {
                 diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_experimentalDecorators_must_also_be_specified_when_option_emitDecoratorMetadata_is_specified));
             }
+            
+            if (options.experimentalAsyncFunctions &&
+                options.target !== ScriptTarget.ES6) {
+                diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_experimentalAsyncFunctions_cannot_be_specified_when_targeting_ES5_or_lower));
+            }
         }
     }
 }

src/compiler/types.ts

@@ -1878,6 +1878,7 @@ namespace ts {
         watch?: boolean;
         isolatedModules?: boolean;
         experimentalDecorators?: boolean;
+        experimentalAsyncFunctions?: boolean;
         emitDecoratorMetadata?: boolean;
         /* @internal */ stripInternal?: boolean;
 

src/harness/harness.ts

@@ -1055,6 +1055,10 @@ module Harness {
                         case 'emitdecoratormetadata':
                             options.emitDecoratorMetadata = setting.value === 'true';
                             break;
+                            
+                        case 'experimentalasyncfunctions':
+                            options.experimentalAsyncFunctions = setting.value === 'true';
+                            break;
 
                         case 'noemithelpers':
                             options.noEmitHelpers = setting.value === 'true';

tests/cases/conformance/async/es6/asyncArrowFunction/asyncArrowFunction10_es6.ts

@@ -1,5 +1,6 @@
 // @target: ES6
 // @noEmitHelpers: true
+// @experimentalAsyncFunctions: true
 
 var foo = async foo(): Promise<void> => {
    // Legal to use 'await' in a type context.

tests/cases/conformance/async/es6/asyncArrowFunction/asyncArrowFunction1_es6.ts

@@ -1,5 +1,6 @@
 // @target: ES6
 // @noEmitHelpers: true
+// @experimentalAsyncFunctions: true
 
 var foo = async (): Promise<void> => {
 };

tests/cases/conformance/async/es6/asyncArrowFunction/asyncArrowFunction2_es6.ts

@@ -1,4 +1,5 @@
 // @target: ES6
 // @noEmitHelpers: true
+// @experimentalAsyncFunctions: true
 var f = (await) => {
 }