Cleaned up async return type check

Author: rbuckton

src/compiler/checker.ts

@@ -824,7 +824,7 @@ namespace ts {
         }
 
         // Resolves a qualified name and any involved aliases
-        function resolveEntityName(name: EntityName | Expression, meaning: SymbolFlags, location?: Node): Symbol {
+        function resolveEntityName(name: EntityName | Expression, meaning: SymbolFlags): Symbol {
             if (nodeIsMissing(name)) {
                 return undefined;
             }
@@ -833,7 +833,7 @@ namespace ts {
             if (name.kind === SyntaxKind.Identifier) {
                 let message = meaning === SymbolFlags.Namespace ? Diagnostics.Cannot_find_namespace_0 : Diagnostics.Cannot_find_name_0;
 
-                symbol = resolveName(location || name, (<Identifier>name).text, meaning, message, <Identifier>name);
+                symbol = resolveName(name, (<Identifier>name).text, meaning, message, <Identifier>name);
                 if (!symbol) {
                     return undefined;
                 }
@@ -842,7 +842,7 @@ namespace ts {
                 let left = name.kind === SyntaxKind.QualifiedName ? (<QualifiedName>name).left : (<PropertyAccessExpression>name).expression;
                 let right = name.kind === SyntaxKind.QualifiedName ? (<QualifiedName>name).right : (<PropertyAccessExpression>name).name;
 
-                let namespace = resolveEntityName(left, SymbolFlags.Namespace, location);
+                let namespace = resolveEntityName(left, SymbolFlags.Namespace);
                 if (!namespace || namespace === unknownSymbol || nodeIsMissing(right)) {
                     return undefined;
                 }
@@ -8839,7 +8839,6 @@ namespace ts {
             }
 
             if (produceDiagnostics) {
-                checkCollisionWithAwaiterVariablesInGeneratedCode(node, node.name);
                 checkCollisionWithArgumentsInGeneratedCode(node);
                 if (compilerOptions.noImplicitAny && !node.type) {
                     switch (node.kind) {
@@ -9632,18 +9631,18 @@ namespace ts {
           * a `resolve` function as one of its arguments and results in an object with a 
           * callable `then` signature.
           */
-        function checkAsyncFunctionReturnType(node: SignatureDeclaration): Type {
+        function checkAsyncFunctionReturnType(node: FunctionLikeDeclaration): Type {
             let globalPromiseConstructorLikeType = getGlobalPromiseConstructorLikeType();
             if (globalPromiseConstructorLikeType === emptyObjectType) {
                 // If we couldn't resolve the global PromiseConstructorLike type we cannot verify
                 // compatibility with __awaiter.
                 return unknownType;
             }
 
-            // The return type of an async function will be the type of the instance. For this
-            // to be a type compatible with our async function emit, we must also check that
-            // the type of the declaration (e.g. the static side or "constructor" type of the 
-            // promise) is a compatible `PromiseConstructorLike`.
+            // As part of our emit for an async function, we will need to emit the entity name of
+            // the return type annotation as an expression. To meet the necessary runtime semantics
+            // for __awaiter, we must also check that the type of the declaration (e.g. the static 
+            // side or "constructor" of the promise type) is compatible `PromiseConstructorLike`.
             //
             // An example might be (from lib.es6.d.ts):
             //
@@ -9666,36 +9665,33 @@ namespace ts {
             //
             // When we get the type of the `Promise` symbol here, we get the type of the static
             // side of the `Promise` class, which would be `{ new <T>(...): Promise<T> }`.
-            let returnType = getTypeFromTypeNode(node.type);
-            let entityName = getEntityNameFromTypeNode(node.type);
-            let resolvedName = entityName ? resolveEntityName(entityName, SymbolFlags.Value, node) : undefined;
-            if (!resolvedName || !returnType.symbol) {
-                error(node, Diagnostics.An_async_function_or_method_must_have_a_valid_awaitable_return_type);
-                return unknownType;
+            
+            let promiseType = getTypeFromTypeNode(node.type);
+            let promiseConstructor = getMergedSymbol(promiseType.symbol);
+            if (!promiseConstructor || !symbolIsValue(promiseConstructor)) {
+                error(node, Diagnostics.Type_0_is_not_a_valid_async_function_return_type, typeToString(promiseType));
+                return unknownType
             }
-
-            if (getMergedSymbol(resolvedName) !== getMergedSymbol(returnType.symbol)) {
-                // If we were unable to resolve the return type as a value, report an error.
-                let identifier = getFirstIdentifier(entityName);
-                error(resolvedName.valueDeclaration, Diagnostics.Duplicate_identifier_0_Compiler_uses_declaration_1_to_support_async_functions,
-                    identifier.text,
-                    identifier.text);
+            
+            // Validate the promise constructor type.
+            let promiseConstructorType = getTypeOfSymbol(promiseConstructor);
+            if (!checkTypeAssignableTo(promiseConstructorType, globalPromiseConstructorLikeType, node, Diagnostics.Type_0_is_not_a_valid_async_function_return_type)) {
                 return unknownType;
             }
 
-            // When we emit the async function, we need to ensure we emit any imports that might 
-            // otherwise have been elided if the return type were only ever referenced in a type
-            // position. As such, we check the entity name as an expression.
-            let declaredType = checkExpression(entityName);
-
-            if (!isTypeAssignableTo(declaredType, globalPromiseConstructorLikeType)) {
-                // If the declared type of the return type is not assignable to a PromiseConstructorLike, report an error.
-                error(node, ts.Diagnostics.An_async_function_or_method_must_have_a_valid_awaitable_return_type);
+            // Verify there is no local declaration that could collide with the promise constructor.
+            let promiseName = getEntityNameFromTypeNode(node.type);
+            let root = getFirstIdentifier(promiseName);
+            let rootSymbol = getSymbol(node.locals, root.text, SymbolFlags.Value);
+            if (rootSymbol) {
+                error(rootSymbol.valueDeclaration, Diagnostics.Duplicate_identifier_0_Compiler_uses_declaration_1_to_support_async_functions,
+                    root.text,
+                    getFullyQualifiedName(promiseConstructor));
                 return unknownType;
             }
-            
+
             // Get and return the awaited type of the return type.
-            return getAwaitedType(returnType, node, Diagnostics.An_async_function_or_method_must_have_a_valid_awaitable_return_type);
+            return getAwaitedType(promiseType, node, Diagnostics.An_async_function_or_method_must_have_a_valid_awaitable_return_type);
         }
 
         /** Check a decorator */
@@ -10093,22 +10089,6 @@ namespace ts {
                 }
             }
         }
-
-        function checkCollisionWithAwaiterVariablesInGeneratedCode(node: Node, name: DeclarationName): void {
-            if (!name || name.kind !== SyntaxKind.Identifier || isTypeNode(name)) {
-                return;
-            }
-            
-            let identifier = <Identifier>name;
-            let container = getContainingFunction(name);
-            if (container && isAsyncFunctionLike(container) && node.kind !== SyntaxKind.Identifier) {
-                let promiseConstructorName = getEntityNameFromTypeNode(container.type);
-                let firstIdentifier = promiseConstructorName ? getFirstIdentifier(promiseConstructorName) : undefined;
-                if (firstIdentifier && firstIdentifier.text === identifier.text) {
-                    error(node, Diagnostics.Duplicate_identifier_0_Compiler_uses_declaration_1_to_support_async_functions, identifier.text, getTextOfNode(promiseConstructorName));
-                }
-            }
-        }
 
         // Check that a parameter initializer contains no references to parameters declared to the right of itself
         function checkParameterInitializer(node: VariableLikeDeclaration): void {
@@ -10954,7 +10934,6 @@ namespace ts {
                 checkTypeNameIsReserved(node.name, Diagnostics.Class_name_cannot_be_0);
                 checkCollisionWithCapturedThisVariable(node, node.name);
                 checkCollisionWithRequireExportsInGeneratedCode(node, node.name);
-                checkCollisionWithAwaiterVariablesInGeneratedCode(node, node.name);
             }
             checkTypeParameters(node.typeParameters);
             checkExportsOnMergedDeclarations(node);
@@ -11398,7 +11377,6 @@ namespace ts {
             checkTypeNameIsReserved(node.name, Diagnostics.Enum_name_cannot_be_0);
             checkCollisionWithCapturedThisVariable(node, node.name);
             checkCollisionWithRequireExportsInGeneratedCode(node, node.name);
-            checkCollisionWithAwaiterVariablesInGeneratedCode(node, node.name);
             checkExportsOnMergedDeclarations(node);
 
             computeEnumMemberValues(node);

src/compiler/diagnosticInformationMap.generated.ts

@@ -48,6 +48,7 @@ namespace ts {
         A_set_accessor_parameter_cannot_have_an_initializer: { code: 1052, category: DiagnosticCategory.Error, key: "A 'set' accessor parameter cannot have an initializer." },
         A_set_accessor_cannot_have_rest_parameter: { code: 1053, category: DiagnosticCategory.Error, key: "A 'set' accessor cannot have rest parameter." },
         A_get_accessor_cannot_have_parameters: { code: 1054, category: DiagnosticCategory.Error, key: "A 'get' accessor cannot have parameters." },
+        Type_0_is_not_a_valid_async_function_return_type: { code: 1055, category: DiagnosticCategory.Error, key: "Type '{0}' is not a valid async function return type." },
         Accessors_are_only_available_when_targeting_ECMAScript_5_and_higher: { code: 1056, category: DiagnosticCategory.Error, key: "Accessors are only available when targeting ECMAScript 5 and higher." },
         An_async_function_or_method_must_have_a_valid_awaitable_return_type: { code: 1057, category: DiagnosticCategory.Error, key: "An async function or method must have a valid awaitable return type." },
         Operand_for_await_does_not_have_a_valid_callable_then_member: { code: 1058, category: DiagnosticCategory.Error, key: "Operand for 'await' does not have a valid callable 'then' member." },

src/compiler/diagnosticMessages.json

@@ -179,6 +179,10 @@
         "category": "Error",
         "code": 1054
     },
+    "Type '{0}' is not a valid async function return type.": {
+        "category": "Error",
+        "code": 1055  
+    },
     "Accessors are only available when targeting ECMAScript 5 and higher.": {
         "category": "Error",
         "code": 1056

src/compiler/emitter.ts

@@ -49,10 +49,10 @@ var __param = (this && this.__param) || function (paramIndex, decorator) {
 };`;
 
         const awaiterHelper = `
-var __awaiter = (this && this.__awaiter) || function (generator, thisArg, args, PromiseConstructor) {
-    PromiseConstructor || (PromiseConstructor = Promise);
+var __awaiter = (this && this.__awaiter) || function (args, generator) {
+    var PromiseConstructor = args[1] || Promise;
     return new PromiseConstructor(function (resolve, reject) {
-        generator = generator.call(thisArg, args);
+        generator = generator.call(args[0], args[2]);
         function cast(value) { return value instanceof PromiseConstructor ? value : new PromiseConstructor(function (resolve) { resolve(value); }); }
         function onfulfill(value) { try { step("next", value); } catch (e) { reject(e); } }
         function onreject(value) { try { step("throw", value); } catch (e) { reject(e); } }
@@ -3359,6 +3359,7 @@ var __awaiter = (this && this.__awaiter) || function (generator, thisArg, args,
             function emitAsyncFunctionBodyForES6(node: FunctionLikeDeclaration) {
                 let promiseConstructor = getEntityNameFromTypeNode(node.type);
                 let isArrowFunction = node.kind === SyntaxKind.ArrowFunction;
+                let hasLexicalArguments = (resolver.getNodeCheckFlags(node) & NodeCheckFlags.CaptureArguments) !== 0;
                 let args: string;
 
                 // An async function is emit as an outer function that calls an inner
@@ -3373,7 +3374,7 @@ var __awaiter = (this && this.__awaiter) || function (generator, thisArg, args,
                 //  let a = async (b) => { await b; }
                 //
                 //  // output
-                //  let a = (b) => __awaiter(function* (b) {
+                //  let a = (b) => __awaiter([this], function* (b) {
                 //      yield b;
                 //  }, this);
                 //
@@ -3383,9 +3384,9 @@ var __awaiter = (this && this.__awaiter) || function (generator, thisArg, args,
                 //  let a = async (b) => { await arguments[0]; }
                 //
                 //  // output
-                //  let a = (b) => __awaiter(function* (arguments) {
+                //  let a = (b) => __awaiter([this, arguments], function* (arguments) {
                 //      yield arguments[0];
-                //  }, this, arguments);
+                //  });
                 //
                 // The emit for an async function expression without a lexical `arguments` binding
                 // might be:
@@ -3397,7 +3398,7 @@ var __awaiter = (this && this.__awaiter) || function (generator, thisArg, args,
                 //
                 //  // output
                 //  let a = function (b) {
-                //      return __awaiter(function* () {
+                //      return __awaiter([this], function* () {
                 //          yield b;
                 //      }, this);
                 //  }
@@ -3412,9 +3413,24 @@ var __awaiter = (this && this.__awaiter) || function (generator, thisArg, args,
                 //
                 //  // output
                 //  let a = function (b) {
-                //      return __awaiter(function* (arguments) {
+                //      return __awaiter([this, arguments], function* (arguments) {
+                //          yield arguments[0];
+                //      });
+                //  }
+                //
+                // The emit for an async function expression with a lexical `arguments` binding
+                // and a return type annotation might be:
+                //
+                //  // input
+                //  let a = async function (b): MyPromise<any> {
+                //      await arguments[0];
+                //  }
+                //
+                //  // output
+                //  let a = function (b) {
+                //      return __awaiter([this, arguments, MyPromise], function* (arguments) {
                 //          yield arguments[0];
-                //      }, this, arguments);
+                //      });
                 //  }
                 //
 
@@ -3427,42 +3443,27 @@ var __awaiter = (this && this.__awaiter) || function (generator, thisArg, args,
                     write("return");
                 }
 
+                write(" __awaiter([this");
+                if (promiseConstructor || hasLexicalArguments) {
+                    write(", ");
+                    if (promiseConstructor) {
+                        emitNodeWithoutSourceMap(promiseConstructor);
+                    }
+                    if (hasLexicalArguments) {
+                        write(", arguments");
+                    }
+                }
 
                 // Emit the call to __awaiter.
-                let hasLexicalArguments = (resolver.getNodeCheckFlags(node) & NodeCheckFlags.CaptureArguments) !== 0;
                 if (hasLexicalArguments) {
-                    write(" __awaiter(function* (arguments)");
+                    write("], function* (arguments)");
                 }
                 else {
-                    write(" __awaiter(function* ()");
+                    write("], function* ()");
                 }
 
                 // Emit the signature and body for the inner generator function.
                 emitFunctionBody(node);
-                
-                // Emit the current `this` binding.
-                write(",");
-                writeLine();
-                write("this");
-                
-                // Optionally emit the lexical arguments.
-                if (hasLexicalArguments) {
-                    write(", arguments");
-                }
-
-                // If the function has an explicit type annotation for a promise, emit the 
-                // constructor.
-                if (promiseConstructor) {
-                    // If we did not have lexical arguments, supply undefined (void 0) for
-                    // the `arguments` parameter.
-                    if (!hasLexicalArguments) {
-                        write(", void 0");
-                    }
-                    
-                    write(", ");
-                    emitNodeWithoutSourceMap(promiseConstructor);
-                }
-                
                 write(")");
 
                 // If this is not an async arrow, emit the closing brace of the outer function body.

tests/baselines/reference/asyncArrowFunction1_es6.js

@@ -4,6 +4,5 @@ var foo = async (): Promise<void> => {
 };
 
 //// [asyncArrowFunction1_es6.js]
-var foo = () => __awaiter(function* () {
-},
-this, void 0, Promise);
+var foo = () => __awaiter([this, Promise], function* () {
+});

tests/baselines/reference/asyncArrowFunction6_es6.js

@@ -4,6 +4,5 @@ var foo = async (a = await): Promise<void> => {
 }
 
 //// [asyncArrowFunction6_es6.js]
-var foo = (a = yield ) => __awaiter(function* () {
-},
-this, void 0, Promise);
+var foo = (a = yield ) => __awaiter([this, Promise], function* () {
+});

tests/baselines/reference/asyncArrowFunction7_es6.js

@@ -7,10 +7,8 @@ var bar = async (): Promise<void> => {
 }
 
 //// [asyncArrowFunction7_es6.js]
-var bar = () => __awaiter(function* () {
+var bar = () => __awaiter([this, Promise], function* () {
     // 'await' here is an identifier, and not an await expression.
-    var foo = (a = yield ) => __awaiter(function* () {
-    },
-    this, void 0, Promise);
-},
-this, void 0, Promise);
+    var foo = (a = yield ) => __awaiter([this, Promise], function* () {
+    });
+});

tests/baselines/reference/asyncArrowFunction8_es6.js

@@ -5,7 +5,6 @@ var foo = async (): Promise<void> => {
 }
 
 //// [asyncArrowFunction8_es6.js]
-var foo = () => __awaiter(function* () {
+var foo = () => __awaiter([this, Promise], function* () {
     var v = { [yield ]: foo };
-},
-this, void 0, Promise);
+});

tests/baselines/reference/asyncArrowFunctionCapturesArguments_es6.js

@@ -11,7 +11,6 @@ class C {
 class C {
     method() {
         function other() { }
-        var fn = () => __awaiter(function* (arguments) { return yield other.apply(this, arguments); },
-        this, arguments);
+        var fn = () => __awaiter([this, , arguments], function* (arguments) { return yield other.apply(this, arguments); });
     }
 }

tests/baselines/reference/asyncArrowFunctionCapturesThis_es6.js

@@ -9,7 +9,6 @@ class C {
 //// [asyncArrowFunctionCapturesThis_es6.js]
 class C {
     method() {
-        var fn = () => __awaiter(function* () { return yield this; },
-        this);
+        var fn = () => __awaiter([this], function* () { return yield this; });
     }
 }