demo/typescript.js
function checkDecorator(node) {
            var signature = getResolvedSignature(node);
            var returnType = getReturnTypeOfSignature(signature);
            if (returnType.flags & 1 /* Any */) {
                return;
            }
            var expectedReturnType;
            var headMessage = getDiagnosticHeadMessageForDecoratorResolution(node);
            var errorInfo;
            switch (node.parent.kind) {
                case 214 /* ClassDeclaration */:
                    var classSymbol = getSymbolOfNode(node.parent);
                    var classConstructorType = getTypeOfSymbol(classSymbol);
                    expectedReturnType = getUnionType([classConstructorType, voidType]);
                    break;
                case 138 /* Parameter */:
                    expectedReturnType = voidType;
                    errorInfo = ts.chainDiagnosticMessages(errorInfo, ts.Diagnostics.The_return_type_of_a_parameter_decorator_function_must_be_either_void_or_any);
                    break;
                case 141 /* PropertyDeclaration */:
                    expectedReturnType = voidType;
                    errorInfo = ts.chainDiagnosticMessages(errorInfo, ts.Diagnostics.The_return_type_of_a_property_decorator_function_must_be_either_void_or_any);
                    break;
                case 143 /* MethodDeclaration */:
                case 145 /* GetAccessor */:
                case 146 /* SetAccessor */:
                    var methodType = getTypeOfNode(node.parent);
                    var descriptorType = createTypedPropertyDescriptorType(methodType);
                    expectedReturnType = getUnionType([descriptorType, voidType]);
                    break;
            }
            checkTypeAssignableTo(returnType, expectedReturnType, node, headMessage, errorInfo);
        }
function checkDecorator(node) {
            var signature = getResolvedSignature(node);
            var returnType = getReturnTypeOfSignature(signature);
            if (returnType.flags & 1 /* Any */) {
                return;
            }
            var expectedReturnType;
            var headMessage = getDiagnosticHeadMessageForDecoratorResolution(node);
            var errorInfo;
            switch (node.parent.kind) {
                case 214 /* ClassDeclaration */:
                    var classSymbol = getSymbolOfNode(node.parent);
                    var classConstructorType = getTypeOfSymbol(classSymbol);
                    expectedReturnType = getUnionType([classConstructorType, voidType]);
                    break;
                case 138 /* Parameter */:
                    expectedReturnType = voidType;
                    errorInfo = ts.chainDiagnosticMessages(errorInfo, ts.Diagnostics.The_return_type_of_a_parameter_decorator_function_must_be_either_void_or_any);
                    break;
                case 141 /* PropertyDeclaration */:
                    expectedReturnType = voidType;
                    errorInfo = ts.chainDiagnosticMessages(errorInfo, ts.Diagnostics.The_return_type_of_a_property_decorator_function_must_be_either_void_or_any);
                    break;
                case 143 /* MethodDeclaration */:
                case 145 /* GetAccessor */:
                case 146 /* SetAccessor */:
                    var methodType = getTypeOfNode(node.parent);
                    var descriptorType = createTypedPropertyDescriptorType(methodType);
                    expectedReturnType = getUnionType([descriptorType, voidType]);
                    break;
            }
            checkTypeAssignableTo(returnType, expectedReturnType, node, headMessage, errorInfo);
        }
Check a decorator