Support for ES6 Templates

src/compiler/checker.ts

@@ -427,7 +427,7 @@ module ts {
                 if (result.flags & SymbolFlags.BlockScopedVariable) {
                     // Block-scoped variables cannot be used before their definition
                     var declaration = forEach(result.declarations, d => d.flags & NodeFlags.BlockScoped ? d : undefined);
-                    Debug.assert(declaration, "Block-scoped variable declaration is undefined");
+                    Debug.assert(declaration !== undefined, "Block-scoped variable declaration is undefined");
                     var declarationSourceFile = getSourceFileOfNode(declaration);
                     var referenceSourceFile = getSourceFileOfNode(errorLocation);
                     if (declarationSourceFile === referenceSourceFile) {
@@ -472,7 +472,7 @@ module ts {
         function getSymbolOfPartOfRightHandSideOfImport(entityName: EntityName, importDeclaration?: ImportDeclaration): Symbol {
             if (!importDeclaration) {
                 importDeclaration = getAncestor(entityName, SyntaxKind.ImportDeclaration);
-                Debug.assert(importDeclaration);
+                Debug.assert(importDeclaration !== undefined);
             }
             // There are three things we might try to look for. In the following examples,
             // the search term is enclosed in |...|:
@@ -3334,7 +3334,6 @@ module ts {
                 }
                 if (reportErrors) {
                     headMessage = headMessage || Diagnostics.Type_0_is_not_assignable_to_type_1;
-                    Debug.assert(headMessage);
                     reportError(headMessage, typeToString(source), typeToString(target));
                 }
                 return Ternary.False;
@@ -4912,7 +4911,7 @@ module ts {
             }
             return createArrayType(getUnionType(elementTypes));
         }
-
+        
         function isNumericName(name: string) {
             // The intent of numeric names is that
             //     - they are names with text in a numeric form, and that
@@ -4937,7 +4936,7 @@ module ts {
             // with the strings '"Infinity"', '"-Infinity"', and '"NaN"' respectively.
             return (+name).toString() === name;
         }
-
+        
         function checkObjectLiteral(node: ObjectLiteral, contextualMapper?: TypeMapper): Type {
             var members = node.symbol.members;
             var properties: SymbolTable = {};
@@ -5660,6 +5659,13 @@ module ts {
             return getReturnTypeOfSignature(signature);
         }
 
+        function checkTaggedTemplateExpression(node: TaggedTemplateExpression): Type {
+            // TODO (drosen): Make sure substitutions are assignable to the tag's arguments.
+            checkExpression(node.tag);
+            checkExpression(node.template);
+            return anyType;
+        }
+
         function checkTypeAssertion(node: TypeAssertion): Type {
             var exprType = checkExpression(node.operand);
             var targetType = getTypeFromTypeNode(node.type);
@@ -6170,6 +6176,19 @@ module ts {
             return getUnionType([type1, type2]);
         }
 
+        function checkTemplateExpression(node: TemplateExpression): Type {
+            // We just want to check each expressions, but we are unconcerned with
+            // the type of each expression, as any value may be coerced into a string.
+            // It is worth asking whether this is what we really want though.
+            // A place where we actually *are* concerned with the expressions' types are
+            // in tagged templates.
+            forEach((<TemplateExpression>node).templateSpans, templateSpan => {
+                checkExpression(templateSpan.expression);
+            });
+
+            return stringType;
+        }
+
         function checkExpressionWithContextualType(node: Expression, contextualType: Type, contextualMapper?: TypeMapper): Type {
             var saveContextualType = node.contextualType;
             node.contextualType = contextualType;
@@ -6223,7 +6242,10 @@ module ts {
                     return booleanType;
                 case SyntaxKind.NumericLiteral:
                     return numberType;
+                case SyntaxKind.TemplateExpression:
+                    return checkTemplateExpression(<TemplateExpression>node);
                 case SyntaxKind.StringLiteral:
+                case SyntaxKind.NoSubstitutionTemplateLiteral:
                     return stringType;
                 case SyntaxKind.RegularExpressionLiteral:
                     return globalRegExpType;
@@ -6240,6 +6262,8 @@ module ts {
                 case SyntaxKind.CallExpression:
                 case SyntaxKind.NewExpression:
                     return checkCallExpression(<CallExpression>node);
+                case SyntaxKind.TaggedTemplateExpression:
+                    return checkTaggedTemplateExpression(<TaggedTemplateExpression>node);
                 case SyntaxKind.TypeAssertion:
                     return checkTypeAssertion(<TypeAssertion>node);
                 case SyntaxKind.ParenExpression:
@@ -7549,17 +7573,17 @@ module ts {
                             errorMessage = Diagnostics.Class_0_defines_instance_member_function_1_but_extended_class_2_defines_it_as_instance_member_accessor;
                         }
                         else {
-                            Debug.assert(derived.flags & SymbolFlags.Property);
+                            Debug.assert((derived.flags & SymbolFlags.Property) !== 0);
                             errorMessage = Diagnostics.Class_0_defines_instance_member_function_1_but_extended_class_2_defines_it_as_instance_member_property;
                         }
                     }
                     else if (base.flags & SymbolFlags.Property) {
-                        Debug.assert(derived.flags & SymbolFlags.Method);
+                        Debug.assert((derived.flags & SymbolFlags.Method) !== 0);
                         errorMessage = Diagnostics.Class_0_defines_instance_member_property_1_but_extended_class_2_defines_it_as_instance_member_function;
                     }
                     else {
-                        Debug.assert(base.flags & SymbolFlags.Accessor);
-                        Debug.assert(derived.flags & SymbolFlags.Method);
+                        Debug.assert((base.flags & SymbolFlags.Accessor) !== 0);
+                        Debug.assert((derived.flags & SymbolFlags.Method) !== 0);
                         errorMessage = Diagnostics.Class_0_defines_instance_member_accessor_1_but_extended_class_2_defines_it_as_instance_member_function;
                     }
 
@@ -8016,6 +8040,7 @@ module ts {
                 case SyntaxKind.IndexedAccess:
                 case SyntaxKind.CallExpression:
                 case SyntaxKind.NewExpression:
+                case SyntaxKind.TaggedTemplateExpression:
                 case SyntaxKind.TypeAssertion:
                 case SyntaxKind.ParenExpression:
                 case SyntaxKind.PrefixOperator:
@@ -8293,6 +8318,9 @@ module ts {
                         case SyntaxKind.CallExpression:
                         case SyntaxKind.NewExpression:
                             return (<CallExpression>parent).typeArguments && (<CallExpression>parent).typeArguments.indexOf(node) >= 0;
+                        case SyntaxKind.TaggedTemplateExpression:
+                            // TODO (drosen): TaggedTemplateExpressions may eventually support type arguments.
+                            return false;
                     }
             }
 

src/compiler/core.ts

@@ -19,6 +19,12 @@ module ts {
         [index: string]: T;
     }
 
+    export enum Comparison {
+        LessThan    = -1,
+        EqualTo     = 0,
+        GreaterThan = 1
+    }
+
     export interface StringSet extends Map<any> { }
 
     export function forEach<T, U>(array: T[], callback: (element: T) => U): U {
@@ -93,6 +99,7 @@ module ts {
     export function concatenate<T>(array1: T[], array2: T[]): T[] {
         if (!array2 || !array2.length) return array1;
         if (!array1 || !array1.length) return array2;
+
         return array1.concat(array2);
     }
 
@@ -326,11 +333,11 @@ module ts {
         };
     }
 
-    export function compareValues<T>(a: T, b: T): number {
-        if (a === b) return 0;
-        if (a === undefined) return -1;
-        if (b === undefined) return 1;
-        return a < b ? -1 : 1;
+    export function compareValues<T>(a: T, b: T): Comparison {
+        if (a === b) return Comparison.EqualTo;
+        if (a === undefined) return Comparison.LessThan;
+        if (b === undefined) return Comparison.GreaterThan;
+        return a < b ? Comparison.LessThan : Comparison.GreaterThan;
     }
 
     function getDiagnosticFilename(diagnostic: Diagnostic): string {
@@ -355,7 +362,7 @@ module ts {
         var previousDiagnostic = diagnostics[0];
         for (var i = 1; i < diagnostics.length; i++) {
             var currentDiagnostic = diagnostics[i];
-            var isDupe = compareDiagnostics(currentDiagnostic, previousDiagnostic) === 0;
+            var isDupe = compareDiagnostics(currentDiagnostic, previousDiagnostic) === Comparison.EqualTo;
             if (!isDupe) {
                 newDiagnostics.push(currentDiagnostic);
                 previousDiagnostic = currentDiagnostic;
@@ -644,7 +651,7 @@ module ts {
             return currentAssertionLevel >= level;
         }
 
-        export function assert(expression: any, message?: string, verboseDebugInfo?: () => string): void {
+        export function assert(expression: boolean, message?: string, verboseDebugInfo?: () => string): void {
             if (!expression) {
                 var verboseDebugString = "";
                 if (verboseDebugInfo) {

src/compiler/diagnosticInformationMap.generated.ts

@@ -121,6 +121,8 @@ module ts {
         const_declarations_can_only_be_declared_inside_a_block: { code: 1156, category: DiagnosticCategory.Error, key: "'const' declarations can only be declared inside a block." },
         let_declarations_can_only_be_declared_inside_a_block: { code: 1157, category: DiagnosticCategory.Error, key: "'let' declarations can only be declared inside a block." },
         Aliased_type_cannot_be_an_object_type_literal_Use_an_interface_declaration_instead: { code: 1158, category: DiagnosticCategory.Error, key: "Aliased type cannot be an object type literal. Use an interface declaration instead." },
+        Invalid_template_literal_expected: { code: 1159, category: DiagnosticCategory.Error, key: "Invalid template literal; expected '}'" },
+        Tagged_templates_are_only_available_when_targeting_ECMAScript_6_and_higher: { code: 1160, category: DiagnosticCategory.Error, key: "Tagged templates are only available when targeting ECMAScript 6 and higher." },
         Duplicate_identifier_0: { code: 2300, category: DiagnosticCategory.Error, key: "Duplicate identifier '{0}'." },
         Initializer_of_instance_member_variable_0_cannot_reference_identifier_1_declared_in_the_constructor: { code: 2301, category: DiagnosticCategory.Error, key: "Initializer of instance member variable '{0}' cannot reference identifier '{1}' declared in the constructor." },
         Static_members_cannot_reference_class_type_parameters: { code: 2302, category: DiagnosticCategory.Error, key: "Static members cannot reference class type parameters." },

src/compiler/diagnosticMessages.json

@@ -475,6 +475,14 @@
         "category": "Error",
         "code": 1158
     },
+    "Invalid template literal; expected '}'": {
+        "category": "Error",
+        "code": 1159
+    },
+    "Tagged templates are only available when targeting ECMAScript 6 and higher.": {
+        "category": "Error",
+        "code": 1160
+    },
 
     "Duplicate identifier '{0}'.": {
         "category": "Error",

src/compiler/emitter.ts

@@ -786,14 +786,123 @@ module ts {
                 }
             }
 
-            function emitLiteral(node: LiteralExpression) {
-                var text = getSourceTextOfLocalNode(node);
-                if (node.kind === SyntaxKind.StringLiteral && compilerOptions.sourceMap) {
+            function emitLiteral(node: LiteralExpression): void {
+                var text = getLiteralText();
+
+                if (compilerOptions.sourceMap && (node.kind === SyntaxKind.StringLiteral || isTemplateLiteralKind(node.kind))) {
                     writer.writeLiteral(text);
                 }
                 else {
                     write(text);
                 }
+
+                function getLiteralText() {
+                    if (compilerOptions.target < ScriptTarget.ES6 && isTemplateLiteralKind(node.kind)) {
+                        return getTemplateLiteralAsStringLiteral(node)
+                    }
+
+                    return getSourceTextOfLocalNode(node);
+                }
+            }
+
+            function getTemplateLiteralAsStringLiteral(node: LiteralExpression): string {
+                return '"' + escapeString(node.text) + '"';
+            }
+
+            function emitTemplateExpression(node: TemplateExpression): void {
+                // In ES6 mode and above, we can simply emit each portion of a template in order, but in
+                // ES3 & ES5 we must convert the template expression into a series of string concatenations.
+                if (compilerOptions.target >= ScriptTarget.ES6) {
+                    forEachChild(node, emit);
+                    return;
+                }
+
+                Debug.assert(node.parent.kind !== SyntaxKind.TaggedTemplateExpression);
+
+                var templateNeedsParens = isExpression(node.parent)
+                    && node.parent.kind !== SyntaxKind.ParenExpression
+                    && comparePrecedenceToBinaryPlus(node.parent) !== Comparison.LessThan;
+
+                if (templateNeedsParens) {
+                    write("(");
+                }
+
+                emitLiteral(node.head);
+
+                forEach(node.templateSpans, templateSpan => {
+                    // Check if the expression has operands and binds its operands less closely than binary '+'.
+                    // If it does, we need to wrap the expression in parentheses. Otherwise, something like
+                    //    `abc${ 1 << 2}`
+                    // becomes
+                    //    "abc" + 1 << 2 + ""
+                    // which is really
+                    //    ("abc" + 1) << (2 + "")
+                    // rather than
+                    //    "abc" + (1 << 2) + ""
+                    var needsParens = templateSpan.expression.kind !== SyntaxKind.ParenExpression
+                        && comparePrecedenceToBinaryPlus(templateSpan.expression) !== Comparison.GreaterThan;
+
+                    write(" + ");
+
+                    if (needsParens) {
+                        write("(");
+                    }
+                    emit(templateSpan.expression);
+                    if (needsParens) {
+                        write(")");
+                    }
+
+                    // Only emit if the literal is non-empty.
+                    // The binary '+' operator is left-associative, so the first string concatenation will force
+                    // the result up to this point to be a string. Emitting a '+ ""' has no semantic effect.
+                    if (templateSpan.literal.text.length !== 0) {
+                        write(" + ")
+                        emitLiteral(templateSpan.literal);
+                    }
+                });
+
+                if (templateNeedsParens) {
+                    write(")");
+                }
+
+                /**
+                 * Returns whether the expression has lesser, greater,
+                 * or equal precedence to the binary '+' operator
+                 */
+                function comparePrecedenceToBinaryPlus(expression: Expression): Comparison {
+                    // All binary expressions have lower precedence than '+' apart from '*', '/', and '%'.
+                    // All unary operators have a higher precedence apart from yield.
+                    // Arrow functions and conditionals have a lower precedence, 
+                    // although we convert the former into regular function expressions in ES5 mode,
+                    // and in ES6 mode this function won't get called anyway.
+                    // 
+                    // TODO (drosen): Note that we need to account for the upcoming 'yield' and
+                    //                spread ('...') unary operators that are anticipated for ES6.
+                    Debug.assert(compilerOptions.target <= ScriptTarget.ES5);
+                    switch (expression.kind) {
+                        case SyntaxKind.BinaryExpression:
+                            switch ((<BinaryExpression>expression).operator) {
+                                case SyntaxKind.AsteriskToken:
+                                case SyntaxKind.SlashToken:
+                                case SyntaxKind.PercentToken:
+                                    return Comparison.GreaterThan;
+                                case SyntaxKind.PlusToken:
+                                    return Comparison.EqualTo;
+                                default:
+                                    return Comparison.LessThan;
+                            }
+                        case SyntaxKind.ConditionalExpression:
+                            return Comparison.LessThan;
+                        default:
+                            return Comparison.GreaterThan;
+                    }
+                }
+
+            }
+
+            function emitTemplateSpan(span: TemplateSpan) {
+                emit(span.expression);
+                emit(span.literal);
             }
 
             // This function specifically handles numeric/string literals for enum and accessor 'identifiers'.
@@ -977,6 +1086,13 @@ module ts {
                 }
             }
 
+            function emitTaggedTemplateExpression(node: TaggedTemplateExpression): void {
+                Debug.assert(compilerOptions.target >= ScriptTarget.ES6, "Trying to emit a tagged template in pre-ES6 mode.");
+                emit(node.tag);
+                write(" ");
+                emit(node.template);
+            }
+
             function emitParenExpression(node: ParenExpression) {
                 if (node.expression.kind === SyntaxKind.TypeAssertion) {
                     var operand = (<TypeAssertion>node.expression).operand;
@@ -2085,7 +2201,15 @@ module ts {
                     case SyntaxKind.NumericLiteral:
                     case SyntaxKind.StringLiteral:
                     case SyntaxKind.RegularExpressionLiteral:
+                    case SyntaxKind.NoSubstitutionTemplateLiteral:
+                    case SyntaxKind.TemplateHead:
+                    case SyntaxKind.TemplateMiddle:
+                    case SyntaxKind.TemplateTail:
                         return emitLiteral(<LiteralExpression>node);
+                    case SyntaxKind.TemplateExpression:
+                        return emitTemplateExpression(<TemplateExpression>node);
+                    case SyntaxKind.TemplateSpan:
+                        return emitTemplateSpan(<TemplateSpan>node);
                     case SyntaxKind.QualifiedName:
                         return emitPropertyAccess(<QualifiedName>node);
                     case SyntaxKind.ArrayLiteral:
@@ -2102,6 +2226,8 @@ module ts {
                         return emitCallExpression(<CallExpression>node);
                     case SyntaxKind.NewExpression:
                         return emitNewExpression(<NewExpression>node);
+                    case SyntaxKind.TaggedTemplateExpression:
+                        return emitTaggedTemplateExpression(<TaggedTemplateExpression>node);
                     case SyntaxKind.TypeAssertion:
                         return emit((<TypeAssertion>node).operand);
                     case SyntaxKind.ParenExpression: