Template literal types and mapped type 'as' clauses

src/compiler/diagnosticMessages.json

@@ -3028,6 +3028,10 @@
         "category": "Error",
         "code": 2792
     },
+    "Template type argument '{0}' is not literal type or a generic type.": {
+        "category": "Error",
+        "code": 2793
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

src/compiler/emitter.ts

@@ -1313,6 +1313,8 @@ namespace ts {
                         return emitConstructSignature(<ConstructSignatureDeclaration>node);
                     case SyntaxKind.IndexSignature:
                         return emitIndexSignature(<IndexSignatureDeclaration>node);
+                    case SyntaxKind.TemplateTypeSpan:
+                        return emitTemplateTypeSpan(<TemplateTypeSpan>node);
 
                     // Types
                     case SyntaxKind.TypePredicate:
@@ -1357,6 +1359,8 @@ namespace ts {
                         return emitMappedType(<MappedTypeNode>node);
                     case SyntaxKind.LiteralType:
                         return emitLiteralType(<LiteralTypeNode>node);
+                    case SyntaxKind.TemplateType:
+                        return emitTemplateType(<TemplateTypeNode>node);
                     case SyntaxKind.ImportType:
                         return emitImportTypeNode(<ImportTypeNode>node);
                     case SyntaxKind.JSDocAllType:
@@ -2006,6 +2010,20 @@ namespace ts {
             writeTrailingSemicolon();
         }
 
+        function emitTemplateTypeSpan(node: TemplateTypeSpan) {
+            const keyword = node.casing === TemplateCasing.Uppercase ? "uppercase" :
+                node.casing === TemplateCasing.Lowercase ? "lowercase" :
+                node.casing === TemplateCasing.Capitalize ? "capitalize" :
+                node.casing === TemplateCasing.Uncapitalize ? "uncapitalize" :
+                undefined;
+            if (keyword) {
+                writeKeyword(keyword);
+                writeSpace();
+            }
+            emit(node.type);
+            emit(node.literal);
+        }
+
         function emitSemicolonClassElement() {
             writeTrailingSemicolon();
         }
@@ -2198,6 +2216,12 @@ namespace ts {
             writePunctuation("[");
 
             pipelineEmit(EmitHint.MappedTypeParameter, node.typeParameter);
+            if (node.nameType) {
+                writeSpace();
+                writeKeyword("as");
+                writeSpace();
+                emit(node.nameType);
+            }
 
             writePunctuation("]");
             if (node.questionToken) {
@@ -2224,6 +2248,11 @@ namespace ts {
             emitExpression(node.literal);
         }
 
+        function emitTemplateType(node: TemplateTypeNode) {
+            emit(node.head);
+            emitList(node, node.templateSpans, ListFormat.TemplateExpressionSpans);
+        }
+
         function emitImportTypeNode(node: ImportTypeNode) {
             if (node.isTypeOf) {
                 writeKeyword("typeof");

src/compiler/factory/nodeFactory.ts

@@ -94,6 +94,8 @@ namespace ts {
             updateConstructSignature,
             createIndexSignature,
             updateIndexSignature,
+            createTemplateTypeSpan,
+            updateTemplateTypeSpan,
             createKeywordTypeNode,
             createTypePredicateNode,
             updateTypePredicateNode,
@@ -138,6 +140,8 @@ namespace ts {
             updateMappedTypeNode,
             createLiteralTypeNode,
             updateLiteralTypeNode,
+            createTemplateType,
+            updateTemplateType,
             createObjectBindingPattern,
             updateObjectBindingPattern,
             createArrayBindingPattern,
@@ -1596,6 +1600,25 @@ namespace ts {
                 : node;
         }
 
+        // @api
+        function createTemplateTypeSpan(casing: TemplateCasing, type: TypeNode, literal: TemplateMiddle | TemplateTail) {
+            const node = createBaseNode<TemplateTypeSpan>(SyntaxKind.TemplateTypeSpan);
+            node.casing = casing;
+            node.type = type;
+            node.literal = literal;
+            node.transformFlags = TransformFlags.ContainsTypeScript;
+            return node;
+        }
+
+        // @api
+        function updateTemplateTypeSpan(casing: TemplateCasing, node: TemplateTypeSpan, type: TypeNode, literal: TemplateMiddle | TemplateTail) {
+            return node.casing !== casing
+                || node.type !== type
+                || node.literal !== literal
+                ? update(createTemplateTypeSpan(casing, type, literal), node)
+                : node;
+        }
+
         //
         // Types
         //
@@ -1887,6 +1910,23 @@ namespace ts {
                 : node;
         }
 
+        // @api
+        function createTemplateType(head: TemplateHead, templateSpans: readonly TemplateTypeSpan[]) {
+            const node = createBaseNode<TemplateTypeNode>(SyntaxKind.TemplateType);
+            node.head = head;
+            node.templateSpans = createNodeArray(templateSpans);
+            node.transformFlags = TransformFlags.ContainsTypeScript;
+            return node;
+        }
+
+        // @api
+        function updateTemplateType(node: TemplateTypeNode, head: TemplateHead, templateSpans: readonly TemplateTypeSpan[]) {
+            return node.head !== head
+                || node.templateSpans !== templateSpans
+                ? update(createTemplateType(head, templateSpans), node)
+                : node;
+        }
+
         // @api
         function createImportTypeNode(argument: TypeNode, qualifier?: EntityName, typeArguments?: readonly TypeNode[], isTypeOf = false) {
             const node = createBaseNode<ImportTypeNode>(SyntaxKind.ImportType);
@@ -1964,23 +2004,25 @@ namespace ts {
         }
 
         // @api
-        function createMappedTypeNode(readonlyToken: ReadonlyKeyword | PlusToken | MinusToken | undefined, typeParameter: TypeParameterDeclaration, questionToken: QuestionToken | PlusToken | MinusToken | undefined, type: TypeNode | undefined): MappedTypeNode {
+        function createMappedTypeNode(readonlyToken: ReadonlyKeyword | PlusToken | MinusToken | undefined, typeParameter: TypeParameterDeclaration, nameType: TypeNode | undefined, questionToken: QuestionToken | PlusToken | MinusToken | undefined, type: TypeNode | undefined): MappedTypeNode {
             const node = createBaseNode<MappedTypeNode>(SyntaxKind.MappedType);
             node.readonlyToken = readonlyToken;
             node.typeParameter = typeParameter;
+            node.nameType = nameType;
             node.questionToken = questionToken;
             node.type = type;
             node.transformFlags = TransformFlags.ContainsTypeScript;
             return node;
         }
 
         // @api
-        function updateMappedTypeNode(node: MappedTypeNode, readonlyToken: ReadonlyKeyword | PlusToken | MinusToken | undefined, typeParameter: TypeParameterDeclaration, questionToken: QuestionToken | PlusToken | MinusToken | undefined, type: TypeNode | undefined): MappedTypeNode {
+        function updateMappedTypeNode(node: MappedTypeNode, readonlyToken: ReadonlyKeyword | PlusToken | MinusToken | undefined, typeParameter: TypeParameterDeclaration, nameType: TypeNode | undefined, questionToken: QuestionToken | PlusToken | MinusToken | undefined, type: TypeNode | undefined): MappedTypeNode {
             return node.readonlyToken !== readonlyToken
                 || node.typeParameter !== typeParameter
+                || node.nameType !== nameType
                 || node.questionToken !== questionToken
                 || node.type !== type
-                ? update(createMappedTypeNode(readonlyToken, typeParameter, questionToken, type), node)
+                ? update(createMappedTypeNode(readonlyToken, typeParameter, nameType, questionToken, type), node)
                 : node;
         }
 

src/compiler/parser.ts

@@ -206,6 +206,7 @@ namespace ts {
             case SyntaxKind.MappedType:
                 return visitNode(cbNode, (<MappedTypeNode>node).readonlyToken) ||
                     visitNode(cbNode, (<MappedTypeNode>node).typeParameter) ||
+                    visitNode(cbNode, (<MappedTypeNode>node).nameType) ||
                     visitNode(cbNode, (<MappedTypeNode>node).questionToken) ||
                     visitNode(cbNode, (<MappedTypeNode>node).type);
             case SyntaxKind.LiteralType:
@@ -424,6 +425,10 @@ namespace ts {
                 return visitNode(cbNode, (<TemplateExpression>node).head) || visitNodes(cbNode, cbNodes, (<TemplateExpression>node).templateSpans);
             case SyntaxKind.TemplateSpan:
                 return visitNode(cbNode, (<TemplateSpan>node).expression) || visitNode(cbNode, (<TemplateSpan>node).literal);
+            case SyntaxKind.TemplateType:
+                return visitNode(cbNode, (<TemplateTypeNode>node).head) || visitNodes(cbNode, cbNodes, (<TemplateTypeNode>node).templateSpans);
+            case SyntaxKind.TemplateTypeSpan:
+                return visitNode(cbNode, (<TemplateTypeSpan>node).type) || visitNode(cbNode, (<TemplateTypeSpan>node).literal);
             case SyntaxKind.ComputedPropertyName:
                 return visitNode(cbNode, (<ComputedPropertyName>node).expression);
             case SyntaxKind.HeritageClause:
@@ -2579,6 +2584,49 @@ namespace ts {
             );
         }
 
+        function parseTemplateType(): TemplateTypeNode {
+            const pos = getNodePos();
+            return finishNode(
+                factory.createTemplateType(
+                    parseTemplateHead(/*isTaggedTemplate*/ false),
+                    parseTemplateTypeSpans()
+                ),
+                pos
+            );
+        }
+
+        function parseTemplateTypeSpans() {
+            const pos = getNodePos();
+            const list = [];
+            let node: TemplateTypeSpan;
+            do {
+                node = parseTemplateTypeSpan();
+                list.push(node);
+            }
+            while (node.literal.kind === SyntaxKind.TemplateMiddle);
+            return createNodeArray(list, pos);
+        }
+
+        function parseTemplateTypeSpan(): TemplateTypeSpan {
+            const pos = getNodePos();
+            return finishNode(
+                factory.createTemplateTypeSpan(
+                    parseTemplateCasing(),
+                    parseType(),
+                    parseLiteralOfTemplateSpan(/*isTaggedTemplate*/ false)
+                ),
+                pos
+            );
+        }
+
+        function parseTemplateCasing(): TemplateCasing {
+            return parseOptional(SyntaxKind.UppercaseKeyword) ? TemplateCasing.Uppercase :
+                parseOptional(SyntaxKind.LowercaseKeyword) ? TemplateCasing.Lowercase :
+                parseOptional(SyntaxKind.CapitalizeKeyword) ? TemplateCasing.Capitalize :
+                parseOptional(SyntaxKind.UncapitalizeKeyword) ? TemplateCasing.Uncapitalize :
+                TemplateCasing.None;
+        }
+
         function parseLiteralOfTemplateSpan(isTaggedTemplate: boolean) {
             if (token() === SyntaxKind.CloseBraceToken) {
                 reScanTemplateToken(isTaggedTemplate);
@@ -3247,6 +3295,7 @@ namespace ts {
             }
             parseExpected(SyntaxKind.OpenBracketToken);
             const typeParameter = parseMappedTypeParameter();
+            const nameType = parseOptional(SyntaxKind.AsKeyword) ? parseType() : undefined;
             parseExpected(SyntaxKind.CloseBracketToken);
             let questionToken: QuestionToken | PlusToken | MinusToken | undefined;
             if (token() === SyntaxKind.QuestionToken || token() === SyntaxKind.PlusToken || token() === SyntaxKind.MinusToken) {
@@ -3258,7 +3307,7 @@ namespace ts {
             const type = parseTypeAnnotation();
             parseSemicolon();
             parseExpected(SyntaxKind.CloseBraceToken);
-            return finishNode(factory.createMappedTypeNode(readonlyToken, typeParameter, questionToken, type), pos);
+            return finishNode(factory.createMappedTypeNode(readonlyToken, typeParameter, nameType, questionToken, type), pos);
         }
 
         function parseTupleElementType() {
@@ -3439,6 +3488,8 @@ namespace ts {
                     return parseImportType();
                 case SyntaxKind.AssertsKeyword:
                     return lookAhead(nextTokenIsIdentifierOrKeywordOnSameLine) ? parseAssertsTypePredicate() : parseTypeReference();
+                case SyntaxKind.TemplateHead:
+                    return parseTemplateType();
                 default:
                     return parseTypeReference();
             }
@@ -3480,6 +3531,8 @@ namespace ts {
                 case SyntaxKind.InferKeyword:
                 case SyntaxKind.ImportKeyword:
                 case SyntaxKind.AssertsKeyword:
+                case SyntaxKind.NoSubstitutionTemplateLiteral:
+                case SyntaxKind.TemplateHead:
                     return true;
                 case SyntaxKind.FunctionKeyword:
                     return !inStartOfParameter;

src/compiler/scanner.ts

@@ -151,6 +151,10 @@ namespace ts {
         yield: SyntaxKind.YieldKeyword,
         async: SyntaxKind.AsyncKeyword,
         await: SyntaxKind.AwaitKeyword,
+        uppercase: SyntaxKind.UppercaseKeyword,
+        lowercase: SyntaxKind.LowercaseKeyword,
+        capitalize: SyntaxKind.CapitalizeKeyword,
+        uncapitalize: SyntaxKind.UncapitalizeKeyword,
         of: SyntaxKind.OfKeyword,
     };
 
@@ -1508,9 +1512,9 @@ namespace ts {
         }
 
         function getIdentifierToken(): SyntaxKind.Identifier | KeywordSyntaxKind {
-            // Reserved words are between 2 and 11 characters long and start with a lowercase letter
+            // Reserved words are between 2 and 12 characters long and start with a lowercase letter
             const len = tokenValue.length;
-            if (len >= 2 && len <= 11) {
+            if (len >= 2 && len <= 12) {
                 const ch = tokenValue.charCodeAt(0);
                 if (ch >= CharacterCodes.a && ch <= CharacterCodes.z) {
                     const keyword = textToKeyword.get(tokenValue);