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diff --git a/‎src/compiler/checker.ts
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+139-53Lines changed: 139 additions & 53 deletions b/‎src/compiler/checker.ts
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+139-53Lines changed: 139 additions & 53 deletions
diff --git a/‎src/compiler/diagnosticMessages.json
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+4Lines changed: 4 additions & 0 deletions b/‎src/compiler/diagnosticMessages.json
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+4Lines changed: 4 additions & 0 deletions
diff --git a/‎src/compiler/emitter.ts
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-9Lines changed: 0 additions & 9 deletions b/‎src/compiler/emitter.ts
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-9Lines changed: 0 additions & 9 deletions
diff --git a/‎src/compiler/factory/nodeFactory.ts
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+4-6Lines changed: 4 additions & 6 deletions b/‎src/compiler/factory/nodeFactory.ts
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+4-6Lines changed: 4 additions & 6 deletions
diff --git a/‎src/compiler/parser.ts
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+1-10Lines changed: 1 addition & 10 deletions b/‎src/compiler/parser.ts
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+1-10Lines changed: 1 addition & 10 deletions
diff --git a/‎src/compiler/scanner.ts
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+1-4Lines changed: 1 addition & 4 deletions b/‎src/compiler/scanner.ts
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+1-4Lines changed: 1 addition & 4 deletions
diff --git a/‎src/compiler/types.ts
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+15-24Lines changed: 15 additions & 24 deletions b/‎src/compiler/types.ts
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+15-24Lines changed: 15 additions & 24 deletions
diff --git a/‎src/harness/fourslashInterfaceImpl.ts
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+4Lines changed: 4 additions & 0 deletions b/‎src/harness/fourslashInterfaceImpl.ts
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diff --git a/‎src/lib/es5.d.ts
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+20Lines changed: 20 additions & 0 deletions b/‎src/lib/es5.d.ts
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+20Lines changed: 20 additions & 0 deletions
@@ -3043,6 +3043,10 @@
         "category": "Error",
         "code": 2794
     },
+    "The 'intrinsic' keyword can only be used to declare compiler provided intrinsic types.": {
+        "category": "Error",
+        "code": 2795
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
 
@@ -2023,15 +2023,6 @@ namespace ts {
         }
 
         function emitTemplateTypeSpan(node: TemplateLiteralTypeSpan) {
-            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);
         }
 
@@ -1605,21 +1605,19 @@ namespace ts {
         }
 
         // @api
-        function createTemplateLiteralTypeSpan(casing: TemplateCasing, type: TypeNode, literal: TemplateMiddle | TemplateTail) {
+        function createTemplateLiteralTypeSpan(type: TypeNode, literal: TemplateMiddle | TemplateTail) {
             const node = createBaseNode<TemplateLiteralTypeSpan>(SyntaxKind.TemplateLiteralTypeSpan);
-            node.casing = casing;
             node.type = type;
             node.literal = literal;
             node.transformFlags = TransformFlags.ContainsTypeScript;
             return node;
         }
 
         // @api
-        function updateTemplateLiteralTypeSpan(casing: TemplateCasing, node: TemplateLiteralTypeSpan, type: TypeNode, literal: TemplateMiddle | TemplateTail) {
-            return node.casing !== casing
-                || node.type !== type
+        function updateTemplateLiteralTypeSpan(node: TemplateLiteralTypeSpan, type: TypeNode, literal: TemplateMiddle | TemplateTail) {
+            return node.type !== type
                 || node.literal !== literal
-                ? update(createTemplateLiteralTypeSpan(casing, type, literal), node)
+                ? update(createTemplateLiteralTypeSpan(type, literal), node)
                 : node;
         }
 
 
@@ -2618,22 +2618,13 @@ namespace ts {
             const pos = getNodePos();
             return finishNode(
                 factory.createTemplateLiteralTypeSpan(
-                    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);
@@ -6751,7 +6742,7 @@ namespace ts {
             const name = parseIdentifier();
             const typeParameters = parseTypeParameters();
             parseExpected(SyntaxKind.EqualsToken);
-            const type = parseType();
+            const type = token() === SyntaxKind.IntrinsicKeyword && tryParse(parseKeywordAndNoDot) || parseType();
             parseSemicolon();
             const node = factory.createTypeAliasDeclaration(decorators, modifiers, name, typeParameters, type);
             return withJSDoc(finishNode(node, pos), hasJSDoc);
 
@@ -111,6 +111,7 @@ namespace ts {
         infer: SyntaxKind.InferKeyword,
         instanceof: SyntaxKind.InstanceOfKeyword,
         interface: SyntaxKind.InterfaceKeyword,
+        intrinsic: SyntaxKind.IntrinsicKeyword,
         is: SyntaxKind.IsKeyword,
         keyof: SyntaxKind.KeyOfKeyword,
         let: SyntaxKind.LetKeyword,
@@ -151,10 +152,6 @@ 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,
     };
 
 
@@ -167,6 +167,7 @@ namespace ts {
         DeclareKeyword,
         GetKeyword,
         InferKeyword,
+        IntrinsicKeyword,
         IsKeyword,
         KeyOfKeyword,
         ModuleKeyword,
@@ -186,10 +187,6 @@ namespace ts {
         FromKeyword,
         GlobalKeyword,
         BigIntKeyword,
-        UppercaseKeyword,
-        LowercaseKeyword,
-        CapitalizeKeyword,
-        UncapitalizeKeyword,
         OfKeyword, // LastKeyword and LastToken and LastContextualKeyword
 
         // Parse tree nodes
@@ -544,7 +541,6 @@ namespace ts {
         | SyntaxKind.BigIntKeyword
         | SyntaxKind.BooleanKeyword
         | SyntaxKind.BreakKeyword
-        | SyntaxKind.CapitalizeKeyword
         | SyntaxKind.CaseKeyword
         | SyntaxKind.CatchKeyword
         | SyntaxKind.ClassKeyword
@@ -574,10 +570,10 @@ namespace ts {
         | SyntaxKind.InKeyword
         | SyntaxKind.InstanceOfKeyword
         | SyntaxKind.InterfaceKeyword
+        | SyntaxKind.IntrinsicKeyword
         | SyntaxKind.IsKeyword
         | SyntaxKind.KeyOfKeyword
         | SyntaxKind.LetKeyword
-        | SyntaxKind.LowercaseKeyword
         | SyntaxKind.ModuleKeyword
         | SyntaxKind.NamespaceKeyword
         | SyntaxKind.NeverKeyword
@@ -605,11 +601,9 @@ namespace ts {
         | SyntaxKind.TryKeyword
         | SyntaxKind.TypeKeyword
         | SyntaxKind.TypeOfKeyword
-        | SyntaxKind.UncapitalizeKeyword
         | SyntaxKind.UndefinedKeyword
         | SyntaxKind.UniqueKeyword
         | SyntaxKind.UnknownKeyword
-        | SyntaxKind.UppercaseKeyword
         | SyntaxKind.VarKeyword
         | SyntaxKind.VoidKeyword
         | SyntaxKind.WhileKeyword
@@ -635,6 +629,7 @@ namespace ts {
         | SyntaxKind.AnyKeyword
         | SyntaxKind.BigIntKeyword
         | SyntaxKind.BooleanKeyword
+        | SyntaxKind.IntrinsicKeyword
         | SyntaxKind.NeverKeyword
         | SyntaxKind.NumberKeyword
         | SyntaxKind.ObjectKeyword
@@ -1665,19 +1660,10 @@ namespace ts {
     export interface TemplateLiteralTypeSpan extends TypeNode {
         readonly kind: SyntaxKind.TemplateLiteralTypeSpan,
         readonly parent: TemplateLiteralTypeNode;
-        readonly casing: TemplateCasing;
         readonly type: TypeNode;
         readonly literal: TemplateMiddle | TemplateTail;
     }
 
-    export const enum TemplateCasing {
-        None,
-        Uppercase,
-        Lowercase,
-        Capitalize,
-        Uncapitalize,
-    }
-
     // Note: 'brands' in our syntax nodes serve to give us a small amount of nominal typing.
     // Consider 'Expression'.  Without the brand, 'Expression' is actually no different
     // (structurally) than 'Node'.  Because of this you can pass any Node to a function that
@@ -4892,6 +4878,7 @@ namespace ts {
         Substitution    = 1 << 25,  // Type parameter substitution
         NonPrimitive    = 1 << 26,  // intrinsic object type
         TemplateLiteral = 1 << 27,  // Template literal type
+        StringMapping   = 1 << 28,  // Uppercase/Lowercase type
 
         /* @internal */
         AnyOrUnknown = Any | Unknown,
@@ -4909,7 +4896,7 @@ namespace ts {
         Intrinsic = Any | Unknown | String | Number | BigInt | Boolean | BooleanLiteral | ESSymbol | Void | Undefined | Null | Never | NonPrimitive,
         /* @internal */
         Primitive = String | Number | BigInt | Boolean | Enum | EnumLiteral | ESSymbol | Void | Undefined | Null | Literal | UniqueESSymbol,
-        StringLike = String | StringLiteral | TemplateLiteral,
+        StringLike = String | StringLiteral | TemplateLiteral | StringMapping,
         NumberLike = Number | NumberLiteral | Enum,
         BigIntLike = BigInt | BigIntLiteral,
         BooleanLike = Boolean | BooleanLiteral,
@@ -4922,15 +4909,15 @@ namespace ts {
         StructuredType = Object | Union | Intersection,
         TypeVariable = TypeParameter | IndexedAccess,
         InstantiableNonPrimitive = TypeVariable | Conditional | Substitution,
-        InstantiablePrimitive = Index | TemplateLiteral,
+        InstantiablePrimitive = Index | TemplateLiteral | StringMapping,
         Instantiable = InstantiableNonPrimitive | InstantiablePrimitive,
         StructuredOrInstantiable = StructuredType | Instantiable,
         /* @internal */
         ObjectFlagsType = Any | Nullable | Never | Object | Union | Intersection,
         /* @internal */
         Simplifiable = IndexedAccess | Conditional,
         /* @internal */
-        Substructure = Object | Union | Intersection | Index | IndexedAccess | Conditional | Substitution | TemplateLiteral,
+        Substructure = Object | Union | Intersection | Index | IndexedAccess | Conditional | Substitution | TemplateLiteral | StringMapping,
         // 'Narrowable' types are types where narrowing actually narrows.
         // This *should* be every type other than null, undefined, void, and never
         Narrowable = Any | Unknown | StructuredOrInstantiable | StringLike | NumberLike | BigIntLike | BooleanLike | ESSymbol | UniqueESSymbol | NonPrimitive,
@@ -5379,11 +5366,15 @@ namespace ts {
     }
 
     export interface TemplateLiteralType extends InstantiableType {
-        texts: readonly string[];  // Always one element longer than casings/types
-        casings: readonly TemplateCasing[];  // Always at least one element
+        texts: readonly string[];  // Always one element longer than types
         types: readonly Type[];  // Always at least one element
     }
 
+    export interface StringMappingType extends InstantiableType {
+        symbol: Symbol;
+        type: Type;
+    }
+
     // Type parameter substitution (TypeFlags.Substitution)
     // Substitution types are created for type parameters or indexed access types that occur in the
     // true branch of a conditional type. For example, in 'T extends string ? Foo<T> : Bar<T>', the
@@ -6774,8 +6765,8 @@ namespace ts {
         createIndexSignature(decorators: readonly Decorator[] | undefined, modifiers: readonly Modifier[] | undefined, parameters: readonly ParameterDeclaration[], type: TypeNode): IndexSignatureDeclaration;
         /* @internal */ createIndexSignature(decorators: readonly Decorator[] | undefined, modifiers: readonly Modifier[] | undefined, parameters: readonly ParameterDeclaration[], type: TypeNode | undefined): IndexSignatureDeclaration; // eslint-disable-line @typescript-eslint/unified-signatures
         updateIndexSignature(node: IndexSignatureDeclaration, decorators: readonly Decorator[] | undefined, modifiers: readonly Modifier[] | undefined, parameters: readonly ParameterDeclaration[], type: TypeNode): IndexSignatureDeclaration;
-        createTemplateLiteralTypeSpan(casing: TemplateCasing, type: TypeNode, literal: TemplateMiddle | TemplateTail): TemplateLiteralTypeSpan;
-        updateTemplateLiteralTypeSpan(casing: TemplateCasing, node: TemplateLiteralTypeSpan, type: TypeNode, literal: TemplateMiddle | TemplateTail): TemplateLiteralTypeSpan;
+        createTemplateLiteralTypeSpan(type: TypeNode, literal: TemplateMiddle | TemplateTail): TemplateLiteralTypeSpan;
+        updateTemplateLiteralTypeSpan(node: TemplateLiteralTypeSpan, type: TypeNode, literal: TemplateMiddle | TemplateTail): TemplateLiteralTypeSpan;
 
         //
         // Types
 
@@ -1065,6 +1065,10 @@ namespace FourSlashInterface {
             typeEntry("ConstructorParameters"),
             typeEntry("ReturnType"),
             typeEntry("InstanceType"),
+            typeEntry("Uppercase"),
+            typeEntry("Lowercase"),
+            typeEntry("Capitalize"),
+            typeEntry("Uncapitalize"),
             interfaceEntry("ThisType"),
             varEntry("ArrayBuffer"),
             interfaceEntry("ArrayBufferTypes"),
 
@@ -1508,6 +1508,26 @@ type ReturnType<T extends (...args: any) => any> = T extends (...args: any) => i
  */
 type InstanceType<T extends new (...args: any) => any> = T extends new (...args: any) => infer R ? R : any;
 
+/**
+ * Convert string literal type to uppercase
+ */
+type Uppercase<S extends string> = intrinsic;
+
+/**
+ * Convert string literal type to lowercase
+ */
+type Lowercase<S extends string> = intrinsic;
+
+/**
+ * Convert first character of string literal type to uppercase
+ */
+type Capitalize<S extends string> = intrinsic;
+
+/**
+ * Convert first character of string literal type to lowercase
+ */
+type Uncapitalize<S extends string> = intrinsic;
+
 /**
  * Marker for contextual 'this' type
  */