Allow 'null' and 'undefined' as type names

src/compiler/checker.ts

@@ -3411,6 +3411,8 @@ namespace ts {
                 case SyntaxKind.BooleanKeyword:
                 case SyntaxKind.SymbolKeyword:
                 case SyntaxKind.VoidKeyword:
+                case SyntaxKind.UndefinedKeyword:
+                case SyntaxKind.NullKeyword:
                 case SyntaxKind.StringLiteralType:
                     return true;
                 case SyntaxKind.ArrayType:
@@ -4935,6 +4937,10 @@ namespace ts {
                     return esSymbolType;
                 case SyntaxKind.VoidKeyword:
                     return voidType;
+                case SyntaxKind.UndefinedKeyword:
+                    return undefinedType;
+                case SyntaxKind.NullKeyword:
+                    return nullType;
                 case SyntaxKind.ThisType:
                     return getTypeFromThisTypeNode(node);
                 case SyntaxKind.StringLiteralType:

src/compiler/declarationEmitter.ts

@@ -367,6 +367,8 @@ namespace ts {
                 case SyntaxKind.BooleanKeyword:
                 case SyntaxKind.SymbolKeyword:
                 case SyntaxKind.VoidKeyword:
+                case SyntaxKind.UndefinedKeyword:
+                case SyntaxKind.NullKeyword:
                 case SyntaxKind.ThisType:
                 case SyntaxKind.StringLiteralType:
                     return writeTextOfNode(currentText, type);

src/compiler/parser.ts

@@ -2379,12 +2379,14 @@ namespace ts {
                 case SyntaxKind.NumberKeyword:
                 case SyntaxKind.BooleanKeyword:
                 case SyntaxKind.SymbolKeyword:
+                case SyntaxKind.UndefinedKeyword:
                     // If these are followed by a dot, then parse these out as a dotted type reference instead.
                     const node = tryParse(parseKeywordAndNoDot);
                     return node || parseTypeReference();
                 case SyntaxKind.StringLiteral:
                     return parseStringLiteralTypeNode();
                 case SyntaxKind.VoidKeyword:
+                case SyntaxKind.NullKeyword:
                     return parseTokenNode<TypeNode>();
                 case SyntaxKind.ThisKeyword: {
                     const thisKeyword = parseThisTypeNode();
@@ -2416,6 +2418,8 @@ namespace ts {
                 case SyntaxKind.BooleanKeyword:
                 case SyntaxKind.SymbolKeyword:
                 case SyntaxKind.VoidKeyword:
+                case SyntaxKind.UndefinedKeyword:
+                case SyntaxKind.NullKeyword:
                 case SyntaxKind.ThisKeyword:
                 case SyntaxKind.TypeOfKeyword:
                 case SyntaxKind.OpenBraceToken:

src/compiler/scanner.ts

@@ -114,6 +114,7 @@ namespace ts {
         "try": SyntaxKind.TryKeyword,
         "type": SyntaxKind.TypeKeyword,
         "typeof": SyntaxKind.TypeOfKeyword,
+        "undefined": SyntaxKind.UndefinedKeyword,
         "var": SyntaxKind.VarKeyword,
         "void": SyntaxKind.VoidKeyword,
         "while": SyntaxKind.WhileKeyword,

src/compiler/types.ts

@@ -171,6 +171,7 @@ namespace ts {
         StringKeyword,
         SymbolKeyword,
         TypeKeyword,
+        UndefinedKeyword,
         FromKeyword,
         GlobalKeyword,
         OfKeyword, // LastKeyword and LastToken

src/compiler/utilities.ts

@@ -515,6 +515,7 @@ namespace ts {
             case SyntaxKind.StringKeyword:
             case SyntaxKind.BooleanKeyword:
             case SyntaxKind.SymbolKeyword:
+            case SyntaxKind.UndefinedKeyword:
                 return true;
             case SyntaxKind.VoidKeyword:
                 return node.parent.kind !== SyntaxKind.VoidExpression;