Allow union types containing primtives as first argument in instanceof

Author: ahejlsberg

src/compiler/checker.ts

@@ -6776,7 +6776,7 @@ module ts {
             // and the right operand to be of type Any or a subtype of the 'Function' interface type. 
             // The result is always of the Boolean primitive type.
             // NOTE: do not raise error if leftType is unknown as related error was already reported
-            if (!isTypeOfKind(leftType, TypeFlags.Any | TypeFlags.ObjectType | TypeFlags.TypeParameter)) {
+            if (isTypeOfKind(leftType, TypeFlags.Primitive)) {
                 error(node.left, Diagnostics.The_left_hand_side_of_an_instanceof_expression_must_be_of_type_any_an_object_type_or_a_type_parameter);
             }
             // NOTE: do not raise error if right is unknown as related error was already reported

src/compiler/types.ts

@@ -1286,6 +1286,7 @@ module ts {
         Unwidened           = 0x00020000,  // Unwidened type (is or contains Undefined or Null type)
 
         Intrinsic = Any | String | Number | Boolean | Void | Undefined | Null,
+        Primitive = String | Number | Boolean | Void | Undefined | Null | StringLiteral | Enum,
         StringLike = String | StringLiteral,
         NumberLike = Number | Enum,
         ObjectType = Class | Interface | Reference | Tuple | Anonymous,