Ensure createTupleType([]) to return singleton

Author: lefb766

src/compiler/checker.ts

@@ -6210,7 +6210,13 @@ namespace ts {
             return tupleTypes[arity] || (tupleTypes[arity] = createTupleTypeOfArity(arity));
         }
 
-        function createTupleType(elementTypes: Type[]) {
+        function createTupleType(elementTypes: Type[]): TypeReference {
+            // We have to ensure that we get same instance for empty tuple type,
+            // because we use === in isTupleLikeType(type).
+            if (!elementTypes.length && emptyTupleType) {
+                return emptyTupleType;
+            }
+
             return createTypeReference(getTupleTypeOfArity(elementTypes.length), elementTypes);
         }