From bb28444f8c35ab1d7ee8a671564f08d3fc183900 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Tue, 6 Feb 2018 12:27:35 -0800
Subject: [PATCH] Handle all instantiable non-primitive types in homomorphic
 mapped types

---
 src/compiler/checker.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index a93189c81f2..c7cdb922cc6 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -8781,7 +8781,7 @@ namespace ts {
         }
 
         function isMappableType(type: Type) {
-            return type.flags & (TypeFlags.Any | TypeFlags.TypeParameter | TypeFlags.Object | TypeFlags.Intersection | TypeFlags.IndexedAccess);
+            return type.flags & (TypeFlags.Any | TypeFlags.InstantiableNonPrimitive | TypeFlags.Object | TypeFlags.Intersection);
         }
 
         function instantiateAnonymousType(type: AnonymousType, mapper: TypeMapper): AnonymousType {