From 09590bc041c261ba0ccb3d9321fb2499765ec8b6 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Mon, 23 Apr 2018 20:57:11 -0700
Subject: [PATCH] Transform 'keyof (A | B)' to 'keyof A & keyof B'

---
 src/compiler/checker.ts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 75f8715fca7..b94d14d58a5 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -8268,7 +8268,8 @@ namespace ts {
         }
 
         function getIndexType(type: Type, stringsOnly = keyofStringsOnly): Type {
-            return type.flags & TypeFlags.Intersection ? getUnionType(map((<IntersectionType>type).types, t => getIndexType(t, stringsOnly))) :
+            return type.flags & TypeFlags.Union ? getIntersectionType(map((<IntersectionType>type).types, t => getIndexType(t, stringsOnly))) :
+                type.flags & TypeFlags.Intersection ? getUnionType(map((<IntersectionType>type).types, t => getIndexType(t, stringsOnly))) :
                 maybeTypeOfKind(type, TypeFlags.InstantiableNonPrimitive) ? getIndexTypeForGenericType(<InstantiableType | UnionOrIntersectionType>type, stringsOnly) :
                 getObjectFlags(type) & ObjectFlags.Mapped ? getConstraintTypeFromMappedType(<MappedType>type) :
                 type === wildcardType ? wildcardType :