From 93c0f0ca0fd8d1996e11eccff19d12b29ce8b338 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Mon, 17 Dec 2018 14:08:01 -0800
Subject: [PATCH] isEmptyObjectType should check that argument is not generic
 mapped type

---
 src/compiler/checker.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 356ddc2a28e..3f129802194 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11386,7 +11386,7 @@ namespace ts {
         }
 
         function isEmptyObjectType(type: Type): boolean {
-            return type.flags & TypeFlags.Object ? isEmptyResolvedType(resolveStructuredTypeMembers(<ObjectType>type)) :
+            return type.flags & TypeFlags.Object ? !isGenericMappedType(type) && isEmptyResolvedType(resolveStructuredTypeMembers(<ObjectType>type)) :
                 type.flags & TypeFlags.NonPrimitive ? true :
                 type.flags & TypeFlags.Union ? some((<UnionType>type).types, isEmptyObjectType) :
                 type.flags & TypeFlags.Intersection ? every((<UnionType>type).types, isEmptyObjectType) :
@@ -12361,7 +12361,7 @@ namespace ts {
                 }
                 else {
                     // An empty object type is related to any mapped type that includes a '?' modifier.
-                    if (isPartialMappedType(target) && !isGenericMappedType(source) && isEmptyObjectType(source)) {
+                    if (isPartialMappedType(target) && isEmptyObjectType(source)) {
                         return Ternary.True;
                     }
                     if (isGenericMappedType(target)) {