From 82a2ee644078c5f96437086f195b8d8d454e5663 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Fri, 16 Dec 2016 15:01:20 -0800
Subject: [PATCH] Mapped types assignable to objects with 'any' string index
 signature

---
 src/compiler/checker.ts | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 5246bbfc700..9155f24ad34 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7730,8 +7730,11 @@ namespace ts {
                         }
                     }
                 }
-                else if (relation !== identityRelation && isEmptyObjectType(resolveStructuredTypeMembers(<ObjectType>target))) {
-                    return Ternary.True;
+                else if (relation !== identityRelation) {
+                    const resolved = resolveStructuredTypeMembers(<ObjectType>target);
+                    if (isEmptyObjectType(resolved) || resolved.stringIndexInfo && resolved.stringIndexInfo.type.flags & TypeFlags.Any) {
+                        return Ternary.True;
+                    }
                 }
                 return Ternary.False;
             }