From aaa55923e8f8b03d39c6150ee7fdd9d0af522bec Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Fri, 31 May 2019 11:03:49 -0700
Subject: [PATCH] Permit assignment this.xxx when class has index signature

---
 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 8305443a19b..5814b2dcfbf 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -20192,7 +20192,7 @@ namespace ts {
                 markAliasReferenced(parentSymbol, node);
             }
             if (!prop) {
-                const indexInfo = assignmentKind === AssignmentKind.None || !isGenericObjectType(leftType) ? getIndexInfoOfType(apparentType, IndexKind.String) : undefined;
+                const indexInfo = assignmentKind === AssignmentKind.None || !isGenericObjectType(leftType) || isThisTypeParameter(leftType) ? getIndexInfoOfType(apparentType, IndexKind.String) : undefined;
                 if (!(indexInfo && indexInfo.type)) {
                     if (isJSLiteralType(leftType)) {
                         return anyType;