From f6de919407e5134f68dd7a450f77cb2adc3db121 Mon Sep 17 00:00:00 2001
From: Jason Freeman <jfreeman@microsoft.com>
Date: Fri, 13 Mar 2015 15:35:58 -0700
Subject: [PATCH] Add assert in reportNoCommonSupertypeError

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

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 0dacb20ece4..957a3e3630a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -4379,6 +4379,8 @@ module ts {
                     }
                 }
 
+                Debug.assert(!!downfallType, "If there is no common supertype, each type should have a downfallType");
+
                 if (score > bestSupertypeScore) {
                     bestSupertype = types[i];
                     bestSupertypeDownfallType = downfallType;