From e8ddd419dfb93bf612a2b58930877e793ed14a4e Mon Sep 17 00:00:00 2001
From: Nathan Shively-Sanders <nathansa@microsoft.com>
Date: Thu, 22 Oct 2015 11:26:19 -0700
Subject: [PATCH] Root class merged with interface can be extended

I found that merging a class that has no base with an interface that has a
base class causes a crash because `getDefaultConstructSignatures` assumes
that any base must be a class base. Which was true in the previously buggy
state.
---
 src/compiler/checker.ts | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 18443e5997b..fe4171365a1 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -2845,6 +2845,10 @@ namespace ts {
             return type.resolvedBaseConstructorType;
         }
 
+        function hasClassBaseType(type: InterfaceType): boolean {
+            return !!forEach(getBaseTypes(type), t => !!(t.symbol.flags & SymbolFlags.Class));
+        }
+
         function getBaseTypes(type: InterfaceType): ObjectType[] {
             let isClass = type.symbol.flags & SymbolFlags.Class;
             let isInterface = type.symbol.flags & SymbolFlags.Interface;
@@ -3254,7 +3258,7 @@ namespace ts {
         }
 
         function getDefaultConstructSignatures(classType: InterfaceType): Signature[] {
-            if (!getBaseTypes(classType).length) {
+            if (!hasClassBaseType(classType)) {
                 return [createSignature(undefined, classType.localTypeParameters, emptyArray, classType, undefined, 0, false, false)];
             }
             let baseConstructorType = getBaseConstructorTypeOfClass(classType);