From 517d7d983fe04a2843fd64a57e289b1c2b013727 Mon Sep 17 00:00:00 2001
From: Vladimir Matveev <vladima@microsoft.com>
Date: Fri, 19 Feb 2016 22:05:17 -0800
Subject: [PATCH] do not make inferences with the same source\target pair
 multiple times

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

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index dbce5f41ef4..b6e68cb1dc3 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -6524,6 +6524,7 @@ namespace ts {
             let targetStack: Type[];
             let depth = 0;
             let inferiority = 0;
+            const visited: Map<boolean> = {};
             inferFromTypes(source, target);
 
             function isInProcess(source: Type, target: Type) {
@@ -6653,6 +6654,12 @@ namespace ts {
                             return;
                         }
 
+                        const key = source.id + "," + target.id;
+                        if (hasProperty(visited, key)) {
+                            return;
+                        }
+                        visited[key] = true;
+
                         if (depth === 0) {
                             sourceStack = [];
                             targetStack = [];