From b11be803490d5a94c81adfe6fc3b5e20608ac581 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Tue, 17 Apr 2018 16:29:42 -0700
Subject: [PATCH] Don't widen unique symbol types during type inference

---
 src/compiler/checker.ts | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 7ffe7126388..507d9129334 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -12372,14 +12372,13 @@ namespace ts {
                     inferredType = getTypeFromInference(inference);
                 }
 
-                inferredType = getWidenedUniqueESSymbolType(inferredType);
                 inference.inferredType = inferredType;
 
                 const constraint = getConstraintOfTypeParameter(inference.typeParameter);
                 if (constraint) {
                     const instantiatedConstraint = instantiateType(constraint, context);
                     if (!context.compareTypes(inferredType, getTypeWithThisArgument(instantiatedConstraint, inferredType))) {
-                        inference.inferredType = inferredType = getWidenedUniqueESSymbolType(instantiatedConstraint);
+                        inference.inferredType = inferredType = instantiatedConstraint;
                     }
                 }
             }