From 7247d8e33a618650e256d43107b994b24b2bb84e Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Fri, 25 May 2018 10:03:42 -0700
Subject: [PATCH] T extends unknown ? X : Y should eagerly resolve to X

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

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index d1ede654a3d..abd39e46362 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -8984,6 +8984,9 @@ namespace ts {
             if (checkType === wildcardType || extendsType === wildcardType) {
                 return wildcardType;
             }
+            if (extendsType === getTopType()) {
+                return instantiateType(root.trueType, mapper);
+            }
             // If this is a distributive conditional type and the check type is generic we need to defer
             // resolution of the conditional type such that a later instantiation will properly distribute
             // over union types.