From a75449cabc70de2ee74d7d9e4d37847d0e357f1f Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Wed, 21 Mar 2018 13:22:58 -0700
Subject: [PATCH] Revert strict containment check in checkInferType

---
 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 7351bae1539..49b89904bef 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -20605,8 +20605,7 @@ namespace ts {
         }
 
         function checkInferType(node: InferTypeNode) {
-            const ancestor = findAncestor(node, n => n.parent && n.parent.kind === SyntaxKind.ConditionalType);
-            if (!ancestor || (<ConditionalTypeNode>ancestor.parent).extendsType !== ancestor) {
+            if (!findAncestor(node, n => n.parent && n.parent.kind === SyntaxKind.ConditionalType && (<ConditionalTypeNode>n.parent).extendsType === n)) {
                 grammarErrorOnNode(node, Diagnostics.infer_declarations_are_only_permitted_in_the_extends_clause_of_a_conditional_type);
             }
             checkSourceElement(node.typeParameter);