From 3545dcb25a5ff485062dc795748cde6cb655365d Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Thu, 17 Dec 2020 06:33:22 -1000
Subject: [PATCH] With --strictFunctionTypes, always use strict variance for
 strict subtype relation

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

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index fa65b82f41b..b3309f83a76 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -16231,7 +16231,7 @@ namespace ts {
                 return Ternary.False;
             }
 
-            const strictVariance = !(checkMode & SignatureCheckMode.Callback) && strictFunctionTypes && (isStrictSignature(target) || isStrictSignature(source));
+            const strictVariance = !(checkMode & SignatureCheckMode.Callback) && strictFunctionTypes && (checkMode & SignatureCheckMode.StrictArity || isStrictSignature(target));
             let result = Ternary.True;
 
             const sourceThisType = getThisTypeOfSignature(source);