From db840f41c553170f18c1f143d24641dabce40f93 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Tue, 15 Jan 2019 14:44:38 -0800
Subject: [PATCH] Update array/tuple relationship checking

---
 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 f15eb66af6a..dac2d2e29be 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -12622,7 +12622,7 @@ namespace ts {
                             errorInfo = saveErrorInfo;
                         }
                     }
-                    else if (isTupleType(source) && isArrayType(target) || isArrayType(source) && isReadonlyArrayType(target)) {
+                    else if (isReadonlyArrayType(target) ? isArrayType(source) || isTupleType(source) : isArrayType(target) && isTupleType(source) && !source.target.readonly) {
                         return isRelatedTo(getIndexTypeOfType(source, IndexKind.Number) || anyType, getIndexTypeOfType(target, IndexKind.Number) || anyType, reportErrors);
                     }
                     // Even if relationship doesn't hold for unions, intersections, or generic type references,