From 8f020559fbde9d0c8252a3fde5dc4f2890461fb0 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Wed, 17 Jul 2019 18:49:56 -0700
Subject: [PATCH] Treat Array<T> and ReadonlyArray<T> as synonymous in
 inference

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

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 81c2a9590ba..f044ee8e375 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -15587,7 +15587,8 @@ namespace ts {
                         }
                     }
                 }
-                if (getObjectFlags(source) & ObjectFlags.Reference && getObjectFlags(target) & ObjectFlags.Reference && (<TypeReference>source).target === (<TypeReference>target).target) {
+                if (getObjectFlags(source) & ObjectFlags.Reference && getObjectFlags(target) & ObjectFlags.Reference && (
+                    (<TypeReference>source).target === (<TypeReference>target).target || isArrayType(source) && isArrayType(target))) {
                     // If source and target are references to the same generic type, infer from type arguments
                     inferFromTypeArguments((<TypeReference>source).typeArguments || emptyArray, (<TypeReference>target).typeArguments || emptyArray, getVariances((<TypeReference>source).target));
                 }