From 60a057b891f94df3d6ffe3d10fd6b90d475d9315 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Mischler?= <skarab@bluewin.ch>
Date: Wed, 29 Mar 2023 14:38:09 +0200
Subject: [PATCH] Fix `Merge` with optional `any` value (#583)

---
 source/merge.d.ts | 10 +++-------
 test-d/merge.ts   | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/source/merge.d.ts b/source/merge.d.ts
index a69ab773d..bed025650 100644
--- a/source/merge.d.ts
+++ b/source/merge.d.ts
@@ -2,14 +2,10 @@ import type {OmitIndexSignature} from './omit-index-signature';
 import type {PickIndexSignature} from './pick-index-signature';
 import type {EnforceOptional} from './enforce-optional';
 
-// Merges two objects without worrying about index signatures or optional keys.
+// Merges two objects without worrying about index signatures.
 type SimpleMerge<Destination, Source> = {
-	[Key in keyof Destination | keyof Source]: Key extends keyof Source
-		? Source[Key]
-		: Key extends keyof Destination
-			? Destination[Key]
-			: never;
-};
+	[Key in keyof Destination as Key extends keyof Source ? never : Key]: Destination[Key];
+} & Source;
 
 /**
 Merge two types into a new type. Keys of the second type overrides keys of the first type.
diff --git a/test-d/merge.ts b/test-d/merge.ts
index 2f5d1471d..99ae03ae5 100644
--- a/test-d/merge.ts
+++ b/test-d/merge.ts
@@ -134,3 +134,17 @@ expectType<{
 	bar: string;
 	fooBar: string;
 }>(fooBarWithIndexSignature);
+
+declare const destinationWithAny: Merge<{foo?: any}, {bar: true}>;
+
+expectType<{
+	foo?: any;
+	bar: true;
+}>(destinationWithAny);
+
+declare const sourceWithAny: Merge<{foo: true}, {bar?: any}>;
+
+expectType<{
+	foo: true;
+	bar?: any;
+}>(sourceWithAny);