From 855fb642f243b677a10e4b410e7dc06fdbeebf20 Mon Sep 17 00:00:00 2001
From: Haozheng Li <emiya@emiya.com.cn>
Date: Mon, 20 Nov 2023 19:28:13 +0800
Subject: [PATCH] `Join`: Faster handing of readonly empty tuple (#765)

---
 source/join.d.ts | 2 +-
 test-d/join.ts   | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/source/join.d.ts b/source/join.d.ts
index 3418362c..442f85d3 100644
--- a/source/join.d.ts
+++ b/source/join.d.ts
@@ -51,7 +51,7 @@ const path: Join<['hello' | undefined, 'world' | null], '.'> = ['hello', 'world'
 export type Join<
 	Items extends readonly JoinableItem[],
 	Delimiter extends string,
-> = Items extends []
+> = Items extends readonly []
 	? ''
 	: Items extends readonly [JoinableItem?]
 		? `${NullishCoalesce<Items[0], ''>}`
diff --git a/test-d/join.ts b/test-d/join.ts
index 2edf51da..9a7a2015 100644
--- a/test-d/join.ts
+++ b/test-d/join.ts
@@ -48,6 +48,11 @@ const tuple = ['foo', 'bar', 'baz'] as const;
 const joinedTuple: Join<typeof tuple, ','> = 'foo,bar,baz';
 expectType<'foo,bar,baz'>(joinedTuple);
 
+// Typeof of const empty tuple.
+const emptyTuple = [] as const;
+const joinedEmptyTuple: Join<typeof emptyTuple, ','> = '';
+expectType<''>(joinedEmptyTuple);
+
 // Typeof of string[].
 const stringArray = ['foo', 'bar', 'baz'];
 const joinedStringArray: Join<typeof stringArray, ','> = '';