From db81191cd2b4eb786914a4f2618620caeae8b009 Mon Sep 17 00:00:00 2001
From: David Luzar <luzar.david@gmail.com>
Date: Mon, 26 Dec 2022 00:03:06 +0100
Subject: [PATCH] `Join`: Support const tuple values (#533)

---
 source/join.d.ts |  4 ++--
 test-d/join.ts   | 11 +++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/source/join.d.ts b/source/join.d.ts
index 5586b7ed5..df9d39435 100644
--- a/source/join.d.ts
+++ b/source/join.d.ts
@@ -21,13 +21,13 @@ const path: Join<[1, 2, 3], '.'> = [1, 2, 3].join('.');
 @category Template literal
 */
 export type Join<
-	Strings extends Array<string | number>,
+	Strings extends Readonly<Array<string | number>>,
 	Delimiter extends string,
 > = Strings extends []
 	? ''
 	: Strings extends [string | number]
 		? `${Strings[0]}`
-		: Strings extends [
+		: Strings extends readonly [
 			string | number,
 			...infer Rest extends Array<string | number>,
 		]
diff --git a/test-d/join.ts b/test-d/join.ts
index f50477e35..5191e15ad 100644
--- a/test-d/join.ts
+++ b/test-d/join.ts
@@ -21,3 +21,14 @@ expectNotAssignable<'foo.bar.baz'>(emptyDelimiter);
 const emptyInput: Join<[], '.'> = '';
 expectType<''>(emptyInput);
 expectNotAssignable<'foo'>(emptyInput);
+
+// Typeof of const tuple
+const tuple = ['foo', 'bar', 'baz'] as const;
+const joinedTuple: Join<typeof tuple, ','> = 'foo,bar,baz';
+expectType<'foo,bar,baz'>(joinedTuple);
+
+// Typeof of string[]
+const stringArray = ['foo', 'bar', 'baz'];
+const joinedStringArray: Join<typeof stringArray, ','> = '';
+expectType<string>(joinedStringArray);
+expectNotAssignable<'foo,bar,baz'>(joinedStringArray);