From 949c026259eb7d10cb50c92eec01f542b3916e05 Mon Sep 17 00:00:00 2001
From: Jungzl <13jungzl@gmail.com>
Date: Thu, 2 Oct 2025 00:04:03 +0800
Subject: [PATCH] fix: preserve tuple type in `$state.snapshot` (#16864)

* fix: preserve tuple type in `$state.snapshot`

* Update .changeset/lucky-moles-enjoy.md

---------

Co-authored-by: Rich Harris <hello@rich-harris.dev>
---
 .changeset/lucky-moles-enjoy.md  |  5 +++++
 packages/svelte/src/ambient.d.ts | 16 +++++++++-------
 packages/svelte/types/index.d.ts | 16 +++++++++-------
 3 files changed, 23 insertions(+), 14 deletions(-)
 create mode 100644 .changeset/lucky-moles-enjoy.md

diff --git a/.changeset/lucky-moles-enjoy.md b/.changeset/lucky-moles-enjoy.md
new file mode 100644
index 0000000000..ef1dfe4bdd
--- /dev/null
+++ b/.changeset/lucky-moles-enjoy.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: preserve tuple type in `$state.snapshot`
diff --git a/packages/svelte/src/ambient.d.ts b/packages/svelte/src/ambient.d.ts
index 59128e45f0..d655fb648a 100644
--- a/packages/svelte/src/ambient.d.ts
+++ b/packages/svelte/src/ambient.d.ts
@@ -85,13 +85,15 @@ declare namespace $state {
 			? NonReactive<T>
 			: T extends { toJSON(): infer R }
 				? R
-				: T extends Array<infer U>
-					? Array<Snapshot<U>>
-					: T extends object
-						? T extends { [key: string]: any }
-							? { [K in keyof T]: Snapshot<T[K]> }
-							: never
-						: never;
+				: T extends readonly unknown[]
+					? { [K in keyof T]: Snapshot<T[K]> }
+					: T extends Array<infer U>
+						? Array<Snapshot<U>>
+						: T extends object
+							? T extends { [key: string]: any }
+								? { [K in keyof T]: Snapshot<T[K]> }
+								: never
+							: never;
 
 	/**
 	 * Declares state that is _not_ made deeply reactive — instead of mutating it,
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 2c015b5a10..6dc6629faa 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -3171,13 +3171,15 @@ declare namespace $state {
 			? NonReactive<T>
 			: T extends { toJSON(): infer R }
 				? R
-				: T extends Array<infer U>
-					? Array<Snapshot<U>>
-					: T extends object
-						? T extends { [key: string]: any }
-							? { [K in keyof T]: Snapshot<T[K]> }
-							: never
-						: never;
+				: T extends readonly unknown[]
+					? { [K in keyof T]: Snapshot<T[K]> }
+					: T extends Array<infer U>
+						? Array<Snapshot<U>>
+						: T extends object
+							? T extends { [key: string]: any }
+								? { [K in keyof T]: Snapshot<T[K]> }
+								: never
+							: never;
 
 	/**
 	 * Declares state that is _not_ made deeply reactive — instead of mutating it,