From 44f23d2ccf9c82cdcaaf3d6f271f9393327becb8 Mon Sep 17 00:00:00 2001
From: Simon Holthausen <simon.holthausen@vercel.com>
Date: Thu, 2 May 2024 17:55:00 +0200
Subject: [PATCH] fix: adjust order of `derived` function definition overloads

Turns out the order is crucial for not getting a type error
fixes #11415
---
 .changeset/giant-bananas-turn.md     |  5 +++++
 packages/svelte/src/store/index.js   |  4 ++--
 packages/svelte/tests/types/store.ts | 14 ++++++++++++++
 packages/svelte/types/index.d.ts     |  4 ++--
 4 files changed, 23 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/giant-bananas-turn.md

diff --git a/.changeset/giant-bananas-turn.md b/.changeset/giant-bananas-turn.md
new file mode 100644
index 0000000000..df4f40e5a8
--- /dev/null
+++ b/.changeset/giant-bananas-turn.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: adjust order of `derived` function definition overloads
diff --git a/packages/svelte/src/store/index.js b/packages/svelte/src/store/index.js
index e6a2f0a6d3..108af184b0 100644
--- a/packages/svelte/src/store/index.js
+++ b/packages/svelte/src/store/index.js
@@ -111,7 +111,7 @@ export function writable(value, start = noop) {
  * @template T
  * @overload
  * @param {S} stores
- * @param {(values: import('./private.js').StoresValues<S>) => T} fn
+ * @param {(values: import('./private.js').StoresValues<S>, set: (value: T) => void, update: (fn: import('./public.js').Updater<T>) => void) => import('./public.js').Unsubscriber | void} fn
  * @param {T} [initial_value]
  * @returns {import('./public.js').Readable<T>}
  */
@@ -124,7 +124,7 @@ export function writable(value, start = noop) {
  * @template T
  * @overload
  * @param {S} stores
- * @param {(values: import('./private.js').StoresValues<S>, set: (value: T) => void, update: (fn: import('./public.js').Updater<T>) => void) => import('./public.js').Unsubscriber | void} fn
+ * @param {(values: import('./private.js').StoresValues<S>) => T} fn
  * @param {T} [initial_value]
  * @returns {import('./public.js').Readable<T>}
  */
diff --git a/packages/svelte/tests/types/store.ts b/packages/svelte/tests/types/store.ts
index a6e681898c..af1bb65ea9 100644
--- a/packages/svelte/tests/types/store.ts
+++ b/packages/svelte/tests/types/store.ts
@@ -11,3 +11,17 @@ derived([a], ([aVal]) => {
 	aVal === '';
 	return aVal === true;
 });
+
+derived(
+	a,
+	(value, set) => {
+		set('works');
+		// @ts-expect-error
+		set(true);
+
+		value === true;
+		// @ts-expect-error
+		value === '';
+	},
+	''
+);
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 7bfdee575c..a4bea89bc8 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -2157,14 +2157,14 @@ declare module 'svelte/store' {
 	 *
 	 * https://svelte.dev/docs/svelte-store#derived
 	 * */
-	export function derived<S extends Stores, T>(stores: S, fn: (values: StoresValues<S>) => T, initial_value?: T | undefined): Readable<T>;
+	export function derived<S extends Stores, T>(stores: S, fn: (values: StoresValues<S>, set: (value: T) => void, update: (fn: Updater<T>) => void) => Unsubscriber | void, initial_value?: T | undefined): Readable<T>;
 	/**
 	 * Derived value store by synchronizing one or more readable stores and
 	 * applying an aggregation function over its input values.
 	 *
 	 * https://svelte.dev/docs/svelte-store#derived
 	 * */
-	export function derived<S extends Stores, T>(stores: S, fn: (values: StoresValues<S>, set: (value: T) => void, update: (fn: Updater<T>) => void) => Unsubscriber | void, initial_value?: T | undefined): Readable<T>;
+	export function derived<S extends Stores, T>(stores: S, fn: (values: StoresValues<S>) => T, initial_value?: T | undefined): Readable<T>;
 	/**
 	 * Takes a store and returns a new one derived from the old one that is readable.
 	 *