fix: adjust order of derived function definition overloads

.changeset/giant-bananas-turn.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: adjust order of `derived` function definition overloads

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>}
  */

packages/svelte/tests/store/test.ts

@@ -272,7 +272,6 @@ describe('derived', () => {
  const number = writable(1);
  const evens = derived(
  number,
- // @ts-expect-error TODO feels like inference should work here
  (n, set) => {
  if (n % 2 === 0) set(n);
  },
@@ -303,10 +302,8 @@ describe('derived', () => {
  const number = writable(1);
  const evensAndSquaresOf4 = derived(
  number,
- // @ts-expect-error TODO feels like inference should work here
  (n, set, update) => {
  if (n % 2 === 0) set(n);
- // @ts-expect-error TODO feels like inference should work here
  if (n % 4 === 0) update((n) => n * n);
  },
  0
@@ -442,7 +439,6 @@ describe('derived', () => {
  const values: number[] = [];
  const cleaned_up: number[] = [];
 
- // @ts-expect-error TODO feels like inference should work here
  const d = derived(num, ($num, set) => {
  set($num * 2);
 
@@ -516,7 +512,6 @@ describe('derived', () => {
  const a = writable(true);
  let b_started = false;
 
- // @ts-expect-error TODO feels like inference should work here
  const b = derived(a, (_, __) => {
  b_started = true;
  return () => {
@@ -525,7 +520,6 @@ describe('derived', () => {
  };
  });
 
- // @ts-expect-error TODO feels like inference should work here
  const c = derived(a, ($a, set) => {
  if ($a) return b.subscribe(set);
  });

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 === '';
+ },
+ ''
+);

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.
  *