From 60a71cc5934b1c19f86f4aa84288d0676fbe1e49 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 20 Aug 2024 16:11:50 -0400
Subject: [PATCH 1/2] move test

---
 .../_config.js                                                    | 0
 .../main.svelte                                                   | 0
 2 files changed, 0 insertions(+), 0 deletions(-)
 rename packages/svelte/tests/runtime-runes/samples/{state-link-callback => state-link-callback-condition}/_config.js (100%)
 rename packages/svelte/tests/runtime-runes/samples/{state-link-callback => state-link-callback-condition}/main.svelte (100%)

diff --git a/packages/svelte/tests/runtime-runes/samples/state-link-callback/_config.js b/packages/svelte/tests/runtime-runes/samples/state-link-callback-condition/_config.js
similarity index 100%
rename from packages/svelte/tests/runtime-runes/samples/state-link-callback/_config.js
rename to packages/svelte/tests/runtime-runes/samples/state-link-callback-condition/_config.js
diff --git a/packages/svelte/tests/runtime-runes/samples/state-link-callback/main.svelte b/packages/svelte/tests/runtime-runes/samples/state-link-callback-condition/main.svelte
similarity index 100%
rename from packages/svelte/tests/runtime-runes/samples/state-link-callback/main.svelte
rename to packages/svelte/tests/runtime-runes/samples/state-link-callback-condition/main.svelte

From 1534c1d0bbb51d958e852b3a2f0859cd86baf07b Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 20 Aug 2024 16:34:24 -0400
Subject: [PATCH 2/2] fix: invoke `$state.link` callback at the correct time

---
 .changeset/proud-dots-swim.md                 |  5 +++
 .../src/internal/client/reactivity/sources.js | 44 +++++--------------
 .../samples/state-link-callback/_config.js    | 22 ++++++++++
 .../samples/state-link-callback/main.svelte   | 10 +++++
 4 files changed, 49 insertions(+), 32 deletions(-)
 create mode 100644 .changeset/proud-dots-swim.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/state-link-callback/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/state-link-callback/main.svelte

diff --git a/.changeset/proud-dots-swim.md b/.changeset/proud-dots-swim.md
new file mode 100644
index 000000000000..3f86f115aee5
--- /dev/null
+++ b/.changeset/proud-dots-swim.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: invoke `$state.link` callback at the correct time
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index d0c6441040c2..d6cc28c5c716 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -27,6 +27,7 @@ import {
 } from '../constants.js';
 import * as e from '../errors.js';
 import { derived } from './deriveds.js';
+import { render_effect } from './effects.js';
 
 let inspect_effects = new Set();
 
@@ -53,44 +54,23 @@ export function source(v) {
  * @returns {(value?: V) => V}
  */
 export function source_link(get_value, callback) {
-	var was_local = false;
-	var init = false;
-	var local_source = source(/** @type {V} */ (undefined));
+	var s = source(/** @type {V} */ (undefined));
+	var ran = false;
 
-	var linked_derived = derived(() => {
-		var local_value = /** @type {V} */ (get(local_source));
-		var linked_value = get_value();
+	callback ??= (value) => set(s, value);
 
-		if (was_local) {
-			was_local = false;
-			return local_value;
-		}
-
-		return linked_value;
-	});
-
-	return function (/** @type {any} */ value) {
-		if (arguments.length > 0) {
-			was_local = true;
-			set(local_source, value);
-			get(linked_derived);
-			return value;
-		}
-
-		var linked_value = get(linked_derived);
-
-		if (init) {
-			if (callback !== undefined) {
-				untrack(() => callback(linked_value));
-				return local_source.v;
-			}
+	render_effect(() => {
+		if (ran) {
+			callback(get_value());
 		} else {
-			init = true;
+			s.v = get_value();
 		}
+	});
 
-		local_source.v = linked_value;
+	ran = true;
 
-		return linked_value;
+	return function (/** @type {any} */ value) {
+		return arguments.length === 1 ? set(s, /** @type {V} */ (value)) : get(s);
 	};
 }
 
diff --git a/packages/svelte/tests/runtime-runes/samples/state-link-callback/_config.js b/packages/svelte/tests/runtime-runes/samples/state-link-callback/_config.js
new file mode 100644
index 000000000000..978fdb14d608
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/state-link-callback/_config.js
@@ -0,0 +1,22 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<button>0</button><button>0</button>`,
+
+	test({ assert, target, logs }) {
+		const [btn1, btn2] = target.querySelectorAll('button');
+
+		flushSync(() => btn1.click());
+		assert.deepEqual(logs, ['in callback 1']);
+		assert.htmlEqual(target.innerHTML, `<button>1</button><button>1</button>`);
+
+		flushSync(() => btn2.click());
+		assert.deepEqual(logs, ['in callback 1']);
+		assert.htmlEqual(target.innerHTML, `<button>1</button><button>2</button>`);
+
+		flushSync(() => btn1.click());
+		assert.deepEqual(logs, ['in callback 1', 'in callback 2']);
+		assert.htmlEqual(target.innerHTML, `<button>2</button><button>2</button>`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/state-link-callback/main.svelte b/packages/svelte/tests/runtime-runes/samples/state-link-callback/main.svelte
new file mode 100644
index 000000000000..8ef97c454fc5
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/state-link-callback/main.svelte
@@ -0,0 +1,10 @@
+<script>
+	let a = $state(0);
+	let b = $state.link(a, (value) => {
+		console.log(`in callback ${value}`);
+		b = value;
+	});
+</script>
+
+<button onclick={() => a++}>{a}</button>
+<button onclick={() => b++}>{b}</button>