From aabd333d89a4c9241bc3ed57752cb2616dd66b7c Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Mon, 21 Jul 2025 15:22:13 +0200
Subject: [PATCH] fix: ensure subscriptions are picked up correctly by deriveds
 (#16466)

Increment the version to ensure any dependent deriveds are marked dirty when the subscription is picked up again later. If we didn't do this then the comparison of write versions would determine that the derived has a later version than the subscriber, and it would not be re-run.

Fixes #16311
Fixes #15888
---
 .changeset/fresh-penguins-impress.md          |  5 +++
 .../src/reactivity/create-subscriber.js       |  4 ++
 .../samples/store-inside-derived/_config.js   | 45 +++++++++++++++++++
 .../samples/store-inside-derived/main.svelte  | 36 +++++++++++++++
 4 files changed, 90 insertions(+)
 create mode 100644 .changeset/fresh-penguins-impress.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/store-inside-derived/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/store-inside-derived/main.svelte

diff --git a/.changeset/fresh-penguins-impress.md b/.changeset/fresh-penguins-impress.md
new file mode 100644
index 0000000000..35ff4f0aaa
--- /dev/null
+++ b/.changeset/fresh-penguins-impress.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure subscriptions are picked up correctly by deriveds
diff --git a/packages/svelte/src/reactivity/create-subscriber.js b/packages/svelte/src/reactivity/create-subscriber.js
index 4dcac4e6f6..6f9313eb0a 100644
--- a/packages/svelte/src/reactivity/create-subscriber.js
+++ b/packages/svelte/src/reactivity/create-subscriber.js
@@ -82,6 +82,10 @@ export function createSubscriber(start) {
 						if (subscribers === 0) {
 							stop?.();
 							stop = undefined;
+							// Increment the version to ensure any dependent deriveds are marked dirty when the subscription is picked up again later.
+							// If we didn't do this then the comparison of write versions would determine that the derived has a later version than
+							// the subscriber, and it would not be re-run.
+							increment(version);
 						}
 					});
 				};
diff --git a/packages/svelte/tests/runtime-runes/samples/store-inside-derived/_config.js b/packages/svelte/tests/runtime-runes/samples/store-inside-derived/_config.js
new file mode 100644
index 0000000000..de078b1e75
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/store-inside-derived/_config.js
@@ -0,0 +1,45 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test: ({ assert, target }) => {
+		const [loading, increment] = target.querySelectorAll('button');
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<div>$value: 0</div>
+				<div>valueFromStore.current: 0</div>
+				<div>valueDerivedCurrent: 0</div>
+				<button>Loading</button>
+				<button>Increment</button>
+			`
+		);
+
+		loading.click();
+		flushSync();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<div>$value: Loading...</div>
+				<div>valueFromStore.current: Loading...</div>
+				<div>valueDerivedCurrent: Loading...</div>
+				<button>Loading</button>
+				<button>Increment</button>
+			`
+		);
+
+		increment.click();
+		flushSync();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<div>$value: 1</div>
+				<div>valueFromStore.current: 1</div>
+				<div>valueDerivedCurrent: 1</div>
+				<button>Loading</button>
+				<button>Increment</button>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/store-inside-derived/main.svelte b/packages/svelte/tests/runtime-runes/samples/store-inside-derived/main.svelte
new file mode 100644
index 0000000000..06d0a0d4b4
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/store-inside-derived/main.svelte
@@ -0,0 +1,36 @@
+<script>
+  import { fromStore, writable } from 'svelte/store';
+	
+  let isLoading = $state(false);
+
+  const value = writable(0);
+  const valueFromStore = fromStore(value);
+  const valueDerivedCurrent = $derived(valueFromStore.current);
+</script>
+
+<div>
+	$value: {isLoading ? 'Loading...' : $value}
+</div>
+
+<div>
+	valueFromStore.current: {isLoading ? 'Loading...' : valueFromStore.current}
+</div>
+
+<div>
+	valueDerivedCurrent: {isLoading ? 'Loading...' : valueDerivedCurrent}
+</div>
+
+<button
+	onclick={() => {
+		isLoading = true;
+	}}>
+	Loading
+</button>
+
+<button
+	onclick={() => {
+		$value++;
+		isLoading = false;
+	}}>
+	Increment
+</button>