fix: ensure subscriptions are picked up correctly by deriveds

dummdidumm · dummdidumm · commit 36e188b5c681 · 2025-07-21T15:18:57.000+02:00
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
diff --git a/.changeset/fresh-penguins-impress.md 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
@@ -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
@@ -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
@@ -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>

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +'svelte': patch
 +---
++
 +fix: ensure subscriptions are picked up correctly by deriveds