fix: improve handling of unowned derived signals

Author: trueadm

.changeset/slimy-laws-explode.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: improve handling of unowned derived signals

packages/svelte/src/internal/client/runtime.js

@@ -623,8 +623,14 @@ function process_microtask() {
 export function schedule_effect(signal, sync) {
 	const flags = signal.f;
 	if (sync) {
-		execute_effect(signal);
-		set_signal_status(signal, CLEAN);
+		const previously_flushing_effect = is_flushing_effect;
+		try {
+			is_flushing_effect = true;
+			execute_effect(signal);
+			set_signal_status(signal, CLEAN);
+		} finally {
+			is_flushing_effect = previously_flushing_effect;
+		}
 	} else {
 		if (current_scheduler_mode === FLUSH_MICROTASK) {
 			if (!is_micro_task_queued) {

packages/svelte/tests/runtime-runes/samples/derived-unowned-2/Component.svelte

@@ -0,0 +1,12 @@
+<script context="module">
+	class Store {
+		all = $state([1,2,3]);
+		d1 = $derived(this.all.filter(a => a > 2));
+
+		update_value(){
+			this.all = [1,2,3,4,5];
+		}
+	}
+	export const s = new Store();
+
+</script>

packages/svelte/tests/runtime-runes/samples/derived-unowned-2/_config.js

@@ -0,0 +1,15 @@
+import { test } from '../../test';
+
+export default test({
+	html: '<div>d2: 3</div><div>d3: 3</div><div>d4: 3</div>',
+	skip_if_hydrate: 'permanent',
+
+	async test({ assert, target }) {
+		await Promise.resolve();
+		await Promise.resolve();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<div>d2: 3,4,5</div><div>d3: 3,4,5</div><div>d4: 3,4,5</div>'
+		);
+	}
+});

packages/svelte/tests/runtime-runes/samples/derived-unowned-2/main.svelte

@@ -0,0 +1,17 @@
+<script>
+	import {s} from "./Component.svelte";
+	import {onMount}from "svelte";
+
+	let d2 = $derived(s.d1.filter(x => x > 2));
+	let d3 = $derived(s.all.filter(x => x > 2));
+
+	onMount(()=>{
+		queueMicrotask(() => {
+			s.update_value();
+		});
+	});
+</script>
+
+<div>d2: {d2.join(',')}</div>
+<div>d3: {d3.join(',')}</div>
+<div>d4: {d3.join(',')}</div>