From 692dcacdd58498decd43ad260047d8818b98c1f1 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <dg@domgan.com>
Date: Tue, 30 Jan 2024 16:42:59 +0000
Subject: [PATCH] fix: improve handling of unowned derived signals

---
 .changeset/slimy-laws-explode.md                |  5 +++++
 packages/svelte/src/internal/client/runtime.js  | 10 ++++++++--
 .../samples/derived-unowned-2/Component.svelte  | 12 ++++++++++++
 .../samples/derived-unowned-2/_config.js        | 15 +++++++++++++++
 .../samples/derived-unowned-2/main.svelte       | 17 +++++++++++++++++
 5 files changed, 57 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/slimy-laws-explode.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-unowned-2/Component.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-unowned-2/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-unowned-2/main.svelte

diff --git a/.changeset/slimy-laws-explode.md b/.changeset/slimy-laws-explode.md
new file mode 100644
index 000000000000..b3548bd11f4f
--- /dev/null
+++ b/.changeset/slimy-laws-explode.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: improve handling of unowned derived signals
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index e0d5d1087182..41bc9416f090 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/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) {
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-unowned-2/Component.svelte b/packages/svelte/tests/runtime-runes/samples/derived-unowned-2/Component.svelte
new file mode 100644
index 000000000000..8c64dca9a94e
--- /dev/null
+++ b/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>
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-unowned-2/_config.js b/packages/svelte/tests/runtime-runes/samples/derived-unowned-2/_config.js
new file mode 100644
index 000000000000..c9d17a200a4c
--- /dev/null
+++ b/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>'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-unowned-2/main.svelte b/packages/svelte/tests/runtime-runes/samples/derived-unowned-2/main.svelte
new file mode 100644
index 000000000000..6db51236bcbd
--- /dev/null
+++ b/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>