fix: better handle unowned derived signals

.changeset/ten-foxes-repeat.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: better handle unowned derived signals

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

@@ -388,6 +388,8 @@ function remove_consumer(signal, start_index, remove_unowned) {
 				}
 			}
 			if (remove_unowned && consumers_length === 0 && (dependency.f & UNOWNED) !== 0) {
+				// If the signal is unowned then we need to make sure to change it to dirty.
+				set_signal_status(dependency, DIRTY);
 				remove_consumer(
 					/** @type {import('./types.js').ComputationSignal<V>} **/ (dependency),
 					0,

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

@@ -0,0 +1,30 @@
+<script context="module">
+	class Foo {
+		x = $state(5);
+		y = $derived(this.x * 2);
+	}
+	const foo = new Foo();
+
+	let x = $state(2);
+	let y = $derived(x * 2);
+	const bar = {
+		get x() {
+			return x;
+		},
+		set x(val) {
+			x = val;
+		},
+
+		get y() {
+			return y;
+		},
+	};
+</script>
+
+<button onclick={() => foo.x++}>
+	x: {foo.x}, y: {foo.y}
+</button>
+
+<button onclick={() => bar.x++}>
+	x: {bar.x}, y: {bar.y}
+</button>

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

@@ -0,0 +1,71 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	skip_if_hydrate: 'permanent',
+	async test({ assert, target }) {
+		let [btn1, btn2] = target.querySelectorAll('button');
+		const input = target.querySelector('input');
+
+		flushSync(() => {
+			btn1?.click();
+		});
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`<input type="checkbox"><button>x:
+		 6,
+		 y:
+		 12</button><button>x:
+		 2,
+		 y:
+		 4</button>`
+		);
+
+		flushSync(() => {
+			btn2?.click();
+		});
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`<input type="checkbox"><button>x:
+		 6,
+		 y:
+		 12</button><button>x:
+		 3,
+		 y:
+		 6</button>`
+		);
+
+		flushSync(() => {
+			input?.click();
+		});
+
+		assert.htmlEqual(target.innerHTML, `<input type="checkbox">`);
+
+		flushSync(() => {
+			input?.click();
+		});
+
+		[btn1, btn2] = target.querySelectorAll('button');
+
+		flushSync(() => {
+			btn1?.click();
+		});
+
+		flushSync(() => {
+			btn2?.click();
+		});
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`<input type="checkbox"><button>x:
+		 7,
+		 y:
+		 14</button><button>x:
+		 4,
+		 y:
+		 8</button>`
+		);
+	}
+});

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

@@ -0,0 +1,10 @@
+<script>
+	import Component from "./Component.svelte";
+
+	let show = $state(true);
+</script>
+
+<input type="checkbox" bind:checked={show} />
+{#if show}
+	<Component/>
+{/if}