fix: keep effect in the graph if it has an abort controller (#16430)

.changeset/four-kings-drum.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: keep effect in the graph if it has an abort controller

packages/svelte/src/internal/client/reactivity/batch.js

@@ -532,7 +532,9 @@ function flush_queued_effects(effects) {
 				// here (rather than in `update_effect`) allows us to skip the work for
 				// immediate effects.
 				if (effect.deps === null && effect.first === null && effect.nodes_start === null) {
-					if (effect.teardown === null) {
+					// if there's no teardown or abort controller we completely unlink
+					// the effect from the graph
+					if (effect.teardown === null && effect.ac === null) {
 						// remove this effect from the graph
 						unlink_effect(effect);
 					} else {

packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/Component.svelte

@@ -0,0 +1,8 @@
+<script>
+	import { getAbortSignal } from 'svelte';
+
+	$effect(() => {
+		const signal = getAbortSignal()
+		signal.addEventListener('abort', () => console.log('abort'))
+	})
+</script>

packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/_config.js

@@ -0,0 +1,12 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+		assert.deepEqual(logs, ['abort']);
+	}
+});

packages/svelte/tests/runtime-runes/samples/dependencyless-abort-signal/main.svelte

@@ -0,0 +1,10 @@
+<script>
+	import Component from './Component.svelte'
+
+	let show = $state(true)
+</script>
+
+<button onclick={() => (show = !show)}>click</button>
+{#if show}
+	<Component />
+{/if}