fix: cleanup non-branch effects created inside block effects

.changeset/eleven-humans-kneel.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: cleanup non-branch effects created inside block effects

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

@@ -418,6 +418,22 @@ export function destroy_effect_children(signal, remove_dom = false) {
 	}
 }
 
+/**
+ * @param {Effect} signal
+ * @returns {void}
+ */
+export function destroy_block_effect_children(signal) {
+	var effect = signal.first;
+
+	while (effect !== null) {
+		var next = effect.next;
+		if ((effect.f & BRANCH_EFFECT) === 0) {
+			destroy_effect(effect);
+		}
+		effect = next;
+	}
+}
+
 /**
  * @param {Effect} effect
  * @returns {void}
@@ -443,7 +459,9 @@ export function update_effect(effect) {
 	}
 
 	try {
-		if ((flags & BLOCK_EFFECT) === 0) {
+		if ((flags & BLOCK_EFFECT) !== 0) {
+			destroy_block_effect_children(effect);
+		} else {
 			destroy_effect_children(effect);
 		}
 

packages/svelte/tests/runtime-runes/samples/clean-block-inner-effects/_config.js

@@ -0,0 +1,13 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, instance, logs }) {
+		const button = target.querySelector('button');
+		assert.deepEqual(logs, ['effect', 1]);
+		flushSync(() => {
+			button?.click();
+		});
+		assert.deepEqual(logs, ['effect', 1, 'clean', 1, 'effect', 2]);
+	}
+});

packages/svelte/tests/runtime-runes/samples/clean-block-inner-effects/main.svelte

@@ -0,0 +1,18 @@
+<script>
+	let count = $state(1);
+	function track(value){
+		let val = value;
+		$effect(() => {
+			console.log("effect", val);
+			return ()=>{
+				console.log("clean", val);
+			}
+		});
+		return value;
+	}
+</script>
+
+{#if track(count)}
+{/if}
+
+<button onclick={()=> count++}></button>