fix: lost reactivity in boundary snippet

Author: paoloricciuti

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

@@ -35,7 +35,8 @@ import {
 	INSPECT_EFFECT,
 	HEAD_EFFECT,
 	MAYBE_DIRTY,
-	EFFECT_HAS_DERIVED
+	EFFECT_HAS_DERIVED,
+	BOUNDARY_EFFECT
 } from '../constants.js';
 import { set } from './sources.js';
 import * as e from '../errors.js';
@@ -142,7 +143,8 @@ function create_effect(type, fn, sync, push = true) {
 		effect.first === null &&
 		effect.nodes_start === null &&
 		effect.teardown === null &&
-		(effect.f & EFFECT_HAS_DERIVED) === 0;
+		(effect.f & EFFECT_HAS_DERIVED) === 0 &&
+		(effect.f & BOUNDARY_EFFECT) === 0;
 
 	if (!inert && !is_root && push) {
 		if (parent_effect !== null) {

packages/svelte/tests/runtime-runes/samples/const-tag-boundary/_config.js

@@ -2,7 +2,16 @@ import { flushSync } from 'svelte';
 import { test } from '../../test';
 
 export default test({
-	html: '<button></button> 2',
-	mode: ['client']
-	// TODO fix reactivity lost in failed snippet and add a test here
+	html: '<button></button><p>2</p>',
+	mode: ['client'],
+	test({ target, assert }) {
+		const btn = target.querySelector('button');
+		const p = target.querySelector('p');
+
+		flushSync(() => {
+			btn?.click();
+		});
+
+		assert.equal(p?.innerHTML, '4');
+	}
 });

packages/svelte/tests/runtime-runes/samples/const-tag-boundary/main.svelte

@@ -8,7 +8,7 @@
 <svelte:boundary>
 	{@const double = test * 2}
 	{#snippet failed()}
-		{double}
+		<p>{double}</p>
 	{/snippet}
 	<FlakyComponent />
 </svelte:boundary>

packages/svelte/tests/runtime-runes/samples/error-boundary-21/Child.svelte

@@ -0,0 +1,3 @@
+<script>
+	throw new Error();
+</script>

packages/svelte/tests/runtime-runes/samples/error-boundary-21/_config.js

@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: '<button></button><div>0</div>',
+	mode: ['client'],
+	test({ assert, target }) {
+		let btn = target.querySelector('button');
+		let div = target.querySelector('div');
+
+		flushSync(() => {
+			btn?.click();
+		});
+
+		assert.equal(div?.innerHTML, `1`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/error-boundary-21/main.svelte

@@ -0,0 +1,14 @@
+<script>
+	import Child from "./Child.svelte"
+
+	let count = $state(0);
+</script>
+
+<button onclick={()=>count++}></button>
+<svelte:boundary>
+	<Child />
+
+	{#snippet failed()}
+		<div>{count}</div>
+	{/snippet}
+</svelte:boundary>