From 3e6c448cacbb65903b302152d3bd5592abf81f9e Mon Sep 17 00:00:00 2001
From: svelte-triage-bot <team@svelte.com>
Date: Wed, 9 Sep 2026 22:08:45 +0000
Subject: [PATCH] test: cover block components invoked from effects

---
 .changeset/calm-batches-mount.md               |  2 +-
 .../src/internal/client/reactivity/effects.js  |  1 +
 .../Child.svelte                               |  5 +++++
 .../async-component-await-in-effect/_config.js | 13 +++++++++++++
 .../main.svelte                                | 18 ++++++++++++++++++
 .../component-boundary-in-effect/Child.svelte  |  3 +++
 .../component-boundary-in-effect/_config.js    | 13 +++++++++++++
 .../component-boundary-in-effect/main.svelte   | 18 ++++++++++++++++++
 8 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/main.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/main.svelte

diff --git a/.changeset/calm-batches-mount.md b/.changeset/calm-batches-mount.md
index 330f8d37df..9c241ab124 100644
--- a/.changeset/calm-batches-mount.md
+++ b/.changeset/calm-batches-mount.md
@@ -2,4 +2,4 @@
 'svelte': patch
 ---
 
-fix: prevent async component batch crash
+fix: initialize components invoked from effects with a batch
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index e69a639a94..e8c0621677 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -413,6 +413,7 @@ export function deferred_template_effect(fn, sync = [], async = [], blockers = [
  * @param {number} flags
  */
 export function block(fn, flags = 0) {
+	Batch.ensure();
 	var effect = create_effect(BLOCK_EFFECT | flags, fn);
 	if (DEV) {
 		effect.dev_stack = dev_stack;
diff --git a/packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/Child.svelte
new file mode 100644
index 0000000000..2025540df0
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/Child.svelte
@@ -0,0 +1,5 @@
+{#await Promise.resolve('child')}
+	<p data-pending>pending</p>
+{:then value}
+	<p data-child>{value}</p>
+{/await}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/_config.js b/packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/_config.js
new file mode 100644
index 0000000000..a7bb5e425d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/_config.js
@@ -0,0 +1,13 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		target.querySelector('button')?.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>run</button><p data-child="">child</p><span></span>'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/main.svelte
new file mode 100644
index 0000000000..c337ab97f7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-component-await-in-effect/main.svelte
@@ -0,0 +1,18 @@
+<script>
+	import Child from './Child.svelte';
+
+	let anchor = $state();
+	let run = $state(false);
+
+	function capture(node) {
+		anchor = node;
+		return () => (anchor = undefined);
+	}
+
+	$effect(() => {
+		if (run && anchor) Child(anchor, {});
+	});
+</script>
+
+<button onclick={() => (run = !run)}>run</button>
+<span {@attach capture}></span>
diff --git a/packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/Child.svelte b/packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/Child.svelte
new file mode 100644
index 0000000000..cabffef04e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/Child.svelte
@@ -0,0 +1,3 @@
+<svelte:boundary>
+	<p data-child>child</p>
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/_config.js b/packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/_config.js
new file mode 100644
index 0000000000..a7bb5e425d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/_config.js
@@ -0,0 +1,13 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		target.querySelector('button')?.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>run</button><p data-child="">child</p><span></span>'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/main.svelte b/packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/main.svelte
new file mode 100644
index 0000000000..c337ab97f7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/component-boundary-in-effect/main.svelte
@@ -0,0 +1,18 @@
+<script>
+	import Child from './Child.svelte';
+
+	let anchor = $state();
+	let run = $state(false);
+
+	function capture(node) {
+		anchor = node;
+		return () => (anchor = undefined);
+	}
+
+	$effect(() => {
+		if (run && anchor) Child(anchor, {});
+	});
+</script>
+
+<button onclick={() => (run = !run)}>run</button>
+<span {@attach capture}></span>