fix: address bug in before/after update

.changeset/nasty-clocks-exercise.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: corrects a beforeUpdate/afterUpdate bug

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

@@ -960,10 +960,18 @@ export function set_signal_value(signal, value) {
 			schedule_effect(current_effect, false);
 		}
 		mark_signal_consumers(signal, DIRTY, true);
-		// If we have afterUpdates locally on the component, but we're within a render effect
-		// then we will need to manually invoke the beforeUpdate/afterUpdate logic.
+		// This logic checks if there are any render effects queued after the above marking
+		// of consumers. If there are render effects that have the same component context as
+		// the source signal we're writing to, then we can bail-out of this logic as there
+		// will be a render effect in the queue that hopefully takes case of triggering the
+		// beforeUpdate/afterUpdate logic (doing it again here would duplicate them). However,
+		// if the render effects scheduled in the queue are unrelated to the component context,
+		// then we need to trigger the beforeUpdate/afterUpdate logic here instead.
 		// TODO: should we put this being a is_runes check and only run it in non-runes mode?
-		if (current_effect === null && current_queued_pre_and_render_effects.length === 0) {
+		if (
+			current_effect === null &&
+			current_queued_pre_and_render_effects.every((e) => e.context !== component_context)
+		) {
 			const update_callbacks = component_context?.update_callbacks;
 			if (update_callbacks != null) {
 				update_callbacks.before.forEach(/** @param {any} c */ (c) => c());

packages/svelte/tests/runtime-runes/samples/runes-before-after-update/Child.svelte

@@ -0,0 +1,7 @@
+<script>
+	const {count, increment} = $props();
+</script>
+
+<button onclick={increment}>
+	{count}
+</button>

packages/svelte/tests/runtime-runes/samples/runes-before-after-update/_config.js

@@ -0,0 +1,15 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: '<button>0</button>',
+
+	async test({ assert, target, component }) {
+		const [btn] = target.querySelectorAll('button');
+		flushSync(() => {
+			btn.click();
+		});
+		assert.deepEqual(component.log, ['beforeUpdate', 'afterUpdate']);
+		assert.htmlEqual(target.innerHTML, `<button>1</button>`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/runes-before-after-update/main.svelte

@@ -0,0 +1,22 @@
+<script>
+	import Child from './Child.svelte'
+	import {afterUpdate, beforeUpdate} from 'svelte';
+
+	const {log = []} = $props();
+
+	let count = $state(0);
+
+	const increment = () => {
+		count++;
+	}
+
+	beforeUpdate(() => {
+		log.push('beforeUpdate');
+	});
+
+	afterUpdate(() => {
+		log.push('afterUpdate');
+	});
+</script>
+
+<Child count={count} increment={increment} />