fix: only skip updating bound <input> if the input was the source of the change

.changeset/healthy-garlics-do.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: only skip updating bound `<input>` if the input was the source of the change

packages/svelte/src/internal/client/dom/elements/bindings/input.js

@@ -1,3 +1,4 @@
+/** @import { Batch } from '../../../reactivity/batch.js' */
 import { DEV } from 'esm-env';
 import { render_effect, teardown } from '../../../reactivity/effects.js';
 import { listen_to_event_and_reset_event } from './shared.js';
@@ -7,6 +8,7 @@ import { queue_micro_task } from '../../task.js';
 import { hydrating } from '../../hydration.js';
 import { untrack } from '../../../runtime.js';
 import { is_runes } from '../../../context.js';
+import { current_batch } from '../../../reactivity/batch.js';
 
 /**
  * @param {HTMLInputElement} input
@@ -17,6 +19,8 @@ import { is_runes } from '../../../context.js';
 export function bind_value(input, get, set = get) {
 	var runes = is_runes();
 
+	var batches = new WeakSet();
+
 	listen_to_event_and_reset_event(input, 'input', (is_reset) => {
 		if (DEV && input.type === 'checkbox') {
 			// TODO should this happen in prod too?
@@ -28,6 +32,10 @@ export function bind_value(input, get, set = get) {
 		value = is_numberlike_input(input) ? to_number(value) : value;
 		set(value);
 
+		if (current_batch !== null) {
+			batches.add(current_batch);
+		}
+
 		// In runes mode, respect any validation in accessors (doesn't apply in legacy mode,
 		// because we use mutable state which ensures the render effect always runs)
 		if (runes && value !== (value = get())) {
@@ -54,6 +62,10 @@ export function bind_value(input, get, set = get) {
 		(untrack(get) == null && input.value)
 	) {
 		set(is_numberlike_input(input) ? to_number(input.value) : input.value);
+
+		if (current_batch !== null) {
+			batches.add(current_batch);
+		}
 	}
 
 	render_effect(() => {
@@ -64,7 +76,7 @@ export function bind_value(input, get, set = get) {
 
 		var value = get();
 
-		if (input === document.activeElement) {
+		if (input === document.activeElement && batches.has(/** @type {Batch} */ (current_batch))) {
 			// Never rewrite the contents of a focused input. We can get here if, for example,
 			// an update is deferred because of async work depending on the input:
 			//

packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/_config.js

@@ -0,0 +1,40 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client', 'hydrate'],
+
+	async test({ assert, target }) {
+		const [input] = target.querySelectorAll('input');
+
+		flushSync(() => {
+			input.focus();
+			input.dispatchEvent(new KeyboardEvent('keydown', { key: 'ArrowUp', bubbles: true }));
+		});
+		assert.equal(input.value, '2');
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<label>
+					<input /> arrow up/down
+				</label>
+				<p>value = 2</p>
+			`
+		);
+
+		flushSync(() => {
+			input.focus();
+			input.dispatchEvent(new KeyboardEvent('keydown', { key: 'ArrowDown', bubbles: true }));
+		});
+		assert.equal(input.value, '1');
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<label>
+					<input /> arrow up/down
+				</label>
+				<p>value = 1</p>
+			`
+		);
+	}
+});

packages/svelte/tests/runtime-runes/samples/binding-update-while-focused/main.svelte

@@ -0,0 +1,16 @@
+<script>
+	let value = $state('1');
+
+	function onkeydown (e) {
+		let _v = parseFloat(value);
+		if (e.key === 'ArrowUp') _v += 1;
+		else if (e.key === 'ArrowDown') _v -= 1;
+		value = _v.toString();
+	}
+</script>
+
+<label>
+	<input bind:value {onkeydown} /> arrow up/down
+</label>
+
+<p>value = {value}</p>