fix: keep bound inputs in sync in runes mode (#13328)

* fix: keep bound inputs in sync in runes mode

* small tweak, add more detailed explanatory comment

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

.changeset/brown-pens-repeat.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: keep bound inputs in sync in runes mode

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

@@ -5,6 +5,7 @@ import * as e from '../../../errors.js';
 import { get_proxied_value, is } from '../../../proxy.js';
 import { queue_micro_task } from '../../task.js';
 import { hydrating } from '../../hydration.js';
+import { is_runes } from '../../../runtime.js';
 
 /**
  * @param {HTMLInputElement} input
@@ -13,13 +14,24 @@ import { hydrating } from '../../hydration.js';
  * @returns {void}
  */
 export function bind_value(input, get, set = get) {
+	var runes = is_runes();
+
 	listen_to_event_and_reset_event(input, 'input', () => {
 		if (DEV && input.type === 'checkbox') {
 			// TODO should this happen in prod too?
 			e.bind_invalid_checkbox_value();
 		}
 
-		set(is_numberlike_input(input) ? to_number(input.value) : input.value);
+		/** @type {unknown} */
+		var value = is_numberlike_input(input) ? to_number(input.value) : input.value;
+		set(value);
+
+		// 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())) {
+			// @ts-expect-error the value is coerced on assignment
+			input.value = value ?? '';
+		}
 	});
 
 	render_effect(() => {

packages/svelte/tests/runtime-runes/samples/bind-value-state/_config.js

@@ -0,0 +1,27 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<input type="number"><div>0</div>`,
+	mode: ['client', 'hydrate'],
+
+	async test({ assert, target }) {
+		const [input1] = target.querySelectorAll('input');
+		assert.equal(input1.value, '0');
+
+		input1.value = '1';
+		input1.dispatchEvent(new window.InputEvent('input'));
+
+		flushSync();
+
+		assert.equal(input1.value, '1');
+		assert.htmlEqual(target.innerHTML, `<input type="number"><div>1</div>`);
+
+		input1.value = '101';
+		input1.dispatchEvent(new window.InputEvent('input'));
+		flushSync();
+
+		assert.equal(input1.value, '100');
+		assert.htmlEqual(target.innerHTML, `<input type="number"><div>100</div>`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/bind-value-state/main.svelte

@@ -0,0 +1,11 @@
+<script>
+	let v = $state(0)
+	let count = {
+		get v() { return v },
+		set v(x) { {
+			v = Math.min(100, +x)
+		}},
+	};
+</script>
+<input bind:value={count.v} type="number">
+<div>{count.v}</div>