feat: allow dynamic `type` attribute with `bind:value` (#10608)

Since these all share the same underlying small runtime code, there's no reason anymore to not allow it.
closes #10256
closes #3921

.changeset/good-buses-reply.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+feat: allow dynamic `type` attribute with `bind:value`

packages/svelte/src/compiler/phases/2-analyze/validation.js

@@ -435,7 +435,10 @@ const validation = {
 						parent.attributes.find((a) => a.type === 'Attribute' && a.name === 'type')
 					);
 					if (type && !is_text_attribute(type)) {
-						error(type, 'invalid-type-attribute');
+						if (node.name !== 'value' || type.value === true) {
+							error(type, 'invalid-type-attribute');
+						}
+						return; // bind:value can handle dynamic `type` attributes
 					}
 
 					if (node.name === 'checked' && type?.value[0].data !== 'checkbox') {

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

@@ -1018,6 +1018,12 @@ export function selected(dom) {
  */
 export function bind_value(dom, get_value, update) {
 	dom.addEventListener('input', () => {
+		if (DEV && dom.type === 'checkbox') {
+			throw new Error(
+				'Using bind:value together with a checkbox input is not allowed. Use bind:checked instead'
+			);
+		}
+
 		/** @type {any} */
 		let value = dom.value;
 		if (is_numberlike_input(dom)) {
@@ -1027,6 +1033,12 @@ export function bind_value(dom, get_value, update) {
 	});
 
 	render_effect(() => {
+		if (DEV && dom.type === 'checkbox') {
+			throw new Error(
+				'Using bind:value together with a checkbox input is not allowed. Use bind:checked instead'
+			);
+		}
+
 		const value = get_value();
 		// @ts-ignore
 		dom.__value = value;

packages/svelte/tests/runtime-runes/samples/bind-value-input-type-dynamic/_config.js

@@ -0,0 +1,72 @@
+import { tick } from 'svelte';
+import { test, ok } from '../../test';
+
+export default test({
+	html: `
+		<input type=text>
+		<input type=text>
+		<p>x / y</p>
+
+		<button>change to text</button>
+		<button>change to number</button>
+		<button>change to range</button>
+	`,
+	ssrHtml: `
+		<input type=text value=x>
+		<input type=text value=y>
+		<p>x / y</p>
+
+		<button>change to text</button>
+		<button>change to number</button>
+		<button>change to range</button>
+	`,
+	async test({ assert, target }) {
+		const [in1, in2] = target.querySelectorAll('input');
+		const [btn1, btn2, btn3] = target.querySelectorAll('button');
+		const p = target.querySelector('p');
+		ok(p);
+
+		in1.value = '0';
+		in2.value = '1';
+		in1.dispatchEvent(new window.Event('input', { bubbles: true }));
+		in2.dispatchEvent(new window.Event('input', { bubbles: true }));
+		await tick();
+		btn2?.click();
+		await tick();
+		assert.htmlEqual(p.innerHTML, '0 / 1');
+
+		in1.stepUp();
+		in1.dispatchEvent(new window.Event('input', { bubbles: true }));
+		in2.stepUp();
+		in2.dispatchEvent(new window.Event('input', { bubbles: true }));
+		await tick();
+		assert.htmlEqual(p.innerHTML, '1 / 2');
+
+		btn1?.click();
+		await tick();
+		try {
+			in1.stepUp();
+			assert.fail();
+		} catch (e) {
+			// expected
+		}
+
+		btn3?.click();
+		await tick();
+		in1.stepUp();
+		in1.dispatchEvent(new window.Event('input', { bubbles: true }));
+		in2.stepUp();
+		in2.dispatchEvent(new window.Event('input', { bubbles: true }));
+		await tick();
+		assert.htmlEqual(p.innerHTML, '2 / 3');
+
+		btn1?.click();
+		await tick();
+		in1.value = 'a';
+		in2.value = 'b';
+		in1.dispatchEvent(new window.Event('input', { bubbles: true }));
+		in2.dispatchEvent(new window.Event('input', { bubbles: true }));
+		await tick();
+		assert.htmlEqual(p.innerHTML, 'a / b');
+	}
+});

packages/svelte/tests/runtime-runes/samples/bind-value-input-type-dynamic/main.svelte

@@ -0,0 +1,14 @@
+<script>
+	let dynamic = $state('x');
+	let spread = $state('y');
+	let inputType = $state('text');
+	let props = $derived({type: inputType});
+</script>
+
+<input bind:value={dynamic} type={inputType}>
+<input bind:value={spread} {...props}>
+<p>{dynamic} / {spread}</p>
+
+<button onclick={() => inputType = 'text'}>change to text</button>
+<button onclick={() => inputType = 'number'}>change to number</button>
+<button onclick={() => inputType = 'range'}>change to range</button>

packages/svelte/tests/validator/samples/binding-input-type-dynamic/errors.json

@@ -1,14 +0,0 @@
-[
-	{
-		"code": "invalid-type-attribute",
-		"message": "'type' attribute must be a static text value if input uses two-way binding",
-		"start": {
-			"line": 6,
-			"column": 24
-		},
-		"end": {
-			"line": 6,
-			"column": 40
-		}
-	}
-]

packages/svelte/tests/validator/samples/binding-input-type-dynamic/input.svelte

@@ -1,6 +0,0 @@
-<script>
-	let foo;
-	let inputType;
-</script>
-
-<input bind:value={foo} type={inputType}>