fix: transform input defaults from spread

packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/element.js

@@ -11,6 +11,7 @@ import {
 import { regex_starts_with_newline } from '../../../../patterns.js';
 import * as b from '#compiler/builders';
 import {
+	ELEMENT_IS_INPUT,
 	ELEMENT_IS_NAMESPACED,
 	ELEMENT_PRESERVE_ATTRIBUTE_CASE
 } from '../../../../../../constants.js';
@@ -401,6 +402,8 @@ function build_element_spread_attributes(
 		flags |= ELEMENT_IS_NAMESPACED | ELEMENT_PRESERVE_ATTRIBUTE_CASE;
 	} else if (is_custom_element_node(element)) {
 		flags |= ELEMENT_PRESERVE_ATTRIBUTE_CASE;
+	} else if (element.type === 'RegularElement' && element.name === 'input') {
+		flags |= ELEMENT_IS_INPUT;
 	}
 
 	const object = build_spread_object(element, attributes, context);

packages/svelte/src/constants.js

@@ -28,6 +28,7 @@ export const HYDRATION_ERROR = {};
 
 export const ELEMENT_IS_NAMESPACED = 1;
 export const ELEMENT_PRESERVE_ATTRIBUTE_CASE = 1 << 1;
+export const ELEMENT_IS_INPUT = 1 << 2;
 
 export const UNINITIALIZED = Symbol();
 

packages/svelte/src/internal/server/index.js

@@ -8,7 +8,8 @@ import { subscribe_to_store } from '../../store/utils.js';
 import {
 	UNINITIALIZED,
 	ELEMENT_PRESERVE_ATTRIBUTE_CASE,
-	ELEMENT_IS_NAMESPACED
+	ELEMENT_IS_NAMESPACED,
+	ELEMENT_IS_INPUT
 } from '../../constants.js';
 import { escape_html } from '../../escaping.js';
 import { DEV } from 'esm-env';
@@ -187,6 +188,7 @@ export function spread_attributes(attrs, css_hash, classes, styles, flags = 0) {
 
 	const is_html = (flags & ELEMENT_IS_NAMESPACED) === 0;
 	const lowercase = (flags & ELEMENT_PRESERVE_ATTRIBUTE_CASE) === 0;
+	const ignore_defaults = (flags & ELEMENT_IS_INPUT) === 0;
 
 	for (name in attrs) {
 		// omit functions, internal svelte properties and invalid attribute names
@@ -200,6 +202,14 @@ export function spread_attributes(attrs, css_hash, classes, styles, flags = 0) {
 			name = name.toLowerCase();
 		}
 
+		if (!ignore_defaults) {
+			if (name === 'defaultvalue') {
+				name = 'value';
+			} else if (name === 'defaultchecked') {
+				name = 'checked';
+			}
+		}
+
 		attr_str += attr(name, value, is_html && is_boolean_attribute(name));
 	}
 

packages/svelte/tests/runtime-runes/samples/form-default-value-from-spread/_config.js

@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+export default test({
+	mode: ['server'],
+	html: `
+		<input value="a">
+		<input type="checkbox" checked>
+`
+});

packages/svelte/tests/runtime-runes/samples/form-default-value-from-spread/main.svelte

@@ -0,0 +1,7 @@
+<script>
+	let text = { defaultValue: "a" };
+	let checkbox = { defaultChecked: true }
+</script>
+
+<input {...text} />
+<input type="checkbox" {...checkbox} />