fix

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

@@ -22,4 +22,5 @@ export const EFFECT_HAS_DERIVED = 1 << 19;
 
 export const STATE_SYMBOL = Symbol('$state');
 export const STATE_SYMBOL_METADATA = Symbol('$state metadata');
+export const LEGACY_PROPS = Symbol('legacy props');
 export const LOADING_ATTR_SYMBOL = Symbol('');

packages/svelte/src/internal/client/reactivity/props.js

@@ -20,7 +20,13 @@ import {
 } from '../runtime.js';
 import { safe_equals } from './equality.js';
 import * as e from '../errors.js';
-import { BRANCH_EFFECT, LEGACY_DERIVED_PROP, ROOT_EFFECT, STATE_SYMBOL } from '../constants.js';
+import {
+	BRANCH_EFFECT,
+	LEGACY_DERIVED_PROP,
+	LEGACY_PROPS,
+	ROOT_EFFECT,
+	STATE_SYMBOL
+} from '../constants.js';
 import { proxy } from '../proxy.js';
 import { capture_store_binding } from './store.js';
 import { legacy_mode_flag } from '../../flags/index.js';
@@ -283,10 +289,12 @@ export function prop(props, key, flags, fallback) {
 		prop_value = /** @type {V} */ (props[key]);
 	}
 
+	// Can be the case when someone does `mount(Component, props)` with `let props = $state({...})`
+	// or `createClassComponent(Component, props)`
+	var is_entry_props = STATE_SYMBOL in props || LEGACY_PROPS in props;
+
 	var setter =
-		get_descriptor(props, key)?.set ??
+		get_descriptor(props, key)?.set ?? (is_entry_props ? (v) => (props[key] = v) : undefined);
-		// Can be the case when someone does `mount(Component, props)` with `let props = $state({...})`
-		(STATE_SYMBOL in props ? (v) => (props[key] = v) : undefined);
 
 	var fallback_value = /** @type {V} */ (fallback);
 	var fallback_dirty = true;
@@ -307,7 +315,7 @@ export function prop(props, key, flags, fallback) {
 	};
 
 	if (prop_value === undefined && fallback !== undefined) {
-		if (setter && runes) {
+		if (setter && runes && !is_entry_props) {
 			e.props_invalid_value(key);
 		}
 

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

@@ -1,4 +1,4 @@
-import { dev_current_component_function, untrack } from './runtime.js';
+import { dev_current_component_function } from './runtime.js';
 import { get_descriptor, is_array } from '../shared/utils.js';
 import * as e from './errors.js';
 import { FILENAME } from '../../constants.js';
@@ -6,15 +6,6 @@ import { render_effect } from './reactivity/effects.js';
 import * as w from './warnings.js';
 import { capture_store_binding } from './reactivity/store.js';
 
-/** regex of all html void element names */
-const void_element_names =
-	/^(?:area|base|br|col|command|embed|hr|img|input|keygen|link|meta|param|source|track|wbr)$/;
-
-/** @param {string} tag */
-function is_void(tag) {
-	return void_element_names.test(tag) || tag.toLowerCase() === '!doctype';
-}
-
 /**
  * @param {() => any} collection
  * @param {(item: any, index: number) => string} key_fn

packages/svelte/src/legacy/legacy-client.js

@@ -1,5 +1,5 @@
 /** @import { ComponentConstructorOptions, ComponentType, SvelteComponent, Component } from 'svelte' */
-import { DIRTY, MAYBE_DIRTY } from '../internal/client/constants.js';
+import { DIRTY, LEGACY_PROPS, MAYBE_DIRTY } from '../internal/client/constants.js';
 import { user_pre_effect } from '../internal/client/reactivity/effects.js';
 import { mutable_source, set } from '../internal/client/reactivity/sources.js';
 import { hydrate, mount, unmount } from '../internal/client/render.js';
@@ -89,7 +89,7 @@ class Svelte4Component {
 		};
 
 		// Replicate coarse-grained props through a proxy that has a version source for
-		// each property, which is increment on updates to the property itself. Do not
+		// each property, which is incremented on updates to the property itself. Do not
 		// use our $state proxy because that one has fine-grained reactivity.
 		const props = new Proxy(
 			{ ...(options.props || {}), $$events: {} },
@@ -98,26 +98,15 @@ class Svelte4Component {
 					return get(sources.get(prop) ?? add_source(prop, Reflect.get(target, prop)));
 				},
 				has(target, prop) {
+					// Necessary to not throw "invalid binding" validation errors on the component side
+					if (prop === LEGACY_PROPS) return true;
+
 					get(sources.get(prop) ?? add_source(prop, Reflect.get(target, prop)));
 					return Reflect.has(target, prop);
 				},
 				set(target, prop, value) {
 					set(sources.get(prop) ?? add_source(prop, value), value);
 					return Reflect.set(target, prop, value);
-				},
-				getOwnPropertyDescriptor(target, prop) {
-					// TODO this throws "invalid binding" errors on the component side
-					const desc = Reflect.getOwnPropertyDescriptor(target, prop);
-					if (!desc?.configurable) return desc;
-					return {
-						get: () => get(sources.get(prop) ?? add_source(prop, Reflect.get(target, prop))),
-						set: (value) => {
-							set(sources.get(prop) ?? add_source(prop, value), value);
-							return Reflect.set(target, prop, value);
-						},
-						enumerable: desc.enumerable,
-						configurable: desc.configurable
-					};
 				}
 			}
 		);