make it a dev-time validation error that also deals with ...rest props

packages/svelte/src/compiler/phases/3-transform/client/transform-client.js

@@ -239,7 +239,7 @@ export function client_component(source, analysis, options) {
 		);
 	});
 
-	const properties = analysis.exports.map(({ name, alias }) => {
+	const component_returned_object = analysis.exports.map(({ name, alias }) => {
 		const expression = serialize_get_binding(b.id(name), instance_state);
 
 		if (expression.type === 'Identifier' && !options.dev) {
@@ -249,11 +249,26 @@ export function client_component(source, analysis, options) {
 		return b.get(alias ?? name, [b.return(expression)]);
 	});
 
-	if (analysis.accessors) {
+	const properties = [...analysis.instance.scope.declarations].filter(
-		for (const [name, binding] of analysis.instance.scope.declarations) {
+		([name, binding]) =>
-			if ((binding.kind !== 'prop' && binding.kind !== 'bindable_prop') || name.startsWith('$$'))
+			(binding.kind === 'prop' || binding.kind === 'bindable_prop') && !name.startsWith('$$')
-				continue;
+	);
+
+	if (analysis.runes && options.dev) {
+		/** @type {import('estree').Literal[]} */
+		const bindable = [];
+		for (const [name, binding] of properties) {
+			if (binding.kind === 'bindable_prop') {
+				bindable.push(b.literal(binding.prop_alias ?? name));
+			}
+		}
+		instance.body.unshift(
+			b.stmt(b.call('$.validate_prop_bindings', b.id('$$props'), b.array(bindable)))
+		);
+	}
 
+	if (analysis.accessors) {
+		for (const [name, binding] of properties) {
 			const key = binding.prop_alias ?? name;
 			if (
 				binding.kind === 'prop' &&
@@ -265,7 +280,7 @@ export function client_component(source, analysis, options) {
 				continue;
 			}
 
-			properties.push(
+			component_returned_object.push(
 				b.get(key, [b.return(b.call(b.id(name)))]),
 				b.set(key, [b.stmt(b.call(b.id(name), b.id('$$value'))), b.stmt(b.call('$.flushSync'))])
 			);
@@ -273,7 +288,7 @@ export function client_component(source, analysis, options) {
 	}
 
 	if (options.legacy.componentApi) {
-		properties.push(
+		component_returned_object.push(
 			b.init('$set', b.id('$.update_legacy_props')),
 			b.init(
 				'$on',
@@ -289,7 +304,7 @@ export function client_component(source, analysis, options) {
 			)
 		);
 	} else if (options.dev) {
-		properties.push(
+		component_returned_object.push(
 			b.init(
 				'$set',
 				b.thunk(
@@ -357,8 +372,8 @@ export function client_component(source, analysis, options) {
 
 	append_styles();
 	component_block.body.push(
-		properties.length > 0
+		component_returned_object.length > 0
-			? b.return(b.call('$.pop', b.object(properties)))
+			? b.return(b.call('$.pop', b.object(component_returned_object)))
 			: b.stmt(b.call('$.pop'))
 	);
 

packages/svelte/src/compiler/phases/3-transform/client/utils.js

@@ -5,8 +5,7 @@ import {
 	PROPS_IS_LAZY_INITIAL,
 	PROPS_IS_IMMUTABLE,
 	PROPS_IS_RUNES,
-	PROPS_IS_UPDATED,
+	PROPS_IS_UPDATED
-	PROPS_IS_BINDABLE
 } from '../../../../constants.js';
 
 /**
@@ -640,19 +639,6 @@ export function get_prop_source(binding, state, name, initial) {
 		flags |= PROPS_IS_RUNES;
 	}
 
-	if (
-		binding.kind === 'bindable_prop' ||
-		// Make sure that
-		// let { foo: _, ...rest } = $props();
-		// let { foo } = $props.bindable();
-		// marks both `foo` and `_` as bindable to prevent false-positive runtime validation errors
-		[...state.scope.declarations.values()].some(
-			(d) => d.kind === 'bindable_prop' && d.prop_alias === name
-		)
-	) {
-		flags |= PROPS_IS_BINDABLE;
-	}
-
 	if (
 		state.analysis.accessors ||
 		(state.analysis.immutable ? binding.reassigned : binding.mutated)

packages/svelte/src/constants.js

@@ -11,7 +11,6 @@ export const PROPS_IS_IMMUTABLE = 1;
 export const PROPS_IS_RUNES = 1 << 1;
 export const PROPS_IS_UPDATED = 1 << 2;
 export const PROPS_IS_LAZY_INITIAL = 1 << 3;
-export const PROPS_IS_BINDABLE = 1 << 4;
 
 /** List of Element events that will be delegated */
 export const DelegatedEvents = [

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

@@ -1,6 +1,5 @@
 import { DEV } from 'esm-env';
 import {
-	PROPS_IS_BINDABLE,
 	PROPS_IS_IMMUTABLE,
 	PROPS_IS_LAZY_INITIAL,
 	PROPS_IS_RUNES,
@@ -143,15 +142,6 @@ export function prop(props, key, flags, initial) {
 	var prop_value = /** @type {V} */ (props[key]);
 	var setter = get_descriptor(props, key)?.set;
 
-	if ((flags & PROPS_IS_BINDABLE) === 0 && setter) {
-		throw new Error(
-			'ERR_SVELTE_NOT_BINDABLE' +
-				(DEV
-					? `: Cannot bind:${key} because the property was not declared as bindable. To mark a property as bindable, use let \`{ ${key} } = $props.bindable()\` within the component.`
-					: '')
-		);
-	}
-
 	if (prop_value === undefined && initial !== undefined) {
 		if (setter && runes) {
 			// TODO consolidate all these random runtime errors

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

@@ -1,5 +1,5 @@
 import { untrack } from './runtime.js';
-import { is_array } from './utils.js';
+import { get_descriptor, is_array } from './utils.js';
 
 /** regex of all html void element names */
 const void_element_names =
@@ -137,3 +137,22 @@ export function validate_component(component_fn) {
 	}
 	return component_fn;
 }
+
+/**
+ * @param {Record<string, any>} $$props
+ * @param {string[]} bindable
+ */
+export function validate_prop_bindings($$props, bindable) {
+	for (const key in $$props) {
+		if (!bindable.includes(key)) {
+			var setter = get_descriptor($$props, key)?.set;
+
+			if (setter) {
+				throw new Error(
+					`Cannot use bind:${key} on this component because the property was not declared as bindable. ` +
+						`To mark a property as bindable, use let \`{ ${key} } = $props.bindable()\` within the component.`
+				);
+			}
+		}
+	}
+}

packages/svelte/tests/runtime-runes/samples/props-not-bindable-spread/Counter.svelte

@@ -0,0 +1,5 @@
+<script>
+	let { ...rest } = $props();
+</script>
+
+{rest.count}

packages/svelte/tests/runtime-runes/samples/props-not-bindable-spread/_config.js

@@ -0,0 +1,10 @@
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+	error:
+		'Cannot use bind:count on this component because the property was not declared as bindable. To mark a property as bindable, use let `{ count } = $props.bindable()` within the component.',
+	html: `0`
+});

packages/svelte/tests/runtime-runes/samples/props-not-bindable-spread/main.svelte

@@ -0,0 +1,7 @@
+<script>
+    import Counter from './Counter.svelte';
+
+    let count = $state(0);
+</script>
+
+<Counter bind:count />

packages/svelte/tests/runtime-runes/samples/props-not-bindable/_config.js

@@ -1,7 +1,10 @@
 import { test } from '../../test';
 
 export default test({
+	compileOptions: {
+		dev: true
+	},
 	error:
-		'ERR_SVELTE_NOT_BINDABLE: Cannot bind:count because the property was not declared as bindable. To mark a property as bindable, use let `{ count } = $props.bindable()` within the component.',
+		'Cannot use bind:count on this component because the property was not declared as bindable. To mark a property as bindable, use let `{ count } = $props.bindable()` within the component.',
 	html: `0`
 });