invalid-rest-eachblock-binding

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

@@ -298,13 +298,24 @@ const validation = {
 			// TODO handle mutations of non-state/props in runes mode
 		}
 
+		const binding = context.state.scope.get(left.name);
+
 		if (node.name === 'group') {
-			const binding = context.state.scope.get(left.name);
 			if (!binding) {
 				error(node, 'INTERNAL', 'Cannot find declaration for bind:group');
 			}
 		}
 
+		if (binding?.kind === 'each' && binding.metadata?.inside_rest) {
+			warn(
+				context.state.analysis.warnings,
+				binding.node,
+				context.path,
+				'invalid-rest-eachblock-binding',
+				binding.node.name
+			);
+		}
+
 		const parent = context.path.at(-1);
 
 		if (

packages/svelte/src/compiler/phases/scope.js

@@ -112,7 +112,8 @@ export class Scope {
 			prop_alias: null,
 			expression: null,
 			mutation: null,
-			reassigned: false
+			reassigned: false,
+			metadata: null
 		};
 		this.declarations.set(node.name, binding);
 		this.root.conflicts.add(node.name);
@@ -534,7 +535,25 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 
 			// declarations
 			for (const id of extract_identifiers(node.context)) {
-				scope.declare(id, 'each', 'const');
+				const binding = scope.declare(id, 'each', 'const');
+
+				let inside_rest = false;
+				let is_rest_id = false;
+				walk(node.context, null, {
+					Identifier(node) {
+						if (inside_rest && node === id) {
+							is_rest_id = true;
+						}
+					},
+					RestElement(_, { next }) {
+						const prev = inside_rest;
+						inside_rest = true;
+						next();
+						inside_rest = prev;
+					}
+				});
+
+				binding.metadata = { inside_rest: is_rest_id };
 			}
 			if (node.context.type !== 'Identifier') {
 				scope.declare(b.id('$$item'), 'derived', 'synthetic');

packages/svelte/src/compiler/types/index.d.ts

@@ -288,6 +288,11 @@ export interface Binding {
 	expression: Expression | ((id: Identifier) => Expression) | null;
 	/** If this is set, all mutations should use this expression */
 	mutation: ((assignment: AssignmentExpression, context: Context<any, any>) => Expression) | null;
+	/** Additional metadata, varies per binding type */
+	metadata: {
+		/** `true` if is (inside) a rest parameter */
+		inside_rest?: boolean;
+	} | null;
 }
 
 export * from './template.js';

packages/svelte/src/compiler/warnings.js

@@ -197,7 +197,10 @@ const a11y = {
 /** @satisfies {Warnings} */
 const state = {
 	'static-state-reference': () =>
-		`State referenced in its own scope will never update. Did you mean to reference it inside a closure?`
+		`State referenced in its own scope will never update. Did you mean to reference it inside a closure?`,
+	/** @param {string} name */
+	'invalid-rest-eachblock-binding': (name) =>
+		`The rest operator (...) will create a new object and binding '${name}' with the original object will not work`
 };
 
 /** @satisfies {Warnings} */

packages/svelte/tests/validator/samples/rest-eachblock-binding-2/_config.js

@@ -1,4 +0,0 @@
-import { test } from '../../test';
-
-// TODO this likely works in the new world - remove this warning?
-export default test({ skip: true });

packages/svelte/tests/validator/samples/rest-eachblock-binding-3/_config.js

@@ -1,4 +0,0 @@
-import { test } from '../../test';
-
-// TODO this likely works in the new world - remove this warning?
-export default test({ skip: true });

packages/svelte/tests/validator/samples/rest-eachblock-binding-nested-rest/_config.js

@@ -1,4 +0,0 @@
-import { test } from '../../test';
-
-// TODO this maybe works in the new world - remove this warning?
-export default test({ skip: true });

packages/svelte/tests/validator/samples/rest-eachblock-binding/_config.js

@@ -1,4 +0,0 @@
-import { test } from '../../test';
-
-// TODO this likely works in the new world - remove this warning?
-export default test({ skip: true });