fix: ensure event handlers containing arguments are not hoisted

.changeset/serious-socks-cover.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure event handlers containing arguments are not hoisted

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

@@ -168,17 +168,23 @@ function get_delegated_event(node, context) {
 
 	const scope = target_function.metadata.scope;
 	for (const [reference] of scope.references) {
+		// Bail-out if the arguments keyword is used
+		if (reference === 'arguments') {
+			return non_hoistable;
+		}
 		const binding = scope.get(reference);
 
 		if (
 			binding !== null &&
-			// Bail-out if we reference anything from the EachBlock (for now) that mutates in non-runes mode,
-			((!context.state.analysis.runes && binding.kind === 'each') ||
-				// or any normal not reactive bindings that are mutated.
-				binding.kind === 'normal' ||
-				// or any reactive imports (those are rewritten) (can only happen in legacy mode)
-				(binding.kind === 'state' && binding.declaration_kind === 'import')) &&
-			binding.mutated
+			// Bail-out if the the binding is a rest param
+			(binding.declaration_kind === 'rest_param' ||
+				// Bail-out if we reference anything from the EachBlock (for now) that mutates in non-runes mode,
+				(((!context.state.analysis.runes && binding.kind === 'each') ||
+					// or any normal not reactive bindings that are mutated.
+					binding.kind === 'normal' ||
+					// or any reactive imports (those are rewritten) (can only happen in legacy mode)
+					(binding.kind === 'state' && binding.declaration_kind === 'import')) &&
+					binding.mutated))
 		) {
 			return non_hoistable;
 		}

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

@@ -255,7 +255,7 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 	function add_params(scope, params) {
 		for (const param of params) {
 			for (const node of extract_identifiers(param)) {
-				scope.declare(node, 'normal', 'param');
+				scope.declare(node, 'normal', param.type === 'RestElement' ? 'rest_param' : 'param');
 			}
 		}
 	}

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

@@ -237,6 +237,7 @@ export type DeclarationKind =
 	| 'function'
 	| 'import'
 	| 'param'
+	| 'rest_param'
 	| 'synthetic';
 
 export interface Binding {

packages/svelte/tests/runtime-runes/samples/event-arguments-2/_config.js

@@ -0,0 +1,13 @@
+import { test } from '../../test';
+
+export default test({
+	html: `<button>0</button>`,
+
+	async test({ assert, target }) {
+		const [b1] = target.querySelectorAll('button');
+
+		b1?.click();
+		await Promise.resolve();
+		assert.htmlEqual(target.innerHTML, '<button>1</button>');
+	}
+});

packages/svelte/tests/runtime-runes/samples/event-arguments-2/main.svelte

@@ -0,0 +1,8 @@
+<script>
+	let count = $state(0);
+	function increment(...args) {
+			count += args.length;
+	}
+</script>
+
+<button on:click={increment}>{count}</button>

packages/svelte/tests/runtime-runes/samples/event-arguments/_config.js

@@ -0,0 +1,13 @@
+import { test } from '../../test';
+
+export default test({
+	html: `<button>0</button>`,
+
+	async test({ assert, target }) {
+		const [b1] = target.querySelectorAll('button');
+
+		b1?.click();
+		await Promise.resolve();
+		assert.htmlEqual(target.innerHTML, '<button>1</button>');
+	}
+});

packages/svelte/tests/runtime-runes/samples/event-arguments/main.svelte

@@ -0,0 +1,8 @@
+<script>
+	let count = $state(0);
+	function increment() {
+			count += arguments.length;
+	}
+</script>
+
+<button on:click={increment}>{count}</button>