fix: improve compiler attribute validation logic (#12081)

prevent misidentification of bindings as delegatable event handlers if used outside event attribute
Fixes #12074

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

.changeset/hot-rivers-punch.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: prevent misidentification of bindings as delegatable event handlers if used outside event attribute

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

@@ -111,23 +111,24 @@ function get_delegated_event(event_name, handler, context) {
 		if (binding != null) {
 			for (const { path } of binding.references) {
 				const parent = path.at(-1);
-				if (parent == null) {
-					return non_hoistable;
-				}
+				if (parent == null) return non_hoistable;
+
+				const grandparent = path.at(-2);
 
 				/** @type {import('#compiler').RegularElement | null} */
 				let element = null;
 				/** @type {string | null} */
 				let event_name = null;
 				if (parent.type === 'OnDirective') {
-					element = /** @type {import('#compiler').RegularElement} */ (path.at(-2));
+					element = /** @type {import('#compiler').RegularElement} */ (grandparent);
 					event_name = parent.name;
 				} else if (
 					parent.type === 'ExpressionTag' &&
-					is_event_attribute(/** @type {import('#compiler').Attribute} */ (path.at(-2)))
+					grandparent?.type === 'Attribute' &&
+					is_event_attribute(grandparent)
 				) {
 					element = /** @type {import('#compiler').RegularElement} */ (path.at(-3));
-					const attribute = /** @type {import('#compiler').Attribute} */ (path.at(-2));
+					const attribute = /** @type {import('#compiler').Attribute} */ (grandparent);
 					event_name = get_attribute_event_name(attribute.name);
 				}
 

packages/svelte/tests/runtime-runes/samples/event-on-3/_config.js

@@ -0,0 +1,7 @@
+import { test } from '../../test';
+
+export default test({
+	test() {
+		// Compiler shouldn't error
+	}
+});

packages/svelte/tests/runtime-runes/samples/event-on-3/main.svelte

@@ -0,0 +1,5 @@
+<script>
+	function f() {}
+</script>
+
+<input onchange={f}>{f}