fix: warn against accidental global event referenced

.changeset/chilly-snakes-scream.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: warn against accidental global event referenced

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

@@ -1,5 +1,11 @@
 import { error } from '../../errors.js';
-import { extract_identifiers, get_parent, is_text_attribute, object } from '../../utils/ast.js';
+import {
+	extract_identifiers,
+	get_parent,
+	is_expression_attribute,
+	is_text_attribute,
+	object
+} from '../../utils/ast.js';
 import { warn } from '../../warnings.js';
 import fuzzymatch from '../1-parse/utils/fuzzymatch.js';
 import { disallowed_parapgraph_contents, interactive_elements } from '../1-parse/utils/html.js';
@@ -66,12 +72,23 @@ function validate_element(node, context) {
 			}
 
 			if (attribute.name.startsWith('on') && attribute.name.length > 2) {
+				if (!is_expression_attribute(attribute)) {
+					error(attribute, 'invalid-event-attribute-value');
+				}
+
+				const value = attribute.value[0].expression;
 				if (
-					attribute.value === true ||
-					is_text_attribute(attribute) ||
-					attribute.value.length > 1
+					value.type === 'Identifier' &&
+					value.name === attribute.name &&
+					!context.state.scope.get(value.name)
 				) {
-					error(attribute, 'invalid-event-attribute-value');
+					warn(
+						context.state.analysis.warnings,
+						attribute,
+						context.path,
+						'global-event-reference',
+						attribute.name
+					);
 				}
 			}
 

packages/svelte/src/compiler/utils/ast.js

@@ -36,7 +36,7 @@ export function is_text_attribute(attribute) {
  * @param {import('#compiler').Attribute} attribute
  * @returns {attribute is import('#compiler').Attribute & { value: [import('#compiler').ExpressionTag] }}
  */
-function is_expression_attribute(attribute) {
+export function is_expression_attribute(attribute) {
 	return (
 		attribute.value !== true &&
 		attribute.value.length === 1 &&

packages/svelte/src/compiler/warnings.js

@@ -12,7 +12,10 @@ const css = {
 
 /** @satisfies {Warnings} */
 const attributes = {
-	'avoid-is': () => 'The "is" attribute is not supported cross-browser and should be avoided'
+	'avoid-is': () => 'The "is" attribute is not supported cross-browser and should be avoided',
+	/** @param {string} name */
+	'global-event-reference': (name) =>
+		`You are referencing globalThis.${name}. Did you forget to declare a variable with that name?`
 };
 
 /** @satisfies {Warnings} */

packages/svelte/tests/validator/samples/global-event-reference/_config.js

@@ -0,0 +1,3 @@
+import { test } from '../../test';
+
+export default test({});

packages/svelte/tests/validator/samples/global-event-reference/input.svelte

@@ -0,0 +1,9 @@
+<script>
+    let onclick;
+</script>
+
+<button {onclick}></button>
+<button onclick={onclick}></button>
+
+<button {onkeydown}></button>
+<button onkeydown={onkeydown}></button>

packages/svelte/tests/validator/samples/global-event-reference/warnings.json

@@ -0,0 +1,26 @@
+[
+	{
+		"code": "global-event-reference",
+		"message": "You are referencing globalThis.onkeydown. Did you forget to declare a variable with that name?",
+		"start": {
+			"column": 8,
+			"line": 8
+		},
+		"end": {
+			"column": 19,
+			"line": 8
+		}
+	},
+	{
+		"code": "global-event-reference",
+		"message": "You are referencing globalThis.onkeydown. Did you forget to declare a variable with that name?",
+		"start": {
+			"column": 8,
+			"line": 9
+		},
+		"end": {
+			"column": 29,
+			"line": 9
+		}
+	}
+]