Adds invalid test for event-modifiers.

src/validate/html/validateEventHandler.ts

@@ -6,6 +6,8 @@ import { Node } from '../../interfaces';
 
 const validBuiltins = new Set(['set', 'fire', 'destroy']);
 
+const validModifiers = new Set(['stop', 'prevent', 'capture', 'once', 'passive']);
+
 export default function validateEventHandlerCallee(
 	validator: Validator,
 	attribute: Node,
@@ -22,6 +24,17 @@ export default function validateEventHandlerCallee(
 		});
 	}
 
+	const modifiers = attribute.name.split('|').slice(1);
+	if (
+		modifiers.length > 0 &&
+		modifiers.filter(m => !validModifiers.has(m)).length > 0
+	) {
+		validator.error(attribute, {
+			code: 'invalid-event-modifiers',
+			message: `Valid event modifiers are ${[...validModifiers].join(', ')}.`
+		});
+	}
+
 	const { name } = flattenReference(callee);
 
 	if (validCalleeObjects.has(name) || name === 'options') return;

test/validator/samples/event-modifiers-invalid/errors.json

@@ -0,0 +1,15 @@
+[{
+  "message": "Valid event modifiers are stop, prevent, capture, once, passive.",
+  "code": "invalid-event-modifiers",
+  "start": {
+    "line": 1,
+    "column": 8,
+    "character": 8
+  },
+  "end": {
+    "line": 1,
+    "column": 36,
+    "character": 36
+  },
+  "pos": 8
+}]

test/validator/samples/event-modifiers-invalid/input.html

@@ -0,0 +1 @@
+<button on:click|stop|bad="doThat()"></button>