error if ref:foo has a value

src/parse/read/directives.ts

@@ -1,5 +1,6 @@
 import { parseExpressionAt } from 'acorn';
 import repeat from '../../utils/repeat';
+import list from '../../utils/list';
 import { Parser } from '../index';
 
 const DIRECTIVES = {
@@ -137,8 +138,12 @@ export function readDirective(
 		}
 
 		expression = readExpression(parser, expressionStart, quoteMark);
+		if (directive.allowedExpressionTypes) {
 			if (directive.allowedExpressionTypes.indexOf(expression.type) === -1) {
-			parser.error(`Expected ${directive.allowedExpressionTypes.join(' or ')}`, expressionStart);
+				parser.error(`Expected ${list(directive.allowedExpressionTypes)}`, expressionStart);
+			}
+		} else {
+			parser.error(`${directiveName} directives cannot have a value`, expressionStart);
 		}
 	}
 

test/parser/samples/error-ref-value/error.json

@@ -0,0 +1,8 @@
+{
+	"message": "ref directives cannot have a value",
+	"loc": {
+		"line": 1,
+		"column": 14
+	},
+	"pos": 14
+}

test/parser/samples/error-ref-value/input.html

@@ -0,0 +1 @@
+<div ref:foo='bar'></div>