change error message for invalid bindings

src/parse/read/directives.ts

@@ -104,7 +104,7 @@ export function readBindingDirective ( parser: Parser, start: number, name: stri
 		value = parseExpressionAt( source, a );
 
 		if ( value.type !== 'Identifier' && value.type !== 'MemberExpression' ) {
-			parser.error( `Expected valid property name` );
+			parser.error( `Cannot bind to rvalue`, value.start );
 		}
 
 		parser.allowWhitespace();

test/parser/samples/error-binding-rvalue/error.json

@@ -0,0 +1,8 @@
+{
+	"message": "Cannot bind to rvalue",
+	"pos": 19,
+	"loc": {
+		"line": 1,
+		"column": 19
+	}
+}

test/parser/samples/error-binding-rvalue/input.html

@@ -0,0 +1 @@
+<input bind:value='a + b'>