Issue 4289. Separate optional positional and named parameters

tests/language/bad_named_parameters_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Dart test program for testing bad named parameters.
 
 
 class BadNamedParametersTest {
 
-  int f42(int a, [int b = 20, int c = 30]) {
+  int f42(int a, {int b: 20, int c: 30}) {
     return 100*(100*a + b) + c;
   }
 
-  int f52(int a, [int b = 20, int c, int d = 40]) {
+  int f52(int a, {int b: 20, int c, int d: 40}) {
     return 100*(100*(100*a + b) + (c == null ? 0 : c)) + d;
   }
 
   static testMain() {
     BadNamedParametersTest np = new BadNamedParametersTest();
 
     // Verify that NoSuchMethod is called after an error is detected.
     bool caught;
     try {
       caught = false;
@@ skipping 34 matching lines @@
     } on NoSuchMethodError catch (e) {
       caught = true;
     }
     Expect.equals(true, caught);
   }
 }
 
 main() {
   BadNamedParametersTest.testMain();
 }