When generating the error message, don't overrun args.nodes .

frog/member.dart

 // Copyright (c) 2011, 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.
 
 /** A formal parameter to a [Method]. */
 class Parameter {
   FormalNode definition;
   Member method;
 
   String name;
@@ skipping 941 matching lines @@
         if (arg == null) {
           arg = parameters[i].value;
         } else {
           arg = arg.convertTo(context, parameters[i].type, node, isDynamic);
           namedArgsUsed++;
         }
 
         if (arg == null || !parameters[i].isOptional) {
           var msg = _argCountMsg(Math.min(i, args.length), i + 1, atLeast:true);
           return _argError(context, node, target, args, msg,
-              args.nodes[i].span);
+              (i >= args.nodes.length) ? node.span : args.nodes[i].span);
         } else {
           argsCode.add(isConst && arg.isConst
               ? arg.canonicalCode : arg.code);
         }
       }
       Arguments.removeTrailingNulls(argsCode);
     }
 
     if (namedArgsUsed < args.nameCount) {
       // Find the unused argument name
@@ skipping 797 matching lines @@
   }
 
   void forEach(void f(Member member)) {
     factories.forEach((_, Map constructors) {
       constructors.forEach((_, Member member) {
         f(member);
       });
     });
   }
 }