Improve frog error reporting when providing too few or too many arguments.

frog/member.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.
 
 /** A formal parameter to a [Method]. */
 class Parameter {
   FormalNode definition;
   Member method;
 
   String name;
@@ skipping 876 matching lines @@
         var arg = args.getValue(parameters[i].name);
         if (arg != null && arg.needsConversion(parameters[i].type)) {
           return true;
         }
       }
     }
 
     return false;
   }
 
-  static String _argCountMsg(int actual, int expected, [bool atLeast=false]) {
-    return 'wrong number of positional arguments, expected ' +
-        '${atLeast ? "at least " : ""}$expected but found $actual';
+  /** Returns true if any of the parameters are optional. */
+  bool hasOptionalParameters() {
+    return parameters.some((Parameter p) => p.isOptional);
+  }
+
+  String _tooManyArgumentsMsg(int actual, int expected) {
+    return hasOptionalParameters()
+        ? 'too many arguments, expected at most $expected but found $actual'
+        : _wrongArgumentCountMsg(actual, expected);
+  }
+
+  String _tooFewArgumentsMsg(int actual, int expected) {
+    return hasOptionalParameters()
+        ? 'too few arguments, expected at least $expected but found $actual'
+        : _wrongArgumentCountMsg(actual, expected);
+  }
+
+  String _wrongArgumentCountMsg(int actual, int expected) {
+    return 'wrong number of arguments, expected $expected but found $actual';
   }
 
   Value _argError(CallingContext context, Node node, Value target,
       Arguments args, String msg, int argIndex) {
     if (context.showWarnings) {
       SourceSpan span;
       if ((args.nodes == null) || (argIndex >= args.nodes.length)) {
         span = node.span;
       } else {
         span = args.nodes[argIndex].span;
@@ skipping 19 matching lines @@
    * [node] provides a [SourceSpan] for any error messages.
    */
   Value invoke(CallingContext context, Node node, Value target,
       Arguments args) {
 
     var argValues = <Value>[];
     int bareCount = args.bareCount;
     for (int i = 0; i < bareCount; i++) {
       var arg = args.values[i];
       if (i >= parameters.length) {
-        var msg = _argCountMsg(args.length, parameters.length);
+        var msg = _tooManyArgumentsMsg(args.length, parameters.length);
         return _argError(context, node, target, args, msg, i);
       }
       argValues.add(arg.convertTo(context, parameters[i].type));
     }
 
     int namedArgsUsed = 0;
     if (bareCount < parameters.length) {
       genParameterValues(context);
 
       for (int i = bareCount; i < parameters.length; i++) {
         var param = parameters[i];
         var arg = args.getValue(param.name);
         if (arg == null) {
           arg = param.value;
           if (arg == null) {
             // TODO(jmesserly): should we be use the actual constant value here?
             arg = new PureStaticValue(param.type, param.definition.span, true);
           }
         } else {
           arg = arg.convertTo(context, parameters[i].type);
           namedArgsUsed++;
         }
 
         if (arg == null || !parameters[i].isOptional) {
-          var msg = _argCountMsg(Math.min(i, args.length), i + 1, atLeast:true);
+          var msg = _tooFewArgumentsMsg(Math.min(i, args.length), i + 1);
           return _argError(context, node, target, args, msg, i);
         } else {
           argValues.add(arg);
         }
       }
     }
 
     if (namedArgsUsed < args.nameCount) {
       // Find the unused argument name
       var seen = new Set<String>();
@@ skipping 380 matching lines @@
   }
 
   void forEach(void f(Member member)) {
     factories.forEach((_, Map constructors) {
       constructors.forEach((_, Member member) {
         f(member);
       });
     });
   }
 }