Provide better error message when passing wrong number of arguments.

runtime/vm/dart_api_impl.cc

 // 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.
 
 #include "include/dart_api.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart.h"
@@ skipping 3001 matching lines @@
               lookup_class_name.ToCString()));
       return ApiError::New(message);
     } else {
       const String& message = String::Handle(
           String::NewFormatted("%s: could not find constructor '%s'.",
                                current_func, constr_name.ToCString()));
       return ApiError::New(message);
     }
   }
   int extra_args = (constructor.IsConstructor() ? 2 : 1);
-  if (!constructor.AreValidArgumentCounts(num_args + extra_args, 0)) {
+  String& error_message = String::Handle();
+  if (!constructor.AreValidArgumentCounts(num_args + extra_args,
+                                          0,
+                                          &error_message)) {
     const String& message = String::Handle(
-        String::NewFormatted("%s: wrong argument count for constructor '%s': "
-                             "expected %d but saw %d.",
+        String::NewFormatted("%s: wrong argument count for "
+                             "constructor '%s': %s.",
                              current_func,
                              constr_name.ToCString(),
-                             constructor.num_fixed_parameters() - extra_args,
-                             num_args));
+                             error_message.ToCString()));
     return ApiError::New(message);
   }
   return constructor.raw();
 }
 
 
 DART_EXPORT Dart_Handle Dart_New(Dart_Handle clazz,
                                  Dart_Handle constructor_name,
                                  int number_of_arguments,
                                  Dart_Handle* arguments) {
@@ skipping 226 matching lines @@
     // Finalize all classes if needed.
     if (finalize_classes) {
       const char* msg = CheckIsolateState(isolate);
       if (msg != NULL) {
         return Api::NewError(msg);
       }
     }
 
     Function& function = Function::Handle(isolate);
     function = lib.LookupFunctionAllowPrivate(function_name);
-    // LookupFunctionAllowPrivate does not check argument arity, so we
-    // do it here.
-    if (!function.IsNull() &&
-        !function.AreValidArgumentCounts(number_of_arguments, 0)) {
-      function = Function::null();
-    }
     if (function.IsNull()) {
       return Api::NewError("%s: did not find top-level function '%s'.",
                            CURRENT_FUNC,
                            function_name.ToCString());
     }
+    // LookupFunctionAllowPrivate does not check argument arity, so we
+    // do it here.
+    String& error_message = String::Handle();
+    if (!function.AreValidArgumentCounts(number_of_arguments,
+                                         0,
+                                         &error_message)) {
+      return Api::NewError("%s: wrong argument count for function '%s': %s.",
+                           CURRENT_FUNC,
+                           function_name.ToCString(),
+                           error_message.ToCString());
+    }
     return Api::NewHandle(
         isolate, DartEntry::InvokeStatic(function, args, kNoArgNames));
 
   } else {
     return Api::NewError(
         "%s expects argument 'target' to be an object, class, or library.",
         CURRENT_FUNC);
   }
 }
 
@@ skipping 816 matching lines @@
     *buffer_size = 0;
   }
 }
 
 
 DART_EXPORT void Dart_InitFlowGraphPrinting(FileWriterFunction function) {
   Dart::set_flow_graph_writer(function);
 }
 
 }  // namespace dart