Provide better error message when passing wrong number of arguments.

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 9601)
+++ runtime/vm/object.cc	(working copy)
@@ -3690,26 +3690,71 @@
 }
 
 
+intptr_t Function::NumberOfImplicitParameters() const {
+  if (kind() == RawFunction::kConstructor) {
+    if (is_static()) {
+      ASSERT(IsFactory());
+      return 1;  // Type arguments.
+    } else {
+      ASSERT(IsConstructor());
+      return 2;  // Instance, phase.
+    }
+  }
+  if (!is_static()) {
+    return 1;  // Receiver.
+  }
+  return 0;  // No implicit parameters.
+}
+
+
 bool Function::AreValidArgumentCounts(int num_arguments,
-                                      int num_named_arguments) const {
+                                      int num_named_arguments,
+                                      String* error_message) const {
   if (num_arguments > NumberOfParameters()) {
+    if (error_message != NULL) {
+      const intptr_t kMessageBufferSize = 64;
+      char message_buffer[kMessageBufferSize];
+      // Hide implicit parameters to the user.
+      const intptr_t num_hidden_params = NumberOfImplicitParameters();
+      OS::SNPrint(message_buffer,
+                  kMessageBufferSize,
+                  "%d passed, %s%d expected",
+                  num_arguments - num_hidden_params,
+                  num_optional_parameters() > 0 ? "at most " : "",
+                  NumberOfParameters() - num_hidden_params);
+      *error_message = String::New(message_buffer);
+    }
     return false;  // Too many arguments.
   }
   const int num_positional_args = num_arguments - num_named_arguments;
   if (num_positional_args < num_fixed_parameters()) {
+    if (error_message != NULL) {
+      const intptr_t kMessageBufferSize = 64;
+      char message_buffer[kMessageBufferSize];
+      // Hide implicit parameters to the user.
+      const intptr_t num_hidden_params = NumberOfImplicitParameters();
+      OS::SNPrint(message_buffer,
+                  kMessageBufferSize,
+                  "%d %spassed, %d expected",
+                  num_positional_args - num_hidden_params,
+                  num_optional_parameters() > 0 ? "positional " : "",
+                  num_fixed_parameters() - num_hidden_params);
+      *error_message = String::New(message_buffer);
+    }
     return false;  // Too few arguments.
   }
   return true;
 }
 
 
-// TODO(regis): Return some sort of diagnosis information so that we
-// can improve the error messages generated by the parser.
 bool Function::AreValidArguments(int num_arguments,
-                                 const Array& argument_names) const {
+                                 const Array& argument_names,
+                                 String* error_message) const {
   const int num_named_arguments =
       argument_names.IsNull() ? 0 : argument_names.Length();
-  if (!AreValidArgumentCounts(num_arguments, num_named_arguments)) {
+  if (!AreValidArgumentCounts(num_arguments,
+                              num_named_arguments,
+                              error_message)) {
     return false;
   }
   // Verify that all argument names are valid parameter names.
@@ -3729,6 +3774,15 @@
       }
     }
     if (!found) {
+      if (error_message != NULL) {
+        const intptr_t kMessageBufferSize = 64;
+        char message_buffer[kMessageBufferSize];
+        OS::SNPrint(message_buffer,
+                    kMessageBufferSize,
+                    "no optional formal parameter named '%s'",
+                    argument_name.ToCString());
+        *error_message = String::New(message_buffer);
+      }
       return false;
     }
   }