Fix native argument handling

runtime/vm/native_arguments.h

 // 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.
 
 #ifndef VM_NATIVE_ARGUMENTS_H_
 #define VM_NATIVE_ARGUMENTS_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/stub_code.h"
@@ skipping 42 matching lines @@
 //   const Instance& arg0 = Instance::CheckedHandle(arguments.At(0));
 //   const Smi& arg1 = Smi::CheckedHandle(arguments.At(1));
 // The return value is set as follows:
 //   arguments.SetReturn(result);
 // NOTE: Since we pass 'this' as a pass-by-value argument in the stubs we don't
 // have DISALLOW_COPY_AND_ASSIGN in the class definition and do not make it a
 // subclass of ValueObject.
 class NativeArguments {
  public:
   Isolate* isolate() const { return isolate_; }
-  int Count() const { return ArgcBits::decode(argc_tag_); }
+  int ArgCount() const { return ArgcBits::decode(argc_tag_); }
 
   // Returns true if the arguments are those of an instance function call.
   bool ToInstanceFunction() const {
     return InstanceFunctionBit::decode(argc_tag_);
   }
 
   // Returns true if the arguments are those of a closure function call.
   bool ToClosureFunction() const {
     return ClosureFunctionBit::decode(argc_tag_);
   }
 
-  RawObject* At(int index) const {
-    ASSERT(index >=0 && index < Count());
+  RawObject* ArgAt(int index) const {
+    ASSERT((index >= 0) && (index < ArgCount()));
     return (*argv_)[-index];
   }
 
+  int NumHiddenArgs() const {
+    // For static closure functions, the closure at index 0 is hidden.
+    // In the instance closure function case, the receiver is accessed from
+    // the context and the closure at index 0 is hidden, so the apparent
+    // argument count remains unchanged.
+    if (ToClosureFunction() && !ToInstanceFunction()) {
+      return 1;
+    }
+    return 0;
+  }
+
+  int NativeArgCount() const {
+    return ArgCount() - NumHiddenArgs();
+  }
+
+  RawObject* NativeArgAt(int index) const {
+    const int num_hidden_args = NumHiddenArgs();
+    const int actual_index = index + num_hidden_args;
+    ASSERT((actual_index >= num_hidden_args) && (index < ArgCount()));
+    if ((index == 0) && ToClosureFunction() && ToInstanceFunction()) {
+      // Retrieve the receiver from the context.
+      const Context& context = Context::Handle(isolate_->top_context());
+      return context.At(0);
+    } else {
+      return ArgAt(actual_index);
+    }
+  }
+
   void SetReturn(const Object& value) const;
 
   static intptr_t isolate_offset() {
     return OFFSET_OF(NativeArguments, isolate_);
   }
   static intptr_t argc_tag_offset() {
     return OFFSET_OF(NativeArguments, argc_tag_);
   }
   static intptr_t argv_offset() { return OFFSET_OF(NativeArguments, argv_); }
   static intptr_t retval_offset() {
@@ skipping 44 matching lines @@
 
   Isolate* isolate_;  // Current isolate pointer.
   int argc_tag_;  // Encodes argument count and invoked native call type.
   RawObject*(*argv_)[];  // Pointer to an array of arguments to runtime call.
   RawObject** retval_;  // Pointer to the return value area.
 };
 
 }  // namespace dart
 
 #endif  // VM_NATIVE_ARGUMENTS_H_