[api] Expose FunctionCallbackInfo::NewTarget

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 3174 matching lines @@
  */
 template<typename T>
 class FunctionCallbackInfo {
  public:
   V8_INLINE int Length() const;
   V8_INLINE Local<Value> operator[](int i) const;
   V8_INLINE V8_DEPRECATED("Use Data() to explicitly pass Callee instead",
                           Local<Function> Callee() const);
   V8_INLINE Local<Object> This() const;
   V8_INLINE Local<Object> Holder() const;
+  V8_INLINE Local<Value> NewTarget() const;
   V8_INLINE bool IsConstructCall() const;
   V8_INLINE Local<Value> Data() const;
   V8_INLINE Isolate* GetIsolate() const;
   V8_INLINE ReturnValue<T> GetReturnValue() const;
   // This shouldn't be public, but the arm compiler needs it.
-  static const int kArgsLength = 7;
+  static const int kArgsLength = 8;
 
  protected:
   friend class internal::FunctionCallbackArguments;
   friend class internal::CustomArguments<FunctionCallbackInfo>;
   static const int kHolderIndex = 0;
   static const int kIsolateIndex = 1;

[Benedikt Meurer, 2016/04/23 11:45:41]

It'd be nice to remove isolate and callee here (not in the same CL, but
soonish). The isolate can be retrieved from the holder (which is always a
HeapObject), and the callee is deprecated for some time. 

[adamk, 2016/04/25 22:59:55]

Seems reasonable for a followup, indeed. My recollection is that Callee is on
life support, though, and can't yet be removed.

   static const int kReturnValueDefaultValueIndex = 2;
   static const int kReturnValueIndex = 3;
   static const int kDataIndex = 4;
   static const int kCalleeIndex = 5;
   static const int kContextSaveIndex = 6;
+  static const int kNewTargetIndex = 7;
 
   V8_INLINE FunctionCallbackInfo(internal::Object** implicit_args,
                    internal::Object** values,
                    int length,
                    bool is_construct_call);
   internal::Object** implicit_args_;
   internal::Object** values_;
   int length_;
   int is_construct_call_;

[Benedikt Meurer, 2016/04/23 11:45:41]

This can now be removed (and potentially everything necessary to thread it
through), as you can tell whether you were invoked via [[Call]] or [[Construct]]
by checking if NewTarget is undefined. And IsConstructCall() above can do
exactly that.

[adamk, 2016/04/25 22:59:55]

There's one problem with removing this, which is the CallAsConstructor behavior
for non-Function callables (created via
ObjectTemplate::SetCallAsFunctionHandler). It's not clear what NewTarget()
should be in that case. I suppose we could set it as the object itself, but that
seems odd, as it's not "constructable" in the usual sense. Or I could set the
handler function, but that's not right either, at it was _not_ the new_target.
Thoughts?

[adamk, 2016/04/25 23:35:48]

Patch set 4 includes the changes to IsConstructCall.

[Benedikt Meurer, 2016/04/26 04:15:34]

You don't "set" new.target to something. You just pass whatever through whatever
was in rdx/edx/r3/whatever. The HandleApiCallAsConstructor has to thread through
this value.

 };
 
 
 /**
  * The information passed to a property callback about the context
  * of the property access.
  */
 template<typename T>
 class PropertyCallbackInfo {
  public:
@@ skipping 4665 matching lines @@
   return Local<Object>(reinterpret_cast<Object*>(values_ + 1));
 }
 
 
 template<typename T>
 Local<Object> FunctionCallbackInfo<T>::Holder() const {
   return Local<Object>(reinterpret_cast<Object*>(
       &implicit_args_[kHolderIndex]));
 }
 
+template <typename T>
+Local<Value> FunctionCallbackInfo<T>::NewTarget() const {
+  return Local<Value>(
+      reinterpret_cast<Value*>(&implicit_args_[kNewTargetIndex]));
+}
 
-template<typename T>
+template <typename T>
 Local<Value> FunctionCallbackInfo<T>::Data() const {
   return Local<Value>(reinterpret_cast<Value*>(&implicit_args_[kDataIndex]));
 }
 
 
 template<typename T>
 Isolate* FunctionCallbackInfo<T>::GetIsolate() const {
   return *reinterpret_cast<Isolate**>(&implicit_args_[kIsolateIndex]);
 }
 
@@ skipping 853 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // INCLUDE_V8_H_