[es6]: Lexical arguments for arrow functions

src/scopes.cc

 // 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.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/bootstrapper.h"
 #include "src/messages.h"
 #include "src/parser.h"
@@ skipping 310 matching lines @@
           variables_.Declare(this, ast_value_factory_->new_target_string(),
                              CONST, Variable::NEW_TARGET, kCreatedInitialized);
       new_target_->AllocateTo(Variable::PARAMETER, -2);
       new_target_->set_is_used();
     }
   } else {
     DCHECK(outer_scope() != NULL);
     receiver_ = outer_scope()->receiver();
   }
 
-  if (is_function_scope()) {
-    // Declare 'arguments' variable which exists in all functions.
+  if (is_function_scope() && !is_arrow_scope()) {
+    // Declare 'arguments' variable which exists in all non arrow functions.
     // Note that it might never be accessed, in which case it won't be
     // allocated during variable allocation.
     variables_.Declare(this,
                        ast_value_factory_->arguments_string(),
                        VAR,
                        Variable::ARGUMENTS,
                        kCreatedInitialized);
   }
 }
 
@@ skipping 945 matching lines @@
 
 
 void Scope::AllocateHeapSlot(Variable* var) {
   var->AllocateTo(Variable::CONTEXT, num_heap_slots_++);
 }
 
 
 void Scope::AllocateParameterLocals(Isolate* isolate) {
   DCHECK(is_function_scope());
   Variable* arguments = LookupLocal(ast_value_factory_->arguments_string());
-  DCHECK(arguments != NULL);  // functions have 'arguments' declared implicitly
+  // Functions have 'arguments' declared implicitly in all non arrow functions.
+  DCHECK(arguments != nullptr || is_arrow_scope());
 
   bool uses_sloppy_arguments = false;
 
-  if (MustAllocate(arguments) && !HasArgumentsParameter(isolate)) {
+  if (arguments != nullptr && MustAllocate(arguments) &&
+      !HasArgumentsParameter(isolate)) {
     // 'arguments' is used. Unless there is also a parameter called
     // 'arguments', we must be conservative and allocate all parameters to
     // the context assuming they will be captured by the arguments object.
     // If we have a parameter named 'arguments', a (new) value is always
     // assigned to it via the function invocation. Then 'arguments' denotes
     // that specific parameter value and cannot be used to access the
     // parameters, which is why we don't need to allocate an arguments
     // object in that case.
 
     // We are using 'arguments'. Tell the code generator that is needs to
@@ skipping 149 matching lines @@
       (function_ != NULL && function_->proxy()->var()->IsStackLocal() ? 1 : 0);
 }
 
 
 int Scope::ContextLocalCount() const {
   if (num_heap_slots() == 0) return 0;
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS -
       (function_ != NULL && function_->proxy()->var()->IsContextSlot() ? 1 : 0);
 }
 } }  // namespace v8::internal