[es6] implement optional parameters via desugaring (with scoping)

src/variables.cc

 // Copyright 2011 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/ast.h"
 #include "src/scopes.h"
 #include "src/variables.h"
 
@@ skipping 32 matching lines @@
       index_(-1),
       initializer_position_(RelocInfo::kNoPosition),
       has_strong_mode_reference_(false),
       strong_mode_reference_start_position_(RelocInfo::kNoPosition),
       strong_mode_reference_end_position_(RelocInfo::kNoPosition),
       local_if_not_shadowed_(NULL),
       force_context_allocation_(false),
       is_used_(false),
       initialization_flag_(initialization_flag),
       maybe_assigned_(maybe_assigned_flag) {
+  if (scope && scope->is_function_body_scope()) {
+    // The function body is the proper declaration scope, however, the
+    // declaration is added to the outer scope in order to ensure allocation
+    // works correctly. Mark the scope as the outer scope here so that
+    // checking the declaration context works.
+    scope_ = scope->outer_scope();
+    DCHECK(scope_->is_function_scope());
+  }
+
   // Var declared variables never need initialization.
   DCHECK(!(mode == VAR && initialization_flag == kNeedsInitialization));
 }
 
 
 bool Variable::IsGlobalObjectProperty() const {
   // Temporaries are never global, they must always be allocated in the
   // activation frame.
   return (IsDynamicVariableMode(mode_) ||
           (IsDeclaredVariableMode(mode_) && !IsLexicalVariableMode(mode_)))
       && scope_ != NULL && scope_->is_script_scope();
 }
 
 
 int Variable::CompareIndex(Variable* const* v, Variable* const* w) {
   int x = (*v)->index();
   int y = (*w)->index();
   // Consider sorting them according to type as well?
   return x - y;
 }
 
 } }  // namespace v8::internal