Implement proper scoping for "this" in arrow functions

src/ast.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.
 
 #ifndef V8_AST_H_
 #define V8_AST_H_
 
 #include "src/v8.h"
 
 #include "src/assembler.h"
@@ skipping 1617 matching lines @@
   Handle<FixedArray> constant_elements_;
   ZoneList<Expression*>* values_;
 };
 
 
 class VariableProxy FINAL : public Expression {
  public:
   DECLARE_NODE_TYPE(VariableProxy)
 
   bool IsValidReferenceExpression() const OVERRIDE {
-    return !is_resolved() || var()->IsValidReference();
+    return !is_this();
   }
 
   bool IsArguments() const { return is_resolved() && var()->is_arguments(); }
 
   Handle<String> name() const { return raw_name()->string(); }
   const AstRawString* raw_name() const {
     return is_resolved() ? var_->raw_name() : raw_name_;
   }
 
   Variable* var() const {
@@ skipping 37 matching lines @@
   }
   Code::Kind FeedbackICSlotKind(int index) OVERRIDE { return Code::LOAD_IC; }
   FeedbackVectorICSlot VariableFeedbackSlot() {
     DCHECK(!UsesVariableFeedbackSlot() || !variable_feedback_slot_.IsInvalid());
     return variable_feedback_slot_;
   }
 
  protected:
   VariableProxy(Zone* zone, Variable* var, int position);
 
-  VariableProxy(Zone* zone, const AstRawString* name, bool is_this,
-                Interface* interface, int position);
+  VariableProxy(Zone* zone,
+                const AstRawString* name,
+                Variable::Kind variable_kind,
+                Interface* interface,
+                int position);
 
   class IsThisField : public BitField8<bool, 0, 1> {};
   class IsAssignedField : public BitField8<bool, 1, 1> {};
   class IsResolvedField : public BitField8<bool, 2, 1> {};
 
   // Start with 16-bit (or smaller) field, which should get packed together
   // with Expression's trailing 16-bit field.
   uint8_t bit_field_;
   FeedbackVectorICSlot variable_feedback_slot_;
   union {
@@ skipping 1700 matching lines @@
                                 int pos) {
     return new (zone_) ArrayLiteral(zone_, values, literal_index, pos);
   }
 
   VariableProxy* NewVariableProxy(Variable* var,
                                   int pos = RelocInfo::kNoPosition) {
     return new (zone_) VariableProxy(zone_, var, pos);
   }
 
   VariableProxy* NewVariableProxy(const AstRawString* name,
-                                  bool is_this,
                                   Interface* interface = Interface::NewValue(),
                                   int position = RelocInfo::kNoPosition) {
-    return new (zone_) VariableProxy(zone_, name, is_this, interface, position);
+    return new (zone_) VariableProxy(zone_, name,
+                                     (name == ast_value_factory_->this_string())

[wingo, 2015/02/06 17:31:19]

Can we instead change from "bool is_this," to "Variable::Kind variable_kind" ?

That way we avoid the load and comparison of this_string on what is a relatively
hot path of the parser -- perhaps a silly concern -- and we preserve readability
of callers.

[aperez, 2015/02/09 16:08:14]

Acknowledged.

+                                        ? Variable::THIS
+                                        : Variable::NORMAL,
+                                     interface, position);
   }
 
   Property* NewProperty(Expression* obj, Expression* key, int pos) {
     return new (zone_) Property(zone_, obj, key, pos);
   }
 
   Call* NewCall(Expression* expression,
                 ZoneList<Expression*>* arguments,
                 int pos) {
     return new (zone_) Call(zone_, expression, arguments, pos);
@@ skipping 116 matching lines @@
 
  private:
   Zone* zone_;
   AstValueFactory* ast_value_factory_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_AST_H_