Implement proper scoping for "this" in arrow functions

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index 02f7df64b0d62bbaa9c1eb717ce1db6f8d4939b5..09649a182adea2ebf4b41d5bd61aec47466de4eb 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -1635,7 +1635,7 @@ class VariableProxy FINAL : public Expression {
   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(); }
@@ -1693,8 +1693,11 @@ class VariableProxy FINAL : public Expression {
  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> {};
@@ -3415,10 +3418,13 @@ class AstNodeFactory FINAL BASE_EMBEDDED {
   }
 
   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) {