[es6] implement default/optional parameters (WIP / comments)

src/scopes.h

Index: src/scopes.h
diff --git a/src/scopes.h b/src/scopes.h
index 7b372d9643fe4c1c07892139c6ecf1937ed1257e..12362959db4ada59ee3390dd248d0d8b7031f9db 100644
--- a/src/scopes.h
+++ b/src/scopes.h
@@ -87,6 +87,10 @@ class Scope: public ZoneObject {
     scope_name_ = scope_name;
   }
 
+  // Mark the current scope as a scope for evaluating function parameter
+  // expressions (such as initializers for optional parameters)
+  void SetParameterExpressionsScopeFor(Scope* function_scope);
+
   void Initialize();
 
   // Checks if the block scope is redundant, i.e. it does not contain any
@@ -125,7 +129,7 @@ class Scope: public ZoneObject {
   // parameters the rightmost one 'wins'.  However, the implementation
   // expects all parameters to be declared and from left to right.
   Variable* DeclareParameter(const AstRawString* name, VariableMode mode,
-                             bool is_rest = false);
+                             ParameterKind kind = NormalParameter);
 
   // Declare a local variable in this scope. If the variable has been
   // declared before, the previously declared variable is returned.
@@ -509,6 +513,11 @@ class Scope: public ZoneObject {
 
   // Scope tree.
   Scope* outer_scope_;  // the immediately enclosing outer scope, or NULL
+
+  // function scope to search for parameters. This auxiliary scope enables TDZ
+  // semantics for parameters while evaluating parameter expressions.
+  Scope* parameter_scope_;
+
   ZoneList<Scope*> inner_scopes_;  // the immediately enclosed inner scopes
 
   // The scope type.