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

src/scopes.cc

Index: src/scopes.cc
diff --git a/src/scopes.cc b/src/scopes.cc
index 93268ad31905015d78f014430124f70e6e7d1807..f4cf85144a4df19d6142fbccdd0637dbd2cca699 100644
--- a/src/scopes.cc
+++ b/src/scopes.cc
@@ -136,11 +136,21 @@ Scope::Scope(Zone* zone, Scope* inner_scope,
 }
 
 
+void Scope::SetParameterExpressionsScopeFor(Scope* function_scope) {
+  DCHECK(function_scope->outer_scope() == outer_scope());
+  DCHECK(function_scope->is_function_scope());
+  DCHECK_NULL(parameter_scope_);
+  SetScopeName(ast_value_factory_->GetOneByteString("parameter expressions"));
+  parameter_scope_ = function_scope;
+}
+
+
 void Scope::SetDefaults(ScopeType scope_type, Scope* outer_scope,
                         Handle<ScopeInfo> scope_info,
                         FunctionKind function_kind) {
   outer_scope_ = outer_scope;
   scope_type_ = scope_type;
+  parameter_scope_ = nullptr;
   function_kind_ = function_kind;
   block_scope_is_class_scope_ = false;
   scope_name_ = ast_value_factory_->empty_string();
@@ -377,6 +387,13 @@ Scope* Scope::FinalizeBlockScope() {
 
 
 Variable* Scope::LookupLocal(const AstRawString* name) {
+  if (parameter_scope_) {
+    Variable* result = parameter_scope_->variables_.Lookup(name);
+    if (result != nullptr && parameter_scope_->params_.Contains(result)) {
+      return result;
+    }
+  }
+
   Variable* result = variables_.Lookup(name);
   if (result != NULL || scope_info_.is_null()) {
     return result;
@@ -452,12 +469,13 @@ Variable* Scope::Lookup(const AstRawString* name) {
 
 
 Variable* Scope::DeclareParameter(const AstRawString* name, VariableMode mode,
-                                  bool is_rest) {
+                                  ParameterKind kind) {
   DCHECK(!already_resolved());
   DCHECK(is_function_scope());
   Variable* var = variables_.Declare(this, name, mode, Variable::NORMAL,
                                      kCreatedInitialized);
-  if (is_rest) {
+  var->set_parameter_kind(kind);
+  if (kind == RestParameter) {
     DCHECK_NULL(rest_parameter_);
     rest_parameter_ = var;
     rest_index_ = num_parameters();