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

src/scopes.h

Index: src/scopes.h
diff --git a/src/scopes.h b/src/scopes.h
index 5e3dc1f0654bf65c3ee738665fcb7bf2107be63b..2220d9167199f03fe07d3097fc6e0a93d0161131 100644
--- a/src/scopes.h
+++ b/src/scopes.h
@@ -87,7 +87,7 @@ class Scope: public ZoneObject {
   void SetScopeName(const AstRawString* scope_name) {
     scope_name_ = scope_name;
   }
-
+  const AstRawString* scope_name() const { return scope_name_; }
   void Initialize();
 
   // Checks if the block scope is redundant, i.e. it does not contain any
@@ -276,10 +276,15 @@ class Scope: public ZoneObject {
   bool is_function_scope() const {
     return scope_type_ == FUNCTION_SCOPE || scope_type_ == ARROW_SCOPE;
   }
+  bool is_function_body_scope() const {
+    return scope_type_ == FUNCTION_BODY_SCOPE;
+  }
   bool is_module_scope() const { return scope_type_ == MODULE_SCOPE; }
   bool is_script_scope() const { return scope_type_ == SCRIPT_SCOPE; }
   bool is_catch_scope() const { return scope_type_ == CATCH_SCOPE; }
-  bool is_block_scope() const { return scope_type_ == BLOCK_SCOPE; }
+  bool is_block_scope() const {
+    return scope_type_ == BLOCK_SCOPE || scope_type_ == FUNCTION_BODY_SCOPE;
+  }
   bool is_with_scope() const { return scope_type_ == WITH_SCOPE; }
   bool is_arrow_scope() const { return scope_type_ == ARROW_SCOPE; }
   void tag_as_class_scope() {
@@ -290,8 +295,8 @@ class Scope: public ZoneObject {
     return is_block_scope() && block_scope_is_class_scope_;
   }
   bool is_declaration_scope() const {
-    return is_eval_scope() || is_function_scope() ||
-        is_module_scope() || is_script_scope();
+    return is_eval_scope() || is_function_scope() || is_module_scope() ||
+           is_script_scope() || is_function_body_scope();
   }
   bool is_strict_eval_scope() const {
     return is_eval_scope() && is_strict(language_mode_);
@@ -410,6 +415,9 @@ class Scope: public ZoneObject {
   // The scope immediately surrounding this scope, or NULL.
   Scope* outer_scope() const { return outer_scope_; }
 
+  // The inner scope which contains the main "body" of a function (may be null)
+  Scope* function_body() const { return function_body_; }
+
   // The ModuleDescriptor for this scope; only for module scopes.
   ModuleDescriptor* module() const { return module_descriptor_; }
 
@@ -521,6 +529,7 @@ class Scope: public ZoneObject {
   // Scope tree.
   Scope* outer_scope_;  // the immediately enclosing outer scope, or NULL
   ZoneList<Scope*> inner_scopes_;  // the immediately enclosed inner scopes
+  Scope* function_body_;           // The scope for a function body
 
   // The scope type.
   ScopeType scope_type_;