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

src/preparser.cc

 // Copyright 2011 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.
 
 #include <cmath>
 
 #include "src/allocation.h"
 #include "src/base/logging.h"
 #include "src/conversions-inl.h"
 #include "src/conversions.h"
@@ skipping 965 matching lines @@
     Identifier function_name, Scanner::Location function_name_location,
     bool name_is_strict_reserved, FunctionKind kind, int function_token_pos,
     FunctionLiteral::FunctionType function_type,
     FunctionLiteral::ArityRestriction arity_restriction, bool* ok) {
   // Function ::
   //   '(' FormalParameterList? ')' '{' FunctionBody '}'
 
   // Parse function body.
   bool outer_is_script_scope = scope_->is_script_scope();
   Scope* function_scope = NewScope(scope_, FUNCTION_SCOPE);
+  Scope* parameter_scope = NewScope(function_scope, PARAMETER_SCOPE);
   PreParserFactory factory(NULL);
   FunctionState function_state(&function_state_, &scope_, function_scope, kind,
                                &factory);
   FormalParameterErrorLocations error_locs;
 
   bool is_rest = false;
   Expect(Token::LPAREN, CHECK_OK);
   int start_position = scanner()->location().beg_pos;
   function_scope->set_start_position(start_position);
   int num_parameters;
   {
     DuplicateFinder duplicate_finder(scanner()->unicode_cache());
-    num_parameters = ParseFormalParameterList(&duplicate_finder, &error_locs,
-                                              &is_rest, CHECK_OK);
+    PreParserExpressionList initializers = NewExpressionList(0, zone());
+    bool has_initializers = false;
+
+    num_parameters = ParseFormalParameterList(
+        &duplicate_finder, parameter_scope, &error_locs, initializers,
+        &has_initializers, &is_rest, CHECK_OK);
   }
   Expect(Token::RPAREN, CHECK_OK);
   int formals_end_position = scanner()->location().end_pos;
 
   CheckArityRestrictions(num_parameters, arity_restriction, start_position,
                          formals_end_position, CHECK_OK);
 
   // See Parser::ParseFunctionLiteral for more information about lazy parsing
   // and lazy compilation.
   bool is_lazily_parsed =
@@ skipping 124 matching lines @@
 
   DCHECK(!spread_pos.IsValid());
 
   return Expression::Default();
 }
 
 #undef CHECK_OK
 
 
 } }  // v8::internal