[es6] Re-implement rest parameters via desugaring.

src/parser.h

 // Copyright 2012 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.
 
 #ifndef V8_PARSER_H_
 #define V8_PARSER_H_
 
 #include "src/allocation.h"
 #include "src/ast.h"
 #include "src/compiler.h"  // TODO(titzer): remove this include dependency
@@ skipping 957 matching lines @@
                                 ZoneList<const AstRawString*>* names,
                                 bool* ok);
 
   struct DeclarationDescriptor {
     enum Kind { NORMAL, PARAMETER };
     Parser* parser;
     Scope* declaration_scope;
     Scope* scope;
     VariableMode mode;
     bool is_const;
+    bool is_rest;
     bool needs_init;
     int declaration_pos;
     int initialization_pos;
     Token::Value init_op;
     Kind declaration_kind;
   };
 
   struct DeclarationParsingResult {
     struct Declaration {
       Declaration(Expression* pattern, int initializer_position,
                   Expression* initializer)
           : pattern(pattern),
             initializer_position(initializer_position),
             initializer(initializer) {}
 
       Expression* pattern;
       int initializer_position;
       Expression* initializer;
+      bool is_rest = false;
+      int rest_literal_index = 0;
     };
 
     DeclarationParsingResult()
         : declarations(4),
           first_initializer_loc(Scanner::Location::invalid()),
           bindings_loc(Scanner::Location::invalid()) {}
 
     Block* BuildInitializationBlock(ZoneList<const AstRawString*>* names,
                                     bool* ok);
     const AstRawString* SingleName() const;
@@ skipping 301 matching lines @@
 
 
 Expression* ParserTraits::SpreadCallNew(
     Expression* function, ZoneList<v8::internal::Expression*>* args, int pos) {
   return parser_->SpreadCallNew(function, args, pos);
 }
 
 
 void ParserTraits::AddFormalParameter(
     ParserFormalParameters* parameters, Expression* pattern, bool is_rest) {
-  bool is_simple = pattern->IsVariableProxy();
-  DCHECK(parser_->allow_harmony_destructuring() ||
-         parser_->allow_harmony_rest_parameters() || is_simple);
+  bool is_simple = !is_rest && pattern->IsVariableProxy();
+  DCHECK((!is_rest || parser_->allow_harmony_rest_parameters()) ||
+         (!is_simple && parser_->allow_harmony_destructuring()) || is_simple);
   const AstRawString* name = is_simple
                                  ? pattern->AsVariableProxy()->raw_name()
                                  : parser_->ast_value_factory()->empty_string();
   parameters->params.Add(
       ParserFormalParameters::Parameter(name, pattern, is_rest),
       parameters->scope->zone());
 }
 
 
 void ParserTraits::DeclareFormalParameter(
     Scope* scope, const ParserFormalParameters::Parameter& parameter,
     bool is_simple, ExpressionClassifier* classifier) {
   bool is_duplicate = false;
-  // TODO(caitp): Remove special handling for rest once desugaring is in.
-  auto name = is_simple || parameter.is_rest
-      ? parameter.name : parser_->ast_value_factory()->empty_string();
-  auto mode = is_simple || parameter.is_rest ? VAR : TEMPORARY;
+  auto name =
+      is_simple ? parameter.name : parser_->ast_value_factory()->empty_string();
+  auto mode = is_simple ? VAR : TEMPORARY;
   Variable* var =
       scope->DeclareParameter(name, mode, parameter.is_rest, &is_duplicate);
   if (is_duplicate) {
     classifier->RecordDuplicateFormalParameterError(
         parser_->scanner()->location());
   }
   if (is_sloppy(scope->language_mode())) {
     // TODO(sigurds) Mark every parameter as maybe assigned. This is a
     // conservative approximation necessary to account for parameters
     // that are assigned via the arguments array.
@@ skipping 10 matching lines @@
         parser_->BuildParameterInitializationBlock(parameters, ok);
     if (!*ok) return;
     if (init_block != nullptr) {
       body->Add(init_block, parser_->zone());
     }
   }
 }
 } }  // namespace v8::internal
 
 #endif  // V8_PARSER_H_