[es6] Implement proper TDZ for parameters

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index 1974f296f0756b0739ff6970453d1cbad7534a9a..046d580bc0047bbce62b7519c35e1d4cf5371e49 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -558,6 +558,8 @@ struct ParserFormalParameters : public PreParserFormalParameters {
     params.Add(Parameter(name, pattern, is_rest), scope->zone());
     DCHECK(arity == params.length());

[adamk, 2015/08/03 18:43:51]

This code could be responsible for keeping arity in sync for the Parser version,
letting the preparser handle the incrementing in AddFormalParameter (see my
comment in preparser.h).

A more robust alternative: make the |arity| member private in the superclass
(arity_), and add an arity() getter which in the PreParser class returns that
private member and in this version returns params.length().

   }
+
+  const Parameter& at(int i) { return params[i]; }
 };
 
 
@@ -782,13 +784,19 @@ class ParserTraits {
   V8_INLINE Scope* NewScope(Scope* parent_scope, ScopeType scope_type,
                             FunctionKind kind = kNormalFunction);
 
+  V8_INLINE void AddFormalParameter(
+      ParserFormalParameters* parameters, Expression* pattern, bool is_rest);
   V8_INLINE void DeclareFormalParameter(
-      ParserFormalParameters* parameters, Expression* pattern, bool is_rest,
-      ExpressionClassifier* classifier);
+      Scope* scope, const ParserFormalParameters::Parameter& parameter,
+      bool is_simple, ExpressionClassifier* classifier);
   void ParseArrowFunctionFormalParameters(
       ParserFormalParameters* parameters, Expression* params,
       const Scanner::Location& params_loc,
       Scanner::Location* duplicate_loc, bool* ok);
+  void ParseArrowFunctionFormalParameterList(
+      ParserFormalParameters* parameters, Expression* params,
+      const Scanner::Location& params_loc,
+      Scanner::Location* duplicate_loc, bool* ok);
 
   void ReindexLiterals(const ParserFormalParameters& parameters);
 
@@ -1311,24 +1319,33 @@ Expression* ParserTraits::SpreadCallNew(
 }
 
 
-void ParserTraits::DeclareFormalParameter(
-    ParserFormalParameters* parameters, Expression* pattern, bool is_rest,
-    ExpressionClassifier* classifier) {
-  bool is_duplicate = false;
+void ParserTraits::AddFormalParameter(
+    ParserFormalParameters* parameters, Expression* pattern, bool is_rest) {
   bool is_simple = pattern->IsVariableProxy();
-  DCHECK(parser_->allow_harmony_destructuring() || is_simple);
-
+  DCHECK(parser_->allow_harmony_destructuring() ||
+         parser_->allow_harmony_rest_parameters() || is_simple);
   const AstRawString* name = is_simple
                                  ? pattern->AsVariableProxy()->raw_name()
                                  : parser_->ast_value_factory()->empty_string();
-  Variable* var =
-      parameters->scope->DeclareParameter(name, VAR, is_rest, &is_duplicate);
-  parameters->AddParameter(name, is_simple ? nullptr : pattern, is_rest);
+  parameters->AddParameter(name, pattern, is_rest);
+  DCHECK(parameters->arity == parameters->params.length());

[adamk, 2015/08/03 18:43:52]

Nit: DCHECK_EQ

[rossberg, 2015/08/04 15:31:19]

Done.

+}
+
+
+void ParserTraits::DeclareFormalParameter(
+    Scope* scope, const ParserFormalParameters::Parameter& parameter,
+    bool is_simple, ExpressionClassifier* classifier) {
+  bool is_duplicate = false;
+  Variable* var = scope->DeclareParameter(
+      // TODO(caitp): Remove special handling for rest once desugaring is in.
+      is_simple || parameter.is_rest
+          ? parameter.name : parser_->ast_value_factory()->empty_string(),
+      VAR, parameter.is_rest, &is_duplicate);
   if (is_duplicate) {
     classifier->RecordDuplicateFormalParameterError(
         parser_->scanner()->location());
   }
-  if (is_sloppy(parameters->scope->language_mode())) {
+  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.