[es6] implement destructuring assignment

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index 1de6678c1e15ca8c627db9bc0612f1b9c1a32210..28e3606d9d7a8aa830559860762417a707375a05 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -114,6 +114,7 @@ class ParserBase : public Traits {
         allow_harmony_rest_parameters_(false),
         allow_harmony_default_parameters_(false),
         allow_harmony_destructuring_bind_(false),
+        allow_harmony_destructuring_assignment_(false),
         allow_strong_mode_(false),
         allow_legacy_const_(true),
         allow_harmony_do_expressions_(false) {}
@@ -130,6 +131,7 @@ class ParserBase : public Traits {
   ALLOW_ACCESSORS(harmony_rest_parameters);
   ALLOW_ACCESSORS(harmony_default_parameters);
   ALLOW_ACCESSORS(harmony_destructuring_bind);
+  ALLOW_ACCESSORS(harmony_destructuring_assignment);
   ALLOW_ACCESSORS(strong_mode);
   ALLOW_ACCESSORS(legacy_const);
   ALLOW_ACCESSORS(harmony_do_expressions);
@@ -175,6 +177,15 @@ class ParserBase : public Traits {
     Scope* outer_scope_;
   };
 
+  struct DestructuringAssignment {
+   public:
+    DestructuringAssignment(ExpressionT expression, Scope* scope)
+        : assignment(expression), scope(scope) {}
+
+    ExpressionT assignment;
+    Scope* scope;
+  };
+
   class FunctionState BASE_EMBEDDED {
    public:
     FunctionState(FunctionState** function_state_stack, Scope** scope_stack,
@@ -227,6 +238,15 @@ class ParserBase : public Traits {
 
     typename Traits::Type::Factory* factory() { return factory_; }
 
+    const List<DestructuringAssignment>& destructuring_assignments_to_rewrite()
+        const {
+      return destructuring_assignments_to_rewrite_;
+    }
+
+    void AddDestructuringAssignment(DestructuringAssignment pair) {
+      destructuring_assignments_to_rewrite_.Add(pair);
+    }
+
    private:
     // Used to assign an index to each literal that needs materialization in
     // the function.  Includes regexp literals, and boilerplate for object and
@@ -255,6 +275,11 @@ class ParserBase : public Traits {
     FunctionState* outer_function_state_;
     Scope** scope_stack_;
     Scope* outer_scope_;
+
+    List<DestructuringAssignment> destructuring_assignments_to_rewrite_;

[adamk, 2015/11/25 21:05:28]

Please move this to Parser unless there's some reason it's needed in the
preparser.

[caitp (gmail), 2015/11/25 21:41:52]

The list lives in FunctionState, so each FunctionState has its own collection of
assignments to rewrite, and does once the function is ready to be made into an
AST node.

The List is always empty in the PreParser (eg, manipulating the list is
Parser-specific). It might be possible to declare it as like, a void type or
something in the PreParser, but I'm not positive that would realy work.
Thoughts?

I originally stored the list in the Parser and tried to do the rewriting once
ParseProgram had finished (if it had been called), but had issues with that.

+
+    void RewriteDestructuringAssignments();

[adamk, 2015/11/25 21:05:28]

I don't see this defined anywhere (and I don't think it needs to be defined).

[caitp (gmail), 2015/11/25 21:41:52]

Acknowledged.

+
     typename Traits::Type::Factory* factory_;
 
     friend class ParserTraits;
@@ -460,6 +485,10 @@ class ParserBase : public Traits {
                       ok);
   }
 
+  void CheckDestructuringElement(ExpressionT element,
+                                 ExpressionClassifier* classifier, int beg_pos,
+                                 int end_pos);
+
   // Checking the name of a function literal. This has to be done after parsing
   // the function, since the function can declare itself strict.
   void CheckFunctionName(LanguageMode language_mode, IdentifierT function_name,
@@ -538,12 +567,20 @@ class ParserBase : public Traits {
 
   void ReportClassifierError(const ExpressionClassifier::Error& error) {
     Traits::ReportMessageAt(error.location, error.message, error.arg,
-                            kSyntaxError);
+                            error.type);
   }
 
   void ValidateExpression(const ExpressionClassifier* classifier, bool* ok) {
-    if (!classifier->is_valid_expression()) {
-      ReportClassifierError(classifier->expression_error());
+    if (!classifier->is_valid_expression() ||
+        classifier->has_cover_initialized_name()) {
+      const Scanner::Location& a = classifier->expression_error().location;
+      const Scanner::Location& b =
+          classifier->cover_initialized_name_error().location;
+      if (a.beg_pos < 0 || (b.beg_pos >= 0 && a.beg_pos > b.beg_pos)) {
+        ReportClassifierError(classifier->cover_initialized_name_error());
+      } else {
+        ReportClassifierError(classifier->expression_error());
+      }
       *ok = false;
     }
   }
@@ -692,6 +729,8 @@ class ParserBase : public Traits {
   ExpressionT ParseExpression(bool accept_IN, bool* ok);
   ExpressionT ParseExpression(bool accept_IN, ExpressionClassifier* classifier,
                               bool* ok);
+  ExpressionT ParseExpression(bool accept_IN, int flags,
+                              ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseArrayLiteral(ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParsePropertyName(IdentifierT* name, bool* is_get, bool* is_set,
                                 bool* is_static, bool* is_computed_name,
@@ -705,9 +744,23 @@ class ParserBase : public Traits {
   typename Traits::Type::ExpressionList ParseArguments(
       Scanner::Location* first_spread_pos, ExpressionClassifier* classifier,
       bool* ok);
-  ExpressionT ParseAssignmentExpression(bool accept_IN,
+
+  enum AssignmentExpressionFlags {
+    kIsLeftHandSide = 0,
+    kIsRightHandSide = 1 << 0,
+    kIsPatternElement = 1 << 1,
+    kIsPossibleArrowFormals = 1 << 2
+  };
+
+  ExpressionT ParseAssignmentExpression(bool accept_IN, int flags,
                                         ExpressionClassifier* classifier,
                                         bool* ok);
+  ExpressionT ParseAssignmentExpression(bool accept_IN,
+                                        ExpressionClassifier* classifier,
+                                        bool* ok) {
+    return ParseAssignmentExpression(accept_IN, kIsLeftHandSide, classifier,
+                                     ok);
+  }
   ExpressionT ParseYieldExpression(ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseConditionalExpression(bool accept_IN,
                                          ExpressionClassifier* classifier,
@@ -755,10 +808,29 @@ class ParserBase : public Traits {
   ExpressionT CheckAndRewriteReferenceExpression(
       ExpressionT expression, int beg_pos, int end_pos,
       MessageTemplate::Template message, bool* ok);
+  ExpressionT ClassifyAndRewriteReferenceExpression(
+      ExpressionClassifier* classifier, ExpressionT expression, int beg_pos,
+      int end_pos, MessageTemplate::Template message,
+      ParseErrorType type = kSyntaxError);
   ExpressionT CheckAndRewriteReferenceExpression(
       ExpressionT expression, int beg_pos, int end_pos,
       MessageTemplate::Template message, ParseErrorType type, bool* ok);
 
+  bool IsValidReferenceExpression(ExpressionT expression);
+
+  bool IsAssignableIdentifier(ExpressionT expression) {
+    if (!Traits::IsIdentifier(expression)) return false;
+    if (is_strict(language_mode()) &&
+        Traits::IsEvalOrArguments(Traits::AsIdentifier(expression))) {
+      return false;
+    }
+    if (is_strong(language_mode()) &&
+        Traits::IsUndefined(Traits::AsIdentifier(expression))) {
+      return false;
+    }
+    return true;
+  }
+
   // Used to validate property names in object literals and class literals
   enum PropertyKind {
     kAccessorProperty,
@@ -847,6 +919,7 @@ class ParserBase : public Traits {
   bool allow_harmony_rest_parameters_;
   bool allow_harmony_default_parameters_;
   bool allow_harmony_destructuring_bind_;
+  bool allow_harmony_destructuring_assignment_;
   bool allow_strong_mode_;
   bool allow_legacy_const_;
   bool allow_harmony_do_expressions_;
@@ -959,6 +1032,11 @@ class PreParserExpression {
                              right->IsSpreadExpression()));
   }
 
+  static PreParserExpression AssignmentPattern() {
+    return PreParserExpression(TypeField::encode(kExpression) |
+                               ExpressionTypeField::encode(kAssignmentPattern));
+  }
+
   static PreParserExpression ObjectLiteral() {
     return PreParserExpression(TypeField::encode(kObjectLiteralExpression));
   }
@@ -1024,6 +1102,11 @@ class PreParserExpression {
     return PreParserIdentifier(IdentifierTypeField::decode(code_));
   }
 
+  bool IsAssignmentPattern() const {
+    return TypeField::decode(code_) == kExpression &&
+           ExpressionTypeField::decode(code_) == kAssignmentPattern;
+  }
+
   bool IsObjectLiteral() const {
     return TypeField::decode(code_) == kObjectLiteralExpression;
   }
@@ -1131,7 +1214,8 @@ class PreParserExpression {
     kPropertyExpression,
     kCallExpression,
     kSuperCallReference,
-    kNoTemplateTagExpression
+    kNoTemplateTagExpression,
+    kAssignmentPattern
   };
 
   explicit PreParserExpression(uint32_t expression_code)
@@ -1148,6 +1232,7 @@ class PreParserExpression {
   typedef BitField<PreParserIdentifier::Type, TypeField::kNext, 10>
       IdentifierTypeField;
   typedef BitField<bool, TypeField::kNext, 1> HasRestField;
+  typedef BitField<bool, TypeField::kNext, 1> HasCoverInitializedNameField;
 
   uint32_t code_;
 };
@@ -1320,6 +1405,11 @@ class PreParserFactory {
                                     int pos) {
     return PreParserExpression::Default();
   }
+  PreParserExpression NewAssignmentPattern(PreParserExpression pattern,
+                                           int pos) {
+    DCHECK(pattern->IsObjectLiteral() || pattern->IsArrayLiteral());
+    return PreParserExpression::AssignmentPattern();
+  }
   PreParserExpression NewYield(PreParserExpression generator_object,
                                PreParserExpression expression,
                                Yield::Kind yield_kind,
@@ -1750,6 +1840,10 @@ class PreParserTraits {
                                            PreParserExpressionList args,
                                            int pos);
 
+  inline void RewriteDestructuringAssignments() {}
+
+  inline void ShouldRewriteDestructuringAssignment(PreParserExpression) {}
+
  private:
   PreParser* pre_parser_;
 };
@@ -2393,8 +2487,12 @@ ParserBase<Traits>::ParsePrimaryExpression(ExpressionClassifier* classifier,
       // Heuristically try to detect immediately called functions before
       // seeing the call parentheses.
       parenthesized_function_ = (peek() == Token::FUNCTION);
-      ExpressionT expr = this->ParseExpression(true, classifier, CHECK_OK);
+      ExpressionT expr = this->ParseExpression(true, kIsPossibleArrowFormals,
+                                               classifier, CHECK_OK);
       Expect(Token::RPAREN, CHECK_OK);
+      if (peek() != Token::ARROW) {

[adamk, 2015/11/25 21:05:28]

Sorry, I've forgotten if you've answered this already: why are doing this
peeking here now (what does it have to do with parsing destructuring assignment,
that is)?

[caitp (gmail), 2015/11/25 21:41:52]

```

// Valid if: --harmony-destructuring-assignment
var o = ({ a: b } = someObj);

// Valid if: --harmony-default-parameters + --harmony-destructuring-bind, only
if followed by `=>`
var f = ({ a: b } = someObj) => b;
```

Can't eagerly break the initializer in ParseAssignmentExpression unless we know
if the ARROW is there or not, so it defers to the caller and does it here

[adamk, 2015/11/25 21:54:20]

Thanks!

+        ValidateExpression(classifier, CHECK_OK);
+      }
       return expr;
     }
 
@@ -2462,17 +2560,23 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseExpression(
 }
 
 
-// Precedence = 1
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseExpression(
     bool accept_IN, ExpressionClassifier* classifier, bool* ok) {
+  return ParseExpression(accept_IN, kIsLeftHandSide, classifier, ok);
+}
+
+
+template <class Traits>
+typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseExpression(
+    bool accept_IN, int flags, ExpressionClassifier* classifier, bool* ok) {
   // Expression ::
   //   AssignmentExpression
   //   Expression ',' AssignmentExpression
 
   ExpressionClassifier binding_classifier;
-  ExpressionT result =
-      this->ParseAssignmentExpression(accept_IN, &binding_classifier, CHECK_OK);
+  ExpressionT result = this->ParseAssignmentExpression(
+      accept_IN, flags, &binding_classifier, CHECK_OK);
   classifier->Accumulate(binding_classifier,
                          ExpressionClassifier::AllProductions);
   bool is_simple_parameter_list = this->IsIdentifier(result);
@@ -2497,7 +2601,7 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseExpression(
     }
     int pos = position();
     ExpressionT right = this->ParseAssignmentExpression(
-        accept_IN, &binding_classifier, CHECK_OK);
+        accept_IN, flags, &binding_classifier, CHECK_OK);
     if (is_rest) right = factory()->NewSpread(right, pos);
     is_simple_parameter_list =
         is_simple_parameter_list && this->IsIdentifier(right);
@@ -2508,6 +2612,7 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseExpression(
   if (!is_simple_parameter_list || seen_rest) {
     classifier->RecordNonSimpleParameter();
   }
+
   return result;
 }
 
@@ -2544,14 +2649,27 @@ typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseArrayLiteral(
       if (first_spread_index < 0) {
         first_spread_index = values->length();
       }
+
+      CheckDestructuringElement(argument, classifier, start_pos,
+                                scanner()->location().end_pos);
+
+      if (peek() == Token::COMMA) {
+        classifier->RecordPatternError(
+            Scanner::Location(start_pos, scanner()->location().end_pos),
+            MessageTemplate::kElementAfterRest);
+      }
     } else {
-      elem = this->ParseAssignmentExpression(true, classifier, CHECK_OK);
+      elem = this->ParseAssignmentExpression(true, kIsPatternElement,
+                                             classifier, CHECK_OK);
+      if (!this->IsValidReferenceExpression(elem) &&
+          !classifier->is_valid_assignment_pattern()) {
+        classifier->RecordPatternError(
+            Scanner::Location(pos, scanner()->location().end_pos),
+            MessageTemplate::kInvalidDestructuringTarget);
+      }
     }
     values->Add(elem, zone_);
     if (peek() != Token::RBRACK) {
-      if (seen_spread) {
-        BindingPatternUnexpectedToken(classifier);
-      }
       Expect(Token::COMMA, CHECK_OK);
     }
   }
@@ -2675,8 +2793,18 @@ ParserBase<Traits>::ParsePropertyDefinition(
                                CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
       }
       Consume(Token::COLON);
+      int pos = peek_position();
       value = this->ParseAssignmentExpression(
-          true, classifier, CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
+          true, kIsPatternElement, classifier,
+          CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
+
+      if (!this->IsValidReferenceExpression(value) &&
+          !classifier->is_valid_assignment_pattern()) {
+        classifier->RecordPatternError(
+            Scanner::Location(pos, scanner()->location().end_pos),
+            MessageTemplate::kInvalidDestructuringTarget);
+      }
+
       return factory()->NewObjectLiteralProperty(name_expression, value, false,
                                                  *is_computed_name);
     }
@@ -2711,7 +2839,6 @@ ParserBase<Traits>::ParsePropertyDefinition(
           name, next_beg_pos, next_end_pos, scope_, factory());
 
       if (peek() == Token::ASSIGN) {
-        this->ExpressionUnexpectedToken(classifier);
         Consume(Token::ASSIGN);
         ExpressionClassifier rhs_classifier;
         ExpressionT rhs = this->ParseAssignmentExpression(
@@ -2720,6 +2847,9 @@ ParserBase<Traits>::ParsePropertyDefinition(
                                ExpressionClassifier::ExpressionProductions);
         value = factory()->NewAssignment(Token::ASSIGN, lhs, rhs,
                                          RelocInfo::kNoPosition);
+        classifier->RecordCoverInitializedNameError(
+            Scanner::Location(next_beg_pos, scanner()->location().end_pos),
+            MessageTemplate::kInvalidCoverInitializedName);
       } else {
         value = lhs;
       }
@@ -2736,6 +2866,11 @@ ParserBase<Traits>::ParsePropertyDefinition(
     return this->EmptyObjectLiteralProperty();
   }
 
+  // Method definitions are never valid in patterns.
+  classifier->RecordPatternError(
+      Scanner::Location(next_beg_pos, scanner()->location().end_pos),
+      MessageTemplate::kInvalidDestructuringTarget);
+
   if (is_generator || peek() == Token::LPAREN) {
     // MethodDefinition
     //    PropertyName '(' StrictFormalParameters ')' '{' FunctionBody '}'
@@ -2958,7 +3093,7 @@ typename Traits::Type::ExpressionList ParserBase<Traits>::ParseArguments(
 // Precedence = 2
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
-ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
+ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN, int flags,
                                               ExpressionClassifier* classifier,
                                               bool* ok) {
   // AssignmentExpression ::
@@ -2966,7 +3101,11 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
   //   ArrowFunction
   //   YieldExpression
   //   LeftHandSideExpression AssignmentOperator AssignmentExpression
-
+  bool is_rhs = flags & kIsRightHandSide;
+  bool is_pattern_element = flags & kIsPatternElement;
+  bool is_destructuring_assignment = false;
+  bool is_arrow_formals = flags & kIsPossibleArrowFormals;
+  USE(is_arrow_formals);

[adamk, 2015/11/25 21:05:28]

This USE is not needed.

[caitp (gmail), 2015/11/25 21:41:52]

Acknowledged.

   int lhs_beg_pos = peek_position();
 
   if (peek() == Token::YIELD && is_generator()) {
@@ -3012,18 +3151,43 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
     }
     expression = this->ParseArrowFunctionLiteral(
         accept_IN, parameters, arrow_formals_classifier, CHECK_OK);
+    if (is_pattern_element) {
+      classifier->RecordPatternError(
+          Scanner::Location(lhs_beg_pos, scanner()->location().end_pos),
+          MessageTemplate::kInvalidDestructuringTarget);
+    }
     return expression;
   }
 
+  if (this->IsValidReferenceExpression(expression)) {
+    arrow_formals_classifier.ForgiveAssignmentPatternError();
+  }
+
   // "expression" was not itself an arrow function parameter list, but it might
   // form part of one.  Propagate speculative formal parameter error locations.
-  classifier->Accumulate(arrow_formals_classifier,
-                         ExpressionClassifier::StandardProductions |
-                             ExpressionClassifier::FormalParametersProductions);
+  classifier->Accumulate(
+      arrow_formals_classifier,
+      ExpressionClassifier::StandardProductions |
+          ExpressionClassifier::FormalParametersProductions |
+          ExpressionClassifier::CoverInitializedNameProduction);
+
+  bool maybe_pattern =
+      expression->IsObjectLiteral() || expression->IsArrayLiteral();
+  // bool binding_pattern =
+  //    allow_harmony_destructuring_bind() && maybe_pattern && !is_rhs;
 
   if (!Token::IsAssignmentOp(peek())) {
     if (fni_ != NULL) fni_->Leave();
     // Parsed conditional expression only (no assignment).
+    if (is_pattern_element && !this->IsValidReferenceExpression(expression) &&
+        !maybe_pattern) {
+      classifier->RecordPatternError(
+          Scanner::Location(lhs_beg_pos, scanner()->location().end_pos),
+          MessageTemplate::kInvalidDestructuringTarget);
+    } else if (is_rhs && maybe_pattern) {
+      ValidateExpression(classifier, CHECK_OK);
+    }
+
     return expression;
   }
 
@@ -3032,9 +3196,21 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
     BindingPatternUnexpectedToken(classifier);
   }
 
-  expression = this->CheckAndRewriteReferenceExpression(
-      expression, lhs_beg_pos, scanner()->location().end_pos,
-      MessageTemplate::kInvalidLhsInAssignment, CHECK_OK);
+  if (allow_harmony_destructuring_assignment() && maybe_pattern &&
+      peek() == Token::ASSIGN) {
+    classifier->ForgiveCoverInitializedNameError();
+    ValidateAssignmentPattern(classifier, CHECK_OK);
+    is_destructuring_assignment = true;
+  } else if (is_arrow_formals) {
+    expression = this->ClassifyAndRewriteReferenceExpression(
+        classifier, expression, lhs_beg_pos, scanner()->location().end_pos,
+        MessageTemplate::kInvalidLhsInAssignment);
+  } else {
+    expression = this->CheckAndRewriteReferenceExpression(
+        expression, lhs_beg_pos, scanner()->location().end_pos,
+        MessageTemplate::kInvalidLhsInAssignment, CHECK_OK);
+  }
+
   expression = this->MarkExpressionAsAssigned(expression);
 
   Token::Value op = Next();  // Get assignment operator.
@@ -3046,10 +3222,15 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
   int pos = position();
 
   ExpressionClassifier rhs_classifier;
-  ExpressionT right =
-      this->ParseAssignmentExpression(accept_IN, &rhs_classifier, CHECK_OK);
-  classifier->Accumulate(rhs_classifier,
-                         ExpressionClassifier::ExpressionProductions);
+
+  int rhs_flags = flags;
+  rhs_flags &= ~(kIsPatternElement | kIsPossibleArrowFormals);
+  rhs_flags |= kIsRightHandSide;
+  ExpressionT right = this->ParseAssignmentExpression(
+      accept_IN, rhs_flags, &rhs_classifier, CHECK_OK);
+  classifier->Accumulate(
+      rhs_classifier, ExpressionClassifier::ExpressionProductions |
+                          ExpressionClassifier::CoverInitializedNameProduction);
 
   // TODO(1231235): We try to estimate the set of properties set by
   // constructors. We define a new property whenever there is an
@@ -3075,7 +3256,13 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
     fni_->Leave();
   }
 
-  return factory()->NewAssignment(op, expression, right, pos);
+  ExpressionT result = factory()->NewAssignment(op, expression, right, pos);
+
+  if (is_destructuring_assignment) {
+    Traits::ShouldRewriteDestructuringAssignment(result);
+  }
+
+  return result;
 }
 
 template <class Traits>
@@ -4033,6 +4220,8 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
     if (is_strict(language_mode()) || allow_harmony_sloppy()) {
       this->CheckConflictingVarDeclarations(formal_parameters.scope, CHECK_OK);
     }
+
+    Traits::RewriteDestructuringAssignments();
   }
 
   FunctionLiteralT function_literal = factory()->NewFunctionLiteral(
@@ -4164,21 +4353,33 @@ typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::CheckAndRewriteReferenceExpression(
     ExpressionT expression, int beg_pos, int end_pos,
     MessageTemplate::Template message, ParseErrorType type, bool* ok) {
+  ExpressionClassifier classifier;
+  ExpressionT result = ClassifyAndRewriteReferenceExpression(
+      &classifier, expression, beg_pos, end_pos, message, type);
+  ValidateExpression(&classifier, ok);
+  if (!*ok) return this->EmptyExpression();
+  return result;
+}
+
+
+template <typename Traits>
+typename ParserBase<Traits>::ExpressionT
+ParserBase<Traits>::ClassifyAndRewriteReferenceExpression(
+    ExpressionClassifier* classifier, ExpressionT expression, int beg_pos,
+    int end_pos, MessageTemplate::Template message, ParseErrorType type) {
   Scanner::Location location(beg_pos, end_pos);
   if (this->IsIdentifier(expression)) {
     if (is_strict(language_mode()) &&
         this->IsEvalOrArguments(this->AsIdentifier(expression))) {
-      this->ReportMessageAt(location, MessageTemplate::kStrictEvalArguments,
-                            kSyntaxError);
-      *ok = false;
-      return this->EmptyExpression();
+      classifier->RecordExpressionError(
+          location, MessageTemplate::kStrictEvalArguments, kSyntaxError);
+      return expression;
     }
     if (is_strong(language_mode()) &&
         this->IsUndefined(this->AsIdentifier(expression))) {
-      this->ReportMessageAt(location, MessageTemplate::kStrongUndefined,
-                            kSyntaxError);
-      *ok = false;
-      return this->EmptyExpression();
+      classifier->RecordExpressionError(
+          location, MessageTemplate::kStrongUndefined, kSyntaxError);
+      return expression;
     }
   }
   if (expression->IsValidReferenceExpression()) {
@@ -4190,9 +4391,31 @@ ParserBase<Traits>::CheckAndRewriteReferenceExpression(
     ExpressionT error = this->NewThrowReferenceError(message, pos);
     return factory()->NewProperty(expression, error, pos);
   } else {
-    this->ReportMessageAt(location, message, type);
-    *ok = false;
-    return this->EmptyExpression();
+    classifier->RecordExpressionError(location, message, type);
+    return expression;
+  }
+}
+
+
+template <typename Traits>
+bool ParserBase<Traits>::IsValidReferenceExpression(ExpressionT expression) {
+  return this->IsAssignableIdentifier(expression) || expression->IsProperty();
+}
+
+
+template <typename Traits>
+void ParserBase<Traits>::CheckDestructuringElement(
+    ExpressionT expression, ExpressionClassifier* classifier, int begin,
+    int end) {
+  static const MessageTemplate::Template message =
+      MessageTemplate::kInvalidDestructuringTarget;
+  if (!this->IsAssignableIdentifier(expression)) {
+    const Scanner::Location location(begin, end);
+    classifier->RecordBindingPatternError(location, message);
+    if (!expression->IsProperty() &&
+        !(expression->IsObjectLiteral() || expression->IsArrayLiteral())) {
+      classifier->RecordAssignmentPatternError(location, message);
+    }
   }
 }