[es6] implement destructuring assignment

src/preparser.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_PREPARSER_H
 #define V8_PREPARSER_H
 
 #include "src/bailout-reason.h"
 #include "src/expression-classifier.h"
 #include "src/func-name-inferrer.h"
@@ skipping 96 matching lines @@
         scanner_(scanner),
         stack_overflow_(false),
         allow_lazy_(false),
         allow_natives_(false),
         allow_harmony_sloppy_(false),
         allow_harmony_sloppy_function_(false),
         allow_harmony_sloppy_let_(false),
         allow_harmony_rest_parameters_(false),
         allow_harmony_default_parameters_(false),
         allow_harmony_destructuring_(false),
+        allow_harmony_destructuring_assignment_(false),
         allow_strong_mode_(false),
         allow_legacy_const_(true),
         allow_harmony_do_expressions_(false) {}
 
 #define ALLOW_ACCESSORS(name)                           \
   bool allow_##name() const { return allow_##name##_; } \
   void set_allow_##name(bool allow) { allow_##name##_ = allow; }
 
   ALLOW_ACCESSORS(lazy);
   ALLOW_ACCESSORS(natives);
   ALLOW_ACCESSORS(harmony_sloppy);
   ALLOW_ACCESSORS(harmony_sloppy_function);
   ALLOW_ACCESSORS(harmony_sloppy_let);
   ALLOW_ACCESSORS(harmony_rest_parameters);
   ALLOW_ACCESSORS(harmony_default_parameters);
   ALLOW_ACCESSORS(harmony_destructuring);
+  ALLOW_ACCESSORS(harmony_destructuring_assignment);
   ALLOW_ACCESSORS(strong_mode);
   ALLOW_ACCESSORS(legacy_const);
   ALLOW_ACCESSORS(harmony_do_expressions);
 #undef ALLOW_ACCESSORS
 
   uintptr_t stack_limit() const { return stack_limit_; }
 
  protected:
   enum AllowRestrictedIdentifiers {
     kAllowRestrictedIdentifiers,
@@ skipping 25 matching lines @@
         : scope_stack_(scope_stack), outer_scope_(*scope_stack) {
       *scope_stack_ = scope;
     }
     ~BlockState() { *scope_stack_ = outer_scope_; }
 
    private:
     Scope** scope_stack_;
     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,
                   Scope* scope, FunctionKind kind,
                   typename Traits::Type::Factory* factory);
     ~FunctionState();
 
     int NextMaterializedLiteralIndex() {
       return next_materialized_literal_index_++;
     }
@@ skipping 32 matching lines @@
       DCHECK(is_generator());
       generator_object_variable_ = variable;
     }
     typename Traits::Type::GeneratorVariable* generator_object_variable()
         const {
       return generator_object_variable_;
     }
 
     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
     // array literals.
     int next_materialized_literal_index_;
 
     // Properties count estimation.
     int expected_property_count_;
 
     // Location of most recent use of 'this' (invalid if none).
     Scanner::Location this_location_;
 
     // Location of most recent 'return' statement (invalid if none).
     Scanner::Location return_location_;
 
     // Location of call to the "super" constructor (invalid if none).
     Scanner::Location super_location_;
 
     FunctionKind kind_;
     // For generators, this variable may hold the generator object. It variable
     // is used by yield expressions and return statements. It is not necessary
     // for generator functions to have this variable set.
     Variable* generator_object_variable_;
 
     FunctionState** function_state_stack_;
     FunctionState* outer_function_state_;
     Scope** scope_stack_;
     Scope* outer_scope_;
+
+    List<DestructuringAssignment> destructuring_assignments_to_rewrite_;

[adamk, 2015/11/20 22:42:59]

Why does ParserBase need this List? Couldn't it just be in Parser?

+
+    void RewriteDestructuringAssignments();
+
     typename Traits::Type::Factory* factory_;
 
     friend class ParserTraits;
     friend class Checkpoint;
   };
 
   // Annoyingly, arrow functions first parse as comma expressions, then when we
   // see the => we have to go back and reinterpret the arguments as being formal
   // parameters.  To do so we need to reset some of the parser state back to
   // what it was before the arguments were first seen.
@@ skipping 185 matching lines @@
   inline void CheckStrictOctalLiteral(int beg_pos, int end_pos, bool* ok) {
     CheckOctalLiteral(beg_pos, end_pos, MessageTemplate::kStrictOctalLiteral,
                       ok);
   }
 
   inline void CheckTemplateOctalLiteral(int beg_pos, int end_pos, bool* ok) {
     CheckOctalLiteral(beg_pos, end_pos, MessageTemplate::kTemplateOctalLiteral,
                       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,
                          FunctionNameValidity function_name_validity,
                          const Scanner::Location& function_name_loc, bool* ok) {
     if (function_name_validity == kSkipFunctionNameCheck) return;
     // The function name needs to be checked in strict mode.
     if (is_sloppy(language_mode)) return;
 
     if (this->IsEvalOrArguments(function_name)) {
@@ skipping 62 matching lines @@
       Scanner::Location location, Token::Value token,
       MessageTemplate::Template message = MessageTemplate::kUnexpectedToken);
 
 
   void ReportClassifierError(const ExpressionClassifier::Error& error) {
     Traits::ReportMessageAt(error.location, error.message, error.arg,
                             kSyntaxError);
   }
 
   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;
     }
   }
 
   void ValidateFormalParameterInitializer(
       const ExpressionClassifier* classifier, bool* ok) {
     if (!classifier->is_valid_formal_parameter_initializer()) {
       ReportClassifierError(classifier->formal_parameter_initializer_error());
       *ok = false;
     }
@@ skipping 129 matching lines @@
                                 bool* is_static, bool* is_computed_name,
                                 ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseObjectLiteral(ExpressionClassifier* classifier, bool* ok);
   ObjectLiteralPropertyT ParsePropertyDefinition(
       ObjectLiteralCheckerBase* checker, bool in_class, bool has_extends,
       bool is_static, bool* is_computed_name, bool* has_seen_constructor,
       ExpressionClassifier* classifier, bool* ok);
   typename Traits::Type::ExpressionList ParseArguments(
       Scanner::Location* first_spread_pos, ExpressionClassifier* classifier,
       bool* ok);
+
+  enum AssignmentExpressionFlags {
+    kIsLeftHandSide = 0,
+    kIsRightHandSide = 1 << 0,
+    kIsPatternElement = 1 << 1
+  };
+
+  ExpressionT ParseAssignmentExpression(bool accept_IN, int flags,
+                                        ExpressionClassifier* classifier,
+                                        bool* ok);
   ExpressionT ParseAssignmentExpression(bool accept_IN,
                                         ExpressionClassifier* classifier,
-                                        bool* ok);
+                                        bool* ok) {
+    return ParseAssignmentExpression(accept_IN, kIsLeftHandSide, classifier,
+                                     ok);
+  }
   ExpressionT ParseYieldExpression(ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseConditionalExpression(bool accept_IN,
                                          ExpressionClassifier* classifier,
                                          bool* ok);
   ExpressionT ParseBinaryExpression(int prec, bool accept_IN,
                                     ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseUnaryExpression(ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParsePostfixExpression(ExpressionClassifier* classifier,
                                      bool* ok);
   ExpressionT ParseLeftHandSideExpression(ExpressionClassifier* classifier,
@@ skipping 31 matching lines @@
   // Checks if the expression is a valid reference expression (e.g., on the
   // left-hand side of assignments). Although ruled out by ECMA as early errors,
   // we allow calls for web compatibility and rewrite them to a runtime throw.
   ExpressionT CheckAndRewriteReferenceExpression(
       ExpressionT expression, int beg_pos, int end_pos,
       MessageTemplate::Template message, bool* ok);
   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,
     kValueProperty,
     kMethodProperty
   };
 
   class ObjectLiteralCheckerBase {
    public:
     explicit ObjectLiteralCheckerBase(ParserBase* parser) : parser_(parser) {}
@@ skipping 68 matching lines @@
   bool stack_overflow_;
 
   bool allow_lazy_;
   bool allow_natives_;
   bool allow_harmony_sloppy_;
   bool allow_harmony_sloppy_function_;
   bool allow_harmony_sloppy_let_;
   bool allow_harmony_rest_parameters_;
   bool allow_harmony_default_parameters_;
   bool allow_harmony_destructuring_;
+  bool allow_harmony_destructuring_assignment_;
   bool allow_strong_mode_;
   bool allow_legacy_const_;
   bool allow_harmony_do_expressions_;
 };
 
 
 class PreParserIdentifier {
  public:
   PreParserIdentifier() : type_(kUnknownIdentifier) {}
   static PreParserIdentifier Default() {
@@ skipping 92 matching lines @@
 
   static PreParserExpression BinaryOperation(PreParserExpression left,
                                              Token::Value op,
                                              PreParserExpression right) {
     return PreParserExpression(
         TypeField::encode(kBinaryOperationExpression) |
         HasRestField::encode(op == Token::COMMA &&
                              right->IsSpreadExpression()));
   }
 
+  static PreParserExpression AssignmentPattern() {
+    return PreParserExpression(TypeField::encode(kExpression) |
+                               ExpressionTypeField::encode(kAssignmentPattern));
+  }
+
   static PreParserExpression ObjectLiteral() {
     return PreParserExpression(TypeField::encode(kObjectLiteralExpression));
   }
 
   static PreParserExpression ArrayLiteral() {
     return PreParserExpression(TypeField::encode(kArrayLiteralExpression));
   }
 
   static PreParserExpression StringLiteral() {
     return PreParserExpression(TypeField::encode(kStringLiteralExpression));
@@ skipping 45 matching lines @@
 
   bool IsIdentifier() const {
     return TypeField::decode(code_) == kIdentifierExpression;
   }
 
   PreParserIdentifier AsIdentifier() const {
     DCHECK(IsIdentifier());
     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;
   }
 
   bool IsArrayLiteral() const {
     return TypeField::decode(code_) == kArrayLiteralExpression;
   }
 
   bool IsStringLiteral() const {
     return TypeField::decode(code_) == kStringLiteralExpression;
@@ skipping 87 matching lines @@
     kObjectLiteralExpression,
     kArrayLiteralExpression
   };
 
   enum ExpressionType {
     kThisExpression,
     kThisPropertyExpression,
     kPropertyExpression,
     kCallExpression,
     kSuperCallReference,
-    kNoTemplateTagExpression
+    kNoTemplateTagExpression,
+    kAssignmentPattern
   };
 
   explicit PreParserExpression(uint32_t expression_code)
       : code_(expression_code) {}
 
   // The first three bits are for the Type.
   typedef BitField<Type, 0, 3> TypeField;
 
   // The rest of the bits are interpreted depending on the value
   // of the Type field, so they can share the storage.
   typedef BitField<ExpressionType, TypeField::kNext, 3> ExpressionTypeField;
   typedef BitField<bool, TypeField::kNext, 1> IsUseStrictField;
   typedef BitField<bool, IsUseStrictField::kNext, 1> IsUseStrongField;
   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_;
 };
 
 
 // The pre-parser doesn't need to build lists of expressions, identifiers, or
 // the like.
 template <typename T>
 class PreParserList {
  public:
@@ skipping 152 matching lines @@
                                           PreParserExpression left,
                                           PreParserExpression right, int pos) {
     return PreParserExpression::Default();
   }
   PreParserExpression NewAssignment(Token::Value op,
                                     PreParserExpression left,
                                     PreParserExpression right,
                                     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,
                                int pos) {
     return PreParserExpression::Default();
   }
   PreParserExpression NewConditional(PreParserExpression condition,
                                      PreParserExpression then_expression,
                                      PreParserExpression else_expression,
                                      int pos) {
@@ skipping 410 matching lines @@
 
   inline void MaterializeUnspreadArgumentsLiterals(int count);
 
   inline PreParserExpression SpreadCall(PreParserExpression function,
                                         PreParserExpressionList args, int pos);
 
   inline PreParserExpression SpreadCallNew(PreParserExpression function,
                                            PreParserExpressionList args,
                                            int pos);
 
+  inline PreParserExpression RewriteDestructuringAssignmentExpression(
+      PreParserExpression expr) {
+    return expr;
+  }
+
+  inline void RewriteDestructuringAssignments() {}
+
+  inline void ShouldRewriteDestructuringAssignment(PreParserExpression) {}
+
  private:
   PreParser* pre_parser_;
 };
 
 
 // Preparsing checks a JavaScript program and emits preparse-data that helps
 // a later parsing to be faster.
 // See preparse-data-format.h for the data format.
 
 // The PreParser checks that the syntax follows the grammar for JavaScript,
@@ skipping 611 matching lines @@
           return this->EmptyExpression();
         }
         Expect(Token::RPAREN, CHECK_OK);
         return factory()->NewSpread(expr, ellipsis_pos);
       }
       // 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);
       Expect(Token::RPAREN, CHECK_OK);
+      if (peek() != Token::ARROW) {
+        ValidateExpression(classifier, CHECK_OK);
+      }
       return expr;
     }
 
     case Token::CLASS: {
       BindingPatternUnexpectedToken(classifier);
       Consume(Token::CLASS);
       if (!allow_harmony_sloppy() && is_sloppy(language_mode())) {
         ReportMessage(MessageTemplate::kSloppyLexical);
         *ok = false;
         return this->EmptyExpression();
@@ skipping 47 matching lines @@
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseExpression(
     bool accept_IN, bool* ok) {
   ExpressionClassifier classifier;
   ExpressionT result = ParseExpression(accept_IN, &classifier, CHECK_OK);
   ValidateExpression(&classifier, CHECK_OK);
   return result;
 }
 
 
-// Precedence = 1
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseExpression(
     bool accept_IN, ExpressionClassifier* classifier, bool* ok) {
   // Expression ::
   //   AssignmentExpression
   //   Expression ',' AssignmentExpression
 
   ExpressionClassifier binding_classifier;
   ExpressionT result =
       this->ParseAssignmentExpression(accept_IN, &binding_classifier, CHECK_OK);
@@ skipping 25 matching lines @@
     if (is_rest) right = factory()->NewSpread(right, pos);
     is_simple_parameter_list =
         is_simple_parameter_list && this->IsIdentifier(right);
     classifier->Accumulate(binding_classifier,
                            ExpressionClassifier::AllProductions);
     result = factory()->NewBinaryOperation(Token::COMMA, result, right, pos);
   }
   if (!is_simple_parameter_list || seen_rest) {
     classifier->RecordNonSimpleParameter();
   }
+
   return result;
 }
 
 
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParseArrayLiteral(
     ExpressionClassifier* classifier, bool* ok) {
   // ArrayLiteral ::
   //   '[' Expression? (',' Expression?)* ']'
 
@@ skipping 16 matching lines @@
     } else if (peek() == Token::ELLIPSIS) {
       int start_pos = peek_position();
       Consume(Token::ELLIPSIS);
       ExpressionT argument =
           this->ParseAssignmentExpression(true, classifier, CHECK_OK);
       elem = factory()->NewSpread(argument, start_pos);
       seen_spread = true;
       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);
     }
   }
   Expect(Token::RBRACK, CHECK_OK);
 
   // Update the scope information before the pre-parsing bailout.
   int literal_index = function_state_->NextMaterializedLiteralIndex();
 
   return factory()->NewArrayLiteral(values, first_spread_index, literal_index,
                                     is_strong(language_mode()), pos);
@@ skipping 89 matching lines @@
     DCHECK(!is_static);
 
     if (peek() == Token::COLON) {
       // PropertyDefinition
       //    PropertyName ':' AssignmentExpression
       if (!*is_computed_name) {
         checker->CheckProperty(name_token, kValueProperty, false, false,
                                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);
     }
 
     if (Token::IsIdentifier(name_token, language_mode(),
                             this->is_generator()) &&
         (peek() == Token::COMMA || peek() == Token::RBRACE ||
          peek() == Token::ASSIGN)) {
       // PropertyDefinition
       //    IdentifierReference
       //    CoverInitializedName
       //
       // CoverInitializedName
       //    IdentifierReference Initializer?
       if (classifier->duplicate_finder() != nullptr &&
           scanner()->FindSymbol(classifier->duplicate_finder(), 1) != 0) {
         classifier->RecordDuplicateFormalParameterError(scanner()->location());
       }
       if (name_token == Token::LET) {
         classifier->RecordLetPatternError(
             scanner()->location(), MessageTemplate::kLetInLexicalBinding);
       }
 
       ExpressionT lhs = this->ExpressionFromIdentifier(
           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(
             true, &rhs_classifier, CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
         classifier->Accumulate(rhs_classifier,
                                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;
       }
 
       return factory()->NewObjectLiteralProperty(
           name_expression, value, ObjectLiteralProperty::COMPUTED, false,
           false);
     }
   }
 
+  // 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 '}'
     //    '*' PropertyName '(' StrictFormalParameters ')' '{' FunctionBody '}'
     if (!*is_computed_name) {
       checker->CheckProperty(name_token, kMethodProperty, is_static,
                              is_generator,
                              CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
     }
@@ skipping 203 matching lines @@
     // the parser and preparser
     Traits::MaterializeUnspreadArgumentsLiterals(unspread_sequences_count);
   }
 
   return result;
 }
 
 // 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 ::
   //   ConditionalExpression
   //   ArrowFunction
   //   YieldExpression
   //   LeftHandSideExpression AssignmentOperator AssignmentExpression
-
+  bool is_rhs = flags & kIsRightHandSide;
+  bool is_pattern_element = flags & kIsPatternElement;
   int lhs_beg_pos = peek_position();
 
   if (peek() == Token::YIELD && is_generator()) {
     return this->ParseYieldExpression(classifier, ok);
   }
 
   if (fni_ != NULL) fni_->Enter();
   ParserBase<Traits>::Checkpoint checkpoint(this);
   ExpressionClassifier arrow_formals_classifier(classifier->duplicate_finder());
   bool parenthesized_formals = peek() == Token::LPAREN;
@@ skipping 25 matching lines @@
 
     checkpoint.Restore(&parameters.materialized_literals_count);
 
     scope->set_start_position(lhs_beg_pos);
     if (duplicate_loc.IsValid()) {
       arrow_formals_classifier.RecordDuplicateFormalParameterError(
           duplicate_loc);
     }
     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() && 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;
   }
 
   if (!(allow_harmony_destructuring() || allow_harmony_default_parameters())) {
     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);
+    expression = factory()->NewAssignmentPattern(expression, lhs_beg_pos);
+  } else if (!binding_pattern) {
+    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.
   if (op != Token::ASSIGN) {
     classifier->RecordBindingPatternError(scanner()->location(),
                                           MessageTemplate::kUnexpectedToken,
                                           Token::String(op));
   }
   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;
+  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
   // assignment to a property of 'this'. We should probably only add
   // properties if we haven't seen them before. Otherwise we'll
   // probably overestimate the number of properties.
   if (op == Token::ASSIGN && this->IsThisProperty(expression)) {
     function_state_->AddProperty();
   }
 
   this->CheckAssigningFunctionLiteralToProperty(expression, right);
 
   if (fni_ != NULL) {
     // Check if the right hand side is a call to avoid inferring a
     // name if we're dealing with "a = function(){...}();"-like
     // expression.
     if ((op == Token::INIT_VAR
          || op == Token::INIT_CONST_LEGACY
          || op == Token::ASSIGN)
         && (!right->IsCall() && !right->IsCallNew())) {
       fni_->Infer();
     } else {
       fni_->RemoveLastFunction();
     }
     fni_->Leave();
   }
 
-  return factory()->NewAssignment(op, expression, right, pos);
+  ExpressionT result = factory()->NewAssignment(op, expression, right, pos);
+
+  if (expression->IsAssignmentPattern()) {
+    Traits::ShouldRewriteDestructuringAssignment(result);
+  }
+
+  return result;
 }
 
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseYieldExpression(ExpressionClassifier* classifier,
                                          bool* ok) {
   // YieldExpression ::
   //   'yield' ([no line terminator] '*'? AssignmentExpression)?
   int pos = peek_position();
   BindingPatternUnexpectedToken(classifier);
@@ skipping 936 matching lines @@
                                    allow_duplicate_parameters, CHECK_OK);
 
     // Validate strict mode.
     if (is_strict(language_mode())) {
       CheckStrictOctalLiteral(formal_parameters.scope->start_position(),
                               scanner()->location().end_pos, CHECK_OK);
     }
     if (is_strict(language_mode()) || allow_harmony_sloppy()) {
       this->CheckConflictingVarDeclarations(formal_parameters.scope, CHECK_OK);
     }
+
+    Traits::RewriteDestructuringAssignments();
   }
 
   FunctionLiteralT function_literal = factory()->NewFunctionLiteral(
       this->EmptyIdentifierString(), ast_value_factory(),
       formal_parameters.scope, body, materialized_literal_count,
       expected_property_count, num_parameters,
       FunctionLiteral::kNoDuplicateParameters,
       FunctionLiteral::ANONYMOUS_EXPRESSION, FunctionLiteral::kIsFunction,
       FunctionLiteral::kShouldLazyCompile, FunctionKind::kArrowFunction,
       formal_parameters.scope->start_position());
@@ skipping 128 matching lines @@
       return this->EmptyExpression();
     }
     if (is_strong(language_mode()) &&
         this->IsUndefined(this->AsIdentifier(expression))) {
       this->ReportMessageAt(location, MessageTemplate::kStrongUndefined,
                             kSyntaxError);
       *ok = false;
       return this->EmptyExpression();
     }
   }
-  if (expression->IsValidReferenceExpression()) {
+  if (expression->IsValidReferenceExpression() ||
+      expression->IsAssignmentPattern()) {
     return expression;
   } else if (expression->IsCall()) {
     // If it is a call, make it a runtime error for legacy web compatibility.
     // Rewrite `expr' to `expr[throw ReferenceError]'.
     int pos = location.beg_pos;
     ExpressionT error = this->NewThrowReferenceError(message, pos);
     return factory()->NewProperty(expression, error, pos);
   } else {
     this->ReportMessageAt(location, message, type);
     *ok = false;
     return this->EmptyExpression();
   }
 }
 
 
+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()) {
+      classifier->RecordAssignmentPatternError(location, message);
+    }
+  }
+}
+
+
 #undef CHECK_OK
 #undef CHECK_OK_CUSTOM
 
 
 template <typename Traits>
 void ParserBase<Traits>::ObjectLiteralChecker::CheckProperty(
     Token::Value property, PropertyKind type, bool is_static, bool is_generator,
     bool* ok) {
   DCHECK(!is_static);
   DCHECK(!is_generator || type == kMethodProperty);
@@ skipping 41 matching lines @@
       return;
     }
     has_seen_constructor_ = true;
     return;
   }
 }
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PREPARSER_H