xref: /external/v8/src/parsing/parser.cc

// 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.

#include "src/parsing/parser.h"

#include "src/api.h"
#include "src/ast/ast.h"
#include "src/ast/ast-expression-visitor.h"
#include "src/ast/ast-literal-reindexer.h"
#include "src/ast/scopeinfo.h"
#include "src/bailout-reason.h"
#include "src/base/platform/platform.h"
#include "src/bootstrapper.h"
#include "src/char-predicates-inl.h"
#include "src/codegen.h"
#include "src/compiler.h"
#include "src/messages.h"
#include "src/parsing/parameter-initializer-rewriter.h"
#include "src/parsing/parser-base.h"
#include "src/parsing/rewriter.h"
#include "src/parsing/scanner-character-streams.h"
#include "src/runtime/runtime.h"
#include "src/string-stream.h"

namespace v8 {
namespace internal {

ScriptData::ScriptData(const byte* data, int length)
    : owns_data_(false), rejected_(false), data_(data), length_(length) {
  if (!IsAligned(reinterpret_cast<intptr_t>(data), kPointerAlignment)) {
    byte* copy = NewArray<byte>(length);
    DCHECK(IsAligned(reinterpret_cast<intptr_t>(copy), kPointerAlignment));
    CopyBytes(copy, data, length);
    data_ = copy;
    AcquireDataOwnership();
  }
}


ParseInfo::ParseInfo(Zone* zone)
    : zone_(zone),
      flags_(0),
      source_stream_(nullptr),
      source_stream_encoding_(ScriptCompiler::StreamedSource::ONE_BYTE),
      extension_(nullptr),
      compile_options_(ScriptCompiler::kNoCompileOptions),
      script_scope_(nullptr),
      unicode_cache_(nullptr),
      stack_limit_(0),
      hash_seed_(0),
      cached_data_(nullptr),
      ast_value_factory_(nullptr),
      literal_(nullptr),
      scope_(nullptr) {}


ParseInfo::ParseInfo(Zone* zone, Handle<JSFunction> function)
    : ParseInfo(zone, Handle<SharedFunctionInfo>(function->shared())) {
  set_closure(function);
  set_context(Handle<Context>(function->context()));
}


ParseInfo::ParseInfo(Zone* zone, Handle<SharedFunctionInfo> shared)
    : ParseInfo(zone) {
  isolate_ = shared->GetIsolate();

  set_lazy();
  set_hash_seed(isolate_->heap()->HashSeed());
  set_stack_limit(isolate_->stack_guard()->real_climit());
  set_unicode_cache(isolate_->unicode_cache());
  set_language_mode(shared->language_mode());
  set_shared_info(shared);

  Handle<Script> script(Script::cast(shared->script()));
  set_script(script);
  if (!script.is_null() && script->type() == Script::TYPE_NATIVE) {
    set_native();
  }
}


ParseInfo::ParseInfo(Zone* zone, Handle<Script> script) : ParseInfo(zone) {
  isolate_ = script->GetIsolate();

  set_hash_seed(isolate_->heap()->HashSeed());
  set_stack_limit(isolate_->stack_guard()->real_climit());
  set_unicode_cache(isolate_->unicode_cache());
  set_script(script);

  if (script->type() == Script::TYPE_NATIVE) {
    set_native();
  }
}


FunctionEntry ParseData::GetFunctionEntry(int start) {
  // The current pre-data entry must be a FunctionEntry with the given
  // start position.
  if ((function_index_ + FunctionEntry::kSize <= Length()) &&
      (static_cast<int>(Data()[function_index_]) == start)) {
    int index = function_index_;
    function_index_ += FunctionEntry::kSize;
    Vector<unsigned> subvector(&(Data()[index]), FunctionEntry::kSize);
    return FunctionEntry(subvector);
  }
  return FunctionEntry();
}


int ParseData::FunctionCount() {
  int functions_size = FunctionsSize();
  if (functions_size < 0) return 0;
  if (functions_size % FunctionEntry::kSize != 0) return 0;
  return functions_size / FunctionEntry::kSize;
}


bool ParseData::IsSane() {
  if (!IsAligned(script_data_->length(), sizeof(unsigned))) return false;
  // Check that the header data is valid and doesn't specify
  // point to positions outside the store.
  int data_length = Length();
  if (data_length < PreparseDataConstants::kHeaderSize) return false;
  if (Magic() != PreparseDataConstants::kMagicNumber) return false;
  if (Version() != PreparseDataConstants::kCurrentVersion) return false;
  if (HasError()) return false;
  // Check that the space allocated for function entries is sane.
  int functions_size = FunctionsSize();
  if (functions_size < 0) return false;
  if (functions_size % FunctionEntry::kSize != 0) return false;
  // Check that the total size has room for header and function entries.
  int minimum_size =
      PreparseDataConstants::kHeaderSize + functions_size;
  if (data_length < minimum_size) return false;
  return true;
}


void ParseData::Initialize() {
  // Prepares state for use.
  int data_length = Length();
  if (data_length >= PreparseDataConstants::kHeaderSize) {
    function_index_ = PreparseDataConstants::kHeaderSize;
  }
}


bool ParseData::HasError() {
  return Data()[PreparseDataConstants::kHasErrorOffset];
}


unsigned ParseData::Magic() {
  return Data()[PreparseDataConstants::kMagicOffset];
}


unsigned ParseData::Version() {
  return Data()[PreparseDataConstants::kVersionOffset];
}


int ParseData::FunctionsSize() {
  return static_cast<int>(Data()[PreparseDataConstants::kFunctionsSizeOffset]);
}


void Parser::SetCachedData(ParseInfo* info) {
  if (compile_options_ == ScriptCompiler::kNoCompileOptions) {
    cached_parse_data_ = NULL;
  } else {
    DCHECK(info->cached_data() != NULL);
    if (compile_options_ == ScriptCompiler::kConsumeParserCache) {
      cached_parse_data_ = ParseData::FromCachedData(*info->cached_data());
    }
  }
}


FunctionLiteral* Parser::DefaultConstructor(bool call_super, Scope* scope,
                                            int pos, int end_pos,
                                            LanguageMode language_mode) {
  int materialized_literal_count = -1;
  int expected_property_count = -1;
  int parameter_count = 0;
  const AstRawString* name = ast_value_factory()->empty_string();


  FunctionKind kind = call_super ? FunctionKind::kDefaultSubclassConstructor
                                 : FunctionKind::kDefaultBaseConstructor;
  Scope* function_scope = NewScope(scope, FUNCTION_SCOPE, kind);
  SetLanguageMode(function_scope,
                  static_cast<LanguageMode>(language_mode | STRICT));
  // Set start and end position to the same value
  function_scope->set_start_position(pos);
  function_scope->set_end_position(pos);
  ZoneList<Statement*>* body = NULL;

  {
    AstNodeFactory function_factory(ast_value_factory());
    FunctionState function_state(&function_state_, &scope_, function_scope,
                                 kind, &function_factory);

    body = new (zone()) ZoneList<Statement*>(call_super ? 2 : 1, zone());
    if (call_super) {
      // $super_constructor = %_GetSuperConstructor(<this-function>)
      // %reflect_construct($super_constructor, arguments, new.target)
      ZoneList<Expression*>* args =
          new (zone()) ZoneList<Expression*>(2, zone());
      VariableProxy* this_function_proxy = scope_->NewUnresolved(
          factory(), ast_value_factory()->this_function_string(),
          Variable::NORMAL, pos);
      ZoneList<Expression*>* tmp =
          new (zone()) ZoneList<Expression*>(1, zone());
      tmp->Add(this_function_proxy, zone());
      Expression* super_constructor = factory()->NewCallRuntime(
          Runtime::kInlineGetSuperConstructor, tmp, pos);
      args->Add(super_constructor, zone());
      VariableProxy* arguments_proxy = scope_->NewUnresolved(
          factory(), ast_value_factory()->arguments_string(), Variable::NORMAL,
          pos);
      args->Add(arguments_proxy, zone());
      VariableProxy* new_target_proxy = scope_->NewUnresolved(
          factory(), ast_value_factory()->new_target_string(), Variable::NORMAL,
          pos);
      args->Add(new_target_proxy, zone());
      CallRuntime* call = factory()->NewCallRuntime(
          Context::REFLECT_CONSTRUCT_INDEX, args, pos);
      body->Add(factory()->NewReturnStatement(call, pos), zone());
    }

    materialized_literal_count = function_state.materialized_literal_count();
    expected_property_count = function_state.expected_property_count();
  }

  FunctionLiteral* function_literal = factory()->NewFunctionLiteral(
      name, function_scope, body, materialized_literal_count,
      expected_property_count, parameter_count,
      FunctionLiteral::kNoDuplicateParameters,
      FunctionLiteral::kAnonymousExpression,
      FunctionLiteral::kShouldLazyCompile, kind, pos);

  return function_literal;
}


// ----------------------------------------------------------------------------
// Target is a support class to facilitate manipulation of the
// Parser's target_stack_ (the stack of potential 'break' and
// 'continue' statement targets). Upon construction, a new target is
// added; it is removed upon destruction.

class Target BASE_EMBEDDED {
 public:
  Target(Target** variable, BreakableStatement* statement)
      : variable_(variable), statement_(statement), previous_(*variable) {
    *variable = this;
  }

  ~Target() {
    *variable_ = previous_;
  }

  Target* previous() { return previous_; }
  BreakableStatement* statement() { return statement_; }

 private:
  Target** variable_;
  BreakableStatement* statement_;
  Target* previous_;
};


class TargetScope BASE_EMBEDDED {
 public:
  explicit TargetScope(Target** variable)
      : variable_(variable), previous_(*variable) {
    *variable = NULL;
  }

  ~TargetScope() {
    *variable_ = previous_;
  }

 private:
  Target** variable_;
  Target* previous_;
};


// ----------------------------------------------------------------------------
// The CHECK_OK macro is a convenient macro to enforce error
// handling for functions that may fail (by returning !*ok).
//
// CAUTION: This macro appends extra statements after a call,
// thus it must never be used where only a single statement
// is correct (e.g. an if statement branch w/o braces)!

#define CHECK_OK  ok);   \
  if (!*ok) return NULL; \
  ((void)0
#define DUMMY )  // to make indentation work
#undef DUMMY

#define CHECK_FAILED  /**/);   \
  if (failed_) return NULL; \
  ((void)0
#define DUMMY )  // to make indentation work
#undef DUMMY

// ----------------------------------------------------------------------------
// Implementation of Parser

bool ParserTraits::IsEval(const AstRawString* identifier) const {
  return identifier == parser_->ast_value_factory()->eval_string();
}


bool ParserTraits::IsArguments(const AstRawString* identifier) const {
  return identifier == parser_->ast_value_factory()->arguments_string();
}


bool ParserTraits::IsEvalOrArguments(const AstRawString* identifier) const {
  return IsEval(identifier) || IsArguments(identifier);
}

bool ParserTraits::IsUndefined(const AstRawString* identifier) const {
  return identifier == parser_->ast_value_factory()->undefined_string();
}

bool ParserTraits::IsPrototype(const AstRawString* identifier) const {
  return identifier == parser_->ast_value_factory()->prototype_string();
}


bool ParserTraits::IsConstructor(const AstRawString* identifier) const {
  return identifier == parser_->ast_value_factory()->constructor_string();
}


bool ParserTraits::IsThisProperty(Expression* expression) {
  DCHECK(expression != NULL);
  Property* property = expression->AsProperty();
  return property != NULL && property->obj()->IsVariableProxy() &&
         property->obj()->AsVariableProxy()->is_this();
}


bool ParserTraits::IsIdentifier(Expression* expression) {
  VariableProxy* operand = expression->AsVariableProxy();
  return operand != NULL && !operand->is_this();
}


void ParserTraits::PushPropertyName(FuncNameInferrer* fni,
                                    Expression* expression) {
  if (expression->IsPropertyName()) {
    fni->PushLiteralName(expression->AsLiteral()->AsRawPropertyName());
  } else {
    fni->PushLiteralName(
        parser_->ast_value_factory()->anonymous_function_string());
  }
}


void ParserTraits::CheckAssigningFunctionLiteralToProperty(Expression* left,
                                                           Expression* right) {
  DCHECK(left != NULL);
  if (left->IsProperty() && right->IsFunctionLiteral()) {
    right->AsFunctionLiteral()->set_pretenure();
  }
}


Expression* ParserTraits::MarkExpressionAsAssigned(Expression* expression) {
  VariableProxy* proxy =
      expression != NULL ? expression->AsVariableProxy() : NULL;
  if (proxy != NULL) proxy->set_is_assigned();
  return expression;
}


bool ParserTraits::ShortcutNumericLiteralBinaryExpression(
    Expression** x, Expression* y, Token::Value op, int pos,
    AstNodeFactory* factory) {
  if ((*x)->AsLiteral() && (*x)->AsLiteral()->raw_value()->IsNumber() &&
      y->AsLiteral() && y->AsLiteral()->raw_value()->IsNumber()) {
    double x_val = (*x)->AsLiteral()->raw_value()->AsNumber();
    double y_val = y->AsLiteral()->raw_value()->AsNumber();
    bool x_has_dot = (*x)->AsLiteral()->raw_value()->ContainsDot();
    bool y_has_dot = y->AsLiteral()->raw_value()->ContainsDot();
    bool has_dot = x_has_dot || y_has_dot;
    switch (op) {
      case Token::ADD:
        *x = factory->NewNumberLiteral(x_val + y_val, pos, has_dot);
        return true;
      case Token::SUB:
        *x = factory->NewNumberLiteral(x_val - y_val, pos, has_dot);
        return true;
      case Token::MUL:
        *x = factory->NewNumberLiteral(x_val * y_val, pos, has_dot);
        return true;
      case Token::DIV:
        *x = factory->NewNumberLiteral(x_val / y_val, pos, has_dot);
        return true;
      case Token::BIT_OR: {
        int value = DoubleToInt32(x_val) | DoubleToInt32(y_val);
        *x = factory->NewNumberLiteral(value, pos, has_dot);
        return true;
      }
      case Token::BIT_AND: {
        int value = DoubleToInt32(x_val) & DoubleToInt32(y_val);
        *x = factory->NewNumberLiteral(value, pos, has_dot);
        return true;
      }
      case Token::BIT_XOR: {
        int value = DoubleToInt32(x_val) ^ DoubleToInt32(y_val);
        *x = factory->NewNumberLiteral(value, pos, has_dot);
        return true;
      }
      case Token::SHL: {
        int value = DoubleToInt32(x_val) << (DoubleToInt32(y_val) & 0x1f);
        *x = factory->NewNumberLiteral(value, pos, has_dot);
        return true;
      }
      case Token::SHR: {
        uint32_t shift = DoubleToInt32(y_val) & 0x1f;
        uint32_t value = DoubleToUint32(x_val) >> shift;
        *x = factory->NewNumberLiteral(value, pos, has_dot);
        return true;
      }
      case Token::SAR: {
        uint32_t shift = DoubleToInt32(y_val) & 0x1f;
        int value = ArithmeticShiftRight(DoubleToInt32(x_val), shift);
        *x = factory->NewNumberLiteral(value, pos, has_dot);
        return true;
      }
      default:
        break;
    }
  }
  return false;
}


Expression* ParserTraits::BuildUnaryExpression(Expression* expression,
                                               Token::Value op, int pos,
                                               AstNodeFactory* factory) {
  DCHECK(expression != NULL);
  if (expression->IsLiteral()) {
    const AstValue* literal = expression->AsLiteral()->raw_value();
    if (op == Token::NOT) {
      // Convert the literal to a boolean condition and negate it.
      bool condition = literal->BooleanValue();
      return factory->NewBooleanLiteral(!condition, pos);
    } else if (literal->IsNumber()) {
      // Compute some expressions involving only number literals.
      double value = literal->AsNumber();
      bool has_dot = literal->ContainsDot();
      switch (op) {
        case Token::ADD:
          return expression;
        case Token::SUB:
          return factory->NewNumberLiteral(-value, pos, has_dot);
        case Token::BIT_NOT:
          return factory->NewNumberLiteral(~DoubleToInt32(value), pos, has_dot);
        default:
          break;
      }
    }
  }
  // Desugar '+foo' => 'foo*1'
  if (op == Token::ADD) {
    return factory->NewBinaryOperation(
        Token::MUL, expression, factory->NewNumberLiteral(1, pos, true), pos);
  }
  // The same idea for '-foo' => 'foo*(-1)'.
  if (op == Token::SUB) {
    return factory->NewBinaryOperation(
        Token::MUL, expression, factory->NewNumberLiteral(-1, pos), pos);
  }
  // ...and one more time for '~foo' => 'foo^(~0)'.
  if (op == Token::BIT_NOT) {
    return factory->NewBinaryOperation(
        Token::BIT_XOR, expression, factory->NewNumberLiteral(~0, pos), pos);
  }
  return factory->NewUnaryOperation(op, expression, pos);
}


Expression* ParserTraits::NewThrowReferenceError(
    MessageTemplate::Template message, int pos) {
  return NewThrowError(Runtime::kNewReferenceError, message,
                       parser_->ast_value_factory()->empty_string(), pos);
}


Expression* ParserTraits::NewThrowSyntaxError(MessageTemplate::Template message,
                                              const AstRawString* arg,
                                              int pos) {
  return NewThrowError(Runtime::kNewSyntaxError, message, arg, pos);
}


Expression* ParserTraits::NewThrowTypeError(MessageTemplate::Template message,
                                            const AstRawString* arg, int pos) {
  return NewThrowError(Runtime::kNewTypeError, message, arg, pos);
}


Expression* ParserTraits::NewThrowError(Runtime::FunctionId id,
                                        MessageTemplate::Template message,
                                        const AstRawString* arg, int pos) {
  Zone* zone = parser_->zone();
  ZoneList<Expression*>* args = new (zone) ZoneList<Expression*>(2, zone);
  args->Add(parser_->factory()->NewSmiLiteral(message, pos), zone);
  args->Add(parser_->factory()->NewStringLiteral(arg, pos), zone);
  CallRuntime* call_constructor =
      parser_->factory()->NewCallRuntime(id, args, pos);
  return parser_->factory()->NewThrow(call_constructor, pos);
}


void ParserTraits::ReportMessageAt(Scanner::Location source_location,
                                   MessageTemplate::Template message,
                                   const char* arg, ParseErrorType error_type) {
  if (parser_->stack_overflow()) {
    // Suppress the error message (syntax error or such) in the presence of a
    // stack overflow. The isolate allows only one pending exception at at time
    // and we want to report the stack overflow later.
    return;
  }
  parser_->pending_error_handler_.ReportMessageAt(source_location.beg_pos,
                                                  source_location.end_pos,
                                                  message, arg, error_type);
}


void ParserTraits::ReportMessage(MessageTemplate::Template message,
                                 const char* arg, ParseErrorType error_type) {
  Scanner::Location source_location = parser_->scanner()->location();
  ReportMessageAt(source_location, message, arg, error_type);
}


void ParserTraits::ReportMessage(MessageTemplate::Template message,
                                 const AstRawString* arg,
                                 ParseErrorType error_type) {
  Scanner::Location source_location = parser_->scanner()->location();
  ReportMessageAt(source_location, message, arg, error_type);
}


void ParserTraits::ReportMessageAt(Scanner::Location source_location,
                                   MessageTemplate::Template message,
                                   const AstRawString* arg,
                                   ParseErrorType error_type) {
  if (parser_->stack_overflow()) {
    // Suppress the error message (syntax error or such) in the presence of a
    // stack overflow. The isolate allows only one pending exception at at time
    // and we want to report the stack overflow later.
    return;
  }
  parser_->pending_error_handler_.ReportMessageAt(source_location.beg_pos,
                                                  source_location.end_pos,
                                                  message, arg, error_type);
}


const AstRawString* ParserTraits::GetSymbol(Scanner* scanner) {
  const AstRawString* result =
      parser_->scanner()->CurrentSymbol(parser_->ast_value_factory());
  DCHECK(result != NULL);
  return result;
}


const AstRawString* ParserTraits::GetNumberAsSymbol(Scanner* scanner) {
  double double_value = parser_->scanner()->DoubleValue();
  char array[100];
  const char* string =
      DoubleToCString(double_value, Vector<char>(array, arraysize(array)));
  return parser_->ast_value_factory()->GetOneByteString(string);
}


const AstRawString* ParserTraits::GetNextSymbol(Scanner* scanner) {
  return parser_->scanner()->NextSymbol(parser_->ast_value_factory());
}


Expression* ParserTraits::ThisExpression(Scope* scope, AstNodeFactory* factory,
                                         int pos) {
  return scope->NewUnresolved(factory,
                              parser_->ast_value_factory()->this_string(),
                              Variable::THIS, pos, pos + 4);
}


Expression* ParserTraits::SuperPropertyReference(Scope* scope,
                                                 AstNodeFactory* factory,
                                                 int pos) {
  // this_function[home_object_symbol]
  VariableProxy* this_function_proxy = scope->NewUnresolved(
      factory, parser_->ast_value_factory()->this_function_string(),
      Variable::NORMAL, pos);
  Expression* home_object_symbol_literal =
      factory->NewSymbolLiteral("home_object_symbol", RelocInfo::kNoPosition);
  Expression* home_object = factory->NewProperty(
      this_function_proxy, home_object_symbol_literal, pos);
  return factory->NewSuperPropertyReference(
      ThisExpression(scope, factory, pos)->AsVariableProxy(), home_object, pos);
}


Expression* ParserTraits::SuperCallReference(Scope* scope,
                                             AstNodeFactory* factory, int pos) {
  VariableProxy* new_target_proxy = scope->NewUnresolved(
      factory, parser_->ast_value_factory()->new_target_string(),
      Variable::NORMAL, pos);
  VariableProxy* this_function_proxy = scope->NewUnresolved(
      factory, parser_->ast_value_factory()->this_function_string(),
      Variable::NORMAL, pos);
  return factory->NewSuperCallReference(
      ThisExpression(scope, factory, pos)->AsVariableProxy(), new_target_proxy,
      this_function_proxy, pos);
}


Expression* ParserTraits::NewTargetExpression(Scope* scope,
                                              AstNodeFactory* factory,
                                              int pos) {
  static const int kNewTargetStringLength = 10;
  auto proxy = scope->NewUnresolved(
      factory, parser_->ast_value_factory()->new_target_string(),
      Variable::NORMAL, pos, pos + kNewTargetStringLength);
  proxy->set_is_new_target();
  return proxy;
}


Expression* ParserTraits::DefaultConstructor(bool call_super, Scope* scope,
                                             int pos, int end_pos,
                                             LanguageMode mode) {
  return parser_->DefaultConstructor(call_super, scope, pos, end_pos, mode);
}


Literal* ParserTraits::ExpressionFromLiteral(Token::Value token, int pos,
                                             Scanner* scanner,
                                             AstNodeFactory* factory) {
  switch (token) {
    case Token::NULL_LITERAL:
      return factory->NewNullLiteral(pos);
    case Token::TRUE_LITERAL:
      return factory->NewBooleanLiteral(true, pos);
    case Token::FALSE_LITERAL:
      return factory->NewBooleanLiteral(false, pos);
    case Token::SMI: {
      int value = scanner->smi_value();
      return factory->NewSmiLiteral(value, pos);
    }
    case Token::NUMBER: {
      bool has_dot = scanner->ContainsDot();
      double value = scanner->DoubleValue();
      return factory->NewNumberLiteral(value, pos, has_dot);
    }
    default:
      DCHECK(false);
  }
  return NULL;
}


Expression* ParserTraits::ExpressionFromIdentifier(const AstRawString* name,
                                                   int start_position,
                                                   int end_position,
                                                   Scope* scope,
                                                   AstNodeFactory* factory) {
  if (parser_->fni_ != NULL) parser_->fni_->PushVariableName(name);
  return scope->NewUnresolved(factory, name, Variable::NORMAL, start_position,
                              end_position);
}


Expression* ParserTraits::ExpressionFromString(int pos, Scanner* scanner,
                                               AstNodeFactory* factory) {
  const AstRawString* symbol = GetSymbol(scanner);
  if (parser_->fni_ != NULL) parser_->fni_->PushLiteralName(symbol);
  return factory->NewStringLiteral(symbol, pos);
}


Expression* ParserTraits::GetIterator(Expression* iterable,
                                      AstNodeFactory* factory, int pos) {
  Expression* iterator_symbol_literal =
      factory->NewSymbolLiteral("iterator_symbol", RelocInfo::kNoPosition);
  Expression* prop =
      factory->NewProperty(iterable, iterator_symbol_literal, pos);
  Zone* zone = parser_->zone();
  ZoneList<Expression*>* args = new (zone) ZoneList<Expression*>(0, zone);
  return factory->NewCall(prop, args, pos);
}


Literal* ParserTraits::GetLiteralTheHole(int position,
                                         AstNodeFactory* factory) {
  return factory->NewTheHoleLiteral(RelocInfo::kNoPosition);
}


Expression* ParserTraits::ParseV8Intrinsic(bool* ok) {
  return parser_->ParseV8Intrinsic(ok);
}


FunctionLiteral* ParserTraits::ParseFunctionLiteral(
    const AstRawString* name, Scanner::Location function_name_location,
    FunctionNameValidity function_name_validity, FunctionKind kind,
    int function_token_position, FunctionLiteral::FunctionType type,
    FunctionLiteral::ArityRestriction arity_restriction,
    LanguageMode language_mode, bool* ok) {
  return parser_->ParseFunctionLiteral(
      name, function_name_location, function_name_validity, kind,
      function_token_position, type, arity_restriction, language_mode, ok);
}


ClassLiteral* ParserTraits::ParseClassLiteral(
    const AstRawString* name, Scanner::Location class_name_location,
    bool name_is_strict_reserved, int pos, bool* ok) {
  return parser_->ParseClassLiteral(name, class_name_location,
                                    name_is_strict_reserved, pos, ok);
}


Parser::Parser(ParseInfo* info)
    : ParserBase<ParserTraits>(info->zone(), &scanner_, info->stack_limit(),
                               info->extension(), info->ast_value_factory(),
                               NULL, this),
      scanner_(info->unicode_cache()),
      reusable_preparser_(NULL),
      original_scope_(NULL),
      target_stack_(NULL),
      compile_options_(info->compile_options()),
      cached_parse_data_(NULL),
      total_preparse_skipped_(0),
      pre_parse_timer_(NULL),
      parsing_on_main_thread_(true) {
  // Even though we were passed ParseInfo, we should not store it in
  // Parser - this makes sure that Isolate is not accidentally accessed via
  // ParseInfo during background parsing.
  DCHECK(!info->script().is_null() || info->source_stream() != NULL);
  set_allow_lazy(info->allow_lazy_parsing());
  set_allow_natives(FLAG_allow_natives_syntax || info->is_native());
  set_allow_harmony_sloppy(FLAG_harmony_sloppy);
  set_allow_harmony_sloppy_function(FLAG_harmony_sloppy_function);
  set_allow_harmony_sloppy_let(FLAG_harmony_sloppy_let);
  set_allow_harmony_default_parameters(FLAG_harmony_default_parameters);
  set_allow_harmony_destructuring_bind(FLAG_harmony_destructuring_bind);
  set_allow_harmony_destructuring_assignment(
      FLAG_harmony_destructuring_assignment);
  set_allow_strong_mode(FLAG_strong_mode);
  set_allow_legacy_const(FLAG_legacy_const);
  set_allow_harmony_do_expressions(FLAG_harmony_do_expressions);
  set_allow_harmony_function_name(FLAG_harmony_function_name);
  for (int feature = 0; feature < v8::Isolate::kUseCounterFeatureCount;
       ++feature) {
    use_counts_[feature] = 0;
  }
  if (info->ast_value_factory() == NULL) {
    // info takes ownership of AstValueFactory.
    info->set_ast_value_factory(new AstValueFactory(zone(), info->hash_seed()));
    info->set_ast_value_factory_owned();
    ast_value_factory_ = info->ast_value_factory();
  }
}


FunctionLiteral* Parser::ParseProgram(Isolate* isolate, ParseInfo* info) {
  // TODO(bmeurer): We temporarily need to pass allow_nesting = true here,
  // see comment for HistogramTimerScope class.

  // It's OK to use the Isolate & counters here, since this function is only
  // called in the main thread.
  DCHECK(parsing_on_main_thread_);

  HistogramTimerScope timer_scope(isolate->counters()->parse(), true);
  Handle<String> source(String::cast(info->script()->source()));
  isolate->counters()->total_parse_size()->Increment(source->length());
  base::ElapsedTimer timer;
  if (FLAG_trace_parse) {
    timer.Start();
  }
  fni_ = new (zone()) FuncNameInferrer(ast_value_factory(), zone());

  // Initialize parser state.
  CompleteParserRecorder recorder;

  if (produce_cached_parse_data()) {
    log_ = &recorder;
  } else if (consume_cached_parse_data()) {
    cached_parse_data_->Initialize();
  }

  source = String::Flatten(source);
  FunctionLiteral* result;

  if (source->IsExternalTwoByteString()) {
    // Notice that the stream is destroyed at the end of the branch block.
    // The last line of the blocks can't be moved outside, even though they're
    // identical calls.
    ExternalTwoByteStringUtf16CharacterStream stream(
        Handle<ExternalTwoByteString>::cast(source), 0, source->length());
    scanner_.Initialize(&stream);
    result = DoParseProgram(info);
  } else {
    GenericStringUtf16CharacterStream stream(source, 0, source->length());
    scanner_.Initialize(&stream);
    result = DoParseProgram(info);
  }
  if (result != NULL) {
    DCHECK_EQ(scanner_.peek_location().beg_pos, source->length());
  }
  HandleSourceURLComments(isolate, info->script());

  if (FLAG_trace_parse && result != NULL) {
    double ms = timer.Elapsed().InMillisecondsF();
    if (info->is_eval()) {
      PrintF("[parsing eval");
    } else if (info->script()->name()->IsString()) {
      String* name = String::cast(info->script()->name());
      base::SmartArrayPointer<char> name_chars = name->ToCString();
      PrintF("[parsing script: %s", name_chars.get());
    } else {
      PrintF("[parsing script");
    }
    PrintF(" - took %0.3f ms]\n", ms);
  }
  if (produce_cached_parse_data()) {
    if (result != NULL) *info->cached_data() = recorder.GetScriptData();
    log_ = NULL;
  }
  return result;
}


FunctionLiteral* Parser::DoParseProgram(ParseInfo* info) {
  // Note that this function can be called from the main thread or from a
  // background thread. We should not access anything Isolate / heap dependent
  // via ParseInfo, and also not pass it forward.
  DCHECK(scope_ == NULL);
  DCHECK(target_stack_ == NULL);

  Mode parsing_mode = FLAG_lazy && allow_lazy() ? PARSE_LAZILY : PARSE_EAGERLY;
  if (allow_natives() || extension_ != NULL) parsing_mode = PARSE_EAGERLY;

  FunctionLiteral* result = NULL;
  {
    // TODO(wingo): Add an outer SCRIPT_SCOPE corresponding to the native
    // context, which will have the "this" binding for script scopes.
    Scope* scope = NewScope(scope_, SCRIPT_SCOPE);
    info->set_script_scope(scope);
    if (!info->context().is_null() && !info->context()->IsNativeContext()) {
      scope = Scope::DeserializeScopeChain(info->isolate(), zone(),
                                           *info->context(), scope);
      // The Scope is backed up by ScopeInfo (which is in the V8 heap); this
      // means the Parser cannot operate independent of the V8 heap. Tell the
      // string table to internalize strings and values right after they're
      // created. This kind of parsing can only be done in the main thread.
      DCHECK(parsing_on_main_thread_);
      ast_value_factory()->Internalize(info->isolate());
    }
    original_scope_ = scope;
    if (info->is_eval()) {
      if (!scope->is_script_scope() || is_strict(info->language_mode())) {
        parsing_mode = PARSE_EAGERLY;
      }
      scope = NewScope(scope, EVAL_SCOPE);
    } else if (info->is_module()) {
      scope = NewScope(scope, MODULE_SCOPE);
    }

    scope->set_start_position(0);

    // Enter 'scope' with the given parsing mode.
    ParsingModeScope parsing_mode_scope(this, parsing_mode);
    AstNodeFactory function_factory(ast_value_factory());
    FunctionState function_state(&function_state_, &scope_, scope,
                                 kNormalFunction, &function_factory);

    // Don't count the mode in the use counters--give the program a chance
    // to enable script/module-wide strict/strong mode below.
    scope_->SetLanguageMode(info->language_mode());
    ZoneList<Statement*>* body = new(zone()) ZoneList<Statement*>(16, zone());
    bool ok = true;
    int beg_pos = scanner()->location().beg_pos;
    if (info->is_module()) {
      ParseModuleItemList(body, &ok);
    } else {
      ParseStatementList(body, Token::EOS, &ok);
    }

    // The parser will peek but not consume EOS.  Our scope logically goes all
    // the way to the EOS, though.
    scope->set_end_position(scanner()->peek_location().beg_pos);

    if (ok && is_strict(language_mode())) {
      CheckStrictOctalLiteral(beg_pos, scanner()->location().end_pos, &ok);
    }
    if (ok && is_sloppy(language_mode()) && allow_harmony_sloppy_function()) {
      // TODO(littledan): Function bindings on the global object that modify
      // pre-existing bindings should be made writable, enumerable and
      // nonconfigurable if possible, whereas this code will leave attributes
      // unchanged if the property already exists.
      InsertSloppyBlockFunctionVarBindings(scope, &ok);
    }
    if (ok && (is_strict(language_mode()) || allow_harmony_sloppy() ||
               allow_harmony_destructuring_bind())) {
      CheckConflictingVarDeclarations(scope_, &ok);
    }

    if (ok && info->parse_restriction() == ONLY_SINGLE_FUNCTION_LITERAL) {
      if (body->length() != 1 ||
          !body->at(0)->IsExpressionStatement() ||
          !body->at(0)->AsExpressionStatement()->
              expression()->IsFunctionLiteral()) {
        ReportMessage(MessageTemplate::kSingleFunctionLiteral);
        ok = false;
      }
    }

    if (ok) {
      ParserTraits::RewriteDestructuringAssignments();
      result = factory()->NewFunctionLiteral(
          ast_value_factory()->empty_string(), scope_, body,
          function_state.materialized_literal_count(),
          function_state.expected_property_count(), 0,
          FunctionLiteral::kNoDuplicateParameters,
          FunctionLiteral::kGlobalOrEval, FunctionLiteral::kShouldLazyCompile,
          FunctionKind::kNormalFunction, 0);
    }
  }

  // Make sure the target stack is empty.
  DCHECK(target_stack_ == NULL);

  return result;
}


FunctionLiteral* Parser::ParseLazy(Isolate* isolate, ParseInfo* info) {
  // It's OK to use the Isolate & counters here, since this function is only
  // called in the main thread.
  DCHECK(parsing_on_main_thread_);
  HistogramTimerScope timer_scope(isolate->counters()->parse_lazy());
  Handle<String> source(String::cast(info->script()->source()));
  isolate->counters()->total_parse_size()->Increment(source->length());
  base::ElapsedTimer timer;
  if (FLAG_trace_parse) {
    timer.Start();
  }
  Handle<SharedFunctionInfo> shared_info = info->shared_info();

  // Initialize parser state.
  source = String::Flatten(source);
  FunctionLiteral* result;
  if (source->IsExternalTwoByteString()) {
    ExternalTwoByteStringUtf16CharacterStream stream(
        Handle<ExternalTwoByteString>::cast(source),
        shared_info->start_position(),
        shared_info->end_position());
    result = ParseLazy(isolate, info, &stream);
  } else {
    GenericStringUtf16CharacterStream stream(source,
                                             shared_info->start_position(),
                                             shared_info->end_position());
    result = ParseLazy(isolate, info, &stream);
  }

  if (FLAG_trace_parse && result != NULL) {
    double ms = timer.Elapsed().InMillisecondsF();
    base::SmartArrayPointer<char> name_chars =
        result->debug_name()->ToCString();
    PrintF("[parsing function: %s - took %0.3f ms]\n", name_chars.get(), ms);
  }
  return result;
}


FunctionLiteral* Parser::ParseLazy(Isolate* isolate, ParseInfo* info,
                                   Utf16CharacterStream* source) {
  Handle<SharedFunctionInfo> shared_info = info->shared_info();
  scanner_.Initialize(source);
  DCHECK(scope_ == NULL);
  DCHECK(target_stack_ == NULL);

  Handle<String> name(String::cast(shared_info->name()));
  DCHECK(ast_value_factory());
  fni_ = new (zone()) FuncNameInferrer(ast_value_factory(), zone());
  const AstRawString* raw_name = ast_value_factory()->GetString(name);
  fni_->PushEnclosingName(raw_name);

  ParsingModeScope parsing_mode(this, PARSE_EAGERLY);

  // Place holder for the result.
  FunctionLiteral* result = NULL;

  {
    // Parse the function literal.
    Scope* scope = NewScope(scope_, SCRIPT_SCOPE);
    info->set_script_scope(scope);
    if (!info->closure().is_null()) {
      // Ok to use Isolate here, since lazy function parsing is only done in the
      // main thread.
      DCHECK(parsing_on_main_thread_);
      scope = Scope::DeserializeScopeChain(isolate, zone(),
                                           info->closure()->context(), scope);
    }
    original_scope_ = scope;
    AstNodeFactory function_factory(ast_value_factory());
    FunctionState function_state(&function_state_, &scope_, scope,
                                 shared_info->kind(), &function_factory);
    DCHECK(is_sloppy(scope->language_mode()) ||
           is_strict(info->language_mode()));
    DCHECK(info->language_mode() == shared_info->language_mode());
    FunctionLiteral::FunctionType function_type =
        shared_info->is_expression()
            ? (shared_info->is_anonymous()
                   ? FunctionLiteral::kAnonymousExpression
                   : FunctionLiteral::kNamedExpression)
            : FunctionLiteral::kDeclaration;
    bool ok = true;

    if (shared_info->is_arrow()) {
      // TODO(adamk): We should construct this scope from the ScopeInfo.
      Scope* scope =
          NewScope(scope_, FUNCTION_SCOPE, FunctionKind::kArrowFunction);

      // These two bits only need to be explicitly set because we're
      // not passing the ScopeInfo to the Scope constructor.
      // TODO(adamk): Remove these calls once the above NewScope call
      // passes the ScopeInfo.
      if (shared_info->scope_info()->CallsEval()) {
        scope->RecordEvalCall();
      }
      SetLanguageMode(scope, shared_info->language_mode());

      scope->set_start_position(shared_info->start_position());
      ExpressionClassifier formals_classifier;
      ParserFormalParameters formals(scope);
      Checkpoint checkpoint(this);
      {
        // Parsing patterns as variable reference expression creates
        // NewUnresolved references in current scope. Entrer arrow function
        // scope for formal parameter parsing.
        BlockState block_state(&scope_, scope);
        if (Check(Token::LPAREN)) {
          // '(' StrictFormalParameters ')'
          ParseFormalParameterList(&formals, &formals_classifier, &ok);
          if (ok) ok = Check(Token::RPAREN);
        } else {
          // BindingIdentifier
          ParseFormalParameter(&formals, &formals_classifier, &ok);
          if (ok) {
            DeclareFormalParameter(formals.scope, formals.at(0),
                                   &formals_classifier);
          }
        }
      }

      if (ok) {
        checkpoint.Restore(&formals.materialized_literals_count);
        // Pass `accept_IN=true` to ParseArrowFunctionLiteral --- This should
        // not be observable, or else the preparser would have failed.
        Expression* expression =
            ParseArrowFunctionLiteral(true, formals, formals_classifier, &ok);
        if (ok) {
          // Scanning must end at the same position that was recorded
          // previously. If not, parsing has been interrupted due to a stack
          // overflow, at which point the partially parsed arrow function
          // concise body happens to be a valid expression. This is a problem
          // only for arrow functions with single expression bodies, since there
          // is no end token such as "}" for normal functions.
          if (scanner()->location().end_pos == shared_info->end_position()) {
            // The pre-parser saw an arrow function here, so the full parser
            // must produce a FunctionLiteral.
            DCHECK(expression->IsFunctionLiteral());
            result = expression->AsFunctionLiteral();
          } else {
            ok = false;
          }
        }
      }
    } else if (shared_info->is_default_constructor()) {
      result = DefaultConstructor(IsSubclassConstructor(shared_info->kind()),
                                  scope, shared_info->start_position(),
                                  shared_info->end_position(),
                                  shared_info->language_mode());
    } else {
      result = ParseFunctionLiteral(
          raw_name, Scanner::Location::invalid(), kSkipFunctionNameCheck,
          shared_info->kind(), RelocInfo::kNoPosition, function_type,
          FunctionLiteral::kNormalArity, shared_info->language_mode(), &ok);
    }
    // Make sure the results agree.
    DCHECK(ok == (result != NULL));
  }

  // Make sure the target stack is empty.
  DCHECK(target_stack_ == NULL);

  if (result != NULL) {
    Handle<String> inferred_name(shared_info->inferred_name());
    result->set_inferred_name(inferred_name);
  }
  return result;
}


void* Parser::ParseStatementList(ZoneList<Statement*>* body, int end_token,
                                 bool* ok) {
  // StatementList ::
  //   (StatementListItem)* <end_token>

  // Allocate a target stack to use for this set of source
  // elements. This way, all scripts and functions get their own
  // target stack thus avoiding illegal breaks and continues across
  // functions.
  TargetScope scope(&this->target_stack_);

  DCHECK(body != NULL);
  bool directive_prologue = true;     // Parsing directive prologue.

  while (peek() != end_token) {
    if (directive_prologue && peek() != Token::STRING) {
      directive_prologue = false;
    }

    Scanner::Location token_loc = scanner()->peek_location();
    Scanner::Location old_this_loc = function_state_->this_location();
    Scanner::Location old_super_loc = function_state_->super_location();
    Statement* stat = ParseStatementListItem(CHECK_OK);

    if (is_strong(language_mode()) && scope_->is_function_scope() &&
        IsClassConstructor(function_state_->kind())) {
      Scanner::Location this_loc = function_state_->this_location();
      Scanner::Location super_loc = function_state_->super_location();
      if (this_loc.beg_pos != old_this_loc.beg_pos &&
          this_loc.beg_pos != token_loc.beg_pos) {
        ReportMessageAt(this_loc, MessageTemplate::kStrongConstructorThis);
        *ok = false;
        return nullptr;
      }
      if (super_loc.beg_pos != old_super_loc.beg_pos &&
          super_loc.beg_pos != token_loc.beg_pos) {
        ReportMessageAt(super_loc, MessageTemplate::kStrongConstructorSuper);
        *ok = false;
        return nullptr;
      }
    }

    if (stat == NULL || stat->IsEmpty()) {
      directive_prologue = false;   // End of directive prologue.
      continue;
    }

    if (directive_prologue) {
      // A shot at a directive.
      ExpressionStatement* e_stat;
      Literal* literal;
      // Still processing directive prologue?
      if ((e_stat = stat->AsExpressionStatement()) != NULL &&
          (literal = e_stat->expression()->AsLiteral()) != NULL &&
          literal->raw_value()->IsString()) {
        // Check "use strict" directive (ES5 14.1), "use asm" directive, and
        // "use strong" directive (experimental).
        bool use_strict_found =
            literal->raw_value()->AsString() ==
                ast_value_factory()->use_strict_string() &&
            token_loc.end_pos - token_loc.beg_pos ==
                ast_value_factory()->use_strict_string()->length() + 2;
        bool use_strong_found =
            allow_strong_mode() &&
            literal->raw_value()->AsString() ==
                ast_value_factory()->use_strong_string() &&
            token_loc.end_pos - token_loc.beg_pos ==
                ast_value_factory()->use_strong_string()->length() + 2;
        if (use_strict_found || use_strong_found) {
          // Strong mode implies strict mode. If there are several "use strict"
          // / "use strong" directives, do the strict mode changes only once.
          if (is_sloppy(scope_->language_mode())) {
            RaiseLanguageMode(STRICT);
          }

          if (use_strong_found) {
            RaiseLanguageMode(STRONG);
            if (IsClassConstructor(function_state_->kind())) {
              // "use strong" cannot occur in a class constructor body, to avoid
              // unintuitive strong class object semantics.
              ParserTraits::ReportMessageAt(
                  token_loc, MessageTemplate::kStrongConstructorDirective);
              *ok = false;
              return nullptr;
            }
          }
          if (!scope_->HasSimpleParameters()) {
            // TC39 deemed "use strict" directives to be an error when occurring
            // in the body of a function with non-simple parameter list, on
            // 29/7/2015. https://goo.gl/ueA7Ln
            //
            // In V8, this also applies to "use strong " directives.
            const AstRawString* string = literal->raw_value()->AsString();
            ParserTraits::ReportMessageAt(
                token_loc, MessageTemplate::kIllegalLanguageModeDirective,
                string);
            *ok = false;
            return nullptr;
          }
          // Because declarations in strict eval code don't leak into the scope
          // of the eval call, it is likely that functions declared in strict
          // eval code will be used within the eval code, so lazy parsing is
          // probably not a win.
          if (scope_->is_eval_scope()) mode_ = PARSE_EAGERLY;
        } else if (literal->raw_value()->AsString() ==
                       ast_value_factory()->use_asm_string() &&
                   token_loc.end_pos - token_loc.beg_pos ==
                       ast_value_factory()->use_asm_string()->length() + 2) {
          // Store the usage count; The actual use counter on the isolate is
          // incremented after parsing is done.
          ++use_counts_[v8::Isolate::kUseAsm];
          scope_->SetAsmModule();
        } else {
          // Should not change mode, but will increment UseCounter
          // if appropriate. Ditto usages below.
          RaiseLanguageMode(SLOPPY);
        }
      } else {
        // End of the directive prologue.
        directive_prologue = false;
        RaiseLanguageMode(SLOPPY);
      }
    } else {
      RaiseLanguageMode(SLOPPY);
    }

    body->Add(stat, zone());
  }

  return 0;
}


Statement* Parser::ParseStatementListItem(bool* ok) {
  // (Ecma 262 6th Edition, 13.1):
  // StatementListItem:
  //    Statement
  //    Declaration

  if (peek() != Token::CLASS) {
    // No more classes follow; reset the start position for the consecutive
    // class declaration group.
    scope_->set_class_declaration_group_start(-1);
  }

  switch (peek()) {
    case Token::FUNCTION:
      return ParseFunctionDeclaration(NULL, ok);
    case Token::CLASS:
      if (scope_->class_declaration_group_start() < 0) {
        scope_->set_class_declaration_group_start(
            scanner()->peek_location().beg_pos);
      }
      return ParseClassDeclaration(NULL, ok);
    case Token::CONST:
      if (allow_const()) {
        return ParseVariableStatement(kStatementListItem, NULL, ok);
      }
      break;
    case Token::VAR:
      return ParseVariableStatement(kStatementListItem, NULL, ok);
    case Token::LET:
      if (IsNextLetKeyword()) {
        return ParseVariableStatement(kStatementListItem, NULL, ok);
      }
      break;
    default:
      break;
  }
  return ParseStatement(NULL, ok);
}


Statement* Parser::ParseModuleItem(bool* ok) {
  // (Ecma 262 6th Edition, 15.2):
  // ModuleItem :
  //    ImportDeclaration
  //    ExportDeclaration
  //    StatementListItem

  switch (peek()) {
    case Token::IMPORT:
      return ParseImportDeclaration(ok);
    case Token::EXPORT:
      return ParseExportDeclaration(ok);
    default:
      return ParseStatementListItem(ok);
  }
}


void* Parser::ParseModuleItemList(ZoneList<Statement*>* body, bool* ok) {
  // (Ecma 262 6th Edition, 15.2):
  // Module :
  //    ModuleBody?
  //
  // ModuleBody :
  //    ModuleItem*

  DCHECK(scope_->is_module_scope());
  RaiseLanguageMode(STRICT);

  while (peek() != Token::EOS) {
    Statement* stat = ParseModuleItem(CHECK_OK);
    if (stat && !stat->IsEmpty()) {
      body->Add(stat, zone());
    }
  }

  // Check that all exports are bound.
  ModuleDescriptor* descriptor = scope_->module();
  for (ModuleDescriptor::Iterator it = descriptor->iterator(); !it.done();
       it.Advance()) {
    if (scope_->LookupLocal(it.local_name()) == NULL) {
      // TODO(adamk): Pass both local_name and export_name once ParserTraits
      // supports multiple arg error messages.
      // Also try to report this at a better location.
      ParserTraits::ReportMessage(MessageTemplate::kModuleExportUndefined,
                                  it.local_name());
      *ok = false;
      return NULL;
    }
  }

  scope_->module()->Freeze();
  return NULL;
}


const AstRawString* Parser::ParseModuleSpecifier(bool* ok) {
  // ModuleSpecifier :
  //    StringLiteral

  Expect(Token::STRING, CHECK_OK);
  return GetSymbol(scanner());
}


void* Parser::ParseExportClause(ZoneList<const AstRawString*>* export_names,
                                ZoneList<Scanner::Location>* export_locations,
                                ZoneList<const AstRawString*>* local_names,
                                Scanner::Location* reserved_loc, bool* ok) {
  // ExportClause :
  //   '{' '}'
  //   '{' ExportsList '}'
  //   '{' ExportsList ',' '}'
  //
  // ExportsList :
  //   ExportSpecifier
  //   ExportsList ',' ExportSpecifier
  //
  // ExportSpecifier :
  //   IdentifierName
  //   IdentifierName 'as' IdentifierName

  Expect(Token::LBRACE, CHECK_OK);

  Token::Value name_tok;
  while ((name_tok = peek()) != Token::RBRACE) {
    // Keep track of the first reserved word encountered in case our
    // caller needs to report an error.
    if (!reserved_loc->IsValid() &&
        !Token::IsIdentifier(name_tok, STRICT, false)) {
      *reserved_loc = scanner()->location();
    }
    const AstRawString* local_name = ParseIdentifierName(CHECK_OK);
    const AstRawString* export_name = NULL;
    if (CheckContextualKeyword(CStrVector("as"))) {
      export_name = ParseIdentifierName(CHECK_OK);
    }
    if (export_name == NULL) {
      export_name = local_name;
    }
    export_names->Add(export_name, zone());
    local_names->Add(local_name, zone());
    export_locations->Add(scanner()->location(), zone());
    if (peek() == Token::RBRACE) break;
    Expect(Token::COMMA, CHECK_OK);
  }

  Expect(Token::RBRACE, CHECK_OK);

  return 0;
}


ZoneList<ImportDeclaration*>* Parser::ParseNamedImports(int pos, bool* ok) {
  // NamedImports :
  //   '{' '}'
  //   '{' ImportsList '}'
  //   '{' ImportsList ',' '}'
  //
  // ImportsList :
  //   ImportSpecifier
  //   ImportsList ',' ImportSpecifier
  //
  // ImportSpecifier :
  //   BindingIdentifier
  //   IdentifierName 'as' BindingIdentifier

  Expect(Token::LBRACE, CHECK_OK);

  ZoneList<ImportDeclaration*>* result =
      new (zone()) ZoneList<ImportDeclaration*>(1, zone());
  while (peek() != Token::RBRACE) {
    const AstRawString* import_name = ParseIdentifierName(CHECK_OK);
    const AstRawString* local_name = import_name;
    // In the presence of 'as', the left-side of the 'as' can
    // be any IdentifierName. But without 'as', it must be a valid
    // BindingIdentifier.
    if (CheckContextualKeyword(CStrVector("as"))) {
      local_name = ParseIdentifierName(CHECK_OK);
    }
    if (!Token::IsIdentifier(scanner()->current_token(), STRICT, false)) {
      *ok = false;
      ReportMessage(MessageTemplate::kUnexpectedReserved);
      return NULL;
    } else if (IsEvalOrArguments(local_name)) {
      *ok = false;
      ReportMessage(MessageTemplate::kStrictEvalArguments);
      return NULL;
    } else if (is_strong(language_mode()) && IsUndefined(local_name)) {
      *ok = false;
      ReportMessage(MessageTemplate::kStrongUndefined);
      return NULL;
    }
    VariableProxy* proxy = NewUnresolved(local_name, IMPORT);
    ImportDeclaration* declaration =
        factory()->NewImportDeclaration(proxy, import_name, NULL, scope_, pos);
    Declare(declaration, DeclarationDescriptor::NORMAL, true, CHECK_OK);
    result->Add(declaration, zone());
    if (peek() == Token::RBRACE) break;
    Expect(Token::COMMA, CHECK_OK);
  }

  Expect(Token::RBRACE, CHECK_OK);

  return result;
}


Statement* Parser::ParseImportDeclaration(bool* ok) {
  // ImportDeclaration :
  //   'import' ImportClause 'from' ModuleSpecifier ';'
  //   'import' ModuleSpecifier ';'
  //
  // ImportClause :
  //   NameSpaceImport
  //   NamedImports
  //   ImportedDefaultBinding
  //   ImportedDefaultBinding ',' NameSpaceImport
  //   ImportedDefaultBinding ',' NamedImports
  //
  // NameSpaceImport :
  //   '*' 'as' ImportedBinding

  int pos = peek_position();
  Expect(Token::IMPORT, CHECK_OK);

  Token::Value tok = peek();

  // 'import' ModuleSpecifier ';'
  if (tok == Token::STRING) {
    const AstRawString* module_specifier = ParseModuleSpecifier(CHECK_OK);
    scope_->module()->AddModuleRequest(module_specifier, zone());
    ExpectSemicolon(CHECK_OK);
    return factory()->NewEmptyStatement(pos);
  }

  // Parse ImportedDefaultBinding if present.
  ImportDeclaration* import_default_declaration = NULL;
  if (tok != Token::MUL && tok != Token::LBRACE) {
    const AstRawString* local_name =
        ParseIdentifier(kDontAllowRestrictedIdentifiers, CHECK_OK);
    VariableProxy* proxy = NewUnresolved(local_name, IMPORT);
    import_default_declaration = factory()->NewImportDeclaration(
        proxy, ast_value_factory()->default_string(), NULL, scope_, pos);
    Declare(import_default_declaration, DeclarationDescriptor::NORMAL, true,
            CHECK_OK);
  }

  const AstRawString* module_instance_binding = NULL;
  ZoneList<ImportDeclaration*>* named_declarations = NULL;
  if (import_default_declaration == NULL || Check(Token::COMMA)) {
    switch (peek()) {
      case Token::MUL: {
        Consume(Token::MUL);
        ExpectContextualKeyword(CStrVector("as"), CHECK_OK);
        module_instance_binding =
            ParseIdentifier(kDontAllowRestrictedIdentifiers, CHECK_OK);
        // TODO(ES6): Add an appropriate declaration.
        break;
      }

      case Token::LBRACE:
        named_declarations = ParseNamedImports(pos, CHECK_OK);
        break;

      default:
        *ok = false;
        ReportUnexpectedToken(scanner()->current_token());
        return NULL;
    }
  }

  ExpectContextualKeyword(CStrVector("from"), CHECK_OK);
  const AstRawString* module_specifier = ParseModuleSpecifier(CHECK_OK);
  scope_->module()->AddModuleRequest(module_specifier, zone());

  if (module_instance_binding != NULL) {
    // TODO(ES6): Set the module specifier for the module namespace binding.
  }

  if (import_default_declaration != NULL) {
    import_default_declaration->set_module_specifier(module_specifier);
  }

  if (named_declarations != NULL) {
    for (int i = 0; i < named_declarations->length(); ++i) {
      named_declarations->at(i)->set_module_specifier(module_specifier);
    }
  }

  ExpectSemicolon(CHECK_OK);
  return factory()->NewEmptyStatement(pos);
}


Statement* Parser::ParseExportDefault(bool* ok) {
  //  Supports the following productions, starting after the 'default' token:
  //    'export' 'default' FunctionDeclaration
  //    'export' 'default' ClassDeclaration
  //    'export' 'default' AssignmentExpression[In] ';'

  Expect(Token::DEFAULT, CHECK_OK);
  Scanner::Location default_loc = scanner()->location();

  ZoneList<const AstRawString*> names(1, zone());
  Statement* result = NULL;
  switch (peek()) {
    case Token::FUNCTION:
      // TODO(ES6): Support parsing anonymous function declarations here.
      result = ParseFunctionDeclaration(&names, CHECK_OK);
      break;

    case Token::CLASS:
      // TODO(ES6): Support parsing anonymous class declarations here.
      result = ParseClassDeclaration(&names, CHECK_OK);
      break;

    default: {
      int pos = peek_position();
      ExpressionClassifier classifier;
      Expression* expr = ParseAssignmentExpression(true, &classifier, CHECK_OK);
      expr = ParserTraits::RewriteNonPattern(expr, &classifier, CHECK_OK);

      ExpectSemicolon(CHECK_OK);
      result = factory()->NewExpressionStatement(expr, pos);
      break;
    }
  }

  const AstRawString* default_string = ast_value_factory()->default_string();

  DCHECK_LE(names.length(), 1);
  if (names.length() == 1) {
    scope_->module()->AddLocalExport(default_string, names.first(), zone(), ok);
    if (!*ok) {
      ParserTraits::ReportMessageAt(
          default_loc, MessageTemplate::kDuplicateExport, default_string);
      return NULL;
    }
  } else {
    // TODO(ES6): Assign result to a const binding with the name "*default*"
    // and add an export entry with "*default*" as the local name.
  }

  return result;
}


Statement* Parser::ParseExportDeclaration(bool* ok) {
  // ExportDeclaration:
  //    'export' '*' 'from' ModuleSpecifier ';'
  //    'export' ExportClause ('from' ModuleSpecifier)? ';'
  //    'export' VariableStatement
  //    'export' Declaration
  //    'export' 'default' ... (handled in ParseExportDefault)

  int pos = peek_position();
  Expect(Token::EXPORT, CHECK_OK);

  Statement* result = NULL;
  ZoneList<const AstRawString*> names(1, zone());
  switch (peek()) {
    case Token::DEFAULT:
      return ParseExportDefault(ok);

    case Token::MUL: {
      Consume(Token::MUL);
      ExpectContextualKeyword(CStrVector("from"), CHECK_OK);
      const AstRawString* module_specifier = ParseModuleSpecifier(CHECK_OK);
      scope_->module()->AddModuleRequest(module_specifier, zone());
      // TODO(ES6): scope_->module()->AddStarExport(...)
      ExpectSemicolon(CHECK_OK);
      return factory()->NewEmptyStatement(pos);
    }

    case Token::LBRACE: {
      // There are two cases here:
      //
      // 'export' ExportClause ';'
      // and
      // 'export' ExportClause FromClause ';'
      //
      // In the first case, the exported identifiers in ExportClause must
      // not be reserved words, while in the latter they may be. We
      // pass in a location that gets filled with the first reserved word
      // encountered, and then throw a SyntaxError if we are in the
      // non-FromClause case.
      Scanner::Location reserved_loc = Scanner::Location::invalid();
      ZoneList<const AstRawString*> export_names(1, zone());
      ZoneList<Scanner::Location> export_locations(1, zone());
      ZoneList<const AstRawString*> local_names(1, zone());
      ParseExportClause(&export_names, &export_locations, &local_names,
                        &reserved_loc, CHECK_OK);
      const AstRawString* indirect_export_module_specifier = NULL;
      if (CheckContextualKeyword(CStrVector("from"))) {
        indirect_export_module_specifier = ParseModuleSpecifier(CHECK_OK);
      } else if (reserved_loc.IsValid()) {
        // No FromClause, so reserved words are invalid in ExportClause.
        *ok = false;
        ReportMessageAt(reserved_loc, MessageTemplate::kUnexpectedReserved);
        return NULL;
      }
      ExpectSemicolon(CHECK_OK);
      const int length = export_names.length();
      DCHECK_EQ(length, local_names.length());
      DCHECK_EQ(length, export_locations.length());
      if (indirect_export_module_specifier == NULL) {
        for (int i = 0; i < length; ++i) {
          scope_->module()->AddLocalExport(export_names[i], local_names[i],
                                           zone(), ok);
          if (!*ok) {
            ParserTraits::ReportMessageAt(export_locations[i],
                                          MessageTemplate::kDuplicateExport,
                                          export_names[i]);
            return NULL;
          }
        }
      } else {
        scope_->module()->AddModuleRequest(indirect_export_module_specifier,
                                           zone());
        for (int i = 0; i < length; ++i) {
          // TODO(ES6): scope_->module()->AddIndirectExport(...);(
        }
      }
      return factory()->NewEmptyStatement(pos);
    }

    case Token::FUNCTION:
      result = ParseFunctionDeclaration(&names, CHECK_OK);
      break;

    case Token::CLASS:
      result = ParseClassDeclaration(&names, CHECK_OK);
      break;

    case Token::VAR:
    case Token::LET:
    case Token::CONST:
      result = ParseVariableStatement(kStatementListItem, &names, CHECK_OK);
      break;

    default:
      *ok = false;
      ReportUnexpectedToken(scanner()->current_token());
      return NULL;
  }

  // Extract declared names into export declarations.
  ModuleDescriptor* descriptor = scope_->module();
  for (int i = 0; i < names.length(); ++i) {
    descriptor->AddLocalExport(names[i], names[i], zone(), ok);
    if (!*ok) {
      // TODO(adamk): Possibly report this error at the right place.
      ParserTraits::ReportMessage(MessageTemplate::kDuplicateExport, names[i]);
      return NULL;
    }
  }

  DCHECK_NOT_NULL(result);
  return result;
}


Statement* Parser::ParseStatement(ZoneList<const AstRawString*>* labels,
                                  bool* ok) {
  // Statement ::
  //   EmptyStatement
  //   ...

  if (peek() == Token::SEMICOLON) {
    Next();
    return factory()->NewEmptyStatement(RelocInfo::kNoPosition);
  }
  return ParseSubStatement(labels, ok);
}


Statement* Parser::ParseSubStatement(ZoneList<const AstRawString*>* labels,
                                     bool* ok) {
  // Statement ::
  //   Block
  //   VariableStatement
  //   EmptyStatement
  //   ExpressionStatement
  //   IfStatement
  //   IterationStatement
  //   ContinueStatement
  //   BreakStatement
  //   ReturnStatement
  //   WithStatement
  //   LabelledStatement
  //   SwitchStatement
  //   ThrowStatement
  //   TryStatement
  //   DebuggerStatement

  // Note: Since labels can only be used by 'break' and 'continue'
  // statements, which themselves are only valid within blocks,
  // iterations or 'switch' statements (i.e., BreakableStatements),
  // labels can be simply ignored in all other cases; except for
  // trivial labeled break statements 'label: break label' which is
  // parsed into an empty statement.
  switch (peek()) {
    case Token::LBRACE:
      return ParseBlock(labels, ok);

    case Token::SEMICOLON:
      if (is_strong(language_mode())) {
        ReportMessageAt(scanner()->peek_location(),
                        MessageTemplate::kStrongEmpty);
        *ok = false;
        return NULL;
      }
      Next();
      return factory()->NewEmptyStatement(RelocInfo::kNoPosition);

    case Token::IF:
      return ParseIfStatement(labels, ok);

    case Token::DO:
      return ParseDoWhileStatement(labels, ok);

    case Token::WHILE:
      return ParseWhileStatement(labels, ok);

    case Token::FOR:
      return ParseForStatement(labels, ok);

    case Token::CONTINUE:
    case Token::BREAK:
    case Token::RETURN:
    case Token::THROW:
    case Token::TRY: {
      // These statements must have their labels preserved in an enclosing
      // block
      if (labels == NULL) {
        return ParseStatementAsUnlabelled(labels, ok);
      } else {
        Block* result =
            factory()->NewBlock(labels, 1, false, RelocInfo::kNoPosition);
        Target target(&this->target_stack_, result);
        Statement* statement = ParseStatementAsUnlabelled(labels, CHECK_OK);
        if (result) result->statements()->Add(statement, zone());
        return result;
      }
    }

    case Token::WITH:
      return ParseWithStatement(labels, ok);

    case Token::SWITCH:
      return ParseSwitchStatement(labels, ok);

    case Token::FUNCTION: {
      // FunctionDeclaration is only allowed in the context of SourceElements
      // (Ecma 262 5th Edition, clause 14):
      // SourceElement:
      //    Statement
      //    FunctionDeclaration
      // Common language extension is to allow function declaration in place
      // of any statement. This language extension is disabled in strict mode.
      //
      // In Harmony mode, this case also handles the extension:
      // Statement:
      //    GeneratorDeclaration
      if (is_strict(language_mode())) {
        ReportMessageAt(scanner()->peek_location(),
                        MessageTemplate::kStrictFunction);
        *ok = false;
        return NULL;
      }
      return ParseFunctionDeclaration(NULL, ok);
    }

    case Token::DEBUGGER:
      return ParseDebuggerStatement(ok);

    case Token::VAR:
      return ParseVariableStatement(kStatement, NULL, ok);

    case Token::CONST:
      // In ES6 CONST is not allowed as a Statement, only as a
      // LexicalDeclaration, however we continue to allow it in sloppy mode for
      // backwards compatibility.
      if (is_sloppy(language_mode()) && allow_legacy_const()) {
        return ParseVariableStatement(kStatement, NULL, ok);
      }

    // Fall through.
    default:
      return ParseExpressionOrLabelledStatement(labels, ok);
  }
}

Statement* Parser::ParseStatementAsUnlabelled(
    ZoneList<const AstRawString*>* labels, bool* ok) {
  switch (peek()) {
    case Token::CONTINUE:
      return ParseContinueStatement(ok);

    case Token::BREAK:
      return ParseBreakStatement(labels, ok);

    case Token::RETURN:
      return ParseReturnStatement(ok);

    case Token::THROW:
      return ParseThrowStatement(ok);

    case Token::TRY:
      return ParseTryStatement(ok);

    default:
      UNREACHABLE();
      return NULL;
  }
}


VariableProxy* Parser::NewUnresolved(const AstRawString* name,
                                     VariableMode mode) {
  // If we are inside a function, a declaration of a var/const variable is a
  // truly local variable, and the scope of the variable is always the function
  // scope.
  // Let/const variables in harmony mode are always added to the immediately
  // enclosing scope.
  Scope* scope =
      IsLexicalVariableMode(mode) ? scope_ : scope_->DeclarationScope();
  return scope->NewUnresolved(factory(), name, Variable::NORMAL,
                              scanner()->location().beg_pos,
                              scanner()->location().end_pos);
}


Variable* Parser::Declare(Declaration* declaration,
                          DeclarationDescriptor::Kind declaration_kind,
                          bool resolve, bool* ok, Scope* scope) {
  VariableProxy* proxy = declaration->proxy();
  DCHECK(proxy->raw_name() != NULL);
  const AstRawString* name = proxy->raw_name();
  VariableMode mode = declaration->mode();
  bool is_function_declaration = declaration->IsFunctionDeclaration();
  if (scope == nullptr) scope = scope_;
  Scope* declaration_scope =
      IsLexicalVariableMode(mode) ? scope : scope->DeclarationScope();
  Variable* var = NULL;

  // If a suitable scope exists, then we can statically declare this
  // variable and also set its mode. In any case, a Declaration node
  // will be added to the scope so that the declaration can be added
  // to the corresponding activation frame at runtime if necessary.
  // For instance, var declarations inside a sloppy eval scope need
  // to be added to the calling function context. Similarly, strict
  // mode eval scope and lexical eval bindings do not leak variable
  // declarations to the caller's scope so we declare all locals, too.
  if (declaration_scope->is_function_scope() ||
      declaration_scope->is_block_scope() ||
      declaration_scope->is_module_scope() ||
      declaration_scope->is_script_scope() ||
      (declaration_scope->is_eval_scope() &&
       (is_strict(declaration_scope->language_mode()) ||
        IsLexicalVariableMode(mode)))) {
    // Declare the variable in the declaration scope.
    var = declaration_scope->LookupLocal(name);
    if (var == NULL) {
      // Declare the name.
      Variable::Kind kind = Variable::NORMAL;
      int declaration_group_start = -1;
      if (is_function_declaration) {
        kind = Variable::FUNCTION;
      } else if (declaration->IsVariableDeclaration() &&
                 declaration->AsVariableDeclaration()->is_class_declaration()) {
        kind = Variable::CLASS;
        declaration_group_start =
            declaration->AsVariableDeclaration()->declaration_group_start();
      }
      var = declaration_scope->DeclareLocal(
          name, mode, declaration->initialization(), kind, kNotAssigned,
          declaration_group_start);
    } else if (((IsLexicalVariableMode(mode) ||
                 IsLexicalVariableMode(var->mode())) &&
                // Allow duplicate function decls for web compat, see bug 4693.
                (is_strict(language_mode()) || !is_function_declaration ||
                 !var->is_function())) ||
               ((mode == CONST_LEGACY || var->mode() == CONST_LEGACY) &&
                !declaration_scope->is_script_scope())) {
      // The name was declared in this scope before; check for conflicting
      // re-declarations. We have a conflict if either of the declarations is
      // not a var (in script scope, we also have to ignore legacy const for
      // compatibility). There is similar code in runtime.cc in the Declare
      // functions. The function CheckConflictingVarDeclarations checks for
      // var and let bindings from different scopes whereas this is a check for
      // conflicting declarations within the same scope. This check also covers
      // the special case
      //
      // function () { let x; { var x; } }
      //
      // because the var declaration is hoisted to the function scope where 'x'
      // is already bound.
      DCHECK(IsDeclaredVariableMode(var->mode()));
      if (is_strict(language_mode()) ||
          (allow_harmony_sloppy() && mode != CONST_LEGACY &&
           var->mode() != CONST_LEGACY)) {
        // In harmony we treat re-declarations as early errors. See
        // ES5 16 for a definition of early errors.
        if (declaration_kind == DeclarationDescriptor::NORMAL) {
          ParserTraits::ReportMessage(MessageTemplate::kVarRedeclaration, name);
        } else {
          ParserTraits::ReportMessage(MessageTemplate::kParamDupe);
        }
        *ok = false;
        return nullptr;
      }
      Expression* expression = NewThrowSyntaxError(
          MessageTemplate::kVarRedeclaration, name, declaration->position());
      declaration_scope->SetIllegalRedeclaration(expression);
    } else if (mode == VAR) {
      var->set_maybe_assigned();
    }
  } else if (declaration_scope->is_eval_scope() &&
             is_sloppy(declaration_scope->language_mode()) &&
             !IsLexicalVariableMode(mode)) {
    // In a var binding in a sloppy direct eval, pollute the enclosing scope
    // with this new binding by doing the following:
    // The proxy is bound to a lookup variable to force a dynamic declaration
    // using the DeclareLookupSlot runtime function.
    Variable::Kind kind = Variable::NORMAL;
    // TODO(sigurds) figure out if kNotAssigned is OK here
    var = new (zone()) Variable(declaration_scope, name, mode, kind,
                                declaration->initialization(), kNotAssigned);
    var->AllocateTo(VariableLocation::LOOKUP, -1);
    var->SetFromEval();
    resolve = true;
  }


  // We add a declaration node for every declaration. The compiler
  // will only generate code if necessary. In particular, declarations
  // for inner local variables that do not represent functions won't
  // result in any generated code.
  //
  // Note that we always add an unresolved proxy even if it's not
  // used, simply because we don't know in this method (w/o extra
  // parameters) if the proxy is needed or not. The proxy will be
  // bound during variable resolution time unless it was pre-bound
  // below.
  //
  // WARNING: This will lead to multiple declaration nodes for the
  // same variable if it is declared several times. This is not a
  // semantic issue as long as we keep the source order, but it may be
  // a performance issue since it may lead to repeated
  // RuntimeHidden_DeclareLookupSlot calls.
  declaration_scope->AddDeclaration(declaration);

  if (mode == CONST_LEGACY && declaration_scope->is_script_scope()) {
    // For global const variables we bind the proxy to a variable.
    DCHECK(resolve);  // should be set by all callers
    Variable::Kind kind = Variable::NORMAL;
    var = new (zone()) Variable(declaration_scope, name, mode, kind,
                                kNeedsInitialization, kNotAssigned);
  }

  // If requested and we have a local variable, bind the proxy to the variable
  // at parse-time. This is used for functions (and consts) declared inside
  // statements: the corresponding function (or const) variable must be in the
  // function scope and not a statement-local scope, e.g. as provided with a
  // 'with' statement:
  //
  //   with (obj) {
  //     function f() {}
  //   }
  //
  // which is translated into:
  //
  //   with (obj) {
  //     // in this case this is not: 'var f; f = function () {};'
  //     var f = function () {};
  //   }
  //
  // Note that if 'f' is accessed from inside the 'with' statement, it
  // will be allocated in the context (because we must be able to look
  // it up dynamically) but it will also be accessed statically, i.e.,
  // with a context slot index and a context chain length for this
  // initialization code. Thus, inside the 'with' statement, we need
  // both access to the static and the dynamic context chain; the
  // runtime needs to provide both.
  if (resolve && var != NULL) {
    proxy->BindTo(var);
  }
  return var;
}


// Language extension which is only enabled for source files loaded
// through the API's extension mechanism.  A native function
// declaration is resolved by looking up the function through a
// callback provided by the extension.
Statement* Parser::ParseNativeDeclaration(bool* ok) {
  int pos = peek_position();
  Expect(Token::FUNCTION, CHECK_OK);
  // Allow "eval" or "arguments" for backward compatibility.
  const AstRawString* name =
      ParseIdentifier(kAllowRestrictedIdentifiers, CHECK_OK);
  Expect(Token::LPAREN, CHECK_OK);
  bool done = (peek() == Token::RPAREN);
  while (!done) {
    ParseIdentifier(kAllowRestrictedIdentifiers, CHECK_OK);
    done = (peek() == Token::RPAREN);
    if (!done) {
      Expect(Token::COMMA, CHECK_OK);
    }
  }
  Expect(Token::RPAREN, CHECK_OK);
  Expect(Token::SEMICOLON, CHECK_OK);

  // Make sure that the function containing the native declaration
  // isn't lazily compiled. The extension structures are only
  // accessible while parsing the first time not when reparsing
  // because of lazy compilation.
  // TODO(adamk): Should this be ClosureScope()?
  scope_->DeclarationScope()->ForceEagerCompilation();

  // TODO(1240846): It's weird that native function declarations are
  // introduced dynamically when we meet their declarations, whereas
  // other functions are set up when entering the surrounding scope.
  VariableProxy* proxy = NewUnresolved(name, VAR);
  Declaration* declaration =
      factory()->NewVariableDeclaration(proxy, VAR, scope_, pos);
  Declare(declaration, DeclarationDescriptor::NORMAL, true, CHECK_OK);
  NativeFunctionLiteral* lit = factory()->NewNativeFunctionLiteral(
      name, extension_, RelocInfo::kNoPosition);
  return factory()->NewExpressionStatement(
      factory()->NewAssignment(Token::INIT, proxy, lit, RelocInfo::kNoPosition),
      pos);
}


Statement* Parser::ParseFunctionDeclaration(
    ZoneList<const AstRawString*>* names, bool* ok) {
  // FunctionDeclaration ::
  //   'function' Identifier '(' FormalParameterListopt ')' '{' FunctionBody '}'
  // GeneratorDeclaration ::
  //   'function' '*' Identifier '(' FormalParameterListopt ')'
  //      '{' FunctionBody '}'
  Expect(Token::FUNCTION, CHECK_OK);
  int pos = position();
  bool is_generator = Check(Token::MUL);
  bool is_strict_reserved = false;
  const AstRawString* name = ParseIdentifierOrStrictReservedWord(
      &is_strict_reserved, CHECK_OK);

  FuncNameInferrer::State fni_state(fni_);
  if (fni_ != NULL) fni_->PushEnclosingName(name);
  FunctionLiteral* fun = ParseFunctionLiteral(
      name, scanner()->location(),
      is_strict_reserved ? kFunctionNameIsStrictReserved
                         : kFunctionNameValidityUnknown,
      is_generator ? FunctionKind::kGeneratorFunction
                   : FunctionKind::kNormalFunction,
      pos, FunctionLiteral::kDeclaration, FunctionLiteral::kNormalArity,
      language_mode(), CHECK_OK);

  // Even if we're not at the top-level of the global or a function
  // scope, we treat it as such and introduce the function with its
  // initial value upon entering the corresponding scope.
  // In ES6, a function behaves as a lexical binding, except in
  // a script scope, or the initial scope of eval or another function.
  VariableMode mode =
      is_strong(language_mode())
          ? CONST
          : (is_strict(language_mode()) || allow_harmony_sloppy_function()) &&
                    !scope_->is_declaration_scope()
                ? LET
                : VAR;
  VariableProxy* proxy = NewUnresolved(name, mode);
  Declaration* declaration =
      factory()->NewFunctionDeclaration(proxy, mode, fun, scope_, pos);
  Declare(declaration, DeclarationDescriptor::NORMAL, true, CHECK_OK);
  if (names) names->Add(name, zone());
  EmptyStatement* empty = factory()->NewEmptyStatement(RelocInfo::kNoPosition);
  if (is_sloppy(language_mode()) && allow_harmony_sloppy_function() &&
      !scope_->is_declaration_scope()) {
    SloppyBlockFunctionStatement* delegate =
        factory()->NewSloppyBlockFunctionStatement(empty, scope_);
    scope_->DeclarationScope()->sloppy_block_function_map()->Declare(name,
                                                                     delegate);
    return delegate;
  }
  return empty;
}


Statement* Parser::ParseClassDeclaration(ZoneList<const AstRawString*>* names,
                                         bool* ok) {
  // ClassDeclaration ::
  //   'class' Identifier ('extends' LeftHandExpression)? '{' ClassBody '}'
  //
  // A ClassDeclaration
  //
  //   class C { ... }
  //
  // has the same semantics as:
  //
  //   let C = class C { ... };
  //
  // so rewrite it as such.

  Expect(Token::CLASS, CHECK_OK);
  if (!allow_harmony_sloppy() && is_sloppy(language_mode())) {
    ReportMessage(MessageTemplate::kSloppyLexical);
    *ok = false;
    return NULL;
  }

  int pos = position();
  bool is_strict_reserved = false;
  const AstRawString* name =
      ParseIdentifierOrStrictReservedWord(&is_strict_reserved, CHECK_OK);
  ClassLiteral* value = ParseClassLiteral(name, scanner()->location(),
                                          is_strict_reserved, pos, CHECK_OK);

  VariableMode mode = is_strong(language_mode()) ? CONST : LET;
  VariableProxy* proxy = NewUnresolved(name, mode);
  const bool is_class_declaration = true;
  Declaration* declaration = factory()->NewVariableDeclaration(
      proxy, mode, scope_, pos, is_class_declaration,
      scope_->class_declaration_group_start());
  Variable* outer_class_variable =
      Declare(declaration, DeclarationDescriptor::NORMAL, true, CHECK_OK);
  proxy->var()->set_initializer_position(position());
  // This is needed because a class ("class Name { }") creates two bindings (one
  // in the outer scope, and one in the class scope). The method is a function
  // scope inside the inner scope (class scope). The consecutive class
  // declarations are in the outer scope.
  if (value->class_variable_proxy() && value->class_variable_proxy()->var() &&
      outer_class_variable->is_class()) {
    // In some cases, the outer variable is not detected as a class variable;
    // this happens e.g., for lazy methods. They are excluded from strong mode
    // checks for now. TODO(marja, rossberg): re-create variables with the
    // correct Kind and remove this hack.
    value->class_variable_proxy()
        ->var()
        ->AsClassVariable()
        ->set_declaration_group_start(
            outer_class_variable->AsClassVariable()->declaration_group_start());
  }

  Assignment* assignment =
      factory()->NewAssignment(Token::INIT, proxy, value, pos);
  Statement* assignment_statement =
      factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
  if (names) names->Add(name, zone());
  return assignment_statement;
}


Block* Parser::ParseBlock(ZoneList<const AstRawString*>* labels,
                          bool finalize_block_scope, bool* ok) {
  // The harmony mode uses block elements instead of statements.
  //
  // Block ::
  //   '{' StatementList '}'

  // Construct block expecting 16 statements.
  Block* body =
      factory()->NewBlock(labels, 16, false, RelocInfo::kNoPosition);
  Scope* block_scope = NewScope(scope_, BLOCK_SCOPE);

  // Parse the statements and collect escaping labels.
  Expect(Token::LBRACE, CHECK_OK);
  block_scope->set_start_position(scanner()->location().beg_pos);
  { BlockState block_state(&scope_, block_scope);
    Target target(&this->target_stack_, body);

    while (peek() != Token::RBRACE) {
      Statement* stat = ParseStatementListItem(CHECK_OK);
      if (stat && !stat->IsEmpty()) {
        body->statements()->Add(stat, zone());
      }
    }
  }
  Expect(Token::RBRACE, CHECK_OK);
  block_scope->set_end_position(scanner()->location().end_pos);
  if (finalize_block_scope) {
    block_scope = block_scope->FinalizeBlockScope();
  }
  body->set_scope(block_scope);
  return body;
}


Block* Parser::ParseBlock(ZoneList<const AstRawString*>* labels, bool* ok) {
  return ParseBlock(labels, true, ok);
}


Block* Parser::DeclarationParsingResult::BuildInitializationBlock(
    ZoneList<const AstRawString*>* names, bool* ok) {
  Block* result = descriptor.parser->factory()->NewBlock(
      NULL, 1, true, descriptor.declaration_pos);
  for (auto declaration : declarations) {
    PatternRewriter::DeclareAndInitializeVariables(
        result, &descriptor, &declaration, names, CHECK_OK);
  }
  return result;
}


Block* Parser::ParseVariableStatement(VariableDeclarationContext var_context,
                                      ZoneList<const AstRawString*>* names,
                                      bool* ok) {
  // VariableStatement ::
  //   VariableDeclarations ';'

  // The scope of a var/const declared variable anywhere inside a function
  // is the entire function (ECMA-262, 3rd, 10.1.3, and 12.2). Thus we can
  // transform a source-level var/const declaration into a (Function)
  // Scope declaration, and rewrite the source-level initialization into an
  // assignment statement. We use a block to collect multiple assignments.
  //
  // We mark the block as initializer block because we don't want the
  // rewriter to add a '.result' assignment to such a block (to get compliant
  // behavior for code such as print(eval('var x = 7')), and for cosmetic
  // reasons when pretty-printing. Also, unless an assignment (initialization)
  // is inside an initializer block, it is ignored.

  DeclarationParsingResult parsing_result;
  ParseVariableDeclarations(var_context, &parsing_result, CHECK_OK);
  ExpectSemicolon(CHECK_OK);

  Block* result = parsing_result.BuildInitializationBlock(names, CHECK_OK);
  return result;
}


void Parser::ParseVariableDeclarations(VariableDeclarationContext var_context,
                                       DeclarationParsingResult* parsing_result,
                                       bool* ok) {
  // VariableDeclarations ::
  //   ('var' | 'const' | 'let') (Identifier ('=' AssignmentExpression)?)+[',']
  //
  // The ES6 Draft Rev3 specifies the following grammar for const declarations
  //
  // ConstDeclaration ::
  //   const ConstBinding (',' ConstBinding)* ';'
  // ConstBinding ::
  //   Identifier '=' AssignmentExpression
  //
  // TODO(ES6):
  // ConstBinding ::
  //   BindingPattern '=' AssignmentExpression

  parsing_result->descriptor.parser = this;
  parsing_result->descriptor.declaration_kind = DeclarationDescriptor::NORMAL;
  parsing_result->descriptor.declaration_pos = peek_position();
  parsing_result->descriptor.initialization_pos = peek_position();
  parsing_result->descriptor.mode = VAR;
  // True if the binding needs initialization. 'let' and 'const' declared
  // bindings are created uninitialized by their declaration nodes and
  // need initialization. 'var' declared bindings are always initialized
  // immediately by their declaration nodes.
  parsing_result->descriptor.needs_init = false;
  if (peek() == Token::VAR) {
    if (is_strong(language_mode())) {
      Scanner::Location location = scanner()->peek_location();
      ReportMessageAt(location, MessageTemplate::kStrongVar);
      *ok = false;
      return;
    }
    Consume(Token::VAR);
  } else if (peek() == Token::CONST && allow_const()) {
    Consume(Token::CONST);
    if (is_sloppy(language_mode()) && allow_legacy_const()) {
      parsing_result->descriptor.mode = CONST_LEGACY;
      ++use_counts_[v8::Isolate::kLegacyConst];
    } else {
      DCHECK(is_strict(language_mode()) || allow_harmony_sloppy());
      DCHECK(var_context != kStatement);
      parsing_result->descriptor.mode = CONST;
    }
    parsing_result->descriptor.needs_init = true;
  } else if (peek() == Token::LET && allow_let()) {
    Consume(Token::LET);
    DCHECK(var_context != kStatement);
    parsing_result->descriptor.mode = LET;
    parsing_result->descriptor.needs_init = true;
  } else {
    UNREACHABLE();  // by current callers
  }

  parsing_result->descriptor.scope = scope_;
  parsing_result->descriptor.hoist_scope = nullptr;


  bool first_declaration = true;
  int bindings_start = peek_position();
  bool is_for_iteration_variable;
  do {
    FuncNameInferrer::State fni_state(fni_);

    // Parse name.
    if (!first_declaration) Consume(Token::COMMA);

    Expression* pattern;
    int decl_pos = peek_position();
    {
      ExpressionClassifier pattern_classifier;
      Token::Value next = peek();
      pattern = ParsePrimaryExpression(&pattern_classifier, ok);
      if (!*ok) return;
      ValidateBindingPattern(&pattern_classifier, ok);
      if (!*ok) return;
      if (IsLexicalVariableMode(parsing_result->descriptor.mode)) {
        ValidateLetPattern(&pattern_classifier, ok);
        if (!*ok) return;
      }
      if (!allow_harmony_destructuring_bind() && !pattern->IsVariableProxy()) {
        ReportUnexpectedToken(next);
        *ok = false;
        return;
      }
    }

    bool is_pattern =
        (pattern->IsObjectLiteral() || pattern->IsArrayLiteral()) &&
        !pattern->is_parenthesized();

    Scanner::Location variable_loc = scanner()->location();
    const AstRawString* single_name =
        pattern->IsVariableProxy() ? pattern->AsVariableProxy()->raw_name()
                                   : nullptr;
    if (single_name != nullptr) {
      if (fni_ != NULL) fni_->PushVariableName(single_name);
    }

    is_for_iteration_variable =
        var_context == kForStatement &&
        (peek() == Token::IN || PeekContextualKeyword(CStrVector("of")));
    if (is_for_iteration_variable &&
        (parsing_result->descriptor.mode == CONST ||
         parsing_result->descriptor.mode == CONST_LEGACY)) {
      parsing_result->descriptor.needs_init = false;
    }

    Expression* value = NULL;
    // Harmony consts have non-optional initializers.
    int initializer_position = RelocInfo::kNoPosition;
    if (Check(Token::ASSIGN)) {
      ExpressionClassifier classifier;
      value = ParseAssignmentExpression(var_context != kForStatement,
                                        &classifier, ok);
      if (!*ok) return;
      value = ParserTraits::RewriteNonPattern(value, &classifier, ok);
      if (!*ok) return;
      variable_loc.end_pos = scanner()->location().end_pos;

      if (!parsing_result->first_initializer_loc.IsValid()) {
        parsing_result->first_initializer_loc = variable_loc;
      }

      // Don't infer if it is "a = function(){...}();"-like expression.
      if (single_name) {
        if (fni_ != NULL && value->AsCall() == NULL &&
            value->AsCallNew() == NULL) {
          fni_->Infer();
        } else {
          fni_->RemoveLastFunction();
        }
      }

      if (allow_harmony_function_name() && single_name) {
        if (value->IsFunctionLiteral()) {
          auto function_literal = value->AsFunctionLiteral();
          if (function_literal->is_anonymous()) {
            function_literal->set_raw_name(single_name);
          }
        } else if (value->IsClassLiteral()) {
          auto class_literal = value->AsClassLiteral();
          if (class_literal->raw_name() == nullptr) {
            class_literal->set_raw_name(single_name);
          }
        }
      }

      // End position of the initializer is after the assignment expression.
      initializer_position = scanner()->location().end_pos;
    } else {
      if ((parsing_result->descriptor.mode == CONST || is_pattern) &&
          !is_for_iteration_variable) {
        ParserTraits::ReportMessageAt(
            Scanner::Location(decl_pos, scanner()->location().end_pos),
            MessageTemplate::kDeclarationMissingInitializer,
            is_pattern ? "destructuring" : "const");
        *ok = false;
        return;
      }
      // End position of the initializer is after the variable.
      initializer_position = position();
    }

    // Make sure that 'const x' and 'let x' initialize 'x' to undefined.
    if (value == NULL && parsing_result->descriptor.needs_init) {
      value = GetLiteralUndefined(position());
    }

    parsing_result->declarations.Add(DeclarationParsingResult::Declaration(
        pattern, initializer_position, value));
    first_declaration = false;
  } while (peek() == Token::COMMA);

  parsing_result->bindings_loc =
      Scanner::Location(bindings_start, scanner()->location().end_pos);
}


static bool ContainsLabel(ZoneList<const AstRawString*>* labels,
                          const AstRawString* label) {
  DCHECK(label != NULL);
  if (labels != NULL) {
    for (int i = labels->length(); i-- > 0; ) {
      if (labels->at(i) == label) {
        return true;
      }
    }
  }
  return false;
}


Statement* Parser::ParseExpressionOrLabelledStatement(
    ZoneList<const AstRawString*>* labels, bool* ok) {
  // ExpressionStatement | LabelledStatement ::
  //   Expression ';'
  //   Identifier ':' Statement
  //
  // ExpressionStatement[Yield] :
  //   [lookahead  {{, function, class, let [}] Expression[In, ?Yield] ;

  int pos = peek_position();

  switch (peek()) {
    case Token::FUNCTION:
    case Token::LBRACE:
      UNREACHABLE();  // Always handled by the callers.
    case Token::CLASS:
      ReportUnexpectedToken(Next());
      *ok = false;
      return nullptr;

    case Token::THIS:
      if (!FLAG_strong_this) break;
      // Fall through.
    case Token::SUPER:
      if (is_strong(language_mode()) &&
          IsClassConstructor(function_state_->kind())) {
        bool is_this = peek() == Token::THIS;
        Expression* expr;
        ExpressionClassifier classifier;
        if (is_this) {
          expr = ParseStrongInitializationExpression(&classifier, CHECK_OK);
        } else {
          expr = ParseStrongSuperCallExpression(&classifier, CHECK_OK);
        }
        expr = ParserTraits::RewriteNonPattern(expr, &classifier, CHECK_OK);
        switch (peek()) {
          case Token::SEMICOLON:
            Consume(Token::SEMICOLON);
            break;
          case Token::RBRACE:
          case Token::EOS:
            break;
          default:
            if (!scanner()->HasAnyLineTerminatorBeforeNext()) {
              ReportMessageAt(function_state_->this_location(),
                              is_this
                                  ? MessageTemplate::kStrongConstructorThis
                                  : MessageTemplate::kStrongConstructorSuper);
              *ok = false;
              return nullptr;
            }
        }
        return factory()->NewExpressionStatement(expr, pos);
      }
      break;

    default:
      break;
  }

  bool starts_with_idenfifier = peek_any_identifier();
  Expression* expr = ParseExpression(true, CHECK_OK);
  if (peek() == Token::COLON && starts_with_idenfifier && expr != NULL &&
      expr->AsVariableProxy() != NULL &&
      !expr->AsVariableProxy()->is_this()) {
    // Expression is a single identifier, and not, e.g., a parenthesized
    // identifier.
    VariableProxy* var = expr->AsVariableProxy();
    const AstRawString* label = var->raw_name();
    // TODO(1240780): We don't check for redeclaration of labels
    // during preparsing since keeping track of the set of active
    // labels requires nontrivial changes to the way scopes are
    // structured.  However, these are probably changes we want to
    // make later anyway so we should go back and fix this then.
    if (ContainsLabel(labels, label) || TargetStackContainsLabel(label)) {
      ParserTraits::ReportMessage(MessageTemplate::kLabelRedeclaration, label);
      *ok = false;
      return NULL;
    }
    if (labels == NULL) {
      labels = new(zone()) ZoneList<const AstRawString*>(4, zone());
    }
    labels->Add(label, zone());
    // Remove the "ghost" variable that turned out to be a label
    // from the top scope. This way, we don't try to resolve it
    // during the scope processing.
    scope_->RemoveUnresolved(var);
    Expect(Token::COLON, CHECK_OK);
    return ParseStatement(labels, ok);
  }

  // If we have an extension, we allow a native function declaration.
  // A native function declaration starts with "native function" with
  // no line-terminator between the two words.
  if (extension_ != NULL && peek() == Token::FUNCTION &&
      !scanner()->HasAnyLineTerminatorBeforeNext() && expr != NULL &&
      expr->AsVariableProxy() != NULL &&
      expr->AsVariableProxy()->raw_name() ==
          ast_value_factory()->native_string() &&
      !scanner()->literal_contains_escapes()) {
    return ParseNativeDeclaration(ok);
  }

  // Parsed expression statement, followed by semicolon.
  // Detect attempts at 'let' declarations in sloppy mode.
  if (!allow_harmony_sloppy_let() && peek() == Token::IDENTIFIER &&
      expr->AsVariableProxy() != NULL &&
      expr->AsVariableProxy()->raw_name() ==
          ast_value_factory()->let_string()) {
    ReportMessage(MessageTemplate::kSloppyLexical, NULL);
    *ok = false;
    return NULL;
  }
  ExpectSemicolon(CHECK_OK);
  return factory()->NewExpressionStatement(expr, pos);
}


IfStatement* Parser::ParseIfStatement(ZoneList<const AstRawString*>* labels,
                                      bool* ok) {
  // IfStatement ::
  //   'if' '(' Expression ')' Statement ('else' Statement)?

  int pos = peek_position();
  Expect(Token::IF, CHECK_OK);
  Expect(Token::LPAREN, CHECK_OK);
  Expression* condition = ParseExpression(true, CHECK_OK);
  Expect(Token::RPAREN, CHECK_OK);
  Statement* then_statement = ParseSubStatement(labels, CHECK_OK);
  Statement* else_statement = NULL;
  if (peek() == Token::ELSE) {
    Next();
    else_statement = ParseSubStatement(labels, CHECK_OK);
  } else {
    else_statement = factory()->NewEmptyStatement(RelocInfo::kNoPosition);
  }
  return factory()->NewIfStatement(
      condition, then_statement, else_statement, pos);
}


Statement* Parser::ParseContinueStatement(bool* ok) {
  // ContinueStatement ::
  //   'continue' Identifier? ';'

  int pos = peek_position();
  Expect(Token::CONTINUE, CHECK_OK);
  const AstRawString* label = NULL;
  Token::Value tok = peek();
  if (!scanner()->HasAnyLineTerminatorBeforeNext() &&
      tok != Token::SEMICOLON && tok != Token::RBRACE && tok != Token::EOS) {
    // ECMA allows "eval" or "arguments" as labels even in strict mode.
    label = ParseIdentifier(kAllowRestrictedIdentifiers, CHECK_OK);
  }
  IterationStatement* target = LookupContinueTarget(label, CHECK_OK);
  if (target == NULL) {
    // Illegal continue statement.
    MessageTemplate::Template message = MessageTemplate::kIllegalContinue;
    if (label != NULL) {
      message = MessageTemplate::kUnknownLabel;
    }
    ParserTraits::ReportMessage(message, label);
    *ok = false;
    return NULL;
  }
  ExpectSemicolon(CHECK_OK);
  return factory()->NewContinueStatement(target, pos);
}


Statement* Parser::ParseBreakStatement(ZoneList<const AstRawString*>* labels,
                                       bool* ok) {
  // BreakStatement ::
  //   'break' Identifier? ';'

  int pos = peek_position();
  Expect(Token::BREAK, CHECK_OK);
  const AstRawString* label = NULL;
  Token::Value tok = peek();
  if (!scanner()->HasAnyLineTerminatorBeforeNext() &&
      tok != Token::SEMICOLON && tok != Token::RBRACE && tok != Token::EOS) {
    // ECMA allows "eval" or "arguments" as labels even in strict mode.
    label = ParseIdentifier(kAllowRestrictedIdentifiers, CHECK_OK);
  }
  // Parse labeled break statements that target themselves into
  // empty statements, e.g. 'l1: l2: l3: break l2;'
  if (label != NULL && ContainsLabel(labels, label)) {
    ExpectSemicolon(CHECK_OK);
    return factory()->NewEmptyStatement(pos);
  }
  BreakableStatement* target = NULL;
  target = LookupBreakTarget(label, CHECK_OK);
  if (target == NULL) {
    // Illegal break statement.
    MessageTemplate::Template message = MessageTemplate::kIllegalBreak;
    if (label != NULL) {
      message = MessageTemplate::kUnknownLabel;
    }
    ParserTraits::ReportMessage(message, label);
    *ok = false;
    return NULL;
  }
  ExpectSemicolon(CHECK_OK);
  return factory()->NewBreakStatement(target, pos);
}


Statement* Parser::ParseReturnStatement(bool* ok) {
  // ReturnStatement ::
  //   'return' Expression? ';'

  // Consume the return token. It is necessary to do that before
  // reporting any errors on it, because of the way errors are
  // reported (underlining).
  Expect(Token::RETURN, CHECK_OK);
  Scanner::Location loc = scanner()->location();
  function_state_->set_return_location(loc);

  Token::Value tok = peek();
  Statement* result;
  Expression* return_value;
  if (scanner()->HasAnyLineTerminatorBeforeNext() ||
      tok == Token::SEMICOLON ||
      tok == Token::RBRACE ||
      tok == Token::EOS) {
    if (IsSubclassConstructor(function_state_->kind())) {
      return_value = ThisExpression(scope_, factory(), loc.beg_pos);
    } else {
      return_value = GetLiteralUndefined(position());
    }
  } else {
    if (is_strong(language_mode()) &&
        IsClassConstructor(function_state_->kind())) {
      int pos = peek_position();
      ReportMessageAt(Scanner::Location(pos, pos + 1),
                      MessageTemplate::kStrongConstructorReturnValue);
      *ok = false;
      return NULL;
    }

    int pos = peek_position();
    return_value = ParseExpression(true, CHECK_OK);

    if (IsSubclassConstructor(function_state_->kind())) {
      // For subclass constructors we need to return this in case of undefined
      // and throw an exception in case of a non object.
      //
      //   return expr;
      //
      // Is rewritten as:
      //
      //   return (temp = expr) === undefined ? this :
      //       %_IsJSReceiver(temp) ? temp : throw new TypeError(...);
      Variable* temp = scope_->NewTemporary(
          ast_value_factory()->empty_string());
      Assignment* assign = factory()->NewAssignment(
          Token::ASSIGN, factory()->NewVariableProxy(temp), return_value, pos);

      Expression* throw_expression =
          NewThrowTypeError(MessageTemplate::kDerivedConstructorReturn,
                            ast_value_factory()->empty_string(), pos);

      // %_IsJSReceiver(temp)
      ZoneList<Expression*>* is_spec_object_args =
          new (zone()) ZoneList<Expression*>(1, zone());
      is_spec_object_args->Add(factory()->NewVariableProxy(temp), zone());
      Expression* is_spec_object_call = factory()->NewCallRuntime(
          Runtime::kInlineIsJSReceiver, is_spec_object_args, pos);

      // %_IsJSReceiver(temp) ? temp : throw_expression
      Expression* is_object_conditional = factory()->NewConditional(
          is_spec_object_call, factory()->NewVariableProxy(temp),
          throw_expression, pos);

      // temp === undefined
      Expression* is_undefined = factory()->NewCompareOperation(
          Token::EQ_STRICT, assign,
          factory()->NewUndefinedLiteral(RelocInfo::kNoPosition), pos);

      // is_undefined ? this : is_object_conditional
      return_value = factory()->NewConditional(
          is_undefined, ThisExpression(scope_, factory(), pos),
          is_object_conditional, pos);
    }

    return_value->MarkTail();
  }
  ExpectSemicolon(CHECK_OK);

  if (is_generator()) {
    Expression* generator = factory()->NewVariableProxy(
        function_state_->generator_object_variable());
    Expression* yield = factory()->NewYield(
        generator, return_value, Yield::kFinal, loc.beg_pos);
    result = factory()->NewExpressionStatement(yield, loc.beg_pos);
  } else {
    result = factory()->NewReturnStatement(return_value, loc.beg_pos);
  }

  Scope* decl_scope = scope_->DeclarationScope();
  if (decl_scope->is_script_scope() || decl_scope->is_eval_scope()) {
    ReportMessageAt(loc, MessageTemplate::kIllegalReturn);
    *ok = false;
    return NULL;
  }
  return result;
}


Statement* Parser::ParseWithStatement(ZoneList<const AstRawString*>* labels,
                                      bool* ok) {
  // WithStatement ::
  //   'with' '(' Expression ')' Statement

  Expect(Token::WITH, CHECK_OK);
  int pos = position();

  if (is_strict(language_mode())) {
    ReportMessage(MessageTemplate::kStrictWith);
    *ok = false;
    return NULL;
  }

  Expect(Token::LPAREN, CHECK_OK);
  Expression* expr = ParseExpression(true, CHECK_OK);
  Expect(Token::RPAREN, CHECK_OK);

  scope_->DeclarationScope()->RecordWithStatement();
  Scope* with_scope = NewScope(scope_, WITH_SCOPE);
  Block* body;
  { BlockState block_state(&scope_, with_scope);
    with_scope->set_start_position(scanner()->peek_location().beg_pos);

    // The body of the with statement must be enclosed in an additional
    // lexical scope in case the body is a FunctionDeclaration.
    body = factory()->NewBlock(labels, 1, false, RelocInfo::kNoPosition);
    Scope* block_scope = NewScope(scope_, BLOCK_SCOPE);
    block_scope->set_start_position(scanner()->location().beg_pos);
    {
      BlockState block_state(&scope_, block_scope);
      Target target(&this->target_stack_, body);
      Statement* stmt = ParseSubStatement(labels, CHECK_OK);
      body->statements()->Add(stmt, zone());
      block_scope->set_end_position(scanner()->location().end_pos);
      block_scope = block_scope->FinalizeBlockScope();
      body->set_scope(block_scope);
    }

    with_scope->set_end_position(scanner()->location().end_pos);
  }
  return factory()->NewWithStatement(with_scope, expr, body, pos);
}


CaseClause* Parser::ParseCaseClause(bool* default_seen_ptr, bool* ok) {
  // CaseClause ::
  //   'case' Expression ':' StatementList
  //   'default' ':' StatementList

  Expression* label = NULL;  // NULL expression indicates default case
  if (peek() == Token::CASE) {
    Expect(Token::CASE, CHECK_OK);
    label = ParseExpression(true, CHECK_OK);
  } else {
    Expect(Token::DEFAULT, CHECK_OK);
    if (*default_seen_ptr) {
      ReportMessage(MessageTemplate::kMultipleDefaultsInSwitch);
      *ok = false;
      return NULL;
    }
    *default_seen_ptr = true;
  }
  Expect(Token::COLON, CHECK_OK);
  int pos = position();
  ZoneList<Statement*>* statements =
      new(zone()) ZoneList<Statement*>(5, zone());
  Statement* stat = NULL;
  while (peek() != Token::CASE &&
         peek() != Token::DEFAULT &&
         peek() != Token::RBRACE) {
    stat = ParseStatementListItem(CHECK_OK);
    statements->Add(stat, zone());
  }
  if (is_strong(language_mode()) && stat != NULL && !stat->IsJump() &&
      peek() != Token::RBRACE) {
    ReportMessageAt(scanner()->location(),
                    MessageTemplate::kStrongSwitchFallthrough);
    *ok = false;
    return NULL;
  }
  return factory()->NewCaseClause(label, statements, pos);
}


Statement* Parser::ParseSwitchStatement(ZoneList<const AstRawString*>* labels,
                                        bool* ok) {
  // SwitchStatement ::
  //   'switch' '(' Expression ')' '{' CaseClause* '}'
  // In order to get the CaseClauses to execute in their own lexical scope,
  // but without requiring downstream code to have special scope handling
  // code for switch statements, desugar into blocks as follows:
  // {  // To group the statements--harmless to evaluate Expression in scope
  //   .tag_variable = Expression;
  //   {  // To give CaseClauses a scope
  //     switch (.tag_variable) { CaseClause* }
  //   }
  // }

  Block* switch_block =
      factory()->NewBlock(NULL, 2, false, RelocInfo::kNoPosition);
  int switch_pos = peek_position();

  Expect(Token::SWITCH, CHECK_OK);
  Expect(Token::LPAREN, CHECK_OK);
  Expression* tag = ParseExpression(true, CHECK_OK);
  Expect(Token::RPAREN, CHECK_OK);

  Variable* tag_variable =
      scope_->NewTemporary(ast_value_factory()->dot_switch_tag_string());
  Assignment* tag_assign = factory()->NewAssignment(
      Token::ASSIGN, factory()->NewVariableProxy(tag_variable), tag,
      tag->position());
  Statement* tag_statement =
      factory()->NewExpressionStatement(tag_assign, RelocInfo::kNoPosition);
  switch_block->statements()->Add(tag_statement, zone());

  // make statement: undefined;
  // This is needed so the tag isn't returned as the value, in case the switch
  // statements don't have a value.
  switch_block->statements()->Add(
      factory()->NewExpressionStatement(
          factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
          RelocInfo::kNoPosition),
      zone());

  Block* cases_block =
      factory()->NewBlock(NULL, 1, false, RelocInfo::kNoPosition);
  Scope* cases_scope = NewScope(scope_, BLOCK_SCOPE);
  cases_scope->SetNonlinear();

  SwitchStatement* switch_statement =
      factory()->NewSwitchStatement(labels, switch_pos);

  cases_scope->set_start_position(scanner()->location().beg_pos);
  {
    BlockState cases_block_state(&scope_, cases_scope);
    Target target(&this->target_stack_, switch_statement);

    Expression* tag_read = factory()->NewVariableProxy(tag_variable);

    bool default_seen = false;
    ZoneList<CaseClause*>* cases =
        new (zone()) ZoneList<CaseClause*>(4, zone());
    Expect(Token::LBRACE, CHECK_OK);
    while (peek() != Token::RBRACE) {
      CaseClause* clause = ParseCaseClause(&default_seen, CHECK_OK);
      cases->Add(clause, zone());
    }
    switch_statement->Initialize(tag_read, cases);
    cases_block->statements()->Add(switch_statement, zone());
  }
  Expect(Token::RBRACE, CHECK_OK);

  cases_scope->set_end_position(scanner()->location().end_pos);
  cases_scope = cases_scope->FinalizeBlockScope();
  cases_block->set_scope(cases_scope);

  switch_block->statements()->Add(cases_block, zone());

  return switch_block;
}


Statement* Parser::ParseThrowStatement(bool* ok) {
  // ThrowStatement ::
  //   'throw' Expression ';'

  Expect(Token::THROW, CHECK_OK);
  int pos = position();
  if (scanner()->HasAnyLineTerminatorBeforeNext()) {
    ReportMessage(MessageTemplate::kNewlineAfterThrow);
    *ok = false;
    return NULL;
  }
  Expression* exception = ParseExpression(true, CHECK_OK);
  ExpectSemicolon(CHECK_OK);

  return factory()->NewExpressionStatement(
      factory()->NewThrow(exception, pos), pos);
}


TryStatement* Parser::ParseTryStatement(bool* ok) {
  // TryStatement ::
  //   'try' Block Catch
  //   'try' Block Finally
  //   'try' Block Catch Finally
  //
  // Catch ::
  //   'catch' '(' Identifier ')' Block
  //
  // Finally ::
  //   'finally' Block

  Expect(Token::TRY, CHECK_OK);
  int pos = position();

  Block* try_block = ParseBlock(NULL, CHECK_OK);

  Token::Value tok = peek();
  if (tok != Token::CATCH && tok != Token::FINALLY) {
    ReportMessage(MessageTemplate::kNoCatchOrFinally);
    *ok = false;
    return NULL;
  }

  Scope* catch_scope = NULL;
  Variable* catch_variable = NULL;
  Block* catch_block = NULL;
  if (tok == Token::CATCH) {
    Consume(Token::CATCH);

    Expect(Token::LPAREN, CHECK_OK);
    catch_scope = NewScope(scope_, CATCH_SCOPE);
    catch_scope->set_start_position(scanner()->location().beg_pos);

    ExpressionClassifier pattern_classifier;
    Expression* pattern = ParsePrimaryExpression(&pattern_classifier, CHECK_OK);
    ValidateBindingPattern(&pattern_classifier, CHECK_OK);

    const AstRawString* name = ast_value_factory()->dot_catch_string();
    bool is_simple = pattern->IsVariableProxy();
    if (is_simple) {
      auto proxy = pattern->AsVariableProxy();
      scope_->RemoveUnresolved(proxy);
      name = proxy->raw_name();
    }

    catch_variable = catch_scope->DeclareLocal(name, VAR, kCreatedInitialized,
                                               Variable::NORMAL);

    Expect(Token::RPAREN, CHECK_OK);

    {
      BlockState block_state(&scope_, catch_scope);

      // TODO(adamk): Make a version of ParseBlock that takes a scope and
      // a block.
      catch_block =
          factory()->NewBlock(nullptr, 16, false, RelocInfo::kNoPosition);
      Scope* block_scope = NewScope(scope_, BLOCK_SCOPE);

      block_scope->set_start_position(scanner()->location().beg_pos);
      {
        BlockState block_state(&scope_, block_scope);
        Target target(&this->target_stack_, catch_block);

        if (!is_simple) {
          DeclarationDescriptor descriptor;
          descriptor.declaration_kind = DeclarationDescriptor::NORMAL;
          descriptor.parser = this;
          descriptor.scope = scope_;
          descriptor.hoist_scope = nullptr;
          descriptor.mode = LET;
          descriptor.needs_init = true;
          descriptor.declaration_pos = pattern->position();
          descriptor.initialization_pos = pattern->position();

          DeclarationParsingResult::Declaration decl(
              pattern, pattern->position(),
              factory()->NewVariableProxy(catch_variable));

          PatternRewriter::DeclareAndInitializeVariables(
              catch_block, &descriptor, &decl, nullptr, CHECK_OK);
        }

        Expect(Token::LBRACE, CHECK_OK);
        while (peek() != Token::RBRACE) {
          Statement* stat = ParseStatementListItem(CHECK_OK);
          if (stat && !stat->IsEmpty()) {
            catch_block->statements()->Add(stat, zone());
          }
        }
        Consume(Token::RBRACE);
      }
      block_scope->set_end_position(scanner()->location().end_pos);
      block_scope = block_scope->FinalizeBlockScope();
      catch_block->set_scope(block_scope);
    }

    catch_scope->set_end_position(scanner()->location().end_pos);
    tok = peek();
  }

  Block* finally_block = NULL;
  DCHECK(tok == Token::FINALLY || catch_block != NULL);
  if (tok == Token::FINALLY) {
    Consume(Token::FINALLY);
    finally_block = ParseBlock(NULL, CHECK_OK);
  }

  // Simplify the AST nodes by converting:
  //   'try B0 catch B1 finally B2'
  // to:
  //   'try { try B0 catch B1 } finally B2'

  if (catch_block != NULL && finally_block != NULL) {
    // If we have both, create an inner try/catch.
    DCHECK(catch_scope != NULL && catch_variable != NULL);
    TryCatchStatement* statement =
        factory()->NewTryCatchStatement(try_block, catch_scope, catch_variable,
                                        catch_block, RelocInfo::kNoPosition);
    try_block = factory()->NewBlock(NULL, 1, false, RelocInfo::kNoPosition);
    try_block->statements()->Add(statement, zone());
    catch_block = NULL;  // Clear to indicate it's been handled.
  }

  TryStatement* result = NULL;
  if (catch_block != NULL) {
    DCHECK(finally_block == NULL);
    DCHECK(catch_scope != NULL && catch_variable != NULL);
    result = factory()->NewTryCatchStatement(try_block, catch_scope,
                                             catch_variable, catch_block, pos);
  } else {
    DCHECK(finally_block != NULL);
    result = factory()->NewTryFinallyStatement(try_block, finally_block, pos);
  }

  return result;
}


DoWhileStatement* Parser::ParseDoWhileStatement(
    ZoneList<const AstRawString*>* labels, bool* ok) {
  // DoStatement ::
  //   'do' Statement 'while' '(' Expression ')' ';'

  DoWhileStatement* loop =
      factory()->NewDoWhileStatement(labels, peek_position());
  Target target(&this->target_stack_, loop);

  Expect(Token::DO, CHECK_OK);
  Statement* body = ParseSubStatement(NULL, CHECK_OK);
  Expect(Token::WHILE, CHECK_OK);
  Expect(Token::LPAREN, CHECK_OK);

  Expression* cond = ParseExpression(true, CHECK_OK);
  Expect(Token::RPAREN, CHECK_OK);

  // Allow do-statements to be terminated with and without
  // semi-colons. This allows code such as 'do;while(0)return' to
  // parse, which would not be the case if we had used the
  // ExpectSemicolon() functionality here.
  if (peek() == Token::SEMICOLON) Consume(Token::SEMICOLON);

  if (loop != NULL) loop->Initialize(cond, body);
  return loop;
}


WhileStatement* Parser::ParseWhileStatement(
    ZoneList<const AstRawString*>* labels, bool* ok) {
  // WhileStatement ::
  //   'while' '(' Expression ')' Statement

  WhileStatement* loop = factory()->NewWhileStatement(labels, peek_position());
  Target target(&this->target_stack_, loop);

  Expect(Token::WHILE, CHECK_OK);
  Expect(Token::LPAREN, CHECK_OK);
  Expression* cond = ParseExpression(true, CHECK_OK);
  Expect(Token::RPAREN, CHECK_OK);
  Statement* body = ParseSubStatement(NULL, CHECK_OK);

  if (loop != NULL) loop->Initialize(cond, body);
  return loop;
}


// !%_IsJSReceiver(result = iterator.next()) &&
//     %ThrowIteratorResultNotAnObject(result)
Expression* Parser::BuildIteratorNextResult(Expression* iterator,
                                            Variable* result, int pos) {
  Expression* next_literal = factory()->NewStringLiteral(
      ast_value_factory()->next_string(), RelocInfo::kNoPosition);
  Expression* next_property =
      factory()->NewProperty(iterator, next_literal, RelocInfo::kNoPosition);
  ZoneList<Expression*>* next_arguments =
      new (zone()) ZoneList<Expression*>(0, zone());
  Expression* next_call =
      factory()->NewCall(next_property, next_arguments, pos);
  Expression* result_proxy = factory()->NewVariableProxy(result);
  Expression* left =
      factory()->NewAssignment(Token::ASSIGN, result_proxy, next_call, pos);

  // %_IsJSReceiver(...)
  ZoneList<Expression*>* is_spec_object_args =
      new (zone()) ZoneList<Expression*>(1, zone());
  is_spec_object_args->Add(left, zone());
  Expression* is_spec_object_call = factory()->NewCallRuntime(
      Runtime::kInlineIsJSReceiver, is_spec_object_args, pos);

  // %ThrowIteratorResultNotAnObject(result)
  Expression* result_proxy_again = factory()->NewVariableProxy(result);
  ZoneList<Expression*>* throw_arguments =
      new (zone()) ZoneList<Expression*>(1, zone());
  throw_arguments->Add(result_proxy_again, zone());
  Expression* throw_call = factory()->NewCallRuntime(
      Runtime::kThrowIteratorResultNotAnObject, throw_arguments, pos);

  return factory()->NewBinaryOperation(
      Token::AND,
      factory()->NewUnaryOperation(Token::NOT, is_spec_object_call, pos),
      throw_call, pos);
}


void Parser::InitializeForEachStatement(ForEachStatement* stmt,
                                        Expression* each, Expression* subject,
                                        Statement* body,
                                        bool is_destructuring) {
  DCHECK(!is_destructuring || allow_harmony_destructuring_assignment());
  ForOfStatement* for_of = stmt->AsForOfStatement();

  if (for_of != NULL) {
    Variable* iterator = scope_->NewTemporary(
        ast_value_factory()->dot_iterator_string());
    Variable* result = scope_->NewTemporary(
        ast_value_factory()->dot_result_string());

    Expression* assign_iterator;
    Expression* next_result;
    Expression* result_done;
    Expression* assign_each;

    // iterator = subject[Symbol.iterator]()
    // Hackily disambiguate o from o.next and o [Symbol.iterator]().
    // TODO(verwaest): Come up with a better solution.
    assign_iterator = factory()->NewAssignment(
        Token::ASSIGN, factory()->NewVariableProxy(iterator),
        GetIterator(subject, factory(), subject->position() - 2),
        subject->position());

    // !%_IsJSReceiver(result = iterator.next()) &&
    //     %ThrowIteratorResultNotAnObject(result)
    {
      // result = iterator.next()
      Expression* iterator_proxy = factory()->NewVariableProxy(iterator);
      // Hackily disambiguate o from o.next and o [Symbol.iterator]().
      // TODO(verwaest): Come up with a better solution.
      next_result = BuildIteratorNextResult(iterator_proxy, result,
                                            subject->position() - 1);
    }

    // result.done
    {
      Expression* done_literal = factory()->NewStringLiteral(
          ast_value_factory()->done_string(), RelocInfo::kNoPosition);
      Expression* result_proxy = factory()->NewVariableProxy(result);
      result_done = factory()->NewProperty(
          result_proxy, done_literal, RelocInfo::kNoPosition);
    }

    // each = result.value
    {
      Expression* value_literal = factory()->NewStringLiteral(
          ast_value_factory()->value_string(), RelocInfo::kNoPosition);
      Expression* result_proxy = factory()->NewVariableProxy(result);
      Expression* result_value = factory()->NewProperty(
          result_proxy, value_literal, RelocInfo::kNoPosition);
      assign_each = factory()->NewAssignment(Token::ASSIGN, each, result_value,
                                             RelocInfo::kNoPosition);
      if (is_destructuring) {
        assign_each = PatternRewriter::RewriteDestructuringAssignment(
            this, assign_each->AsAssignment(), scope_);
      }
    }

    for_of->Initialize(each, subject, body,
                       assign_iterator,
                       next_result,
                       result_done,
                       assign_each);
  } else {
    if (is_destructuring) {
      Variable* temp =
          scope_->NewTemporary(ast_value_factory()->empty_string());
      VariableProxy* temp_proxy = factory()->NewVariableProxy(temp);
      Expression* assign_each = PatternRewriter::RewriteDestructuringAssignment(
          this, factory()->NewAssignment(Token::ASSIGN, each, temp_proxy,
                                         RelocInfo::kNoPosition),
          scope_);
      auto block =
          factory()->NewBlock(nullptr, 2, false, RelocInfo::kNoPosition);
      block->statements()->Add(factory()->NewExpressionStatement(
                                   assign_each, RelocInfo::kNoPosition),
                               zone());
      block->statements()->Add(body, zone());
      body = block;
      each = factory()->NewVariableProxy(temp);
    }
    stmt->Initialize(each, subject, body);
  }
}


Statement* Parser::DesugarLexicalBindingsInForStatement(
    Scope* inner_scope, bool is_const, ZoneList<const AstRawString*>* names,
    ForStatement* loop, Statement* init, Expression* cond, Statement* next,
    Statement* body, bool* ok) {
  // ES6 13.7.4.8 specifies that on each loop iteration the let variables are
  // copied into a new environment.  Moreover, the "next" statement must be
  // evaluated not in the environment of the just completed iteration but in
  // that of the upcoming one.  We achieve this with the following desugaring.
  // Extra care is needed to preserve the completion value of the original loop.
  //
  // We are given a for statement of the form
  //
  //  labels: for (let/const x = i; cond; next) body
  //
  // and rewrite it as follows.  Here we write {{ ... }} for init-blocks, ie.,
  // blocks whose ignore_completion_value_ flag is set.
  //
  //  {
  //    let/const x = i;
  //    temp_x = x;
  //    first = 1;
  //    undefined;
  //    outer: for (;;) {
  //      let/const x = temp_x;
  //      {{ if (first == 1) {
  //           first = 0;
  //         } else {
  //           next;
  //         }
  //         flag = 1;
  //         if (!cond) break;
  //      }}
  //      labels: for (; flag == 1; flag = 0, temp_x = x) {
  //        body
  //      }
  //      {{ if (flag == 1)  // Body used break.
  //           break;
  //      }}
  //    }
  //  }

  DCHECK(names->length() > 0);
  Scope* for_scope = scope_;
  ZoneList<Variable*> temps(names->length(), zone());

  Block* outer_block = factory()->NewBlock(NULL, names->length() + 4, false,
                                           RelocInfo::kNoPosition);

  // Add statement: let/const x = i.
  outer_block->statements()->Add(init, zone());

  const AstRawString* temp_name = ast_value_factory()->dot_for_string();

  // For each lexical variable x:
  //   make statement: temp_x = x.
  for (int i = 0; i < names->length(); i++) {
    VariableProxy* proxy = NewUnresolved(names->at(i), LET);
    Variable* temp = scope_->NewTemporary(temp_name);
    VariableProxy* temp_proxy = factory()->NewVariableProxy(temp);
    Assignment* assignment = factory()->NewAssignment(
        Token::ASSIGN, temp_proxy, proxy, RelocInfo::kNoPosition);
    Statement* assignment_statement = factory()->NewExpressionStatement(
        assignment, RelocInfo::kNoPosition);
    outer_block->statements()->Add(assignment_statement, zone());
    temps.Add(temp, zone());
  }

  Variable* first = NULL;
  // Make statement: first = 1.
  if (next) {
    first = scope_->NewTemporary(temp_name);
    VariableProxy* first_proxy = factory()->NewVariableProxy(first);
    Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
    Assignment* assignment = factory()->NewAssignment(
        Token::ASSIGN, first_proxy, const1, RelocInfo::kNoPosition);
    Statement* assignment_statement =
        factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
    outer_block->statements()->Add(assignment_statement, zone());
  }

  // make statement: undefined;
  outer_block->statements()->Add(
      factory()->NewExpressionStatement(
          factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
          RelocInfo::kNoPosition),
      zone());

  // Make statement: outer: for (;;)
  // Note that we don't actually create the label, or set this loop up as an
  // explicit break target, instead handing it directly to those nodes that
  // need to know about it. This should be safe because we don't run any code
  // in this function that looks up break targets.
  ForStatement* outer_loop =
      factory()->NewForStatement(NULL, RelocInfo::kNoPosition);
  outer_block->statements()->Add(outer_loop, zone());

  outer_block->set_scope(for_scope);
  scope_ = inner_scope;

  Block* inner_block =
      factory()->NewBlock(NULL, 3, false, RelocInfo::kNoPosition);
  Block* ignore_completion_block = factory()->NewBlock(
      NULL, names->length() + 3, true, RelocInfo::kNoPosition);
  ZoneList<Variable*> inner_vars(names->length(), zone());
  // For each let variable x:
  //    make statement: let/const x = temp_x.
  VariableMode mode = is_const ? CONST : LET;
  for (int i = 0; i < names->length(); i++) {
    VariableProxy* proxy = NewUnresolved(names->at(i), mode);
    Declaration* declaration = factory()->NewVariableDeclaration(
        proxy, mode, scope_, RelocInfo::kNoPosition);
    Declare(declaration, DeclarationDescriptor::NORMAL, true, CHECK_OK);
    inner_vars.Add(declaration->proxy()->var(), zone());
    VariableProxy* temp_proxy = factory()->NewVariableProxy(temps.at(i));
    Assignment* assignment = factory()->NewAssignment(
        Token::INIT, proxy, temp_proxy, RelocInfo::kNoPosition);
    Statement* assignment_statement =
        factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
    DCHECK(init->position() != RelocInfo::kNoPosition);
    proxy->var()->set_initializer_position(init->position());
    ignore_completion_block->statements()->Add(assignment_statement, zone());
  }

  // Make statement: if (first == 1) { first = 0; } else { next; }
  if (next) {
    DCHECK(first);
    Expression* compare = NULL;
    // Make compare expression: first == 1.
    {
      Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
      VariableProxy* first_proxy = factory()->NewVariableProxy(first);
      compare = factory()->NewCompareOperation(Token::EQ, first_proxy, const1,
                                               RelocInfo::kNoPosition);
    }
    Statement* clear_first = NULL;
    // Make statement: first = 0.
    {
      VariableProxy* first_proxy = factory()->NewVariableProxy(first);
      Expression* const0 = factory()->NewSmiLiteral(0, RelocInfo::kNoPosition);
      Assignment* assignment = factory()->NewAssignment(
          Token::ASSIGN, first_proxy, const0, RelocInfo::kNoPosition);
      clear_first =
          factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
    }
    Statement* clear_first_or_next = factory()->NewIfStatement(
        compare, clear_first, next, RelocInfo::kNoPosition);
    ignore_completion_block->statements()->Add(clear_first_or_next, zone());
  }

  Variable* flag = scope_->NewTemporary(temp_name);
  // Make statement: flag = 1.
  {
    VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
    Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
    Assignment* assignment = factory()->NewAssignment(
        Token::ASSIGN, flag_proxy, const1, RelocInfo::kNoPosition);
    Statement* assignment_statement =
        factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
    ignore_completion_block->statements()->Add(assignment_statement, zone());
  }

  // Make statement: if (!cond) break.
  if (cond) {
    Statement* stop =
        factory()->NewBreakStatement(outer_loop, RelocInfo::kNoPosition);
    Statement* noop = factory()->NewEmptyStatement(RelocInfo::kNoPosition);
    ignore_completion_block->statements()->Add(
        factory()->NewIfStatement(cond, noop, stop, cond->position()), zone());
  }

  inner_block->statements()->Add(ignore_completion_block, zone());
  // Make cond expression for main loop: flag == 1.
  Expression* flag_cond = NULL;
  {
    Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
    VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
    flag_cond = factory()->NewCompareOperation(Token::EQ, flag_proxy, const1,
                                               RelocInfo::kNoPosition);
  }

  // Create chain of expressions "flag = 0, temp_x = x, ..."
  Statement* compound_next_statement = NULL;
  {
    Expression* compound_next = NULL;
    // Make expression: flag = 0.
    {
      VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
      Expression* const0 = factory()->NewSmiLiteral(0, RelocInfo::kNoPosition);
      compound_next = factory()->NewAssignment(Token::ASSIGN, flag_proxy,
                                               const0, RelocInfo::kNoPosition);
    }

    // Make the comma-separated list of temp_x = x assignments.
    int inner_var_proxy_pos = scanner()->location().beg_pos;
    for (int i = 0; i < names->length(); i++) {
      VariableProxy* temp_proxy = factory()->NewVariableProxy(temps.at(i));
      VariableProxy* proxy =
          factory()->NewVariableProxy(inner_vars.at(i), inner_var_proxy_pos);
      Assignment* assignment = factory()->NewAssignment(
          Token::ASSIGN, temp_proxy, proxy, RelocInfo::kNoPosition);
      compound_next = factory()->NewBinaryOperation(
          Token::COMMA, compound_next, assignment, RelocInfo::kNoPosition);
    }

    compound_next_statement = factory()->NewExpressionStatement(
        compound_next, RelocInfo::kNoPosition);
  }

  // Make statement: labels: for (; flag == 1; flag = 0, temp_x = x)
  // Note that we re-use the original loop node, which retains its labels
  // and ensures that any break or continue statements in body point to
  // the right place.
  loop->Initialize(NULL, flag_cond, compound_next_statement, body);
  inner_block->statements()->Add(loop, zone());

  // Make statement: {{if (flag == 1) break;}}
  {
    Expression* compare = NULL;
    // Make compare expresion: flag == 1.
    {
      Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
      VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
      compare = factory()->NewCompareOperation(Token::EQ, flag_proxy, const1,
                                               RelocInfo::kNoPosition);
    }
    Statement* stop =
        factory()->NewBreakStatement(outer_loop, RelocInfo::kNoPosition);
    Statement* empty = factory()->NewEmptyStatement(RelocInfo::kNoPosition);
    Statement* if_flag_break =
        factory()->NewIfStatement(compare, stop, empty, RelocInfo::kNoPosition);
    Block* ignore_completion_block =
        factory()->NewBlock(NULL, 1, true, RelocInfo::kNoPosition);
    ignore_completion_block->statements()->Add(if_flag_break, zone());
    inner_block->statements()->Add(ignore_completion_block, zone());
  }

  inner_scope->set_end_position(scanner()->location().end_pos);
  inner_block->set_scope(inner_scope);
  scope_ = for_scope;

  outer_loop->Initialize(NULL, NULL, NULL, inner_block);
  return outer_block;
}


Statement* Parser::ParseForStatement(ZoneList<const AstRawString*>* labels,
                                     bool* ok) {
  // ForStatement ::
  //   'for' '(' Expression? ';' Expression? ';' Expression? ')' Statement

  int stmt_pos = peek_position();
  bool is_const = false;
  Statement* init = NULL;
  ZoneList<const AstRawString*> lexical_bindings(1, zone());

  // Create an in-between scope for let-bound iteration variables.
  Scope* saved_scope = scope_;
  Scope* for_scope = NewScope(scope_, BLOCK_SCOPE);
  scope_ = for_scope;
  Expect(Token::FOR, CHECK_OK);
  Expect(Token::LPAREN, CHECK_OK);
  for_scope->set_start_position(scanner()->location().beg_pos);
  bool is_let_identifier_expression = false;
  DeclarationParsingResult parsing_result;
  if (peek() != Token::SEMICOLON) {
    if (peek() == Token::VAR || (peek() == Token::CONST && allow_const()) ||
        (peek() == Token::LET && IsNextLetKeyword())) {
      ParseVariableDeclarations(kForStatement, &parsing_result, CHECK_OK);
      is_const = parsing_result.descriptor.mode == CONST;

      int num_decl = parsing_result.declarations.length();
      bool accept_IN = num_decl >= 1;
      ForEachStatement::VisitMode mode;
      int each_beg_pos = scanner()->location().beg_pos;
      int each_end_pos = scanner()->location().end_pos;

      if (accept_IN && CheckInOrOf(&mode, ok)) {
        if (!*ok) return nullptr;
        if (num_decl != 1) {
          const char* loop_type =
              mode == ForEachStatement::ITERATE ? "for-of" : "for-in";
          ParserTraits::ReportMessageAt(
              parsing_result.bindings_loc,
              MessageTemplate::kForInOfLoopMultiBindings, loop_type);
          *ok = false;
          return nullptr;
        }
        DeclarationParsingResult::Declaration& decl =
            parsing_result.declarations[0];
        if (parsing_result.first_initializer_loc.IsValid() &&
            (is_strict(language_mode()) || mode == ForEachStatement::ITERATE ||
             IsLexicalVariableMode(parsing_result.descriptor.mode) ||
             !decl.pattern->IsVariableProxy())) {
          if (mode == ForEachStatement::ITERATE) {
            ReportMessageAt(parsing_result.first_initializer_loc,
                            MessageTemplate::kForOfLoopInitializer);
          } else {
            // TODO(caitp): This should be an error in sloppy mode too.
            ReportMessageAt(parsing_result.first_initializer_loc,
                            MessageTemplate::kForInLoopInitializer);
          }
          *ok = false;
          return nullptr;
        }

        Block* init_block = nullptr;

        // special case for legacy for (var/const x =.... in)
        if (!IsLexicalVariableMode(parsing_result.descriptor.mode) &&
            decl.pattern->IsVariableProxy() && decl.initializer != nullptr) {
          const AstRawString* name =
              decl.pattern->AsVariableProxy()->raw_name();
          VariableProxy* single_var = scope_->NewUnresolved(
              factory(), name, Variable::NORMAL, each_beg_pos, each_end_pos);
          init_block = factory()->NewBlock(
              nullptr, 2, true, parsing_result.descriptor.declaration_pos);
          init_block->statements()->Add(
              factory()->NewExpressionStatement(
                  factory()->NewAssignment(Token::ASSIGN, single_var,
                                           decl.initializer,
                                           RelocInfo::kNoPosition),
                  RelocInfo::kNoPosition),
              zone());
        }

        // Rewrite a for-in/of statement of the form
        //
        //   for (let/const/var x in/of e) b
        //
        // into
        //
        //   {
        //     <let x' be a temporary variable>
        //     for (x' in/of e) {
        //       let/const/var x;
        //       x = x';
        //       b;
        //     }
        //     let x;  // for TDZ
        //   }

        Variable* temp = scope_->NewTemporary(
            ast_value_factory()->dot_for_string());
        ForEachStatement* loop =
            factory()->NewForEachStatement(mode, labels, stmt_pos);
        Target target(&this->target_stack_, loop);

        Expression* enumerable = ParseExpression(true, CHECK_OK);

        Expect(Token::RPAREN, CHECK_OK);

        Scope* body_scope = NewScope(scope_, BLOCK_SCOPE);
        body_scope->set_start_position(scanner()->location().beg_pos);
        scope_ = body_scope;

        Statement* body = ParseSubStatement(NULL, CHECK_OK);

        Block* body_block =
            factory()->NewBlock(NULL, 3, false, RelocInfo::kNoPosition);

        auto each_initialization_block =
            factory()->NewBlock(nullptr, 1, true, RelocInfo::kNoPosition);
        {
          auto descriptor = parsing_result.descriptor;
          descriptor.declaration_pos = RelocInfo::kNoPosition;
          descriptor.initialization_pos = RelocInfo::kNoPosition;
          decl.initializer = factory()->NewVariableProxy(temp);

          PatternRewriter::DeclareAndInitializeVariables(
              each_initialization_block, &descriptor, &decl,
              IsLexicalVariableMode(descriptor.mode) ? &lexical_bindings
                                                     : nullptr,
              CHECK_OK);
        }

        body_block->statements()->Add(each_initialization_block, zone());
        body_block->statements()->Add(body, zone());
        VariableProxy* temp_proxy =
            factory()->NewVariableProxy(temp, each_beg_pos, each_end_pos);
        InitializeForEachStatement(loop, temp_proxy, enumerable, body_block,
                                   false);
        scope_ = for_scope;
        body_scope->set_end_position(scanner()->location().end_pos);
        body_scope = body_scope->FinalizeBlockScope();
        if (body_scope != nullptr) {
          body_block->set_scope(body_scope);
        }

        // Create a TDZ for any lexically-bound names.
        if (IsLexicalVariableMode(parsing_result.descriptor.mode)) {
          DCHECK_NULL(init_block);

          init_block =
              factory()->NewBlock(nullptr, 1, false, RelocInfo::kNoPosition);

          for (int i = 0; i < lexical_bindings.length(); ++i) {
            // TODO(adamk): This needs to be some sort of special
            // INTERNAL variable that's invisible to the debugger
            // but visible to everything else.
            VariableProxy* tdz_proxy = NewUnresolved(lexical_bindings[i], LET);
            Declaration* tdz_decl = factory()->NewVariableDeclaration(
                tdz_proxy, LET, scope_, RelocInfo::kNoPosition);
            Variable* tdz_var = Declare(tdz_decl, DeclarationDescriptor::NORMAL,
                                        true, CHECK_OK);
            tdz_var->set_initializer_position(position());
          }
        }

        scope_ = saved_scope;
        for_scope->set_end_position(scanner()->location().end_pos);
        for_scope = for_scope->FinalizeBlockScope();
        // Parsed for-in loop w/ variable declarations.
        if (init_block != nullptr) {
          init_block->statements()->Add(loop, zone());
          if (for_scope != nullptr) {
            init_block->set_scope(for_scope);
          }
          return init_block;
        } else {
          DCHECK_NULL(for_scope);
          return loop;
        }
      } else {
        init = parsing_result.BuildInitializationBlock(
            IsLexicalVariableMode(parsing_result.descriptor.mode)
                ? &lexical_bindings
                : nullptr,
            CHECK_OK);
      }
    } else {
      int lhs_beg_pos = peek_position();
      ExpressionClassifier classifier;
      Expression* expression = ParseExpression(false, &classifier, CHECK_OK);
      int lhs_end_pos = scanner()->location().end_pos;
      ForEachStatement::VisitMode mode;
      is_let_identifier_expression =
          expression->IsVariableProxy() &&
          expression->AsVariableProxy()->raw_name() ==
              ast_value_factory()->let_string();

      bool is_for_each = CheckInOrOf(&mode, ok);
      if (!*ok) return nullptr;
      bool is_destructuring =
          is_for_each && allow_harmony_destructuring_assignment() &&
          (expression->IsArrayLiteral() || expression->IsObjectLiteral());

      if (is_destructuring) {
        ValidateAssignmentPattern(&classifier, CHECK_OK);
      } else {
        expression =
            ParserTraits::RewriteNonPattern(expression, &classifier, CHECK_OK);
      }

      if (is_for_each) {
        if (!is_destructuring) {
          expression = this->CheckAndRewriteReferenceExpression(
              expression, lhs_beg_pos, lhs_end_pos,
              MessageTemplate::kInvalidLhsInFor, kSyntaxError, CHECK_OK);
        }

        ForEachStatement* loop =
            factory()->NewForEachStatement(mode, labels, stmt_pos);
        Target target(&this->target_stack_, loop);

        Expression* enumerable = ParseExpression(true, CHECK_OK);
        Expect(Token::RPAREN, CHECK_OK);

        // Make a block around the statement in case a lexical binding
        // is introduced, e.g. by a FunctionDeclaration.
        // This block must not use for_scope as its scope because if a
        // lexical binding is introduced which overlaps with the for-in/of,
        // expressions in head of the loop should actually have variables
        // resolved in the outer scope.
        Scope* body_scope = NewScope(for_scope, BLOCK_SCOPE);
        scope_ = body_scope;
        Block* block =
            factory()->NewBlock(NULL, 1, false, RelocInfo::kNoPosition);
        Statement* body = ParseSubStatement(NULL, CHECK_OK);
        block->statements()->Add(body, zone());
        InitializeForEachStatement(loop, expression, enumerable, block,
                                   is_destructuring);
        scope_ = saved_scope;
        body_scope->set_end_position(scanner()->location().end_pos);
        body_scope = body_scope->FinalizeBlockScope();
        if (body_scope != nullptr) {
          block->set_scope(body_scope);
        }
        for_scope->set_end_position(scanner()->location().end_pos);
        for_scope = for_scope->FinalizeBlockScope();
        DCHECK(for_scope == nullptr);
        // Parsed for-in loop.
        return loop;

      } else {
        init = factory()->NewExpressionStatement(expression, lhs_beg_pos);
      }
    }
  }

  // Standard 'for' loop
  ForStatement* loop = factory()->NewForStatement(labels, stmt_pos);
  Target target(&this->target_stack_, loop);

  // Parsed initializer at this point.
  // Detect attempts at 'let' declarations in sloppy mode.
  if (!allow_harmony_sloppy_let() && peek() == Token::IDENTIFIER &&
      is_sloppy(language_mode()) && is_let_identifier_expression) {
    ReportMessage(MessageTemplate::kSloppyLexical, NULL);
    *ok = false;
    return NULL;
  }
  Expect(Token::SEMICOLON, CHECK_OK);

  // If there are let bindings, then condition and the next statement of the
  // for loop must be parsed in a new scope.
  Scope* inner_scope = NULL;
  if (lexical_bindings.length() > 0) {
    inner_scope = NewScope(for_scope, BLOCK_SCOPE);
    inner_scope->set_start_position(scanner()->location().beg_pos);
    scope_ = inner_scope;
  }

  Expression* cond = NULL;
  if (peek() != Token::SEMICOLON) {
    cond = ParseExpression(true, CHECK_OK);
  }
  Expect(Token::SEMICOLON, CHECK_OK);

  Statement* next = NULL;
  if (peek() != Token::RPAREN) {
    Expression* exp = ParseExpression(true, CHECK_OK);
    next = factory()->NewExpressionStatement(exp, exp->position());
  }
  Expect(Token::RPAREN, CHECK_OK);

  Statement* body = ParseSubStatement(NULL, CHECK_OK);

  Statement* result = NULL;
  if (lexical_bindings.length() > 0) {
    scope_ = for_scope;
    result = DesugarLexicalBindingsInForStatement(
                 inner_scope, is_const, &lexical_bindings, loop, init, cond,
                 next, body, CHECK_OK);
    scope_ = saved_scope;
    for_scope->set_end_position(scanner()->location().end_pos);
  } else {
    scope_ = saved_scope;
    for_scope->set_end_position(scanner()->location().end_pos);
    for_scope = for_scope->FinalizeBlockScope();
    if (for_scope) {
      // Rewrite a for statement of the form
      //   for (const x = i; c; n) b
      //
      // into
      //
      //   {
      //     const x = i;
      //     for (; c; n) b
      //   }
      //
      // or, desugar
      //   for (; c; n) b
      // into
      //   {
      //     for (; c; n) b
      //   }
      // just in case b introduces a lexical binding some other way, e.g., if b
      // is a FunctionDeclaration.
      Block* block =
          factory()->NewBlock(NULL, 2, false, RelocInfo::kNoPosition);
      if (init != nullptr) {
        block->statements()->Add(init, zone());
      }
      block->statements()->Add(loop, zone());
      block->set_scope(for_scope);
      loop->Initialize(NULL, cond, next, body);
      result = block;
    } else {
      loop->Initialize(init, cond, next, body);
      result = loop;
    }
  }
  return result;
}


DebuggerStatement* Parser::ParseDebuggerStatement(bool* ok) {
  // In ECMA-262 'debugger' is defined as a reserved keyword. In some browser
  // contexts this is used as a statement which invokes the debugger as i a
  // break point is present.
  // DebuggerStatement ::
  //   'debugger' ';'

  int pos = peek_position();
  Expect(Token::DEBUGGER, CHECK_OK);
  ExpectSemicolon(CHECK_OK);
  return factory()->NewDebuggerStatement(pos);
}


bool CompileTimeValue::IsCompileTimeValue(Expression* expression) {
  if (expression->IsLiteral()) return true;
  MaterializedLiteral* lit = expression->AsMaterializedLiteral();
  return lit != NULL && lit->is_simple();
}


Handle<FixedArray> CompileTimeValue::GetValue(Isolate* isolate,
                                              Expression* expression) {
  Factory* factory = isolate->factory();
  DCHECK(IsCompileTimeValue(expression));
  Handle<FixedArray> result = factory->NewFixedArray(2, TENURED);
  ObjectLiteral* object_literal = expression->AsObjectLiteral();
  if (object_literal != NULL) {
    DCHECK(object_literal->is_simple());
    if (object_literal->fast_elements()) {
      result->set(kLiteralTypeSlot, Smi::FromInt(OBJECT_LITERAL_FAST_ELEMENTS));
    } else {
      result->set(kLiteralTypeSlot, Smi::FromInt(OBJECT_LITERAL_SLOW_ELEMENTS));
    }
    result->set(kElementsSlot, *object_literal->constant_properties());
  } else {
    ArrayLiteral* array_literal = expression->AsArrayLiteral();
    DCHECK(array_literal != NULL && array_literal->is_simple());
    result->set(kLiteralTypeSlot, Smi::FromInt(ARRAY_LITERAL));
    result->set(kElementsSlot, *array_literal->constant_elements());
  }
  return result;
}


CompileTimeValue::LiteralType CompileTimeValue::GetLiteralType(
    Handle<FixedArray> value) {
  Smi* literal_type = Smi::cast(value->get(kLiteralTypeSlot));
  return static_cast<LiteralType>(literal_type->value());
}


Handle<FixedArray> CompileTimeValue::GetElements(Handle<FixedArray> value) {
  return Handle<FixedArray>(FixedArray::cast(value->get(kElementsSlot)));
}


void ParserTraits::ParseArrowFunctionFormalParameters(
    ParserFormalParameters* parameters, Expression* expr,
    const Scanner::Location& params_loc, bool* ok) {
  if (parameters->Arity() >= Code::kMaxArguments) {
    ReportMessageAt(params_loc, MessageTemplate::kMalformedArrowFunParamList);
    *ok = false;
    return;
  }

  // ArrowFunctionFormals ::
  //    Binary(Token::COMMA, NonTailArrowFunctionFormals, Tail)
  //    Tail
  // NonTailArrowFunctionFormals ::
  //    Binary(Token::COMMA, NonTailArrowFunctionFormals, VariableProxy)
  //    VariableProxy
  // Tail ::
  //    VariableProxy
  //    Spread(VariableProxy)
  //
  // As we need to visit the parameters in left-to-right order, we recurse on
  // the left-hand side of comma expressions.
  //
  if (expr->IsBinaryOperation()) {
    BinaryOperation* binop = expr->AsBinaryOperation();
    // The classifier has already run, so we know that the expression is a valid
    // arrow function formals production.
    DCHECK_EQ(binop->op(), Token::COMMA);
    Expression* left = binop->left();
    Expression* right = binop->right();
    ParseArrowFunctionFormalParameters(parameters, left, params_loc, ok);
    if (!*ok) return;
    // LHS of comma expression should be unparenthesized.
    expr = right;
  }

  // Only the right-most expression may be a rest parameter.
  DCHECK(!parameters->has_rest);

  bool is_rest = expr->IsSpread();
  if (is_rest) {
    expr = expr->AsSpread()->expression();
    parameters->has_rest = true;
  }
  if (parameters->is_simple) {
    parameters->is_simple = !is_rest && expr->IsVariableProxy();
  }

  Expression* initializer = nullptr;
  if (expr->IsVariableProxy()) {
    // When the formal parameter was originally seen, it was parsed as a
    // VariableProxy and recorded as unresolved in the scope.  Here we undo that
    // parse-time side-effect for parameters that are single-names (not
    // patterns; for patterns that happens uniformly in
    // PatternRewriter::VisitVariableProxy).
    parser_->scope_->RemoveUnresolved(expr->AsVariableProxy());
  } else if (expr->IsAssignment()) {
    Assignment* assignment = expr->AsAssignment();
    DCHECK(parser_->allow_harmony_default_parameters());
    DCHECK(!assignment->is_compound());
    initializer = assignment->value();
    expr = assignment->target();

    // TODO(adamk): Only call this if necessary.
    RewriteParameterInitializerScope(parser_->stack_limit(), initializer,
                                     parser_->scope_, parameters->scope);
  }

  // TODO(adamk): params_loc.end_pos is not the correct initializer position,
  // but it should be conservative enough to trigger hole checks for variables
  // referenced in the initializer (if any).
  AddFormalParameter(parameters, expr, initializer, params_loc.end_pos,
                     is_rest);
}


DoExpression* Parser::ParseDoExpression(bool* ok) {
  // AssignmentExpression ::
  //     do '{' StatementList '}'
  int pos = peek_position();

  Expect(Token::DO, CHECK_OK);
  Variable* result =
      scope_->NewTemporary(ast_value_factory()->dot_result_string());
  Block* block = ParseBlock(nullptr, false, CHECK_OK);
  DoExpression* expr = factory()->NewDoExpression(block, result, pos);
  if (!Rewriter::Rewrite(this, expr, ast_value_factory())) {
    *ok = false;
    return nullptr;
  }
  block->set_scope(block->scope()->FinalizeBlockScope());
  return expr;
}


void ParserTraits::ParseArrowFunctionFormalParameterList(
    ParserFormalParameters* parameters, Expression* expr,
    const Scanner::Location& params_loc,
    Scanner::Location* duplicate_loc, bool* ok) {
  if (expr->IsEmptyParentheses()) return;

  ParseArrowFunctionFormalParameters(parameters, expr, params_loc, ok);
  if (!*ok) return;

  ExpressionClassifier classifier;
  if (!parameters->is_simple) {
    classifier.RecordNonSimpleParameter();
  }
  for (int i = 0; i < parameters->Arity(); ++i) {
    auto parameter = parameters->at(i);
    DeclareFormalParameter(parameters->scope, parameter, &classifier);
    if (!duplicate_loc->IsValid()) {
      *duplicate_loc = classifier.duplicate_formal_parameter_error().location;
    }
  }
  DCHECK_EQ(parameters->is_simple, parameters->scope->has_simple_parameters());
}


void ParserTraits::ReindexLiterals(const ParserFormalParameters& parameters) {
  if (parser_->function_state_->materialized_literal_count() > 0) {
    AstLiteralReindexer reindexer;

    for (const auto p : parameters.params) {
      if (p.pattern != nullptr) reindexer.Reindex(p.pattern);
      if (p.initializer != nullptr) reindexer.Reindex(p.initializer);
    }

    DCHECK(reindexer.count() <=
           parser_->function_state_->materialized_literal_count());
  }
}


FunctionLiteral* Parser::ParseFunctionLiteral(
    const AstRawString* function_name, Scanner::Location function_name_location,
    FunctionNameValidity function_name_validity, FunctionKind kind,
    int function_token_pos, FunctionLiteral::FunctionType function_type,
    FunctionLiteral::ArityRestriction arity_restriction,
    LanguageMode language_mode, bool* ok) {
  // Function ::
  //   '(' FormalParameterList? ')' '{' FunctionBody '}'
  //
  // Getter ::
  //   '(' ')' '{' FunctionBody '}'
  //
  // Setter ::
  //   '(' PropertySetParameterList ')' '{' FunctionBody '}'

  int pos = function_token_pos == RelocInfo::kNoPosition
      ? peek_position() : function_token_pos;

  bool is_generator = IsGeneratorFunction(kind);

  // Anonymous functions were passed either the empty symbol or a null
  // handle as the function name.  Remember if we were passed a non-empty
  // handle to decide whether to invoke function name inference.
  bool should_infer_name = function_name == NULL;

  // We want a non-null handle as the function name.
  if (should_infer_name) {
    function_name = ast_value_factory()->empty_string();
  }

  // Function declarations are function scoped in normal mode, so they are
  // hoisted. In harmony block scoping mode they are block scoped, so they
  // are not hoisted.
  //
  // One tricky case are function declarations in a local sloppy-mode eval:
  // their declaration is hoisted, but they still see the local scope. E.g.,
  //
  // function() {
  //   var x = 0
  //   try { throw 1 } catch (x) { eval("function g() { return x }") }
  //   return g()
  // }
  //
  // needs to return 1. To distinguish such cases, we need to detect
  // (1) whether a function stems from a sloppy eval, and
  // (2) whether it actually hoists across the eval.
  // Unfortunately, we do not represent sloppy eval scopes, so we do not have
  // either information available directly, especially not when lazily compiling
  // a function like 'g'. We hence rely on the following invariants:
  // - (1) is the case iff the innermost scope of the deserialized scope chain
  //   under which we compile is _not_ a declaration scope. This holds because
  //   in all normal cases, function declarations are fully hoisted to a
  //   declaration scope and compiled relative to that.
  // - (2) is the case iff the current declaration scope is still the original
  //   one relative to the deserialized scope chain. Otherwise we must be
  //   compiling a function in an inner declaration scope in the eval, e.g. a
  //   nested function, and hoisting works normally relative to that.
  Scope* declaration_scope = scope_->DeclarationScope();
  Scope* original_declaration_scope = original_scope_->DeclarationScope();
  Scope* scope = function_type == FunctionLiteral::kDeclaration &&
                         is_sloppy(language_mode) &&
                         !allow_harmony_sloppy_function() &&
                         (original_scope_ == original_declaration_scope ||
                          declaration_scope != original_declaration_scope)
                     ? NewScope(declaration_scope, FUNCTION_SCOPE, kind)
                     : NewScope(scope_, FUNCTION_SCOPE, kind);
  SetLanguageMode(scope, language_mode);
  ZoneList<Statement*>* body = NULL;
  int arity = -1;
  int materialized_literal_count = -1;
  int expected_property_count = -1;
  DuplicateFinder duplicate_finder(scanner()->unicode_cache());
  ExpressionClassifier formals_classifier(&duplicate_finder);
  FunctionLiteral::EagerCompileHint eager_compile_hint =
      parenthesized_function_ ? FunctionLiteral::kShouldEagerCompile
                              : FunctionLiteral::kShouldLazyCompile;
  bool should_be_used_once_