src/parsing/preparse-data.cc

// Copyright 2017 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/preparse-data.h"

#include <vector>

#include "src/ast/scopes.h"
#include "src/ast/variables.h"
#include "src/handles/handles.h"
#include "src/objects/objects-inl.h"
#include "src/objects/shared-function-info.h"
#include "src/parsing/parser.h"
#include "src/parsing/preparse-data-impl.h"
#include "src/parsing/preparser.h"
#include "src/roots/roots.h"
#include "src/zone/zone-list-inl.h"  // crbug.com/v8/8816
#include "src/zone/zone-utils.h"

namespace v8 {
namespace internal {

namespace {

using ScopeSloppyEvalCanExtendVarsBit = base::BitField8<bool, 0, 1>;
using InnerScopeCallsEvalField = ScopeSloppyEvalCanExtendVarsBit::Next<bool, 1>;
using NeedsPrivateNameContextChainRecalcField =
    InnerScopeCallsEvalField::Next<bool, 1>;
using ShouldSaveClassVariableIndexField =
    NeedsPrivateNameContextChainRecalcField::Next<bool, 1>;

using VariableMaybeAssignedField = base::BitField8<bool, 0, 1>;
using VariableContextAllocatedField = VariableMaybeAssignedField::Next<bool, 1>;

using HasDataField = base::BitField<bool, 0, 1>;
using LengthEqualsParametersField = HasDataField::Next<bool, 1>;
using NumberOfParametersField = LengthEqualsParametersField::Next<uint16_t, 16>;

using LanguageField = base::BitField8<LanguageMode, 0, 1>;
using UsesSuperField = LanguageField::Next<bool, 1>;
STATIC_ASSERT(LanguageModeSize <= LanguageField::kNumValues);

}  // namespace

/*

  Internal data format for the backing store of PreparseDataBuilder and
  PreparseData::scope_data (on the heap):

  (Skippable function data:)
  ------------------------------------
  | scope_data_start (debug only)    |
  ------------------------------------
  | data for inner function n        |
  | ...                              |
  ------------------------------------
  | data for inner function 1        |
  | ...                              |
  ------------------------------------
  (Scope allocation data:)             << scope_data_start points here in debug
  ------------------------------------
  magic value (debug only)
  ------------------------------------
  scope positions (debug only)
  ------------------------------------
  | scope type << only in debug      |
  | eval                             |
  | ----------------------           |
  | | data for variables |           |
  | | ...                |           |
  | ----------------------           |
  ------------------------------------
  ------------------------------------
  | data for inner scope m           | << but not for function scopes
  | ...                              |
  ------------------------------------
  ...
  ------------------------------------
  | data for inner scope 1           |
  | ...                              |
  ------------------------------------

  PreparseData::child_data is an array of PreparseData objects, one
  for each skippable inner function.

  ConsumedPreparseData wraps a PreparseData and reads data from it.

 */

PreparseDataBuilder::PreparseDataBuilder(Zone* zone,
                                         PreparseDataBuilder* parent_builder,
                                         std::vector<void*>* children_buffer)
    : parent_(parent_builder),
      byte_data_(),
      children_buffer_(children_buffer),
      function_scope_(nullptr),
      function_length_(-1),
      num_inner_functions_(0),
      num_inner_with_data_(0),
      bailed_out_(false),
      has_data_(false) {}

void PreparseDataBuilder::DataGatheringScope::Start(
    DeclarationScope* function_scope) {
  Zone* main_zone = preparser_->main_zone();
  builder_ = main_zone->New<PreparseDataBuilder>(
      main_zone, preparser_->preparse_data_builder(),
      preparser_->preparse_data_builder_buffer());
  preparser_->set_preparse_data_builder(builder_);
  function_scope->set_preparse_data_builder(builder_);
}

void PreparseDataBuilder::DataGatheringScope::Close() {
  PreparseDataBuilder* parent = builder_->parent_;
  preparser_->set_preparse_data_builder(parent);
  builder_->FinalizeChildren(preparser_->main_zone());

  if (parent == nullptr) return;
  if (!builder_->HasDataForParent()) return;
  parent->AddChild(builder_);
}

void PreparseDataBuilder::ByteData::Start(std::vector<uint8_t>* buffer) {
  DCHECK(!is_finalized_);
  byte_data_ = buffer;
  DCHECK_EQ(byte_data_->size(), 0);
  DCHECK_EQ(index_, 0);
}

// This struct is just a type tag for Zone::NewArray<T>(size_t) call.
struct RawPreparseData {};

void PreparseDataBuilder::ByteData::Finalize(Zone* zone) {
  uint8_t* raw_zone_data = zone->NewArray<uint8_t, RawPreparseData>(index_);
  memcpy(raw_zone_data, byte_data_->data(), index_);
  byte_data_->resize(0);
  zone_byte_data_ = Vector<uint8_t>(raw_zone_data, index_);
#ifdef DEBUG
  is_finalized_ = true;
#endif
}

void PreparseDataBuilder::ByteData::Reserve(size_t bytes) {
  // Make sure we have at least {bytes} capacity left in the buffer_.
  DCHECK_LE(length(), byte_data_->size());
  size_t capacity = byte_data_->size() - length();
  if (capacity >= bytes) return;
  size_t delta = bytes - capacity;
  byte_data_->insert(byte_data_->end(), delta, 0);
}

int PreparseDataBuilder::ByteData::length() const { return index_; }

void PreparseDataBuilder::ByteData::Add(uint8_t byte) {
  DCHECK_LE(0, index_);
  DCHECK_LT(index_, byte_data_->size());
  (*byte_data_)[index_++] = byte;
}

#ifdef DEBUG
void PreparseDataBuilder::ByteData::WriteUint32(uint32_t data) {
  DCHECK(!is_finalized_);
  Add(kUint32Size);
  Add(data & 0xFF);
  Add((data >> 8) & 0xFF);
  Add((data >> 16) & 0xFF);
  Add((data >> 24) & 0xFF);
  free_quarters_in_last_byte_ = 0;
}

void PreparseDataBuilder::ByteData::SaveCurrentSizeAtFirstUint32() {
  int current_length = length();
  index_ = 0;
  CHECK_EQ(byte_data_->at(0), kUint32Size);
  WriteUint32(current_length);
  index_ = current_length;
}
#endif

void PreparseDataBuilder::ByteData::WriteVarint32(uint32_t data) {
#ifdef DEBUG
  // Save expected item size in debug mode.
  Add(kVarint32MinSize);
#endif
  // See ValueSerializer::WriteVarint.
  do {
    uint8_t next_byte = (data & 0x7F);
    data >>= 7;
    // Add continue bit.
    if (data) next_byte |= 0x80;
    Add(next_byte & 0xFF);
  } while (data);
#ifdef DEBUG
  Add(kVarint32EndMarker);
#endif
  free_quarters_in_last_byte_ = 0;
}

void PreparseDataBuilder::ByteData::WriteUint8(uint8_t data) {
  DCHECK(!is_finalized_);
#ifdef DEBUG
  // Save expected item size in debug mode.
  Add(kUint8Size);
#endif
  Add(data);
  free_quarters_in_last_byte_ = 0;
}

void PreparseDataBuilder::ByteData::WriteQuarter(uint8_t data) {
  DCHECK(!is_finalized_);
  DCHECK_LE(data, 3);
  if (free_quarters_in_last_byte_ == 0) {
#ifdef DEBUG
    // Save a marker in debug mode.
    Add(kQuarterMarker);
#endif
    Add(0);
    free_quarters_in_last_byte_ = 3;
  } else {
    --free_quarters_in_last_byte_;
  }

  uint8_t shift_amount = free_quarters_in_last_byte_ * 2;
  DCHECK_EQ(byte_data_->at(index_ - 1) & (3 << shift_amount), 0);
  (*byte_data_)[index_ - 1] |= (data << shift_amount);
}

void PreparseDataBuilder::DataGatheringScope::SetSkippableFunction(
    DeclarationScope* function_scope, int function_length,
    int num_inner_functions) {
  DCHECK_NULL(builder_->function_scope_);
  builder_->function_scope_ = function_scope;
  DCHECK_EQ(builder_->num_inner_functions_, 0);
  builder_->function_length_ = function_length;
  builder_->num_inner_functions_ = num_inner_functions;
  builder_->parent_->has_data_ = true;
}

bool PreparseDataBuilder::HasInnerFunctions() const {
  return !children_.empty();
}

bool PreparseDataBuilder::HasData() const { return !bailed_out_ && has_data_; }

bool PreparseDataBuilder::HasDataForParent() const {
  return HasData() || function_scope_ != nullptr;
}

void PreparseDataBuilder::AddChild(PreparseDataBuilder* child) {
  DCHECK(!finalized_children_);
  children_buffer_.Add(child);
}

void PreparseDataBuilder::FinalizeChildren(Zone* zone) {
  DCHECK(!finalized_children_);
  Vector<PreparseDataBuilder*> children =
      CloneVector(zone, children_buffer_.ToConstVector());
  children_buffer_.Rewind();
  children_ = children;
#ifdef DEBUG
  finalized_children_ = true;
#endif
}

bool PreparseDataBuilder::ScopeNeedsData(Scope* scope) {
  if (scope->is_function_scope()) {
    // Default constructors don't need data (they cannot contain inner functions
    // defined by the user). Other functions do.
    return !IsDefaultConstructor(scope->AsDeclarationScope()->function_kind());
  }
  if (!scope->is_hidden()) {
    for (Variable* var : *scope->locals()) {
      if (IsSerializableVariableMode(var->mode())) return true;
    }
  }
  for (Scope* inner = scope->inner_scope(); inner != nullptr;
       inner = inner->sibling()) {
    if (ScopeNeedsData(inner)) return true;
  }
  return false;
}

bool PreparseDataBuilder::SaveDataForSkippableFunction(
    PreparseDataBuilder* builder) {
  DeclarationScope* function_scope = builder->function_scope_;
  // Start position is used for a sanity check when consuming the data, we could
  // remove it in the future if we're very pressed for space but it's been good
  // at catching bugs in the wild so far.
  byte_data_.WriteVarint32(function_scope->start_position());
  byte_data_.WriteVarint32(function_scope->end_position());

  bool has_data = builder->HasData();
  bool length_equals_parameters =
      function_scope->num_parameters() == builder->function_length_;
  uint32_t has_data_and_num_parameters =
      HasDataField::encode(has_data) |
      LengthEqualsParametersField::encode(length_equals_parameters) |
      NumberOfParametersField::encode(function_scope->num_parameters());
  byte_data_.WriteVarint32(has_data_and_num_parameters);
  if (!length_equals_parameters) {
    byte_data_.WriteVarint32(builder->function_length_);
  }
  byte_data_.WriteVarint32(builder->num_inner_functions_);

  uint8_t language_and_super =
      LanguageField::encode(function_scope->language_mode()) |
      UsesSuperField::encode(function_scope->NeedsHomeObject());
  byte_data_.WriteQuarter(language_and_super);
  return has_data;
}

void PreparseDataBuilder::SaveScopeAllocationData(DeclarationScope* scope,
                                                  Parser* parser) {
  if (!has_data_) return;
  DCHECK(HasInnerFunctions());

  byte_data_.Start(parser->preparse_data_buffer());

#ifdef DEBUG
  // Reserve Uint32 for scope_data_start debug info.
  byte_data_.Reserve(kUint32Size);
  byte_data_.WriteUint32(0);
#endif
  byte_data_.Reserve(children_.size() * kSkippableFunctionMaxDataSize);
  DCHECK(finalized_children_);
  for (const auto& builder : children_) {
    // Keep track of functions with inner data. {children_} contains also the
    // builders that have no inner functions at all.
    if (SaveDataForSkippableFunction(builder)) num_inner_with_data_++;
  }

  // Don't save incomplete scope information when bailed out.
  if (!bailed_out_) {
#ifdef DEBUG
  // function data items, kSkippableMinFunctionDataSize each.
  CHECK_GE(byte_data_.length(), kPlaceholderSize);
  CHECK_LE(byte_data_.length(), std::numeric_limits<uint32_t>::max());

  byte_data_.SaveCurrentSizeAtFirstUint32();
  // For a data integrity check, write a value between data about skipped
  // inner funcs and data about variables.
  byte_data_.Reserve(kUint32Size * 3);
  byte_data_.WriteUint32(kMagicValue);
  byte_data_.WriteUint32(scope->start_position());
  byte_data_.WriteUint32(scope->end_position());
#endif

  if (ScopeNeedsData(scope)) SaveDataForScope(scope);
  }
  byte_data_.Finalize(parser->factory()->zone());
}

void PreparseDataBuilder::SaveDataForScope(Scope* scope) {
  DCHECK_NE(scope->end_position(), kNoSourcePosition);
  DCHECK(ScopeNeedsData(scope));

#ifdef DEBUG
  byte_data_.Reserve(kUint8Size);
  byte_data_.WriteUint8(scope->scope_type());
#endif

  uint8_t eval_and_private_recalc =
      ScopeSloppyEvalCanExtendVarsBit::encode(
          scope->is_declaration_scope() &&
          scope->AsDeclarationScope()->sloppy_eval_can_extend_vars()) |
      InnerScopeCallsEvalField::encode(scope->inner_scope_calls_eval()) |
      NeedsPrivateNameContextChainRecalcField::encode(
          scope->is_function_scope() &&
          scope->AsDeclarationScope()
              ->needs_private_name_context_chain_recalc()) |
      ShouldSaveClassVariableIndexField::encode(
          scope->is_class_scope() &&
          scope->AsClassScope()->should_save_class_variable_index());
  byte_data_.Reserve(kUint8Size);
  byte_data_.WriteUint8(eval_and_private_recalc);

  if (scope->is_function_scope()) {
    Variable* function = scope->AsDeclarationScope()->function_var();
    if (function != nullptr) SaveDataForVariable(function);
  }

  for (Variable* var : *scope->locals()) {
    if (IsSerializableVariableMode(var->mode())) SaveDataForVariable(var);
  }

  SaveDataForInnerScopes(scope);
}

void PreparseDataBuilder::SaveDataForVariable(Variable* var) {
#ifdef DEBUG
  // Store the variable name in debug mode; this way we can check that we
  // restore data to the correct variable.
  const AstRawString* name = var->raw_name();
  byte_data_.Reserve(kUint32Size + (name->length() + 1) * kUint8Size);
  byte_data_.WriteUint8(name->is_one_byte());
  byte_data_.WriteUint32(name->length());
  for (int i = 0; i < name->length(); ++i) {
    byte_data_.WriteUint8(name->raw_data()[i]);
  }
#endif

  byte variable_data = VariableMaybeAssignedField::encode(
                           var->maybe_assigned() == kMaybeAssigned) |
                       VariableContextAllocatedField::encode(
                           var->has_forced_context_allocation());
  byte_data_.Reserve(kUint8Size);
  byte_data_.WriteQuarter(variable_data);
}

void PreparseDataBuilder::SaveDataForInnerScopes(Scope* scope) {
  // Inner scopes are stored in the reverse order, but we'd like to write the
  // data in the logical order. There might be many inner scopes, so we don't
  // want to recurse here.
  for (Scope* inner = scope->inner_scope(); inner != nullptr;
       inner = inner->sibling()) {
    if (inner->IsSkippableFunctionScope()) {
      // Don't save data about function scopes, since they'll have their own
      // PreparseDataBuilder where their data is saved.
      DCHECK_NOT_NULL(inner->AsDeclarationScope()->preparse_data_builder());
      continue;
    }
    if (!ScopeNeedsData(inner)) continue;
    SaveDataForScope(inner);
  }
}


Handle<PreparseData> PreparseDataBuilder::ByteData::CopyToHeap(
    Isolate* isolate, int children_length) {
  DCHECK(is_finalized_);
  int data_length = zone_byte_data_.length();
  Handle<PreparseData> data =
      isolate->factory()->NewPreparseData(data_length, children_length);
  data->copy_in(0, zone_byte_data_.begin(), data_length);
  return data;
}

Handle<PreparseData> PreparseDataBuilder::ByteData::CopyToLocalHeap(
    LocalIsolate* isolate, int children_length) {
  DCHECK(is_finalized_);
  int data_length = zone_byte_data_.length();
  Handle<PreparseData> data =
      isolate->factory()->NewPreparseData(data_length, children_length);
  data->copy_in(0, zone_byte_data_.begin(), data_length);
  return data;
}

Handle<PreparseData> PreparseDataBuilder::Serialize(Isolate* isolate) {
  DCHECK(HasData());
  DCHECK(!ThisOrParentBailedOut());
  Handle<PreparseData> data =
      byte_data_.CopyToHeap(isolate, num_inner_with_data_);
  int i = 0;
  DCHECK(finalized_children_);
  for (const auto& builder : children_) {
    if (!builder->HasData()) continue;
    Handle<PreparseData> child_data = builder->Serialize(isolate);
    data->set_child(i++, *child_data);
  }
  DCHECK_EQ(i, data->children_length());
  return data;
}

Handle<PreparseData> PreparseDataBuilder::Serialize(LocalIsolate* isolate) {
  DCHECK(HasData());
  DCHECK(!ThisOrParentBailedOut());
  Handle<PreparseData> data =
      byte_data_.CopyToLocalHeap(isolate, num_inner_with_data_);
  int i = 0;
  DCHECK(finalized_children_);
  for (const auto& builder : children_) {
    if (!builder->HasData()) continue;
    Handle<PreparseData> child_data = builder->Serialize(isolate);
    data->set_child(i++, *child_data);
  }
  DCHECK_EQ(i, data->children_length());
  return data;
}

ZonePreparseData* PreparseDataBuilder::Serialize(Zone* zone) {
  DCHECK(HasData());
  DCHECK(!ThisOrParentBailedOut());
  ZonePreparseData* data = byte_data_.CopyToZone(zone, num_inner_with_data_);
  int i = 0;
  DCHECK(finalized_children_);
  for (const auto& builder : children_) {
    if (!builder->HasData()) continue;
    ZonePreparseData* child = builder->Serialize(zone);
    data->set_child(i++, child);
  }
  DCHECK_EQ(i, data->children_length());
  return data;
}

class BuilderProducedPreparseData final : public ProducedPreparseData {
 public:
  explicit BuilderProducedPreparseData(PreparseDataBuilder* builder)
      : builder_(builder) {
    DCHECK(builder->HasData());
  }

  Handle<PreparseData> Serialize(Isolate* isolate) final {
    return builder_->Serialize(isolate);
  }

  Handle<PreparseData> Serialize(LocalIsolate* isolate) final {
    return builder_->Serialize(isolate);
  }

  ZonePreparseData* Serialize(Zone* zone) final {
    return builder_->Serialize(zone);
  }

 private:
  PreparseDataBuilder* builder_;
};

class OnHeapProducedPreparseData final : public ProducedPreparseData {
 public:
  explicit OnHeapProducedPreparseData(Handle<PreparseData> data)
      : data_(data) {}

  Handle<PreparseData> Serialize(Isolate* isolate) final {
    DCHECK(!data_->is_null());
    return data_;
  }

  Handle<PreparseData> Serialize(LocalIsolate* isolate) final {
    // Not required.
    UNREACHABLE();
  }

  ZonePreparseData* Serialize(Zone* zone) final {
    // Not required.
    UNREACHABLE();
  }

 private:
  Handle<PreparseData> data_;
};

class ZoneProducedPreparseData final : public ProducedPreparseData {
 public:
  explicit ZoneProducedPreparseData(ZonePreparseData* data) : data_(data) {}

  Handle<PreparseData> Serialize(Isolate* isolate) final {
    return data_->Serialize(isolate);
  }

  Handle<PreparseData> Serialize(LocalIsolate* isolate) final {
    return data_->Serialize(isolate);
  }

  ZonePreparseData* Serialize(Zone* zone) final { return data_; }

 private:
  ZonePreparseData* data_;
};

ProducedPreparseData* ProducedPreparseData::For(PreparseDataBuilder* builder,
                                                Zone* zone) {
  return zone->New<BuilderProducedPreparseData>(builder);
}

ProducedPreparseData* ProducedPreparseData::For(Handle<PreparseData> data,
                                                Zone* zone) {
  return zone->New<OnHeapProducedPreparseData>(data);
}

ProducedPreparseData* ProducedPreparseData::For(ZonePreparseData* data,
                                                Zone* zone) {
  return zone->New<ZoneProducedPreparseData>(data);
}

template <class Data>
ProducedPreparseData*
BaseConsumedPreparseData<Data>::GetDataForSkippableFunction(
    Zone* zone, int start_position, int* end_position, int* num_parameters,
    int* function_length, int* num_inner_functions, bool* uses_super_property,
    LanguageMode* language_mode) {
  // The skippable function *must* be the next function in the data. Use the
  // start position as a sanity check.
  typename ByteData::ReadingScope reading_scope(this);
  CHECK(scope_data_->HasRemainingBytes(
      PreparseByteDataConstants::kSkippableFunctionMinDataSize));
  int start_position_from_data = scope_data_->ReadVarint32();
  CHECK_EQ(start_position, start_position_from_data);
  *end_position = scope_data_->ReadVarint32();
  DCHECK_GT(*end_position, start_position);

  uint32_t has_data_and_num_parameters = scope_data_->ReadVarint32();
  bool has_data = HasDataField::decode(has_data_and_num_parameters);
  *num_parameters =
      NumberOfParametersField::decode(has_data_and_num_parameters);
  bool length_equals_parameters =
      LengthEqualsParametersField::decode(has_data_and_num_parameters);
  if (length_equals_parameters) {
    *function_length = *num_parameters;
  } else {
    *function_length = scope_data_->ReadVarint32();
  }
  *num_inner_functions = scope_data_->ReadVarint32();

  uint8_t language_and_super = scope_data_->ReadQuarter();
  *language_mode = LanguageMode(LanguageField::decode(language_and_super));
  *uses_super_property = UsesSuperField::decode(language_and_super);

  if (!has_data) return nullptr;

  // Retrieve the corresponding PreparseData and associate it to the
  // skipped function. If the skipped functions contains inner functions, those
  // can be skipped when the skipped function is eagerly parsed.
  return GetChildData(zone, child_index_++);
}

template <class Data>
void BaseConsumedPreparseData<Data>::RestoreScopeAllocationData(
    DeclarationScope* scope, AstValueFactory* ast_value_factory, Zone* zone) {
  DCHECK_EQ(scope->scope_type(), ScopeType::FUNCTION_SCOPE);
  typename ByteData::ReadingScope reading_scope(this);

#ifdef DEBUG
  int magic_value_from_data = scope_data_->ReadUint32();
  // Check that we've consumed all inner function data.
  DCHECK_EQ(magic_value_from_data, ByteData::kMagicValue);

  int start_position_from_data = scope_data_->ReadUint32();
  int end_position_from_data = scope_data_->ReadUint32();
  DCHECK_EQ(start_position_from_data, scope->start_position());
  DCHECK_EQ(end_position_from_data, scope->end_position());
#endif

  RestoreDataForScope(scope, ast_value_factory, zone);

  // Check that we consumed all scope data.
  DCHECK_EQ(scope_data_->RemainingBytes(), 0);
}

template <typename Data>
void BaseConsumedPreparseData<Data>::RestoreDataForScope(
    Scope* scope, AstValueFactory* ast_value_factory, Zone* zone) {
  if (scope->is_declaration_scope() &&
      scope->AsDeclarationScope()->is_skipped_function()) {
    return;
  }

  // It's possible that scope is not present in the data at all (since PreParser
  // doesn't create the corresponding scope). In this case, the Scope won't
  // contain any variables for which we need the data.
  if (!PreparseDataBuilder::ScopeNeedsData(scope)) return;

  // scope_type is stored only in debug mode.
  DCHECK_EQ(scope_data_->ReadUint8(), scope->scope_type());

  CHECK(scope_data_->HasRemainingBytes(ByteData::kUint8Size));
  uint32_t scope_data_flags = scope_data_->ReadUint8();
  if (ScopeSloppyEvalCanExtendVarsBit::decode(scope_data_flags)) {
    scope->RecordEvalCall();
  }
  if (InnerScopeCallsEvalField::decode(scope_data_flags)) {
    scope->RecordInnerScopeEvalCall();
  }
  if (NeedsPrivateNameContextChainRecalcField::decode(scope_data_flags)) {
    scope->AsDeclarationScope()->RecordNeedsPrivateNameContextChainRecalc();
  }
  if (ShouldSaveClassVariableIndexField::decode(scope_data_flags)) {
    Variable* var;
    // An anonymous class whose class variable needs to be saved do not
    // have the class variable created during reparse since we skip parsing
    // the inner scopes that contain potential access to static private
    // methods. So create it now.
    if (scope->AsClassScope()->is_anonymous_class()) {
      var = scope->AsClassScope()->DeclareClassVariable(
          ast_value_factory, nullptr, kNoSourcePosition);
      AstNodeFactory factory(ast_value_factory, zone);
      Declaration* declaration =
          factory.NewVariableDeclaration(kNoSourcePosition);
      scope->declarations()->Add(declaration);
      declaration->set_var(var);
    } else {
      var = scope->AsClassScope()->class_variable();
      DCHECK_NOT_NULL(var);
    }
    var->set_is_used();
    var->ForceContextAllocation();
    scope->AsClassScope()->set_should_save_class_variable_index();
  }

  if (scope->is_function_scope()) {
    Variable* function = scope->AsDeclarationScope()->function_var();
    if (function != nullptr) RestoreDataForVariable(function);
  }
  for (Variable* var : *scope->locals()) {
    if (IsSerializableVariableMode(var->mode())) RestoreDataForVariable(var);
  }

  RestoreDataForInnerScopes(scope, ast_value_factory, zone);
}

template <typename Data>
void BaseConsumedPreparseData<Data>::RestoreDataForVariable(Variable* var) {
#ifdef DEBUG
  const AstRawString* name = var->raw_name();
  bool data_one_byte = scope_data_->ReadUint8();
  DCHECK_IMPLIES(name->is_one_byte(), data_one_byte);
  DCHECK_EQ(scope_data_->ReadUint32(), static_cast<uint32_t>(name->length()));
  if (!name->is_one_byte() && data_one_byte) {
    // It's possible that "name" is a two-byte representation of the string
    // stored in the data.
    for (int i = 0; i < 2 * name->length(); i += 2) {
#if defined(V8_TARGET_LITTLE_ENDIAN)
      DCHECK_EQ(scope_data_->ReadUint8(), name->raw_data()[i]);
      DCHECK_EQ(0, name->raw_data()[i + 1]);
#else
      DCHECK_EQ(scope_data_->ReadUint8(), name->raw_data()[i + 1]);
      DCHECK_EQ(0, name->raw_data()[i]);
#endif  // V8_TARGET_LITTLE_ENDIAN
    }
  } else {
    for (int i = 0; i < name->length(); ++i) {
      DCHECK_EQ(scope_data_->ReadUint8(), name->raw_data()[i]);
    }
  }
#endif
  uint8_t variable_data = scope_data_->ReadQuarter();
  if (VariableMaybeAssignedField::decode(variable_data)) {
    var->SetMaybeAssigned();
  }
  if (VariableContextAllocatedField::decode(variable_data)) {
    var->set_is_used();
    var->ForceContextAllocation();
  }
}

template <typename Data>
void BaseConsumedPreparseData<Data>::RestoreDataForInnerScopes(
    Scope* scope, AstValueFactory* ast_value_factory, Zone* zone) {
  for (Scope* inner = scope->inner_scope(); inner != nullptr;
       inner = inner->sibling()) {
    RestoreDataForScope(inner, ast_value_factory, zone);
  }
}

#ifdef DEBUG
template <class Data>
bool BaseConsumedPreparseData<Data>::VerifyDataStart() {
  typename ByteData::ReadingScope reading_scope(this);
  // The first uint32 contains the size of the skippable function data.
  int scope_data_start = scope_data_->ReadUint32();
  scope_data_->SetPosition(scope_data_start);
  CHECK_EQ(scope_data_->ReadUint32(), ByteData::kMagicValue);
  // The first data item is scope_data_start. Skip over it.
  scope_data_->SetPosition(ByteData::kPlaceholderSize);
  return true;
}
#endif

PreparseData OnHeapConsumedPreparseData::GetScopeData() { return *data_; }

ProducedPreparseData* OnHeapConsumedPreparseData::GetChildData(Zone* zone,
                                                               int index) {
  DisallowHeapAllocation no_gc;
  Handle<PreparseData> child_data_handle(data_->get_child(index), isolate_);
  return ProducedPreparseData::For(child_data_handle, zone);
}

OnHeapConsumedPreparseData::OnHeapConsumedPreparseData(
    Isolate* isolate, Handle<PreparseData> data)
    : BaseConsumedPreparseData<PreparseData>(), isolate_(isolate), data_(data) {
  DCHECK_NOT_NULL(isolate);
  DCHECK(data->IsPreparseData());
  DCHECK(VerifyDataStart());
}

ZonePreparseData::ZonePreparseData(Zone* zone, Vector<uint8_t>* byte_data,
                                   int children_length)
    : byte_data_(byte_data->begin(), byte_data->end(), zone),
      children_(children_length, zone) {}

Handle<PreparseData> ZonePreparseData::Serialize(Isolate* isolate) {
  int data_size = static_cast<int>(byte_data()->size());
  int child_data_length = children_length();
  Handle<PreparseData> result =
      isolate->factory()->NewPreparseData(data_size, child_data_length);
  result->copy_in(0, byte_data()->data(), data_size);

  for (int i = 0; i < child_data_length; i++) {
    ZonePreparseData* child = get_child(i);
    DCHECK_NOT_NULL(child);
    Handle<PreparseData> child_data = child->Serialize(isolate);
    result->set_child(i, *child_data);
  }
  return result;
}

Handle<PreparseData> ZonePreparseData::Serialize(LocalIsolate* isolate) {
  int data_size = static_cast<int>(byte_data()->size());
  int child_data_length = children_length();
  Handle<PreparseData> result =
      isolate->factory()->NewPreparseData(data_size, child_data_length);
  result->copy_in(0, byte_data()->data(), data_size);

  for (int i = 0; i < child_data_length; i++) {
    ZonePreparseData* child = get_child(i);
    DCHECK_NOT_NULL(child);
    Handle<PreparseData> child_data = child->Serialize(isolate);
    result->set_child(i, *child_data);
  }
  return result;
}

ZoneConsumedPreparseData::ZoneConsumedPreparseData(Zone* zone,
                                                   ZonePreparseData* data)
    : data_(data), scope_data_wrapper_(data_->byte_data()) {
  DCHECK(VerifyDataStart());
}

ZoneVectorWrapper ZoneConsumedPreparseData::GetScopeData() {
  return scope_data_wrapper_;
}

ProducedPreparseData* ZoneConsumedPreparseData::GetChildData(Zone* zone,
                                                             int child_index) {
  CHECK_GT(data_->children_length(), child_index);
  ZonePreparseData* child_data = data_->get_child(child_index);
  if (child_data == nullptr) return nullptr;
  return ProducedPreparseData::For(child_data, zone);
}

std::unique_ptr<ConsumedPreparseData> ConsumedPreparseData::For(
    Isolate* isolate, Handle<PreparseData> data) {
  DCHECK(!data.is_null());
  return std::make_unique<OnHeapConsumedPreparseData>(isolate, data);
}

std::unique_ptr<ConsumedPreparseData> ConsumedPreparseData::For(
    Zone* zone, ZonePreparseData* data) {
  if (data == nullptr) return {};
  return std::make_unique<ZoneConsumedPreparseData>(zone, data);
}

}  // namespace internal
}  // namespace v8