src/debug/debug-scopes.cc

// Copyright 2015 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/debug/debug-scopes.h"

#include <memory>

#include "src/ast/ast.h"
#include "src/ast/scopes.h"
#include "src/common/globals.h"
#include "src/debug/debug.h"
#include "src/execution/frames-inl.h"
#include "src/execution/isolate-inl.h"
#include "src/objects/js-generator-inl.h"
#include "src/objects/source-text-module.h"
#include "src/objects/string-set-inl.h"
#include "src/parsing/parse-info.h"
#include "src/parsing/parsing.h"
#include "src/parsing/rewriter.h"
#include "src/utils/ostreams.h"

namespace v8 {
namespace internal {

ScopeIterator::ScopeIterator(Isolate* isolate, FrameInspector* frame_inspector,
                             ReparseStrategy strategy)
    : isolate_(isolate),
      frame_inspector_(frame_inspector),
      function_(frame_inspector_->GetFunction()),
      script_(frame_inspector_->GetScript()) {
  if (!frame_inspector->GetContext()->IsContext()) {
    // Optimized frame, context or function cannot be materialized. Give up.
    return;
  }
  context_ = Handle<Context>::cast(frame_inspector->GetContext());

  // We should not instantiate a ScopeIterator for wasm frames.
  DCHECK_NE(Script::TYPE_WASM, frame_inspector->GetScript()->type());

  TryParseAndRetrieveScopes(strategy);
}

ScopeIterator::~ScopeIterator() = default;

Handle<Object> ScopeIterator::GetFunctionDebugName() const {
  if (!function_.is_null()) return JSFunction::GetDebugName(function_);

  if (!context_->IsNativeContext()) {
    DisallowHeapAllocation no_gc;
    ScopeInfo closure_info = context_->closure_context().scope_info();
    Handle<String> debug_name(closure_info.FunctionDebugName(), isolate_);
    if (debug_name->length() > 0) return debug_name;
  }
  return isolate_->factory()->undefined_value();
}

ScopeIterator::ScopeIterator(Isolate* isolate, Handle<JSFunction> function)
    : isolate_(isolate), context_(function->context(), isolate) {
  if (!function->shared().IsSubjectToDebugging()) {
    context_ = Handle<Context>();
    return;
  }
  script_ = handle(Script::cast(function->shared().script()), isolate);
  UnwrapEvaluationContext();
}

ScopeIterator::ScopeIterator(Isolate* isolate,
                             Handle<JSGeneratorObject> generator)
    : isolate_(isolate),
      generator_(generator),
      function_(generator->function(), isolate),
      context_(generator->context(), isolate),
      script_(Script::cast(function_->shared().script()), isolate) {
  CHECK(function_->shared().IsSubjectToDebugging());
  TryParseAndRetrieveScopes(ReparseStrategy::kFunctionLiteral);
}

void ScopeIterator::Restart() {
  DCHECK_NOT_NULL(frame_inspector_);
  function_ = frame_inspector_->GetFunction();
  context_ = Handle<Context>::cast(frame_inspector_->GetContext());
  current_scope_ = start_scope_;
  DCHECK_NOT_NULL(current_scope_);
  UnwrapEvaluationContext();
}

namespace {

// Takes the scope of a parsed script, a function and a break location
// inside the function. The result is the innermost lexical scope around
// the break point, which serves as the starting point of the ScopeIterator.
// And the scope of the function that was passed in (called closure scope).
//
// The start scope is guaranteed to be either the closure scope itself,
// or a child of the closure scope.
class ScopeChainRetriever {
 public:
  ScopeChainRetriever(DeclarationScope* scope, Handle<JSFunction> function,
                      int position)
      : scope_(scope),
        break_scope_start_(function->shared().StartPosition()),
        break_scope_end_(function->shared().EndPosition()),
        is_default_constructor_(
            IsDefaultConstructor(function->shared().kind())),
        position_(position) {
    DCHECK_NOT_NULL(scope);
    RetrieveScopes();
  }

  DeclarationScope* ClosureScope() { return closure_scope_; }
  Scope* StartScope() { return start_scope_; }

 private:
  DeclarationScope* scope_;
  const int break_scope_start_;
  const int break_scope_end_;
  const bool is_default_constructor_;
  const int position_;

  DeclarationScope* closure_scope_ = nullptr;
  Scope* start_scope_ = nullptr;

  void RetrieveScopes() {
    if (is_default_constructor_) {
      // Even though the DefaultBaseConstructor is a child of a Class scope, the
      // source positions are *not* nested. This means the actual scope for the
      // DefaultBaseConstructor needs to be found by doing a DFS.
      RetrieveScopeChainDefaultConstructor(scope_);
    } else {
      RetrieveScopeChain();
    }
    DCHECK_NOT_NULL(closure_scope_);
    DCHECK_NOT_NULL(start_scope_);
  }

  bool RetrieveScopeChainDefaultConstructor(Scope* scope) {
    const int beg_pos = scope->start_position();
    const int end_pos = scope->end_position();
    if (beg_pos == position_ && end_pos == position_) {
      DCHECK(scope->is_function_scope());
      DCHECK(
          IsDefaultConstructor(scope->AsDeclarationScope()->function_kind()));
      start_scope_ = scope;
      closure_scope_ = scope->AsDeclarationScope();
      return true;
    }

    for (Scope* inner_scope = scope->inner_scope(); inner_scope != nullptr;
         inner_scope = inner_scope->sibling()) {
      if (RetrieveScopeChainDefaultConstructor(inner_scope)) return true;
    }
    return false;
  }

  void RetrieveScopeChain() {
    Scope* parent = nullptr;
    Scope* current = scope_;
    SetClosureScopeIfFound(current);

    while (parent != current) {
      parent = current;
      for (Scope* inner_scope = current->inner_scope(); inner_scope != nullptr;
           inner_scope = inner_scope->sibling()) {
        if (SetClosureScopeIfFound(inner_scope) ||
            ContainsPosition(inner_scope)) {
          current = inner_scope;
          break;
        }
      }
    }
    start_scope_ = current;
  }

  bool SetClosureScopeIfFound(Scope* scope) {
    const int start = scope->start_position();
    const int end = scope->end_position();
    if (start == break_scope_start_ && end == break_scope_end_) {
      closure_scope_ = scope->AsDeclarationScope();
      return true;
    }
    return false;
  }

  bool ContainsPosition(Scope* scope) {
    const int start = scope->start_position();
    const int end = scope->end_position();
    // In case the closure_scope_ hasn't been found yet, we are less strict
    // about recursing downwards. This might be the case for nested arrow
    // functions that have the same end position.
    const bool position_fits_end =
        closure_scope_ ? position_ < end : position_ <= end;
    return start < position_ && position_fits_end;
  }
};

}  // namespace

void ScopeIterator::TryParseAndRetrieveScopes(ReparseStrategy strategy) {
  // Catch the case when the debugger stops in an internal function.
  Handle<SharedFunctionInfo> shared_info(function_->shared(), isolate_);
  Handle<ScopeInfo> scope_info(shared_info->scope_info(), isolate_);
  if (shared_info->script().IsUndefined(isolate_)) {
    current_scope_ = closure_scope_ = nullptr;
    context_ = handle(function_->context(), isolate_);
    function_ = Handle<JSFunction>();
    return;
  }

  // Class fields initializer functions don't have any scope
  // information. We short circuit the parsing of the class literal
  // and return an empty context here.
  if (IsClassMembersInitializerFunction(shared_info->kind())) {
    current_scope_ = closure_scope_ = nullptr;
    context_ = Handle<Context>();
    function_ = Handle<JSFunction>();
    return;
  }

  bool ignore_nested_scopes = false;
  if (shared_info->HasBreakInfo() && frame_inspector_ != nullptr) {
    // The source position at return is always the end of the function,
    // which is not consistent with the current scope chain. Therefore all
    // nested with, catch and block contexts are skipped, and we can only
    // inspect the function scope.
    // This can only happen if we set a break point inside right before the
    // return, which requires a debug info to be available.
    Handle<DebugInfo> debug_info(shared_info->GetDebugInfo(), isolate_);

    // Find the break point where execution has stopped.
    BreakLocation location = BreakLocation::FromFrame(debug_info, GetFrame());

    ignore_nested_scopes = location.IsReturn();
  }

  // Reparse the code and analyze the scopes.
  // Depending on the choosen strategy, the whole script or just
  // the closure is re-parsed for function scopes.
  Handle<Script> script(Script::cast(shared_info->script()), isolate_);

  // Pick between flags for a single function compilation, or an eager
  // compilation of the whole script.
  UnoptimizedCompileFlags flags =
      (scope_info->scope_type() == FUNCTION_SCOPE &&
       strategy == ReparseStrategy::kFunctionLiteral)
          ? UnoptimizedCompileFlags::ForFunctionCompile(isolate_, *shared_info)
          : UnoptimizedCompileFlags::ForScriptCompile(isolate_, *script)
                .set_is_eager(true);

  MaybeHandle<ScopeInfo> maybe_outer_scope;
  if (scope_info->scope_type() == EVAL_SCOPE || script->is_wrapped()) {
    flags.set_is_eval(true);
    if (!context_->IsNativeContext()) {
      maybe_outer_scope = handle(context_->scope_info(), isolate_);
    }
    // Language mode may be inherited from the eval caller.
    // Retrieve it from shared function info.
    flags.set_outer_language_mode(shared_info->language_mode());
  } else if (scope_info->scope_type() == MODULE_SCOPE) {
    DCHECK(flags.is_module());
  } else {
    DCHECK(scope_info->scope_type() == SCRIPT_SCOPE ||
           scope_info->scope_type() == FUNCTION_SCOPE);
  }

  UnoptimizedCompileState compile_state(isolate_);

  info_ = std::make_unique<ParseInfo>(isolate_, flags, &compile_state);

  const bool parse_result =
      flags.is_toplevel()
          ? parsing::ParseProgram(info_.get(), script, maybe_outer_scope,
                                  isolate_, parsing::ReportStatisticsMode::kNo)
          : parsing::ParseFunction(info_.get(), shared_info, isolate_,
                                   parsing::ReportStatisticsMode::kNo);

  if (parse_result) {
    DeclarationScope* literal_scope = info_->literal()->scope();

    ScopeChainRetriever scope_chain_retriever(literal_scope, function_,
                                              GetSourcePosition());
    start_scope_ = scope_chain_retriever.StartScope();
    current_scope_ = start_scope_;

    // In case of a FUNCTION_SCOPE, the ScopeIterator expects
    // {closure_scope_} to be set to the scope of the function.
    closure_scope_ = scope_info->scope_type() == FUNCTION_SCOPE
                         ? scope_chain_retriever.ClosureScope()
                         : literal_scope;

    if (ignore_nested_scopes) {
      current_scope_ = closure_scope_;
      start_scope_ = current_scope_;
      // ignore_nested_scopes is only used for the return-position breakpoint,
      // so we can safely assume that the closure context for the current
      // function exists if it needs one.
      if (closure_scope_->NeedsContext()) {
        context_ = handle(context_->closure_context(), isolate_);
      }
    }

    UnwrapEvaluationContext();
  } else {
    // A failed reparse indicates that the preparser has diverged from the
    // parser, that the preparse data given to the initial parse was faulty, or
    // a stack overflow.
    // TODO(leszeks): This error is pretty unexpected, so we could report the
    // error in debug mode. Better to not fail in release though, in case it's
    // just a stack overflow.

    // Silently fail by presenting an empty context chain.
    context_ = Handle<Context>();
  }
}

void ScopeIterator::UnwrapEvaluationContext() {
  if (!context_->IsDebugEvaluateContext()) return;
  Context current = *context_;
  do {
    Object wrapped = current.get(Context::WRAPPED_CONTEXT_INDEX);
    if (wrapped.IsContext()) {
      current = Context::cast(wrapped);
    } else {
      DCHECK(!current.previous().is_null());
      current = current.previous();
    }
  } while (current.IsDebugEvaluateContext());
  context_ = handle(current, isolate_);
}

Handle<JSObject> ScopeIterator::MaterializeScopeDetails() {
  // Calculate the size of the result.
  Handle<FixedArray> details =
      isolate_->factory()->NewFixedArray(kScopeDetailsSize);
  // Fill in scope details.
  details->set(kScopeDetailsTypeIndex, Smi::FromInt(Type()));
  Handle<JSObject> scope_object = ScopeObject(Mode::ALL);
  details->set(kScopeDetailsObjectIndex, *scope_object);
  if (Type() == ScopeTypeGlobal || Type() == ScopeTypeScript) {
    return isolate_->factory()->NewJSArrayWithElements(details);
  } else if (HasContext()) {
    Handle<Object> closure_name = GetFunctionDebugName();
    details->set(kScopeDetailsNameIndex, *closure_name);
    details->set(kScopeDetailsStartPositionIndex,
                 Smi::FromInt(start_position()));
    details->set(kScopeDetailsEndPositionIndex, Smi::FromInt(end_position()));
    if (InInnerScope()) {
      details->set(kScopeDetailsFunctionIndex, *function_);
    }
  }
  return isolate_->factory()->NewJSArrayWithElements(details);
}

bool ScopeIterator::HasPositionInfo() {
  return InInnerScope() || !context_->IsNativeContext();
}

int ScopeIterator::start_position() {
  if (InInnerScope()) return current_scope_->start_position();
  if (context_->IsNativeContext()) return 0;
  return context_->closure_context().scope_info().StartPosition();
}

int ScopeIterator::end_position() {
  if (InInnerScope()) return current_scope_->end_position();
  if (context_->IsNativeContext()) return 0;
  return context_->closure_context().scope_info().EndPosition();
}

bool ScopeIterator::DeclaresLocals(Mode mode) const {
  ScopeType type = Type();

  if (type == ScopeTypeWith) return mode == Mode::ALL;
  if (type == ScopeTypeGlobal) return mode == Mode::ALL;

  bool declares_local = false;
  auto visitor = [&](Handle<String> name, Handle<Object> value,
                     ScopeType scope_type) {
    declares_local = true;
    return true;
  };
  VisitScope(visitor, mode);
  return declares_local;
}

bool ScopeIterator::HasContext() const {
  return !InInnerScope() || NeedsAndHasContext();
}

bool ScopeIterator::NeedsAndHasContext() const {
  if (!current_scope_->NeedsContext()) return false;
  // Generally, if a scope needs a context, then we can assume that it has a
  // context. However, the stack check during function entry happens before the
  // function has a chance to create and push its own context, so we must check
  // for the case where the function is executing in its parent context. This
  // case is only possible in function scopes; top-level code (modules and
  // non-module scripts) begin execution in the context they need and don't have
  // a separate step to push the correct context.
  return !(current_scope_ == closure_scope_ &&
           current_scope_->is_function_scope() && !function_.is_null() &&
           function_->context() == *context_);
}

void ScopeIterator::AdvanceOneScope() {
  if (NeedsAndHasContext()) {
    DCHECK(!context_->previous().is_null());
    context_ = handle(context_->previous(), isolate_);
  }
  DCHECK(current_scope_->outer_scope() != nullptr);
  current_scope_ = current_scope_->outer_scope();
}

void ScopeIterator::AdvanceToNonHiddenScope() {
  do {
    AdvanceOneScope();
  } while (current_scope_->is_hidden());
}

void ScopeIterator::AdvanceContext() {
  DCHECK(!context_->IsNativeContext());
  context_ = handle(context_->previous(), isolate_);

  // While advancing one context, we need to advance at least one
  // scope, but until we hit the next scope that actually requires
  // a context. All the locals collected along the way build the
  // blocklist for debug-evaluate for this context.
  locals_ = StringSet::New(isolate_);
  do {
    if (!current_scope_ || !current_scope_->outer_scope()) break;

    current_scope_ = current_scope_->outer_scope();
    CollectLocalsFromCurrentScope();
  } while (!NeedsAndHasContext());
}

void ScopeIterator::Next() {
  DCHECK(!Done());

  ScopeType scope_type = Type();

  if (scope_type == ScopeTypeGlobal) {
    // The global scope is always the last in the chain.
    DCHECK(context_->IsNativeContext());
    context_ = Handle<Context>();
    DCHECK(Done());
    return;
  }

  bool leaving_closure = current_scope_ == closure_scope_;

  if (scope_type == ScopeTypeScript) {
    DCHECK_IMPLIES(InInnerScope() && !leaving_closure,
                   current_scope_->is_script_scope());
    seen_script_scope_ = true;
    if (context_->IsScriptContext()) {
      context_ = handle(context_->previous(), isolate_);
    }
  } else if (!InInnerScope()) {
    AdvanceContext();
  } else {
    DCHECK_NOT_NULL(current_scope_);
    AdvanceToNonHiddenScope();

    if (leaving_closure) {
      DCHECK(current_scope_ != closure_scope_);
      // Edge case when we just go past {closure_scope_}. This case
      // already needs to start collecting locals for the blocklist.
      locals_ = StringSet::New(isolate_);
      CollectLocalsFromCurrentScope();
    }
  }

  if (leaving_closure) function_ = Handle<JSFunction>();

  UnwrapEvaluationContext();
}

// Return the type of the current scope.
ScopeIterator::ScopeType ScopeIterator::Type() const {
  DCHECK(!Done());
  if (InInnerScope()) {
    switch (current_scope_->scope_type()) {
      case FUNCTION_SCOPE:
        DCHECK_IMPLIES(NeedsAndHasContext(),
                       context_->IsFunctionContext() ||
                           context_->IsDebugEvaluateContext());
        return ScopeTypeLocal;
      case MODULE_SCOPE:
        DCHECK_IMPLIES(NeedsAndHasContext(), context_->IsModuleContext());
        return ScopeTypeModule;
      case SCRIPT_SCOPE:
        DCHECK_IMPLIES(NeedsAndHasContext(), context_->IsScriptContext() ||
                                                 context_->IsNativeContext());
        return ScopeTypeScript;
      case WITH_SCOPE:
        DCHECK_IMPLIES(NeedsAndHasContext(), context_->IsWithContext());
        return ScopeTypeWith;
      case CATCH_SCOPE:
        DCHECK(context_->IsCatchContext());
        return ScopeTypeCatch;
      case BLOCK_SCOPE:
      case CLASS_SCOPE:
        DCHECK_IMPLIES(NeedsAndHasContext(), context_->IsBlockContext());
        return ScopeTypeBlock;
      case EVAL_SCOPE:
        DCHECK_IMPLIES(NeedsAndHasContext(), context_->IsEvalContext());
        return ScopeTypeEval;
    }
    UNREACHABLE();
  }
  if (context_->IsNativeContext()) {
    DCHECK(context_->global_object().IsJSGlobalObject());
    // If we are at the native context and have not yet seen script scope,
    // fake it.
    return seen_script_scope_ ? ScopeTypeGlobal : ScopeTypeScript;
  }
  if (context_->IsFunctionContext() || context_->IsEvalContext() ||
      context_->IsDebugEvaluateContext()) {
    return ScopeTypeClosure;
  }
  if (context_->IsCatchContext()) {
    return ScopeTypeCatch;
  }
  if (context_->IsBlockContext()) {
    return ScopeTypeBlock;
  }
  if (context_->IsModuleContext()) {
    return ScopeTypeModule;
  }
  if (context_->IsScriptContext()) {
    return ScopeTypeScript;
  }
  DCHECK(context_->IsWithContext());
  return ScopeTypeWith;
}

Handle<JSObject> ScopeIterator::ScopeObject(Mode mode) {
  DCHECK(!Done());

  ScopeType type = Type();
  if (type == ScopeTypeGlobal) {
    DCHECK_EQ(Mode::ALL, mode);
    return handle(context_->global_proxy(), isolate_);
  }
  if (type == ScopeTypeWith) {
    DCHECK_EQ(Mode::ALL, mode);
    return WithContextExtension();
  }

  Handle<JSObject> scope = isolate_->factory()->NewJSObjectWithNullProto();
  auto visitor = [=](Handle<String> name, Handle<Object> value,
                     ScopeType scope_type) {
    if (value->IsTheHole(isolate_)) {
      // Reflect variables under TDZ as undefined in scope object.
      if (scope_type == ScopeTypeScript &&
          JSReceiver::HasOwnProperty(scope, name).FromMaybe(true)) {
        // We also use the hole to represent overridden let-declarations via
        // REPL mode in a script context. Catch this case.
        return false;
      }
      value = isolate_->factory()->undefined_value();
    }
    JSObject::AddProperty(isolate_, scope, name, value, NONE);
    return false;
  };

  VisitScope(visitor, mode);
  return scope;
}

void ScopeIterator::VisitScope(const Visitor& visitor, Mode mode) const {
  switch (Type()) {
    case ScopeTypeLocal:
    case ScopeTypeClosure:
    case ScopeTypeCatch:
    case ScopeTypeBlock:
    case ScopeTypeEval:
      return VisitLocalScope(visitor, mode, Type());
    case ScopeTypeModule:
      if (InInnerScope()) {
        return VisitLocalScope(visitor, mode, Type());
      }
      DCHECK_EQ(Mode::ALL, mode);
      return VisitModuleScope(visitor);
    case ScopeTypeScript:
      DCHECK_EQ(Mode::ALL, mode);
      return VisitScriptScope(visitor);
    case ScopeTypeWith:
    case ScopeTypeGlobal:
      UNREACHABLE();
  }
}

bool ScopeIterator::SetVariableValue(Handle<String> name,
                                     Handle<Object> value) {
  DCHECK(!Done());
  name = isolate_->factory()->InternalizeString(name);
  switch (Type()) {
    case ScopeTypeGlobal:
    case ScopeTypeWith:
      break;

    case ScopeTypeEval:
    case ScopeTypeBlock:
    case ScopeTypeCatch:
    case ScopeTypeModule:
      if (InInnerScope()) return SetLocalVariableValue(name, value);
      if (Type() == ScopeTypeModule && SetModuleVariableValue(name, value)) {
        return true;
      }
      return SetContextVariableValue(name, value);

    case ScopeTypeLocal:
    case ScopeTypeClosure:
      if (InInnerScope()) {
        DCHECK_EQ(ScopeTypeLocal, Type());
        if (SetLocalVariableValue(name, value)) return true;
        // There may not be an associated context since we're InInnerScope().
        if (!NeedsAndHasContext()) return false;
      } else {
        DCHECK_EQ(ScopeTypeClosure, Type());
        if (SetContextVariableValue(name, value)) return true;
      }
      // The above functions only set variables statically declared in the
      // function. There may be eval-introduced variables. Check them in
      // SetContextExtensionValue.
      return SetContextExtensionValue(name, value);

    case ScopeTypeScript:
      return SetScriptVariableValue(name, value);
  }
  return false;
}

bool ScopeIterator::ClosureScopeHasThisReference() const {
  return !closure_scope_->has_this_declaration() &&
         closure_scope_->HasThisReference();
}

void ScopeIterator::CollectLocalsFromCurrentScope() {
  DCHECK(locals_->IsStringSet());
  for (Variable* var : *current_scope_->locals()) {
    if (var->location() == VariableLocation::PARAMETER ||
        var->location() == VariableLocation::LOCAL) {
      locals_ = StringSet::Add(isolate_, locals_, var->name());
    }
  }
}

#ifdef DEBUG
// Debug print of the content of the current scope.
void ScopeIterator::DebugPrint() {
  StdoutStream os;
  DCHECK(!Done());
  switch (Type()) {
    case ScopeIterator::ScopeTypeGlobal:
      os << "Global:\n";
      context_->Print(os);
      break;

    case ScopeIterator::ScopeTypeLocal: {
      os << "Local:\n";
      if (NeedsAndHasContext()) {
        context_->Print(os);
        if (context_->has_extension()) {
          Handle<HeapObject> extension(context_->extension(), isolate_);
          DCHECK(extension->IsJSContextExtensionObject());
          extension->Print(os);
        }
      }
      break;
    }

    case ScopeIterator::ScopeTypeWith:
      os << "With:\n";
      context_->extension().Print(os);
      break;

    case ScopeIterator::ScopeTypeCatch:
      os << "Catch:\n";
      context_->extension().Print(os);
      context_->get(Context::THROWN_OBJECT_INDEX).Print(os);
      break;

    case ScopeIterator::ScopeTypeClosure:
      os << "Closure:\n";
      context_->Print(os);
      if (context_->has_extension()) {
        Handle<HeapObject> extension(context_->extension(), isolate_);
        DCHECK(extension->IsJSContextExtensionObject());
        extension->Print(os);
      }
      break;

    case ScopeIterator::ScopeTypeScript:
      os << "Script:\n";
      context_->global_object().native_context().script_context_table().Print(
          os);
      break;

    default:
      UNREACHABLE();
  }
  PrintF("\n");
}
#endif

int ScopeIterator::GetSourcePosition() {
  if (frame_inspector_) {
    return frame_inspector_->GetSourcePosition();
  } else {
    DCHECK(!generator_.is_null());
    SharedFunctionInfo::EnsureSourcePositionsAvailable(
        isolate_, handle(generator_->function().shared(), isolate_));
    return generator_->source_position();
  }
}

void ScopeIterator::VisitScriptScope(const Visitor& visitor) const {
  Handle<JSGlobalObject> global(context_->global_object(), isolate_);
  Handle<ScriptContextTable> script_contexts(
      global->native_context().script_context_table(), isolate_);

  // Skip the first script since that just declares 'this'.
  for (int context_index = 1;
       context_index < script_contexts->synchronized_used(); context_index++) {
    Handle<Context> context = ScriptContextTable::GetContext(
        isolate_, script_contexts, context_index);
    Handle<ScopeInfo> scope_info(context->scope_info(), isolate_);
    if (VisitContextLocals(visitor, scope_info, context, ScopeTypeScript))
      return;
  }
}

void ScopeIterator::VisitModuleScope(const Visitor& visitor) const {
  DCHECK(context_->IsModuleContext());

  Handle<ScopeInfo> scope_info(context_->scope_info(), isolate_);
  if (VisitContextLocals(visitor, scope_info, context_, ScopeTypeModule))
    return;

  int count_index = scope_info->ModuleVariableCountIndex();
  int module_variable_count = Smi::cast(scope_info->get(count_index)).value();

  Handle<SourceTextModule> module(context_->module(), isolate_);

  for (int i = 0; i < module_variable_count; ++i) {
    int index;
    Handle<String> name;
    {
      String raw_name;
      scope_info->ModuleVariable(i, &raw_name, &index);
      if (ScopeInfo::VariableIsSynthetic(raw_name)) continue;
      name = handle(raw_name, isolate_);
    }
    Handle<Object> value =
        SourceTextModule::LoadVariable(isolate_, module, index);

    if (visitor(name, value, ScopeTypeModule)) return;
  }
}

bool ScopeIterator::VisitContextLocals(const Visitor& visitor,
                                       Handle<ScopeInfo> scope_info,
                                       Handle<Context> context,
                                       ScopeType scope_type) const {
  // Fill all context locals to the context extension.
  for (int i = 0; i < scope_info->ContextLocalCount(); ++i) {
    Handle<String> name(scope_info->ContextLocalName(i), isolate_);
    if (ScopeInfo::VariableIsSynthetic(*name)) continue;
    int context_index = scope_info->ContextHeaderLength() + i;
    Handle<Object> value(context->get(context_index), isolate_);
    if (visitor(name, value, scope_type)) return true;
  }
  return false;
}

bool ScopeIterator::VisitLocals(const Visitor& visitor, Mode mode,
                                ScopeType scope_type) const {
  if (mode == Mode::STACK && current_scope_->is_declaration_scope() &&
      current_scope_->AsDeclarationScope()->has_this_declaration()) {
    // TODO(bmeurer): We should refactor the general variable lookup
    // around "this", since the current way is rather hacky when the
    // receiver is context-allocated.
    auto this_var = current_scope_->AsDeclarationScope()->receiver();
    Handle<Object> receiver =
        this_var->location() == VariableLocation::CONTEXT
            ? handle(context_->get(this_var->index()), isolate_)
            : frame_inspector_ == nullptr
                  ? handle(generator_->receiver(), isolate_)
                  : frame_inspector_->GetReceiver();
    if (receiver->IsOptimizedOut(isolate_)) {
      receiver = isolate_->factory()->undefined_value();
    }
    if (visitor(isolate_->factory()->this_string(), receiver, scope_type))
      return true;
  }

  if (current_scope_->is_function_scope()) {
    Variable* function_var =
        current_scope_->AsDeclarationScope()->function_var();
    if (function_var != nullptr) {
      Handle<JSFunction> function = frame_inspector_ == nullptr
                                        ? function_
                                        : frame_inspector_->GetFunction();
      Handle<String> name = function_var->name();
      if (visitor(name, function, scope_type)) return true;
    }
  }

  for (Variable* var : *current_scope_->locals()) {
    DCHECK(!var->is_this());
    if (ScopeInfo::VariableIsSynthetic(*var->name())) continue;

    int index = var->index();
    Handle<Object> value;
    switch (var->location()) {
      case VariableLocation::LOOKUP:
        UNREACHABLE();
        break;

      case VariableLocation::REPL_GLOBAL:
        // REPL declared variables are ignored for now.
      case VariableLocation::UNALLOCATED:
        continue;

      case VariableLocation::PARAMETER: {
        if (frame_inspector_ == nullptr) {
          // Get the variable from the suspended generator.
          DCHECK(!generator_.is_null());
          FixedArray parameters_and_registers =
              generator_->parameters_and_registers();
          DCHECK_LT(index, parameters_and_registers.length());
          value = handle(parameters_and_registers.get(index), isolate_);
        } else {
          value = frame_inspector_->GetParameter(index);

          if (value->IsOptimizedOut(isolate_)) {
            value = isolate_->factory()->undefined_value();
          }
        }
        break;
      }

      case VariableLocation::LOCAL:
        if (frame_inspector_ == nullptr) {
          // Get the variable from the suspended generator.
          DCHECK(!generator_.is_null());
          FixedArray parameters_and_registers =
              generator_->parameters_and_registers();
          int parameter_count =
              function_->shared().scope_info().ParameterCount();
          index += parameter_count;
          DCHECK_LT(index, parameters_and_registers.length());
          value = handle(parameters_and_registers.get(index), isolate_);
        } else {
          value = frame_inspector_->GetExpression(index);
          if (value->IsOptimizedOut(isolate_)) {
            // We'll rematerialize this later.
            if (current_scope_->is_declaration_scope() &&
                current_scope_->AsDeclarationScope()->arguments() == var) {
              continue;
            }
            value = isolate_->factory()->undefined_value();
          }
        }
        break;

      case VariableLocation::CONTEXT:
        if (mode == Mode::STACK) continue;
        DCHECK(var->IsContextSlot());
        value = handle(context_->get(index), isolate_);
        break;

      case VariableLocation::MODULE: {
        if (mode == Mode::STACK) continue;
        // if (var->IsExport()) continue;
        Handle<SourceTextModule> module(context_->module(), isolate_);
        value = SourceTextModule::LoadVariable(isolate_, module, var->index());
        break;
      }
    }

    if (visitor(var->name(), value, scope_type)) return true;
  }
  return false;
}

// Retrieve the with-context extension object. If the extension object is
// a proxy, return an empty object.
Handle<JSObject> ScopeIterator::WithContextExtension() {
  DCHECK(context_->IsWithContext());
  if (context_->extension_receiver().IsJSProxy()) {
    return isolate_->factory()->NewJSObjectWithNullProto();
  }
  return handle(JSObject::cast(context_->extension_receiver()), isolate_);
}

// Create a plain JSObject which materializes the block scope for the specified
// block context.
void ScopeIterator::VisitLocalScope(const Visitor& visitor, Mode mode,
                                    ScopeType scope_type) const {
  if (InInnerScope()) {
    if (VisitLocals(visitor, mode, scope_type)) return;
    if (mode == Mode::STACK && Type() == ScopeTypeLocal) {
      // Hide |this| in arrow functions that may be embedded in other functions
      // but don't force |this| to be context-allocated. Otherwise we'd find the
      // wrong |this| value.
      if (!closure_scope_->has_this_declaration() &&
          !closure_scope_->HasThisReference()) {
        if (visitor(isolate_->factory()->this_string(),
                    isolate_->factory()->undefined_value(), scope_type))
          return;
      }
      // Add |arguments| to the function scope even if it wasn't used.
      // Currently we don't yet support materializing the arguments object of
      // suspended generators. We'd need to read the arguments out from the
      // suspended generator rather than from an activation as
      // FunctionGetArguments does.
      if (frame_inspector_ != nullptr && !closure_scope_->is_arrow_scope() &&
          (closure_scope_->arguments() == nullptr ||
           frame_inspector_->GetExpression(closure_scope_->arguments()->index())
               ->IsOptimizedOut(isolate_))) {
        JavaScriptFrame* frame = GetFrame();
        Handle<JSObject> arguments = Accessors::FunctionGetArguments(
            frame, frame_inspector_->inlined_frame_index());
        if (visitor(isolate_->factory()->arguments_string(), arguments,
                    scope_type))
          return;
      }
    }
  } else {
    DCHECK_EQ(Mode::ALL, mode);
    Handle<ScopeInfo> scope_info(context_->scope_info(), isolate_);
    if (VisitContextLocals(visitor, scope_info, context_, scope_type)) return;
  }

  if (mode == Mode::ALL && HasContext()) {
    DCHECK(!context_->IsScriptContext());
    DCHECK(!context_->IsNativeContext());
    DCHECK(!context_->IsWithContext());
    if (!context_->scope_info().SloppyEvalCanExtendVars()) return;
    if (context_->extension_object().is_null()) return;
    Handle<JSObject> extension(context_->extension_object(), isolate_);
    Handle<FixedArray> keys =
        KeyAccumulator::GetKeys(extension, KeyCollectionMode::kOwnOnly,
                                ENUMERABLE_STRINGS)
            .ToHandleChecked();

    for (int i = 0; i < keys->length(); i++) {
      // Names of variables introduced by eval are strings.
      DCHECK(keys->get(i).IsString());
      Handle<String> key(String::cast(keys->get(i)), isolate_);
      Handle<Object> value = JSReceiver::GetDataProperty(extension, key);
      if (visitor(key, value, scope_type)) return;
    }
  }
}

bool ScopeIterator::SetLocalVariableValue(Handle<String> variable_name,
                                          Handle<Object> new_value) {
  // TODO(verwaest): Walk parameters backwards, not forwards.
  // TODO(verwaest): Use VariableMap rather than locals() list for lookup.
  for (Variable* var : *current_scope_->locals()) {
    if (String::Equals(isolate_, var->name(), variable_name)) {
      int index = var->index();
      switch (var->location()) {
        case VariableLocation::LOOKUP:
        case VariableLocation::UNALLOCATED:
          // Drop assignments to unallocated locals.
          DCHECK(var->is_this() ||
                 *variable_name == ReadOnlyRoots(isolate_).arguments_string());
          return false;

        case VariableLocation::REPL_GLOBAL:
          // Assignments to REPL declared variables are ignored for now.
          return false;

        case VariableLocation::PARAMETER: {
          if (var->is_this()) return false;
          if (frame_inspector_ == nullptr) {
            // Set the variable in the suspended generator.
            DCHECK(!generator_.is_null());
            Handle<FixedArray> parameters_and_registers(
                generator_->parameters_and_registers(), isolate_);
            DCHECK_LT(index, parameters_and_registers->length());
            parameters_and_registers->set(index, *new_value);
          } else {
            JavaScriptFrame* frame = GetFrame();
            if (frame->is_optimized()) return false;

            frame->SetParameterValue(index, *new_value);
          }
          return true;
        }

        case VariableLocation::LOCAL:
          if (frame_inspector_ == nullptr) {
            // Set the variable in the suspended generator.
            DCHECK(!generator_.is_null());
            int parameter_count =
                function_->shared().scope_info().ParameterCount();
            index += parameter_count;
            Handle<FixedArray> parameters_and_registers(
                generator_->parameters_and_registers(), isolate_);
            DCHECK_LT(index, parameters_and_registers->length());
            parameters_and_registers->set(index, *new_value);
          } else {
            // Set the variable on the stack.
            JavaScriptFrame* frame = GetFrame();
            if (frame->is_optimized()) return false;

            frame->SetExpression(index, *new_value);
          }
          return true;

        case VariableLocation::CONTEXT:
          DCHECK(var->IsContextSlot());
          context_->set(index, *new_value);
          return true;

        case VariableLocation::MODULE:
          if (!var->IsExport()) return false;
          Handle<SourceTextModule> module(context_->module(), isolate_);
          SourceTextModule::StoreVariable(module, var->index(), new_value);
          return true;
      }
      UNREACHABLE();
    }
  }

  return false;
}

bool ScopeIterator::SetContextExtensionValue(Handle<String> variable_name,
                                             Handle<Object> new_value) {
  if (!context_->has_extension()) return false;

  DCHECK(context_->extension_object().IsJSContextExtensionObject());
  Handle<JSObject> ext(context_->extension_object(), isolate_);
  LookupIterator it(isolate_, ext, variable_name, LookupIterator::OWN);
  Maybe<bool> maybe = JSReceiver::HasProperty(&it);
  DCHECK(maybe.IsJust());
  if (!maybe.FromJust()) return false;

  CHECK(Object::SetDataProperty(&it, new_value).ToChecked());
  return true;
}

bool ScopeIterator::SetContextVariableValue(Handle<String> variable_name,
                                            Handle<Object> new_value) {
  DisallowHeapAllocation no_gc;
  VariableMode mode;
  InitializationFlag flag;
  MaybeAssignedFlag maybe_assigned_flag;
  IsStaticFlag is_static_flag;
  int slot_index =
      ScopeInfo::ContextSlotIndex(context_->scope_info(), *variable_name, &mode,
                                  &flag, &maybe_assigned_flag, &is_static_flag);
  if (slot_index < 0) return false;

  context_->set(slot_index, *new_value);
  return true;
}

bool ScopeIterator::SetModuleVariableValue(Handle<String> variable_name,
                                           Handle<Object> new_value) {
  DisallowHeapAllocation no_gc;
  int cell_index;
  VariableMode mode;
  InitializationFlag init_flag;
  MaybeAssignedFlag maybe_assigned_flag;
  cell_index = context_->scope_info().ModuleIndex(
      *variable_name, &mode, &init_flag, &maybe_assigned_flag);

  // Setting imports is currently not supported.
  if (SourceTextModuleDescriptor::GetCellIndexKind(cell_index) !=
      SourceTextModuleDescriptor::kExport) {
    return false;
  }

  Handle<SourceTextModule> module(context_->module(), isolate_);
  SourceTextModule::StoreVariable(module, cell_index, new_value);
  return true;
}

bool ScopeIterator::SetScriptVariableValue(Handle<String> variable_name,
                                           Handle<Object> new_value) {
  Handle<ScriptContextTable> script_contexts(
      context_->global_object().native_context().script_context_table(),
      isolate_);
  ScriptContextTable::LookupResult lookup_result;
  if (ScriptContextTable::Lookup(isolate_, *script_contexts, *variable_name,
                                 &lookup_result)) {
    Handle<Context> script_context = ScriptContextTable::GetContext(
        isolate_, script_contexts, lookup_result.context_index);
    script_context->set(lookup_result.slot_index, *new_value);
    return true;
  }

  return false;
}

}  // namespace internal
}  // namespace v8