Debugger: refactor ScopeIterator, FrameInspector and DebugEvaluate.

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 "src/debug/debug.h"
+#include "src/globals.h"
+#include "src/parser.h"
+#include "src/scopes.h"
+
+namespace v8 {
+namespace internal {
+
+ScopeIterator::ScopeIterator(Isolate* isolate, FrameInspector* frame_inspector,
+                             bool ignore_nested_scopes)
+    : isolate_(isolate),
+      frame_inspector_(frame_inspector),
+      nested_scope_chain_(4),
+      seen_script_scope_(false),
+      failed_(false) {
+  if (!frame_inspector->GetContext()->IsContext() ||
+      !frame_inspector->GetFunction()->IsJSFunction()) {
+    // Optimized frame, context or function cannot be materialized. Give up.
+    return;
+  }
+
+  context_ = Handle<Context>(Context::cast(frame_inspector->GetContext()));
+
+  // Catch the case when the debugger stops in an internal function.
+  Handle<JSFunction> function = GetFunction();
+  Handle<SharedFunctionInfo> shared_info(function->shared());
+  Handle<ScopeInfo> scope_info(shared_info->scope_info());
+  if (shared_info->script() == isolate->heap()->undefined_value()) {
+    while (context_->closure() == *function) {
+      context_ = Handle<Context>(context_->previous(), isolate_);
+    }
+    return;
+  }
+
+  // Currently it takes too much time to find nested scopes due to script
+  // parsing. Sometimes we want to run the ScopeIterator as fast as possible
+  // (for example, while collecting async call stacks on every
+  // addEventListener call), even if we drop some nested scopes.
+  // Later we may optimize getting the nested scopes (cache the result?)
+  // and include nested scopes into the "fast" iteration case as well.
+
+  if (!ignore_nested_scopes && shared_info->HasDebugInfo()) {
+    // 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());
+
+    // PC points to the instruction after the current one, possibly a break
+    // location as well. So the "- 1" to exclude it from the search.
+    Address call_pc = GetFrame()->pc() - 1;
+
+    // Find the break point where execution has stopped.
+    BreakLocation location =
+        BreakLocation::FromAddress(debug_info, ALL_BREAK_LOCATIONS, call_pc);
+
+    ignore_nested_scopes = location.IsReturn();
+  }
+
+  if (ignore_nested_scopes) {
+    if (scope_info->HasContext()) {
+      context_ = Handle<Context>(context_->declaration_context(), isolate_);
+    } else {
+      while (context_->closure() == *function) {
+        context_ = Handle<Context>(context_->previous(), isolate_);
+      }
+    }
+    if (scope_info->scope_type() == FUNCTION_SCOPE ||
+        scope_info->scope_type() == ARROW_SCOPE) {
+      nested_scope_chain_.Add(scope_info);
+    }
+  } else {
+    // Reparse the code and analyze the scopes.
+    Handle<Script> script(Script::cast(shared_info->script()));
+    Scope* scope = NULL;
+
+    // Check whether we are in global, eval or function code.
+    Handle<ScopeInfo> scope_info(shared_info->scope_info());

[brucedawson, 2015/08/10 18:08:08]

This variable shadows the same-named variable in the outer scope declared at
line 33. This is probably harmless but perhaps (I really don't know) inefficient
since they seem to be recording the same information.

FYI.

This was noticed as a new /analyze warning:
debug-scopes.cc(86) : warning C6246: Local declaration of 'scope_info' hides
declaration of the same name in outer scope. See previous declaration at line
'33'.

Fixing is not required.

[Yang, 2015/08/11 08:13:36]

You are right. This is indeed redundant. I simply copied over old code and did
not notice. I'll follow up with a new CL.

+    Zone zone;
+    if (scope_info->scope_type() != FUNCTION_SCOPE &&
+        scope_info->scope_type() != ARROW_SCOPE) {
+      // Global or eval code.
+      ParseInfo info(&zone, script);
+      if (scope_info->scope_type() == SCRIPT_SCOPE) {
+        info.set_global();
+      } else {
+        DCHECK(scope_info->scope_type() == EVAL_SCOPE);
+        info.set_eval();
+        info.set_context(Handle<Context>(function->context()));
+      }
+      if (Parser::ParseStatic(&info) && Scope::Analyze(&info)) {
+        scope = info.function()->scope();
+      }
+      RetrieveScopeChain(scope, shared_info);
+    } else {
+      // Function code
+      ParseInfo info(&zone, function);
+      if (Parser::ParseStatic(&info) && Scope::Analyze(&info)) {
+        scope = info.function()->scope();
+      }
+      RetrieveScopeChain(scope, shared_info);
+    }
+  }
+}
+
+
+ScopeIterator::ScopeIterator(Isolate* isolate, Handle<JSFunction> function)
+    : isolate_(isolate),
+      frame_inspector_(NULL),
+      context_(function->context()),
+      seen_script_scope_(false),
+      failed_(false) {
+  if (function->IsBuiltin()) context_ = Handle<Context>();
+}
+
+
+MUST_USE_RESULT MaybeHandle<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;
+  ASSIGN_RETURN_ON_EXCEPTION(isolate_, scope_object, ScopeObject(), JSObject);
+  details->set(kScopeDetailsObjectIndex, *scope_object);
+  return isolate_->factory()->NewJSArrayWithElements(details);
+}
+
+
+void ScopeIterator::Next() {
+  DCHECK(!failed_);
+  ScopeType scope_type = Type();
+  if (scope_type == ScopeTypeGlobal) {
+    // The global scope is always the last in the chain.
+    DCHECK(context_->IsNativeContext());
+    context_ = Handle<Context>();
+    return;
+  }
+  if (scope_type == ScopeTypeScript) {
+    seen_script_scope_ = true;
+    if (context_->IsScriptContext()) {
+      context_ = Handle<Context>(context_->previous(), isolate_);
+    }
+    if (!nested_scope_chain_.is_empty()) {
+      DCHECK_EQ(nested_scope_chain_.last()->scope_type(), SCRIPT_SCOPE);
+      nested_scope_chain_.RemoveLast();
+      DCHECK(nested_scope_chain_.is_empty());
+    }
+    CHECK(context_->IsNativeContext());
+    return;
+  }
+  if (nested_scope_chain_.is_empty()) {
+    context_ = Handle<Context>(context_->previous(), isolate_);
+  } else {
+    if (nested_scope_chain_.last()->HasContext()) {
+      DCHECK(context_->previous() != NULL);
+      context_ = Handle<Context>(context_->previous(), isolate_);
+    }
+    nested_scope_chain_.RemoveLast();
+  }
+}
+
+
+// Return the type of the current scope.
+ScopeIterator::ScopeType ScopeIterator::Type() {
+  DCHECK(!failed_);
+  if (!nested_scope_chain_.is_empty()) {
+    Handle<ScopeInfo> scope_info = nested_scope_chain_.last();
+    switch (scope_info->scope_type()) {
+      case FUNCTION_SCOPE:
+      case ARROW_SCOPE:
+        DCHECK(context_->IsFunctionContext() || !scope_info->HasContext());
+        return ScopeTypeLocal;
+      case MODULE_SCOPE:
+        DCHECK(context_->IsModuleContext());
+        return ScopeTypeModule;
+      case SCRIPT_SCOPE:
+        DCHECK(context_->IsScriptContext() || context_->IsNativeContext());
+        return ScopeTypeScript;
+      case WITH_SCOPE:
+        DCHECK(context_->IsWithContext());
+        return ScopeTypeWith;
+      case CATCH_SCOPE:
+        DCHECK(context_->IsCatchContext());
+        return ScopeTypeCatch;
+      case BLOCK_SCOPE:
+        DCHECK(!scope_info->HasContext() || context_->IsBlockContext());
+        return ScopeTypeBlock;
+      case EVAL_SCOPE:
+        UNREACHABLE();
+    }
+  }
+  if (context_->IsNativeContext()) {
+    DCHECK(context_->global_object()->IsGlobalObject());
+    // 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()) {
+    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;
+}
+
+
+MaybeHandle<JSObject> ScopeIterator::ScopeObject() {
+  DCHECK(!failed_);
+  switch (Type()) {
+    case ScopeIterator::ScopeTypeGlobal:
+      return Handle<JSObject>(CurrentContext()->global_object());
+    case ScopeIterator::ScopeTypeScript:
+      return MaterializeScriptScope();
+    case ScopeIterator::ScopeTypeLocal:
+      // Materialize the content of the local scope into a JSObject.
+      DCHECK(nested_scope_chain_.length() == 1);
+      return MaterializeLocalScope();
+    case ScopeIterator::ScopeTypeWith:
+      // Return the with object.
+      return Handle<JSObject>(JSObject::cast(CurrentContext()->extension()));
+    case ScopeIterator::ScopeTypeCatch:
+      return MaterializeCatchScope();
+    case ScopeIterator::ScopeTypeClosure:
+      // Materialize the content of the closure scope into a JSObject.
+      return MaterializeClosure();
+    case ScopeIterator::ScopeTypeBlock:
+      return MaterializeBlockScope();
+    case ScopeIterator::ScopeTypeModule:
+      return MaterializeModuleScope();
+  }
+  UNREACHABLE();
+  return Handle<JSObject>();
+}
+
+
+bool ScopeIterator::HasContext() {
+  ScopeType type = Type();
+  if (type == ScopeTypeBlock || type == ScopeTypeLocal) {
+    if (!nested_scope_chain_.is_empty()) {
+      return nested_scope_chain_.last()->HasContext();
+    }
+  }
+  return true;
+}
+
+
+bool ScopeIterator::SetVariableValue(Handle<String> variable_name,
+                                     Handle<Object> new_value) {
+  DCHECK(!failed_);
+  switch (Type()) {
+    case ScopeIterator::ScopeTypeGlobal:
+      break;
+    case ScopeIterator::ScopeTypeLocal:
+      return SetLocalVariableValue(variable_name, new_value);
+    case ScopeIterator::ScopeTypeWith:
+      break;
+    case ScopeIterator::ScopeTypeCatch:
+      return SetCatchVariableValue(variable_name, new_value);
+    case ScopeIterator::ScopeTypeClosure:
+      return SetClosureVariableValue(variable_name, new_value);
+    case ScopeIterator::ScopeTypeScript:
+      return SetScriptVariableValue(variable_name, new_value);
+    case ScopeIterator::ScopeTypeBlock:
+      return SetBlockVariableValue(variable_name, new_value);
+    case ScopeIterator::ScopeTypeModule:
+      // TODO(2399): should we implement it?
+      break;
+  }
+  return false;
+}
+
+
+Handle<ScopeInfo> ScopeIterator::CurrentScopeInfo() {
+  DCHECK(!failed_);
+  if (!nested_scope_chain_.is_empty()) {
+    return nested_scope_chain_.last();
+  } else if (context_->IsBlockContext()) {
+    return Handle<ScopeInfo>(ScopeInfo::cast(context_->extension()));
+  } else if (context_->IsFunctionContext()) {
+    return Handle<ScopeInfo>(context_->closure()->shared()->scope_info());
+  }
+  return Handle<ScopeInfo>::null();
+}
+
+
+Handle<Context> ScopeIterator::CurrentContext() {
+  DCHECK(!failed_);
+  if (Type() == ScopeTypeGlobal || Type() == ScopeTypeScript ||
+      nested_scope_chain_.is_empty()) {
+    return context_;
+  } else if (nested_scope_chain_.last()->HasContext()) {
+    return context_;
+  } else {
+    return Handle<Context>();
+  }
+}
+
+#ifdef DEBUG
+// Debug print of the content of the current scope.
+void ScopeIterator::DebugPrint() {
+  OFStream os(stdout);
+  DCHECK(!failed_);
+  switch (Type()) {
+    case ScopeIterator::ScopeTypeGlobal:
+      os << "Global:\n";
+      CurrentContext()->Print(os);
+      break;
+
+    case ScopeIterator::ScopeTypeLocal: {
+      os << "Local:\n";
+      GetFunction()->shared()->scope_info()->Print();
+      if (!CurrentContext().is_null()) {
+        CurrentContext()->Print(os);
+        if (CurrentContext()->has_extension()) {
+          Handle<Object> extension(CurrentContext()->extension(), isolate_);
+          if (extension->IsJSContextExtensionObject()) {
+            extension->Print(os);
+          }
+        }
+      }
+      break;
+    }
+
+    case ScopeIterator::ScopeTypeWith:
+      os << "With:\n";
+      CurrentContext()->extension()->Print(os);
+      break;
+
+    case ScopeIterator::ScopeTypeCatch:
+      os << "Catch:\n";
+      CurrentContext()->extension()->Print(os);
+      CurrentContext()->get(Context::THROWN_OBJECT_INDEX)->Print(os);
+      break;
+
+    case ScopeIterator::ScopeTypeClosure:
+      os << "Closure:\n";
+      CurrentContext()->Print(os);
+      if (CurrentContext()->has_extension()) {
+        Handle<Object> extension(CurrentContext()->extension(), isolate_);
+        if (extension->IsJSContextExtensionObject()) {
+          extension->Print(os);
+        }
+      }
+      break;
+
+    case ScopeIterator::ScopeTypeScript:
+      os << "Script:\n";
+      CurrentContext()
+          ->global_object()
+          ->native_context()
+          ->script_context_table()
+          ->Print(os);
+      break;
+
+    default:
+      UNREACHABLE();
+  }
+  PrintF("\n");
+}
+#endif
+
+
+void ScopeIterator::RetrieveScopeChain(Scope* scope,
+                                       Handle<SharedFunctionInfo> shared_info) {
+  if (scope != NULL) {
+    int source_position = frame_inspector_->GetSourcePosition();
+    scope->GetNestedScopeChain(isolate_, &nested_scope_chain_, source_position);
+  } else {
+    // A failed reparse indicates that the preparser has diverged from the
+    // parser or that the preparse data given to the initial parse has been
+    // faulty. We fail in debug mode but in release mode we only provide the
+    // information we get from the context chain but nothing about
+    // completely stack allocated scopes or stack allocated locals.
+    // Or it could be due to stack overflow.
+    DCHECK(isolate_->has_pending_exception());
+    failed_ = true;
+  }
+}
+
+
+MaybeHandle<JSObject> ScopeIterator::MaterializeScriptScope() {
+  Handle<GlobalObject> global(CurrentContext()->global_object());
+  Handle<ScriptContextTable> script_contexts(
+      global->native_context()->script_context_table());
+
+  Handle<JSObject> script_scope =
+      isolate_->factory()->NewJSObject(isolate_->object_function());
+
+  for (int context_index = 0; context_index < script_contexts->used();
+       context_index++) {
+    Handle<Context> context =
+        ScriptContextTable::GetContext(script_contexts, context_index);
+    Handle<ScopeInfo> scope_info(ScopeInfo::cast(context->extension()));
+    CopyContextLocalsToScopeObject(scope_info, context, script_scope);
+  }
+  return script_scope;
+}
+
+
+MaybeHandle<JSObject> ScopeIterator::MaterializeLocalScope() {
+  Handle<JSFunction> function = GetFunction();
+
+  Handle<JSObject> local_scope =
+      isolate_->factory()->NewJSObject(isolate_->object_function());
+  frame_inspector_->MaterializeStackLocals(local_scope, function);
+
+  Handle<Context> frame_context(Context::cast(frame_inspector_->GetContext()));
+
+  HandleScope scope(isolate_);
+  Handle<SharedFunctionInfo> shared(function->shared());
+  Handle<ScopeInfo> scope_info(shared->scope_info());
+
+  if (!scope_info->HasContext()) return local_scope;
+
+  // Third fill all context locals.
+  Handle<Context> function_context(frame_context->declaration_context());
+  CopyContextLocalsToScopeObject(scope_info, function_context, local_scope);
+
+  // Finally copy any properties from the function context extension.
+  // These will be variables introduced by eval.
+  if (function_context->closure() == *function) {
+    if (function_context->has_extension() &&
+        !function_context->IsNativeContext()) {
+      Handle<JSObject> ext(JSObject::cast(function_context->extension()));
+      Handle<FixedArray> keys;
+      ASSIGN_RETURN_ON_EXCEPTION(
+          isolate_, keys, JSReceiver::GetKeys(ext, JSReceiver::INCLUDE_PROTOS),
+          JSObject);
+
+      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)));
+        Handle<Object> value;
+        ASSIGN_RETURN_ON_EXCEPTION(
+            isolate_, value, Object::GetPropertyOrElement(ext, key), JSObject);
+        RETURN_ON_EXCEPTION(isolate_,
+                            Runtime::SetObjectProperty(isolate_, local_scope,
+                                                       key, value, SLOPPY),
+                            JSObject);
+      }
+    }
+  }
+
+  return local_scope;
+}
+
+
+// Create a plain JSObject which materializes the closure content for the
+// context.
+Handle<JSObject> ScopeIterator::MaterializeClosure() {
+  Handle<Context> context = CurrentContext();
+  DCHECK(context->IsFunctionContext());
+
+  Handle<SharedFunctionInfo> shared(context->closure()->shared());
+  Handle<ScopeInfo> scope_info(shared->scope_info());
+
+  // Allocate and initialize a JSObject with all the content of this function
+  // closure.
+  Handle<JSObject> closure_scope =
+      isolate_->factory()->NewJSObject(isolate_->object_function());
+
+  // Fill all context locals to the context extension.
+  CopyContextLocalsToScopeObject(scope_info, context, closure_scope);
+
+  // Finally copy any properties from the function context extension. This will
+  // be variables introduced by eval.
+  if (context->has_extension()) {
+    Handle<JSObject> ext(JSObject::cast(context->extension()));
+    DCHECK(ext->IsJSContextExtensionObject());
+    Handle<FixedArray> keys =
+        JSReceiver::GetKeys(ext, JSReceiver::OWN_ONLY).ToHandleChecked();
+
+    for (int i = 0; i < keys->length(); i++) {
+      HandleScope scope(isolate_);
+      // Names of variables introduced by eval are strings.
+      DCHECK(keys->get(i)->IsString());
+      Handle<String> key(String::cast(keys->get(i)));
+      Handle<Object> value = Object::GetProperty(ext, key).ToHandleChecked();
+      JSObject::SetOwnPropertyIgnoreAttributes(closure_scope, key, value, NONE)
+          .Check();
+    }
+  }
+
+  return closure_scope;
+}
+
+
+// Create a plain JSObject which materializes the scope for the specified
+// catch context.
+Handle<JSObject> ScopeIterator::MaterializeCatchScope() {
+  Handle<Context> context = CurrentContext();
+  DCHECK(context->IsCatchContext());
+  Handle<String> name(String::cast(context->extension()));
+  Handle<Object> thrown_object(context->get(Context::THROWN_OBJECT_INDEX),
+                               isolate_);
+  Handle<JSObject> catch_scope =
+      isolate_->factory()->NewJSObject(isolate_->object_function());
+  JSObject::SetOwnPropertyIgnoreAttributes(catch_scope, name, thrown_object,
+                                           NONE)
+      .Check();
+  return catch_scope;
+}
+
+
+// Create a plain JSObject which materializes the block scope for the specified
+// block context.
+Handle<JSObject> ScopeIterator::MaterializeBlockScope() {
+  Handle<JSObject> block_scope =
+      isolate_->factory()->NewJSObject(isolate_->object_function());
+
+  Handle<Context> context = Handle<Context>::null();
+  if (!nested_scope_chain_.is_empty()) {
+    Handle<ScopeInfo> scope_info = nested_scope_chain_.last();
+    frame_inspector_->MaterializeStackLocals(block_scope, scope_info);
+    if (scope_info->HasContext()) context = CurrentContext();
+  } else {
+    context = CurrentContext();
+  }
+
+  if (!context.is_null()) {
+    Handle<ScopeInfo> scope_info_from_context(
+        ScopeInfo::cast(context->extension()));
+    // Fill all context locals.
+    CopyContextLocalsToScopeObject(scope_info_from_context, context,
+                                   block_scope);
+  }
+  return block_scope;
+}
+
+
+// Create a plain JSObject which materializes the module scope for the specified
+// module context.
+MaybeHandle<JSObject> ScopeIterator::MaterializeModuleScope() {
+  Handle<Context> context = CurrentContext();
+  DCHECK(context->IsModuleContext());
+  Handle<ScopeInfo> scope_info(ScopeInfo::cast(context->extension()));
+
+  // Allocate and initialize a JSObject with all the members of the debugged
+  // module.
+  Handle<JSObject> module_scope =
+      isolate_->factory()->NewJSObject(isolate_->object_function());
+
+  // Fill all context locals.
+  CopyContextLocalsToScopeObject(scope_info, context, module_scope);
+
+  return module_scope;
+}
+
+
+// Set the context local variable value.
+bool ScopeIterator::SetContextLocalValue(Handle<ScopeInfo> scope_info,
+                                         Handle<Context> context,
+                                         Handle<String> variable_name,
+                                         Handle<Object> new_value) {
+  for (int i = 0; i < scope_info->ContextLocalCount(); i++) {
+    Handle<String> next_name(scope_info->ContextLocalName(i));
+    if (String::Equals(variable_name, next_name)) {
+      VariableMode mode;
+      VariableLocation location;
+      InitializationFlag init_flag;
+      MaybeAssignedFlag maybe_assigned_flag;
+      int context_index =
+          ScopeInfo::ContextSlotIndex(scope_info, next_name, &mode, &location,
+                                      &init_flag, &maybe_assigned_flag);
+      context->set(context_index, *new_value);
+      return true;
+    }
+  }
+
+  return false;
+}
+
+
+bool ScopeIterator::SetLocalVariableValue(Handle<String> variable_name,
+                                          Handle<Object> new_value) {
+  JavaScriptFrame* frame = GetFrame();
+  // Optimized frames are not supported.
+  if (frame->is_optimized()) return false;
+
+  Handle<JSFunction> function(frame->function());
+  Handle<SharedFunctionInfo> shared(function->shared());
+  Handle<ScopeInfo> scope_info(shared->scope_info());
+
+  bool default_result = false;
+
+  // Parameters.
+  for (int i = 0; i < scope_info->ParameterCount(); ++i) {
+    HandleScope scope(isolate_);
+    if (String::Equals(handle(scope_info->ParameterName(i)), variable_name)) {
+      frame->SetParameterValue(i, *new_value);
+      // Argument might be shadowed in heap context, don't stop here.
+      default_result = true;
+    }
+  }
+
+  // Stack locals.
+  for (int i = 0; i < scope_info->StackLocalCount(); ++i) {
+    HandleScope scope(isolate_);
+    if (String::Equals(handle(scope_info->StackLocalName(i)), variable_name)) {
+      frame->SetExpression(scope_info->StackLocalIndex(i), *new_value);
+      return true;
+    }
+  }
+
+  if (scope_info->HasContext()) {
+    // Context locals.
+    Handle<Context> frame_context(Context::cast(frame->context()));
+    Handle<Context> function_context(frame_context->declaration_context());
+    if (SetContextLocalValue(scope_info, function_context, variable_name,
+                             new_value)) {
+      return true;
+    }
+
+    // Function context extension. These are variables introduced by eval.
+    if (function_context->closure() == *function) {
+      if (function_context->has_extension() &&
+          !function_context->IsNativeContext()) {
+        Handle<JSObject> ext(JSObject::cast(function_context->extension()));
+
+        Maybe<bool> maybe = JSReceiver::HasProperty(ext, variable_name);
+        DCHECK(maybe.IsJust());
+        if (maybe.FromJust()) {
+          // We don't expect this to do anything except replacing
+          // property value.
+          Runtime::SetObjectProperty(isolate_, ext, variable_name, new_value,
+                                     SLOPPY)
+              .Assert();
+          return true;
+        }
+      }
+    }
+  }
+
+  return default_result;
+}
+
+
+bool ScopeIterator::SetBlockVariableValue(Handle<String> variable_name,
+                                          Handle<Object> new_value) {
+  Handle<ScopeInfo> scope_info = CurrentScopeInfo();
+  JavaScriptFrame* frame = GetFrame();
+
+  for (int i = 0; i < scope_info->StackLocalCount(); ++i) {
+    HandleScope scope(isolate_);
+    if (String::Equals(handle(scope_info->StackLocalName(i)), variable_name)) {
+      frame->SetExpression(scope_info->StackLocalIndex(i), *new_value);
+      return true;
+    }
+  }
+
+  if (HasContext()) {
+    return SetContextLocalValue(scope_info, CurrentContext(), variable_name,
+                                new_value);
+  }
+  return false;
+}
+
+
+// This method copies structure of MaterializeClosure method above.
+bool ScopeIterator::SetClosureVariableValue(Handle<String> variable_name,
+                                            Handle<Object> new_value) {
+  Handle<Context> context = CurrentContext();
+  DCHECK(context->IsFunctionContext());
+
+  // Context locals to the context extension.
+  Handle<SharedFunctionInfo> shared(context->closure()->shared());
+  Handle<ScopeInfo> scope_info(shared->scope_info());
+  if (SetContextLocalValue(scope_info, context, variable_name, new_value)) {
+    return true;
+  }
+
+  // Properties from the function context extension. This will
+  // be variables introduced by eval.
+  if (context->has_extension()) {
+    Handle<JSObject> ext(JSObject::cast(context->extension()));
+    DCHECK(ext->IsJSContextExtensionObject());
+    Maybe<bool> maybe = JSReceiver::HasOwnProperty(ext, variable_name);
+    DCHECK(maybe.IsJust());
+    if (maybe.FromJust()) {
+      // We don't expect this to do anything except replacing property value.
+      JSObject::SetOwnPropertyIgnoreAttributes(ext, variable_name, new_value,
+                                               NONE)
+          .Check();
+      return true;
+    }
+  }
+
+  return false;
+}
+
+
+bool ScopeIterator::SetScriptVariableValue(Handle<String> variable_name,
+                                           Handle<Object> new_value) {
+  Handle<Context> context = CurrentContext();
+  Handle<ScriptContextTable> script_contexts(
+      context->global_object()->native_context()->script_context_table());
+  ScriptContextTable::LookupResult lookup_result;
+  if (ScriptContextTable::Lookup(script_contexts, variable_name,
+                                 &lookup_result)) {
+    Handle<Context> script_context = ScriptContextTable::GetContext(
+        script_contexts, lookup_result.context_index);
+    script_context->set(lookup_result.slot_index, *new_value);
+    return true;
+  }
+
+  return false;
+}
+
+
+bool ScopeIterator::SetCatchVariableValue(Handle<String> variable_name,
+                                          Handle<Object> new_value) {
+  Handle<Context> context = CurrentContext();
+  DCHECK(context->IsCatchContext());
+  Handle<String> name(String::cast(context->extension()));
+  if (!String::Equals(name, variable_name)) {
+    return false;
+  }
+  context->set(Context::THROWN_OBJECT_INDEX, *new_value);
+  return true;
+}
+
+
+void ScopeIterator::CopyContextLocalsToScopeObject(
+    Handle<ScopeInfo> scope_info, Handle<Context> context,
+    Handle<JSObject> scope_object) {
+  Isolate* isolate = scope_info->GetIsolate();
+  int local_count = scope_info->ContextLocalCount();
+  if (local_count == 0) return;
+  // Fill all context locals to the context extension.
+  int first_context_var = scope_info->StackLocalCount();
+  int start = scope_info->ContextLocalNameEntriesIndex();
+  for (int i = 0; i < local_count; ++i) {
+    if (scope_info->LocalIsSynthetic(first_context_var + i)) continue;
+    int context_index = Context::MIN_CONTEXT_SLOTS + i;
+    Handle<Object> value = Handle<Object>(context->get(context_index), isolate);
+    // Reflect variables under TDZ as undefined in scope object.
+    if (value->IsTheHole()) continue;
+    // This should always succeed.
+    // TODO(verwaest): Use AddDataProperty instead.
+    JSObject::SetOwnPropertyIgnoreAttributes(
+        scope_object, handle(String::cast(scope_info->get(i + start))), value,
+        ::NONE)
+        .Check();
+  }
+}
+
+}  // namespace internal
+}  // namespace v8