A brutal approach to V8 script liveedit

src/liveedit.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 17 matching lines @@
 
 #include "v8.h"
 
 #include "liveedit.h"
 #include "compiler.h"
 #include "oprofile-agent.h"
 #include "scopes.h"
 #include "global-handles.h"
 #include "debug.h"
 
+#ifdef ENABLE_DEBUGGER_SUPPORT
+
 namespace v8 {
 namespace internal {
 
+static Handle<JSFunction> LiveEditMakeFunction(bool is_global,
+                                       Compiler::ValidationState validate,
+                                       Handle<Script> script,
+                                       Handle<Context> context,
+                                       v8::Extension* extension,
+                                       ScriptDataImpl* pre_data) {
+  const bool is_eval = false;
+  PostponeInterruptsScope postpone;
+
+  ASSERT(!i::Top::global_context().is_null());
+  script->set_context_data((*i::Top::global_context())->data());
+
+#ifdef ENABLE_DEBUGGER_SUPPORT
+  // no eval or json support
+  // Do not notify debugger (maybe later)
+  //Debugger::OnBeforeCompile(script);
+#endif
+
+  // Only allow non-global compiles for eval.
+  ASSERT(is_eval || is_global);
+
+  // Build AST.
+  FunctionLiteral* lit = MakeAST(is_global, script, extension, pre_data);
+
+  // Check for parse errors.
+  if (lit == NULL) {
+    ASSERT(Top::has_pending_exception());
+    return Handle<JSFunction>::null();
+  }
+
+  // Compile the code.
+  CompilationInfo info(lit, script, is_eval);
+  Handle<Code> code = MakeCodeForLiveEdit(context, &info);
+
+  // Check for stack-overflow exceptions.
+  if (code.is_null()) {
+    Top::StackOverflow();
+    return Handle<JSFunction>::null();
+  }
+
+  const bool support_profiler_in_live_edit = false;
+  if (support_profiler_in_live_edit) {
+  #if defined ENABLE_LOGGING_AND_PROFILING || defined ENABLE_OPROFILE_AGENT
+    // Log the code generation for the script. Check explicit whether logging is
+    // to avoid allocating when not required.
+    if (Logger::is_logging() || OProfileAgent::is_enabled()) {
+      if (script->name()->IsString()) {
+        SmartPointer<char> data =
+            String::cast(script->name())->ToCString(DISALLOW_NULLS);
+        LOG(CodeCreateEvent(is_eval ? Logger::EVAL_TAG : Logger::SCRIPT_TAG,
+                            *code, *data));
+        OProfileAgent::CreateNativeCodeRegion(*data,
+                                              code->instruction_start(),
+                                              code->instruction_size());
+      } else {
+        LOG(CodeCreateEvent(is_eval ? Logger::EVAL_TAG : Logger::SCRIPT_TAG,
+                            *code, ""));
+        OProfileAgent::CreateNativeCodeRegion(is_eval ? "Eval" : "Script",
+                                              code->instruction_start(),
+                                              code->instruction_size());
+      }
+    }
+  #endif
+  }
+
+  // Allocate function.
+  Handle<JSFunction> fun =
+      Factory::NewFunctionBoilerplate(lit->name(),
+                                      lit->materialized_literal_count(),
+                                      code);
+
+  ASSERT_EQ(RelocInfo::kNoPosition, lit->function_token_position());
+  Compiler::SetFunctionInfo(fun, lit, true, script);
+
+  // Hint to the runtime system used when allocating space for initial
+  // property space by setting the expected number of properties for
+  // the instances of the function.
+  SetExpectedNofPropertiesFromEstimate(fun, lit->expected_property_count());
+
+#ifdef ENABLE_DEBUGGER_SUPPORT
+  // Do not notify debugger (maybe later)
+  // Debugger::OnAfterCompile(script, fun);
+#endif
+
+  return fun;
+}
+
+static StaticResource<SafeStringInputBuffer> safe_string_input_buffer;
+
+class UnusedReferenceChecker {
+ public:
+  UnusedReferenceChecker() : head_(NULL) {
+  }
+
+  ~UnusedReferenceChecker() {
+    for (Item* item = head_; item != NULL; item = item->next) {
+      GlobalHandles::Destroy(item->ref);
+    }
+  }
+
+  void Add(Object* obj) {
+    Item* item = new Item();
+    item->next = head_;
+    head_ = item;
+    Object** ref = GlobalHandles::Create(obj).location();
+    GlobalHandles::MakeWeak(ref, item, &Callback);
+    item->ref = ref;
+    item->collected = false;
+  }
+
+  void Check() {
+    Heap::CollectAllGarbage(false);
+    for (Item* item = head_; item != NULL; item = item->next) {
+      if (!item->collected) {
+        const int kSize = 10;
+        Handle<FixedArray> array = Factory::NewFixedArray(kSize);
+        int found = FindReferences(*item->ref, 0, *array, array->length());
+        printf("Item ");
+        (*item->ref)->ShortPrint();
+        printf(" still referenced by %d item(s):\n", found);
+        for (int i = 0; i < found; i++) {
+          if (i >= array->length()) {
+            printf("... there's more.\n");
+            break;
+          }
+          array->get(i)->ShortPrint();
+          printf("\n");
+        }
+      }
+      ASSERT(item->collected);
+    }
+
+  }
+
+  static void Callback(Persistent<Value> object, void* parameter) {
+    Item* item = reinterpret_cast<Item*>(parameter);
+    item->collected = true;
+  }
+
+ private:
+  struct Item : public ZoneObject {
+    Object** ref;
+    bool collected;
+    Item* next;
+  };
+  Item* head_;
+
+  class VisitorImpl : public ObjectVisitor {
+   public:
+    VisitorImpl(Object* target) : target_(target), found_(false) {}
+
+    bool HasFound() {
+      return found_;
+    }
+
+   protected:
+    void VisitPointers(Object** start, Object** end) {
+      for (Object** pp = start; pp < end; pp++) {
+        if (*pp == target_) {
+          found_ = true;
+          break;
+        }
+      }
+    }
+
+   private:
+    Object* target_;
+    bool found_;
+  };
+
+  static int FindReferences(Object* target, int max_references,
+                            FixedArray* instances, int instances_size) {
+    NoHandleAllocation ha;
+    AssertNoAllocation no_alloc;
+
+    // Iterate the heap.
+    int count = 0;
+    HeapIterator iterator;
+    HeapObject* heap_obj = NULL;
+    while (((heap_obj = iterator.next()) != NULL) &&
+           (max_references == 0 || count < max_references)) {
+
+      // Skip context extension objects and argument arrays as these are
+      // checked in the context of functions using them.
+      HeapObject* obj = heap_obj;
+
+      VisitorImpl visitor(target);
+      obj->Iterate(&visitor);
+      if (visitor.HasFound()) {
+        if (instances != NULL && count < instances_size) {
+          instances->set(count, obj);
+        }
+        count++;
+      }
+    }
+
+    // Return the number of referencing objects found.
+    return count;
+  }
+};
+
+void CompileAndAnalyzeScript(Handle<Script> script) {
+  Extension* extension = NULL;
+  Handle<String> source = Handle<String>(String::cast(script->source()));
+  ScriptDataImpl* pre_data = NULL;
+  if (pre_data == NULL && source->length() >= FLAG_min_preparse_length) {
+    Access<SafeStringInputBuffer> buf(&safe_string_input_buffer);
+    buf->Reset(source.location());
+    pre_data = PreParse(source, buf.value(), extension);
+  }
+
+  // Compile the function and add it to the cache.
+  Handle<JSFunction> res = LiveEditMakeFunction(true,
+                        Compiler::DONT_VALIDATE_JSON,
+                        script,
+                        Handle<Context>::null(),
+                        NULL,
+                        pre_data);
+  // Compilation.
+  ASSERT(res->IsJSFunction());
+}
+
+// Let us be careful with double pointers.
+// Here expected input types are explicit.
+template<typename FROM, typename TO>
+TO** DoublePointerNarrowingCast(FROM** from) {
+  TO* t1 = NULL;
+  FROM* t2 = t1;
+  USE(t2);
+  return reinterpret_cast<TO**>(from);
+}
+
+template<typename FROM, typename TO>
+TO** DoublePointerWideningCast(FROM** from) {
+  FROM* t1 = NULL;
+  TO* t2 = t1;
+  USE(t2);
+  return reinterpret_cast<TO**>(from);
+}
+
+// For a function (i.e. closure: code + data) describes expectations that
+// code has about its data. If new version of code has the same expectations
+// as the old version has, all live closure instances may be safely patched
+// with a new code.
+// TODO(peter.rybin): make sure this description is accurate enough.
+class CodeInfo {
+ private:
+  struct ScopeSlotInfo {
+    String** var_name;
+    int index;
+    ScopeSlotInfo() : var_name(NULL) {}
+  };
+
+  Vector<ScopeSlotInfo> slots;
+  int num_parameters;
+
+ public:
+  void RecordNumParameters(int num_parameters) {
+    this->num_parameters = num_parameters;
+  }
+  // Stores the scope info in some internal format.
+  void RecordScopes(Scope* scope) {
+    // Saves some description of scope. It stores name and indexes of
+    // variables in the whole scope chain. Null-named slots delimit
+    // scopes of this chain.
+    Scope* outer_scope = scope->outer_scope();
+    if (outer_scope == NULL) {
+      return;
+    }
+    ZoneList<ScopeSlotInfo> slots(10);
+    do {
+      ZoneList<Variable*> list(10);
+      outer_scope->CollectUsedVariables(&list);
+      int j = 0;
+      for (int i = 0; i < list.length(); i++) {
+        Variable* var1 = list[i];
+        Slot* slot = var1->slot();
+        if (slot != NULL && slot->type() == Slot::CONTEXT) {
+          if (j != i) {
+            list[j] = var1;
+          }
+          j++;
+        }
+      }
+
+      // Sort it.
+      // TODO(peter.rybin): next time try bubble sort.
+      for (int k = 1; k < j; k++) {
+        int l = k;
+        for (int m = k + 1; m < j; m++) {
+          if (list[l]->slot()->index() > list[m]->slot()->index()) {
+            l = m;
+          }
+        }
+        list[k] = list[l];
+      }
+      for (int i = 0; i < j; i++) {
+        ScopeSlotInfo info;
+        info.var_name = DoublePointerNarrowingCast<Object,String>(
+            GlobalHandles::Create(*list[i]->name()).location());
+        info.index = list[i]->slot()->index();
+        slots.Add(info);
+      }
+      slots.Add(ScopeSlotInfo());
+      outer_scope = outer_scope->outer_scope();
+    } while (outer_scope != NULL);
+    this->slots = slots.ToVector();
+  }
+
+  // Compares itself with other info. When they are equal it means that
+  // different code versions have the same expectations about their data.
+  bool CompareTo(CodeInfo* info2) {
+    CodeInfo* info1 = this;
+    if (info1->num_parameters != info2->num_parameters) {
+      return false;
+    }
+    if (info1->slots.length() != info2->slots.length()) {
+      return false;
+    }
+    for (int i = 0; i < info1->slots.length(); i++) {
+      ScopeSlotInfo* slot1 = &info1->slots[i];
+      ScopeSlotInfo* slot2 = &info2->slots[i];
+      if (slot1->index != slot2->index) {
+        return false;
+      }
+      if (slot1->var_name == NULL) {
+        if (slot2->var_name != NULL) {
+          return false;
+        }
+      } else {
+        if (!(*slot1->var_name)->Equals(*slot2->var_name)) {
+          return false;
+        }
+      }
+    }
+    return true;
+  }
+
+  void DisposeHandles() {
+    for (int j = 0; j < slots.length(); j++) {
+      if (slots[j].var_name != NULL) {
+        // TODO does it have to be so brutal?
+        GlobalHandles::Destroy(DoublePointerWideningCast<String,Object>(
+            slots[j].var_name));
+      }
+    }
+  }
+  void Print() {
+    for (int i = 0; i < slots.length(); i++) {
+      if (slots[i].var_name == NULL) {
+        printf(" | ");
+      } else {
+        SmartPointer<char> str = (*slots[i].var_name)->ToCString();
+        printf(" %d/%s", slots[i].index,*str);
+      }
+    }
+    printf(" params %d", num_parameters);
+  }
+};
+
+// Saved information about a function. It is stored in array. It points
+// to other items in this array by their indexes.
+struct FunctionInfo {
+  int outer_index;
+  int next_sibling_index;
+  CodeInfo code_info;
+  int start_pos;
+  int end_pos;
+  Code** function_code;
+
+  FunctionInfo() : function_code(NULL) {}
+};
 
 class FunctionInfoListener {
  public:
+  FunctionInfoListener(): function_infos_(10),
+      current_pos_(-1), last_sibling_pos_(-1) {}
+
+  Vector<FunctionInfo> GetFunctionInfos() {
+    Vector<FunctionInfo> temp = function_infos_.ToVector();
+    // new index -> old index
+
+    ZoneList<int> old_index_map_builder(temp.length());
+    for (int i = 0; i < temp.length(); i++) {
+      old_index_map_builder.Add(i);
+    }
+    Vector<int> old_index_map = old_index_map_builder.ToVector();
+    for (int i = 0; i < temp.length(); i++) {
+      int k = i;
+      for (int j = i + 1; j < temp.length(); j++) {
+        if (temp[k].start_pos > temp[j].start_pos) {
+          k = j;
+        }
+      }
+      if (k != i) {
+        FunctionInfo temp_info = temp[k];
+        int temp_index = old_index_map[k];
+        temp[k] = temp[i];
+        old_index_map[k] = temp_index;
+        temp[i] = temp_info;
+        old_index_map[i] = temp_index;
+      }
+    }
+    int index = 0;
+    ResetIndexes(temp, &index, -1, -1, old_index_map);
+    ASSERT(index == temp.length());
+
+    return temp;
+  }
+
+  static void DisposeData(Vector<FunctionInfo> data) {
+    for (int i = 0; i < data.length(); i++) {
+      FunctionInfo* info = &data[i];
+      CodeInfo* code_info = &info->code_info;
+      code_info->DisposeHandles();
+      if (info->function_code != NULL) {
+        // TODO does it have to be so brutal?
+        GlobalHandles::Destroy(DoublePointerWideningCast<Code,Object>(info->function_code));
+      }
+    }
+  }
+
+  friend class LiveEditFunctionTracker;
+
+ private:
+  void ResetIndexes(Vector<FunctionInfo> array, int* current_index,
+                    int new_parent_index,
+                    int old_parent_index,
+                    Vector<int> old_index_map) {
+    int previous_sibling = -1;
+    while (*current_index < array.length() && array[*current_index].outer_index == old_parent_index) {
+      int index = *current_index;
+      array[index].outer_index = new_parent_index;
+      if (previous_sibling != -1) {
+        array[previous_sibling].next_sibling_index = index;
+      }
+      previous_sibling = index;
+      (*current_index)++;
+      ResetIndexes(array, current_index, index, old_index_map[index], old_index_map);
+    }
+    if (previous_sibling != -1) {
+      array[previous_sibling].next_sibling_index = -1;
+    }
+  }
+
   void FunctionStarted(FunctionLiteral* fun) {
-    // Implementation follows.
+    // printf("Start '%s' %d %d\n", *fun->name()->ToCString(), fun->start_position(), fun->end_position());
+    FunctionInfo info;
+    info.code_info.RecordNumParameters(fun->num_parameters());
+    info.start_pos = fun->start_position();
+    info.end_pos = fun->end_position();
+    info.outer_index = current_pos_;
+    info.next_sibling_index = last_sibling_pos_;
+    last_sibling_pos_ = -1;
+    current_pos_ = function_infos_.length();
+    function_infos_.Add(info);
+    if (info.outer_index != -1) {
+      FunctionInfo& outer_info = function_infos_[info.outer_index];
+      ASSERT(info.start_pos >= outer_info.start_pos);
+      ASSERT(info.end_pos <= outer_info.end_pos);
+    }
   }
 
   void FunctionDone() {
-    // Implementation follows.
+    last_sibling_pos_ = current_pos_;
+    current_pos_ = function_infos_[current_pos_].outer_index;
+    // printf("Done\n");
   }
 
   void FunctionScope(Scope* scope){
-    // Implementation follows.
+    function_infos_[current_pos_].code_info.RecordScopes(scope);
   }
 
   void FunctionCode(Handle<Code> function_code) {
-    // Implementation follows.
-  }
+    function_infos_[current_pos_].function_code = DoublePointerNarrowingCast<Object, Code>(GlobalHandles::Create(*function_code).location());
+  }
+
+  ZoneList<FunctionInfo> function_infos_;
+  int current_pos_;
+  int last_sibling_pos_;
 };
 
 static FunctionInfoListener* active_function_info_listener = NULL;
 
 LiveEditFunctionTracker::LiveEditFunctionTracker(FunctionLiteral* fun) {
   if (active_function_info_listener != NULL) {
     active_function_info_listener->FunctionStarted(fun);
   }
 }
 LiveEditFunctionTracker::~LiveEditFunctionTracker() {
   if (active_function_info_listener != NULL) {
     active_function_info_listener->FunctionDone();
   }
 }
 void LiveEditFunctionTracker::RecordFunctionCode(Handle<Code> code) {
   if (active_function_info_listener != NULL) {
     active_function_info_listener->FunctionCode(code);
   }
 }
 void LiveEditFunctionTracker::RecordFunctionScope(Scope* scope) {
   if (active_function_info_listener != NULL) {
     active_function_info_listener->FunctionScope(scope);
   }
 }
 bool LiveEditFunctionTracker::IsActive() {
   return active_function_info_listener != NULL;
 }
 
+class PosTranslator {
+ public:
+  PosTranslator(int start, int old_len, int new_len)
+      : start_(start), old_len_(old_len), new_len_(new_len) {}
+  int Translate(int pos) {
+    if (pos <= start_) {
+      return pos;
+    }
+    if (pos >= start_ + old_len_) {
+      return pos + new_len_ - old_len_;
+    }
+    return -1;
+  }
+
+ private:
+  int start_;
+  int old_len_;
+  int new_len_;
+};
+
+
+// Chooses the innermost function that covers the change region.
+// TODO(peter.rybin): function should cover change region by its body region,
+// not by its entire text
+int ChooseChangedFunction(Vector<FunctionInfo> fun_infos,
+                          int change_pos, int change_len) {
+
+  // First condition: function should start before the change region.
+  // Function #0 (whole-script function) always does, but we want
+  // the one, that comes last in this list.
+  int index = 0;
+  while (index + 1 < fun_infos.length() &&
+      fun_infos[index + 1].start_pos <= change_pos) {
+    index++;
+  }
+  // Now we have stand at the last function that begins before the change
+  // region. The function that covers entire change region is either
+  // this function or enclosing one.
+  for (; fun_infos[index].end_pos < change_pos + change_len;
+      index = fun_infos[index].outer_index) {
+    ASSERT(index != -1);
+  }
+  return index;
+}
+
+void PatchCode(FunctionInfo* new_info,
+               Handle<SharedFunctionInfo> shared_info,
+               UnusedReferenceChecker* ref_checker) {
+  if (shared_info.is_null()) {
+    // Function not found. Probably it's normal.
+    // TODO explain why it's normal.
+    return;
+  }
+  ref_checker->Add(shared_info->code());
+  shared_info->set_code(*new_info->function_code, UPDATE_WRITE_BARRIER);
+  shared_info->set_start_position(new_info->start_pos);
+  shared_info->set_end_position(new_info->end_pos);
+  // TODO: update breakpoints, original code, constructor stub
+}
+
+void PatchPositions(FunctionInfo* new_info,
+                    Handle<SharedFunctionInfo> shared_info,
+                    PosTranslator* pos_translator) {
+  if (shared_info.is_null()) {
+    // Function not found. Probably it's normal.
+    // TODO explain why it's normal.
+    return;
+  }
+  int new_start_pos = pos_translator->Translate(
+      shared_info->start_position());
+  int new_end_pos = pos_translator->Translate(shared_info->end_position());
+  ASSERT(new_start_pos == new_info->start_pos);
+  ASSERT(new_end_pos == new_info->end_pos);
+  shared_info->set_start_position(new_start_pos);
+  shared_info->set_end_position(new_end_pos);
+
+  // TODO
+  // breakpoints, rinfos, shared function positions
+}
+
+void LinkToOldScript(FunctionInfo* old_info, Handle<Script> old_script,
+                     Handle<SharedFunctionInfo> shared_info) {
+  if (shared_info.is_null()) {
+    // Function not found. Probably it's normal.
+    // TODO explain why it's normal.
+    return;
+  }
+  shared_info->set_script(*old_script);
+}
+
+// Helps to find SharedFunctionInfo based on its source positions.
+class FunctionListHelper {
+ public:
+  FunctionListHelper(Handle<FixedArray> shared_functions,
+                     int shared_functions_len,
+                     Vector<FunctionInfo> info_list)
+      : shared_functions_(shared_functions),
+        shared_functions_len_(shared_functions_len),
+        info_list_(info_list) {
+  }
+
+  Handle<SharedFunctionInfo> Get(int index) {
+    FunctionInfo* old_info = &info_list_[index];
+    for (int i = 0; i < shared_functions_len_; i++) {
+      SharedFunctionInfo* info =
+          SharedFunctionInfo::cast(shared_functions_->get(i));
+      if (info->start_position() == old_info->start_pos &&
+          info->end_position() == old_info->end_pos) {
+        return Handle<SharedFunctionInfo>(info);
+      }
+    }
+    {
+      printf("Failed to find positions %d %d in\n:", old_info->start_pos, old_info->end_pos);
+      for (int i = 0; i < shared_functions_len_; i++) {
+        SharedFunctionInfo* info =
+            SharedFunctionInfo::cast(shared_functions_->get(i));
+        printf("   %d %d\n", info->start_position(), info->end_position());
+      }
+    }
+    return Handle<SharedFunctionInfo>();
+  }
+ private:
+  Handle<FixedArray> shared_functions_;
+  int shared_functions_len_;
+  Vector<FunctionInfo> info_list_;
+};
+
+void ChangeScriptLive(Handle<Script> original_script,
+                      Handle<String> original_source,
+                      Handle<String> new_source,
+                      Handle<FixedArray> function_shared_info,
+                      int function_shared_info_len,
+                      int change_pos, int change_len_old, int change_len_new) {
+
+  printf("Old script:\n");
+  original_source->Print();
+  printf("\n");
+  printf("New script:\n");
+  new_source->Print();
+  printf("\n");
+
+  {
+    CompilationZoneScope zone_scope(DELETE_ON_EXIT);
+
+    Vector<FunctionInfo> old_infos;
+    Vector<FunctionInfo> new_infos;
+    {
+      FunctionInfoListener old_listener;
+      active_function_info_listener = &old_listener;
+      CompileAndAnalyzeScript(original_script);
+      old_infos = old_listener.GetFunctionInfos();
+      active_function_info_listener = NULL;
+      //TODO: check compilation errors
+    }
+
+    // Temporary change source string.
+    original_script->set_source(*new_source);
+    {
+      FunctionInfoListener new_listener;
+      active_function_info_listener = &new_listener;
+      CompileAndAnalyzeScript(original_script);
+      new_infos = new_listener.GetFunctionInfos();
+      active_function_info_listener = NULL;
+      //TODO: check compilation errors
+    }
+    // Change source string back, we'll change it permanently later.
+    original_script->set_source(*original_source);
+
+    int function_being_changed;
+    {
+      int old_func_index =
+          ChooseChangedFunction(old_infos, change_pos, change_len_old);
+      int new_func_index =
+          ChooseChangedFunction(new_infos, change_pos, change_len_new);
+      // Old and new functions should have the same indexes in their lists
+      // up to old_func_index/new_func_index
+      ASSERT(old_func_index == new_func_index);
+      USE(new_func_index);
+      function_being_changed = old_func_index;
+    }
+    printf("Changed function is %d %d (index %d)\n",
+           new_infos[function_being_changed].start_pos,
+           new_infos[function_being_changed].end_pos,
+           function_being_changed);
+
+    // Go to outer functions until code expectations are equal
+    while (!old_infos[function_being_changed].code_info.CompareTo(
+        &new_infos[function_being_changed].code_info)) {
+
+      ASSERT(old_infos[function_being_changed].outer_index ==
+          new_infos[function_being_changed].outer_index);
+      printf("Scope has changed from ");
+      old_infos[function_being_changed].code_info.Print();
+      printf(" to ");
+      new_infos[function_being_changed].code_info.Print();
+      printf("\n");
+      function_being_changed = old_infos[function_being_changed].outer_index;
+      ASSERT(function_being_changed != -1);
+      printf("function has been chosen: %d %d (index %d)\n",
+             new_infos[function_being_changed].start_pos,
+             new_infos[function_being_changed].end_pos,
+             function_being_changed);
+    }
+
+    // TODO(peter.rybin): Check frames on stack.
+    // Committing all changes.
+    original_script->set_source(*new_source);
+
+    Handle<Script> old_script = Factory::NewScript(original_source);
+    old_script->set_name(original_script->name());
+    old_script->set_line_offset(original_script->line_offset());
+    old_script->set_column_offset(original_script->column_offset());
+    old_script->set_data(original_script->data());
+    old_script->set_type(original_script->type());
+    old_script->set_context_data(original_script->context_data());
+    old_script->set_compilation_type(original_script->compilation_type());
+
+    Debugger::OnAfterCompile(old_script, Handle<JSFunction>(), true);
+
+
+    FunctionListHelper old_list_helper(function_shared_info,
+                                       function_shared_info_len, old_infos);
+
+    UnusedReferenceChecker ref_checker;
+
+    PatchCode(&new_infos[function_being_changed],
+              old_list_helper.Get(function_being_changed),
+              &ref_checker);
+
+    PosTranslator translator(change_pos, change_len_old, change_len_new);
+    for (int i = 0; i < function_being_changed; i++) {
+      PatchPositions(&new_infos[i], old_list_helper.Get(i), &translator);
+    }
+
+    // We are jumping to the sibling of our function (in both lists).
+    // From this index all following items in the lists are our siblings
+    // or their inner functions.
+    int old_next_sibling = old_infos[function_being_changed].next_sibling_index;
+    int new_next_sibling = new_infos[function_being_changed].next_sibling_index;
+
+    if (old_next_sibling == -1) {
+      ASSERT(new_next_sibling == -1);
+    } else {
+      ASSERT(old_infos.length() - old_next_sibling ==
+          new_infos.length() - new_next_sibling);
+
+      for (int i = old_next_sibling, j = new_next_sibling;
+          i < old_infos.length(); i++, j++) {
+        PatchPositions(&new_infos[j], old_list_helper.Get(i), &translator);
+      }
+    }
+
+    // All functions before next_sibling index are inner functions of the
+    // function that we are patching. We leave those functions unpatched.
+    for (int i = function_being_changed + 1; i < old_next_sibling; i++) {
+      LinkToOldScript(&old_infos[i], old_script, old_list_helper.Get(i));
+    }
+
+    FunctionInfoListener::DisposeData(old_infos);
+    FunctionInfoListener::DisposeData(new_infos);
+
+    ref_checker.Check();
+  }
+}
+
 } }  // namespace v8::internal
+
+#endif  // ENABLE_DEBUGGER_SUPPORT