Revert of Use a custom Struct for stack trace storage

src/messages.cc

Index: src/messages.cc
diff --git a/src/messages.cc b/src/messages.cc
index 5a63cde73c1e08f59bffc9403e5f1281a7ef87f7..5d033189634d28dc863f243fadf57dc34acefe7c 100644
--- a/src/messages.cc
+++ b/src/messages.cc
@@ -164,47 +164,376 @@
   return GetMessage(isolate, data)->ToCString(DISALLOW_NULLS);
 }
 
+
+CallSite::CallSite(Isolate* isolate, Handle<JSObject> call_site_obj)
+    : isolate_(isolate) {
+  Handle<Object> maybe_function = JSObject::GetDataProperty(
+      call_site_obj, isolate->factory()->call_site_function_symbol());
+  if (maybe_function->IsJSFunction()) {
+    // javascript
+    fun_ = Handle<JSFunction>::cast(maybe_function);
+    receiver_ = JSObject::GetDataProperty(
+        call_site_obj, isolate->factory()->call_site_receiver_symbol());
+  } else {
+    Handle<Object> maybe_wasm_func_index = JSObject::GetDataProperty(
+        call_site_obj, isolate->factory()->call_site_wasm_func_index_symbol());
+    if (!maybe_wasm_func_index->IsSmi()) {
+      // invalid: neither javascript nor wasm
+      return;
+    }
+    // wasm
+    wasm_obj_ = Handle<JSObject>::cast(JSObject::GetDataProperty(
+        call_site_obj, isolate->factory()->call_site_wasm_obj_symbol()));
+    wasm_func_index_ = Smi::cast(*maybe_wasm_func_index)->value();
+    DCHECK(static_cast<int>(wasm_func_index_) >= 0);
+  }
+
+  CHECK(JSObject::GetDataProperty(
+            call_site_obj, isolate->factory()->call_site_position_symbol())
+            ->ToInt32(&pos_));
+}
+
+
+Handle<Object> CallSite::GetFileName() {
+  if (!IsJavaScript()) return isolate_->factory()->null_value();
+  Object* script = fun_->shared()->script();
+  if (!script->IsScript()) return isolate_->factory()->null_value();
+  return Handle<Object>(Script::cast(script)->name(), isolate_);
+}
+
+
+Handle<Object> CallSite::GetFunctionName() {
+  if (IsWasm()) {
+    return wasm::GetWasmFunctionNameOrNull(isolate_, wasm_obj_,
+                                           wasm_func_index_);
+  }
+  Handle<String> result = JSFunction::GetName(fun_);
+  if (result->length() != 0) return result;
+
+  Handle<Object> script(fun_->shared()->script(), isolate_);
+  if (script->IsScript() &&
+      Handle<Script>::cast(script)->compilation_type() ==
+          Script::COMPILATION_TYPE_EVAL) {
+    return isolate_->factory()->eval_string();
+  }
+  return isolate_->factory()->null_value();
+}
+
+Handle<Object> CallSite::GetScriptNameOrSourceUrl() {
+  if (!IsJavaScript()) return isolate_->factory()->null_value();
+  Object* script_obj = fun_->shared()->script();
+  if (!script_obj->IsScript()) return isolate_->factory()->null_value();
+  Handle<Script> script(Script::cast(script_obj), isolate_);
+  Object* source_url = script->source_url();
+  if (source_url->IsString()) return Handle<Object>(source_url, isolate_);
+  return Handle<Object>(script->name(), isolate_);
+}
+
+bool CheckMethodName(Isolate* isolate, Handle<JSObject> obj, Handle<Name> name,
+                     Handle<JSFunction> fun,
+                     LookupIterator::Configuration config) {
+  LookupIterator iter =
+      LookupIterator::PropertyOrElement(isolate, obj, name, config);
+  if (iter.state() == LookupIterator::DATA) {
+    return iter.GetDataValue().is_identical_to(fun);
+  } else if (iter.state() == LookupIterator::ACCESSOR) {
+    Handle<Object> accessors = iter.GetAccessors();
+    if (accessors->IsAccessorPair()) {
+      Handle<AccessorPair> pair = Handle<AccessorPair>::cast(accessors);
+      return pair->getter() == *fun || pair->setter() == *fun;
+    }
+  }
+  return false;
+}
+
+
+Handle<Object> CallSite::GetMethodName() {
+  if (!IsJavaScript() || receiver_->IsNull(isolate_) ||
+      receiver_->IsUndefined(isolate_)) {
+    return isolate_->factory()->null_value();
+  }
+  Handle<JSReceiver> receiver =
+      Object::ToObject(isolate_, receiver_).ToHandleChecked();
+  if (!receiver->IsJSObject()) {
+    return isolate_->factory()->null_value();
+  }
+
+  Handle<JSObject> obj = Handle<JSObject>::cast(receiver);
+  Handle<Object> function_name(fun_->shared()->name(), isolate_);
+  if (function_name->IsString()) {
+    Handle<String> name = Handle<String>::cast(function_name);
+    // ES2015 gives getters and setters name prefixes which must
+    // be stripped to find the property name.
+    if (name->IsUtf8EqualTo(CStrVector("get "), true) ||
+        name->IsUtf8EqualTo(CStrVector("set "), true)) {
+      name = isolate_->factory()->NewProperSubString(name, 4, name->length());
+    }
+    if (CheckMethodName(isolate_, obj, name, fun_,
+                        LookupIterator::PROTOTYPE_CHAIN_SKIP_INTERCEPTOR)) {
+      return name;
+    }
+  }
+
+  HandleScope outer_scope(isolate_);
+  Handle<Object> result;
+  for (PrototypeIterator iter(isolate_, obj, kStartAtReceiver); !iter.IsAtEnd();
+       iter.Advance()) {
+    Handle<Object> current = PrototypeIterator::GetCurrent(iter);
+    if (!current->IsJSObject()) break;
+    Handle<JSObject> current_obj = Handle<JSObject>::cast(current);
+    if (current_obj->IsAccessCheckNeeded()) break;
+    Handle<FixedArray> keys =
+        KeyAccumulator::GetOwnEnumPropertyKeys(isolate_, current_obj);
+    for (int i = 0; i < keys->length(); i++) {
+      HandleScope inner_scope(isolate_);
+      if (!keys->get(i)->IsName()) continue;
+      Handle<Name> name_key(Name::cast(keys->get(i)), isolate_);
+      if (!CheckMethodName(isolate_, current_obj, name_key, fun_,
+                           LookupIterator::OWN_SKIP_INTERCEPTOR))
+        continue;
+      // Return null in case of duplicates to avoid confusion.
+      if (!result.is_null()) return isolate_->factory()->null_value();
+      result = inner_scope.CloseAndEscape(name_key);
+    }
+  }
+
+  if (!result.is_null()) return outer_scope.CloseAndEscape(result);
+  return isolate_->factory()->null_value();
+}
+
+Handle<Object> CallSite::GetTypeName() {
+  // TODO(jgruber): Check for strict/constructor here as in
+  // CallSitePrototypeGetThis.
+
+  if (receiver_->IsNull(isolate_) || receiver_->IsUndefined(isolate_))
+    return isolate_->factory()->null_value();
+
+  if (receiver_->IsJSProxy()) return isolate_->factory()->Proxy_string();
+
+  Handle<JSReceiver> receiver_object =
+      Object::ToObject(isolate_, receiver_).ToHandleChecked();
+  return JSReceiver::GetConstructorName(receiver_object);
+}
+
 namespace {
 
-MaybeHandle<Object> ConstructCallSite(Isolate* isolate,
-                                      Handle<StackTraceFrame> frame) {
-  // Create the JS object.
-
-  Handle<JSFunction> target =
-      handle(isolate->native_context()->callsite_function(), isolate);
-
-  Handle<JSObject> obj;
-  ASSIGN_RETURN_ON_EXCEPTION(isolate, obj, JSObject::New(target, target),
-                             Object);
-
-  RETURN_ON_EXCEPTION(
-      isolate,
-      JSObject::SetOwnPropertyIgnoreAttributes(
-          obj, isolate->factory()->call_site_frame_symbol(), frame, DONT_ENUM),
-      Object);
-
-  return obj;
-}
+Object* EvalFromFunctionName(Isolate* isolate, Handle<Script> script) {
+  if (script->eval_from_shared()->IsUndefined(isolate))
+    return *isolate->factory()->undefined_value();
+
+  Handle<SharedFunctionInfo> shared(
+      SharedFunctionInfo::cast(script->eval_from_shared()));
+  // Find the name of the function calling eval.
+  if (shared->name()->BooleanValue()) {
+    return shared->name();
+  }
+
+  return shared->inferred_name();
+}
+
+Object* EvalFromScript(Isolate* isolate, Handle<Script> script) {
+  if (script->eval_from_shared()->IsUndefined(isolate))
+    return *isolate->factory()->undefined_value();
+
+  Handle<SharedFunctionInfo> eval_from_shared(
+      SharedFunctionInfo::cast(script->eval_from_shared()));
+  return eval_from_shared->script()->IsScript()
+             ? eval_from_shared->script()
+             : *isolate->factory()->undefined_value();
+}
+
+MaybeHandle<String> FormatEvalOrigin(Isolate* isolate, Handle<Script> script) {
+  Handle<Object> sourceURL = Script::GetNameOrSourceURL(script);
+  if (!sourceURL->IsUndefined(isolate)) {
+    DCHECK(sourceURL->IsString());
+    return Handle<String>::cast(sourceURL);
+  }
+
+  IncrementalStringBuilder builder(isolate);
+  builder.AppendCString("eval at ");
+
+  Handle<Object> eval_from_function_name =
+      handle(EvalFromFunctionName(isolate, script), isolate);
+  if (eval_from_function_name->BooleanValue()) {
+    Handle<String> str;
+    ASSIGN_RETURN_ON_EXCEPTION(
+        isolate, str, Object::ToString(isolate, eval_from_function_name),
+        String);
+    builder.AppendString(str);
+  } else {
+    builder.AppendCString("<anonymous>");
+  }
+
+  Handle<Object> eval_from_script_obj =
+      handle(EvalFromScript(isolate, script), isolate);
+  if (eval_from_script_obj->IsScript()) {
+    Handle<Script> eval_from_script =
+        Handle<Script>::cast(eval_from_script_obj);
+    builder.AppendCString(" (");
+    if (eval_from_script->compilation_type() == Script::COMPILATION_TYPE_EVAL) {
+      // Eval script originated from another eval.
+      Handle<String> str;
+      ASSIGN_RETURN_ON_EXCEPTION(
+          isolate, str, FormatEvalOrigin(isolate, eval_from_script), String);
+      builder.AppendString(str);
+    } else {
+      DCHECK(eval_from_script->compilation_type() !=
+             Script::COMPILATION_TYPE_EVAL);
+      // eval script originated from "real" source.
+      Handle<Object> name_obj = handle(eval_from_script->name(), isolate);
+      if (eval_from_script->name()->IsString()) {
+        builder.AppendString(Handle<String>::cast(name_obj));
+
+        Script::PositionInfo info;
+        if (eval_from_script->GetPositionInfo(script->GetEvalPosition(), &info,
+                                              Script::NO_OFFSET)) {
+          builder.AppendCString(":");
+
+          Handle<String> str = isolate->factory()->NumberToString(
+              handle(Smi::FromInt(info.line + 1), isolate));
+          builder.AppendString(str);
+
+          builder.AppendCString(":");
+
+          str = isolate->factory()->NumberToString(
+              handle(Smi::FromInt(info.column + 1), isolate));
+          builder.AppendString(str);
+        }
+      } else {
+        DCHECK(!eval_from_script->name()->IsString());
+        builder.AppendCString("unknown source");
+      }
+    }
+    builder.AppendCString(")");
+  }
+
+  Handle<String> result;
+  ASSIGN_RETURN_ON_EXCEPTION(isolate, result, builder.Finish(), String);
+  return result;
+}
+
+}  // namespace
+
+Handle<Object> CallSite::GetEvalOrigin() {
+  if (IsWasm()) return isolate_->factory()->undefined_value();
+  DCHECK(IsJavaScript());
+
+  Handle<Object> script = handle(fun_->shared()->script(), isolate_);
+  if (!script->IsScript()) return isolate_->factory()->undefined_value();
+
+  return FormatEvalOrigin(isolate_, Handle<Script>::cast(script))
+      .ToHandleChecked();
+}
+
+int CallSite::GetLineNumber() {
+  if (pos_ >= 0 && IsJavaScript()) {
+    Handle<Object> script_obj(fun_->shared()->script(), isolate_);
+    if (script_obj->IsScript()) {
+      Handle<Script> script = Handle<Script>::cast(script_obj);
+      return Script::GetLineNumber(script, pos_) + 1;
+    }
+  }
+  return -1;
+}
+
+
+int CallSite::GetColumnNumber() {
+  if (pos_ >= 0 && IsJavaScript()) {
+    Handle<Object> script_obj(fun_->shared()->script(), isolate_);
+    if (script_obj->IsScript()) {
+      Handle<Script> script = Handle<Script>::cast(script_obj);
+      return Script::GetColumnNumber(script, pos_) + 1;
+    }
+  }
+  return -1;
+}
+
+
+bool CallSite::IsNative() {
+  if (!IsJavaScript()) return false;
+  Handle<Object> script(fun_->shared()->script(), isolate_);
+  return script->IsScript() &&
+         Handle<Script>::cast(script)->type() == Script::TYPE_NATIVE;
+}
+
+
+bool CallSite::IsToplevel() {
+  if (IsWasm()) return false;
+  return receiver_->IsJSGlobalProxy() || receiver_->IsNull(isolate_) ||
+         receiver_->IsUndefined(isolate_);
+}
+
+
+bool CallSite::IsEval() {
+  if (!IsJavaScript()) return false;
+  Handle<Object> script(fun_->shared()->script(), isolate_);
+  return script->IsScript() &&
+         Handle<Script>::cast(script)->compilation_type() ==
+             Script::COMPILATION_TYPE_EVAL;
+}
+
+
+bool CallSite::IsConstructor() {
+  // Builtin exit frames mark constructors by passing a special symbol as the
+  // receiver.
+  Object* ctor_symbol = isolate_->heap()->call_site_constructor_symbol();
+  if (*receiver_ == ctor_symbol) return true;
+  if (!IsJavaScript() || !receiver_->IsJSObject()) return false;
+  Handle<Object> constructor =
+      JSReceiver::GetDataProperty(Handle<JSObject>::cast(receiver_),
+                                  isolate_->factory()->constructor_string());
+  return constructor.is_identical_to(fun_);
+}
+
+namespace {
 
 // Convert the raw frames as written by Isolate::CaptureSimpleStackTrace into
 // a vector of JS CallSite objects.
-MaybeHandle<JSArray> ToCallSites(Isolate* isolate,
-                                 Handle<FixedArray> raw_stack_elements) {
-  const int frame_count = raw_stack_elements->length();
+MaybeHandle<FixedArray> GetStackFrames(Isolate* isolate,
+                                       Handle<Object> raw_stack) {
+  DCHECK(raw_stack->IsJSArray());
+  Handle<JSArray> raw_stack_array = Handle<JSArray>::cast(raw_stack);
+
+  DCHECK(raw_stack_array->elements()->IsFixedArray());
+  Handle<FixedArray> raw_stack_elements =
+      handle(FixedArray::cast(raw_stack_array->elements()), isolate);
+
+  const int raw_stack_len = raw_stack_elements->length();
+  DCHECK(raw_stack_len % 4 == 1);  // Multiples of 4 plus sloppy frames count.
+  const int frame_count = (raw_stack_len - 1) / 4;
+
+  Handle<Object> sloppy_frames_obj =
+      FixedArray::get(*raw_stack_elements, 0, isolate);
+  int sloppy_frames = Handle<Smi>::cast(sloppy_frames_obj)->value();
+
+  int dst_ix = 0;
   Handle<FixedArray> frames = isolate->factory()->NewFixedArray(frame_count);
-
-  for (int i = 0; i < frame_count; i++) {
-    auto frame = Handle<StackTraceFrame>::cast(
-        FixedArray::get(*raw_stack_elements, i, isolate));
+  for (int i = 1; i < raw_stack_len; i += 4) {
+    Handle<Object> recv = FixedArray::get(*raw_stack_elements, i, isolate);
+    Handle<Object> fun = FixedArray::get(*raw_stack_elements, i + 1, isolate);
+    Handle<AbstractCode> code = Handle<AbstractCode>::cast(
+        FixedArray::get(*raw_stack_elements, i + 2, isolate));
+    Handle<Smi> pc =
+        Handle<Smi>::cast(FixedArray::get(*raw_stack_elements, i + 3, isolate));
+
+    Handle<Object> pos =
+        (fun->IsSmi() && pc->value() < 0)
+            ? handle(Smi::FromInt(-1 - pc->value()), isolate)
+            : handle(Smi::FromInt(code->SourcePosition(pc->value())), isolate);
+
+    sloppy_frames--;
+    Handle<Object> strict = isolate->factory()->ToBoolean(sloppy_frames < 0);
 
     Handle<Object> callsite;
-    ASSIGN_RETURN_ON_EXCEPTION(isolate, callsite,
-                               ConstructCallSite(isolate, frame), JSArray);
-
-    frames->set(i, *callsite);
-  }
-
-  return isolate->factory()->NewJSArrayWithElements(frames);
+    ASSIGN_RETURN_ON_EXCEPTION(
+        isolate, callsite,
+        CallSiteUtils::Construct(isolate, recv, fun, pos, strict), FixedArray);
+
+    frames->set(dst_ix++, *callsite);
+  }
+
+  DCHECK_EQ(frame_count, dst_ix);
+  return frames;
 }
 
 MaybeHandle<Object> AppendErrorString(Isolate* isolate, Handle<Object> error,
@@ -261,14 +590,11 @@
 MaybeHandle<Object> ErrorUtils::FormatStackTrace(Isolate* isolate,
                                                  Handle<JSObject> error,
                                                  Handle<Object> raw_stack) {
-  // Extract the raw stack trace fixed array.
-
-  DCHECK(raw_stack->IsJSArray());
-  Handle<JSArray> raw_stack_array = Handle<JSArray>::cast(raw_stack);
-
-  DCHECK(raw_stack_array->elements()->IsFixedArray());
-  Handle<FixedArray> raw_stack_elements =
-      handle(FixedArray::cast(raw_stack_array->elements()), isolate);
+  // Create JS CallSite objects from the raw stack frame array.
+
+  Handle<FixedArray> frames;
+  ASSIGN_RETURN_ON_EXCEPTION(isolate, frames,
+                             GetStackFrames(isolate, raw_stack), Object);
 
   // If there's a user-specified "prepareStackFrames" function, call it on the
   // frames and use its result.
@@ -283,17 +609,12 @@
   const bool in_recursion = isolate->formatting_stack_trace();
   if (prepare_stack_trace->IsJSFunction() && !in_recursion) {
     PrepareStackTraceScope scope(isolate);
-
-    // Create JS CallSite objects from the raw stack frame array.
-
-    Handle<JSArray> frames;
-    ASSIGN_RETURN_ON_EXCEPTION(
-        isolate, frames, ToCallSites(isolate, raw_stack_elements), Object);
+    Handle<JSArray> array = isolate->factory()->NewJSArrayWithElements(frames);
 
     const int argc = 2;
     ScopedVector<Handle<Object>> argv(argc);
     argv[0] = error;
-    argv[1] = frames;
+    argv[1] = array;
 
     Handle<Object> result;
     ASSIGN_RETURN_ON_EXCEPTION(
@@ -302,22 +623,46 @@
         Object);
 
     return result;
-  } else {
-    IncrementalStringBuilder builder(isolate);
-
-    RETURN_ON_EXCEPTION(isolate, AppendErrorString(isolate, error, &builder),
-                        Object);
-
-    for (int i = 0; i < raw_stack_elements->length(); i++) {
-      auto frame = Handle<StackTraceFrame>::cast(
-          FixedArray::get(*raw_stack_elements, i, isolate));
-
-      builder.AppendCString("\n    at ");
-      builder.AppendString(frame->ToString());
-    }
-
-    RETURN_RESULT(isolate, builder.Finish(), Object);
-  }
+  }
+
+  IncrementalStringBuilder builder(isolate);
+
+  RETURN_ON_EXCEPTION(isolate, AppendErrorString(isolate, error, &builder),
+                      Object);
+
+  for (int i = 0; i < frames->length(); i++) {
+    builder.AppendCString("\n    at ");
+
+    Handle<Object> frame = FixedArray::get(*frames, i, isolate);
+    MaybeHandle<String> maybe_frame_string =
+        CallSiteUtils::ToString(isolate, frame);
+    if (maybe_frame_string.is_null()) {
+      // CallSite.toString threw. Try to return a string representation of the
+      // thrown exception instead.
+
+      DCHECK(isolate->has_pending_exception());
+      Handle<Object> pending_exception =
+          handle(isolate->pending_exception(), isolate);
+      isolate->clear_pending_exception();
+
+      maybe_frame_string = ErrorUtils::ToString(isolate, pending_exception);
+      if (maybe_frame_string.is_null()) {
+        // Formatting the thrown exception threw again, give up.
+
+        builder.AppendCString("<error>");
+      } else {
+        // Formatted thrown exception successfully, append it.
+        builder.AppendCString("<error: ");
+        builder.AppendString(maybe_frame_string.ToHandleChecked());
+        builder.AppendCString("<error>");
+      }
+    } else {
+      // CallSite.toString completed without throwing.
+      builder.AppendString(maybe_frame_string.ToHandleChecked());
+    }
+  }
+
+  RETURN_RESULT(isolate, builder.Finish(), Object);
 }
 
 Handle<String> MessageTemplate::FormatMessage(Isolate* isolate,
@@ -557,5 +902,290 @@
                                no_caller, false);
 }
 
+#define SET_CALLSITE_PROPERTY(target, key, value)                        \
+  RETURN_ON_EXCEPTION(                                                   \
+      isolate, JSObject::SetOwnPropertyIgnoreAttributes(                 \
+                   target, isolate->factory()->key(), value, DONT_ENUM), \
+      Object)
+
+MaybeHandle<Object> CallSiteUtils::Construct(Isolate* isolate,
+                                             Handle<Object> receiver,
+                                             Handle<Object> fun,
+                                             Handle<Object> pos,
+                                             Handle<Object> strict_mode) {
+  // Create the JS object.
+
+  Handle<JSFunction> target =
+      handle(isolate->native_context()->callsite_function(), isolate);
+
+  Handle<JSObject> obj;
+  ASSIGN_RETURN_ON_EXCEPTION(isolate, obj, JSObject::New(target, target),
+                             Object);
+
+  // For wasm frames, receiver is the wasm object and fun is the function index
+  // instead of an actual function.
+  const bool is_wasm_object =
+      receiver->IsJSObject() && wasm::IsWasmObject(JSObject::cast(*receiver));
+  if (!fun->IsJSFunction() && !is_wasm_object) {
+    THROW_NEW_ERROR(isolate,
+                    NewTypeError(MessageTemplate::kCallSiteExpectsFunction,
+                                 Object::TypeOf(isolate, receiver),
+                                 Object::TypeOf(isolate, fun)),
+                    Object);
+  }
+
+  if (is_wasm_object) {
+    DCHECK(fun->IsSmi());
+    DCHECK(wasm::GetNumberOfFunctions(JSObject::cast(*receiver)) >
+           Smi::cast(*fun)->value());
+
+    SET_CALLSITE_PROPERTY(obj, call_site_wasm_obj_symbol, receiver);
+    SET_CALLSITE_PROPERTY(obj, call_site_wasm_func_index_symbol, fun);
+  } else {
+    DCHECK(fun->IsJSFunction());
+    SET_CALLSITE_PROPERTY(obj, call_site_receiver_symbol, receiver);
+    SET_CALLSITE_PROPERTY(obj, call_site_function_symbol, fun);
+  }
+
+  DCHECK(pos->IsSmi());
+  SET_CALLSITE_PROPERTY(obj, call_site_position_symbol, pos);
+  SET_CALLSITE_PROPERTY(
+      obj, call_site_strict_symbol,
+      isolate->factory()->ToBoolean(strict_mode->BooleanValue()));
+
+  return obj;
+}
+
+#undef SET_CALLSITE_PROPERTY
+
+namespace {
+
+bool IsNonEmptyString(Handle<Object> object) {
+  return (object->IsString() && String::cast(*object)->length() > 0);
+}
+
+MaybeHandle<JSObject> AppendWasmToString(Isolate* isolate,
+                                         Handle<JSObject> recv,
+                                         CallSite* call_site,
+                                         IncrementalStringBuilder* builder) {
+  Handle<Object> name = call_site->GetFunctionName();
+  if (name->IsNull(isolate)) {
+    builder->AppendCString("<WASM UNNAMED>");
+  } else {
+    DCHECK(name->IsString());
+    builder->AppendString(Handle<String>::cast(name));
+  }
+
+  builder->AppendCString(" (<WASM>[");
+
+  Handle<String> ix = isolate->factory()->NumberToString(
+      handle(Smi::FromInt(call_site->wasm_func_index()), isolate));
+  builder->AppendString(ix);
+
+  builder->AppendCString("]+");
+
+  Handle<Object> pos;
+  ASSIGN_RETURN_ON_EXCEPTION(
+      isolate, pos, JSObject::GetProperty(
+                        recv, isolate->factory()->call_site_position_symbol()),
+      JSObject);
+  DCHECK(pos->IsNumber());
+  builder->AppendString(isolate->factory()->NumberToString(pos));
+  builder->AppendCString(")");
+
+  return recv;
+}
+
+MaybeHandle<JSObject> AppendFileLocation(Isolate* isolate,
+                                         Handle<JSObject> recv,
+                                         CallSite* call_site,
+                                         IncrementalStringBuilder* builder) {
+  if (call_site->IsNative()) {
+    builder->AppendCString("native");
+    return recv;
+  }
+
+  Handle<Object> file_name = call_site->GetScriptNameOrSourceUrl();
+  if (!file_name->IsString() && call_site->IsEval()) {
+    Handle<Object> eval_origin = call_site->GetEvalOrigin();
+    DCHECK(eval_origin->IsString());
+    builder->AppendString(Handle<String>::cast(eval_origin));
+    builder->AppendCString(", ");  // Expecting source position to follow.
+  }
+
+  if (IsNonEmptyString(file_name)) {
+    builder->AppendString(Handle<String>::cast(file_name));
+  } else {
+    // Source code does not originate from a file and is not native, but we
+    // can still get the source position inside the source string, e.g. in
+    // an eval string.
+    builder->AppendCString("<anonymous>");
+  }
+
+  int line_number = call_site->GetLineNumber();
+  if (line_number != -1) {
+    builder->AppendCharacter(':');
+    Handle<String> line_string = isolate->factory()->NumberToString(
+        handle(Smi::FromInt(line_number), isolate), isolate);
+    builder->AppendString(line_string);
+
+    int column_number = call_site->GetColumnNumber();
+    if (column_number != -1) {
+      builder->AppendCharacter(':');
+      Handle<String> column_string = isolate->factory()->NumberToString(
+          handle(Smi::FromInt(column_number), isolate), isolate);
+      builder->AppendString(column_string);
+    }
+  }
+
+  return recv;
+}
+
+int StringIndexOf(Isolate* isolate, Handle<String> subject,
+                  Handle<String> pattern) {
+  if (pattern->length() > subject->length()) return -1;
+  return String::IndexOf(isolate, subject, pattern, 0);
+}
+
+// Returns true iff
+// 1. the subject ends with '.' + pattern, or
+// 2. subject == pattern.
+bool StringEndsWithMethodName(Isolate* isolate, Handle<String> subject,
+                              Handle<String> pattern) {
+  if (String::Equals(subject, pattern)) return true;
+
+  FlatStringReader subject_reader(isolate, String::Flatten(subject));
+  FlatStringReader pattern_reader(isolate, String::Flatten(pattern));
+
+  int pattern_index = pattern_reader.length() - 1;
+  int subject_index = subject_reader.length() - 1;
+  for (int i = 0; i <= pattern_reader.length(); i++) {  // Iterate over len + 1.
+    if (subject_index < 0) {
+      return false;
+    }
+
+    const uc32 subject_char = subject_reader.Get(subject_index);
+    if (i == pattern_reader.length()) {
+      if (subject_char != '.') return false;
+    } else if (subject_char != pattern_reader.Get(pattern_index)) {
+      return false;
+    }
+
+    pattern_index--;
+    subject_index--;
+  }
+
+  return true;
+}
+
+MaybeHandle<JSObject> AppendMethodCall(Isolate* isolate, Handle<JSObject> recv,
+                                       CallSite* call_site,
+                                       IncrementalStringBuilder* builder) {
+  Handle<Object> type_name = call_site->GetTypeName();
+  Handle<Object> method_name = call_site->GetMethodName();
+  Handle<Object> function_name = call_site->GetFunctionName();
+
+  if (IsNonEmptyString(function_name)) {
+    Handle<String> function_string = Handle<String>::cast(function_name);
+    if (IsNonEmptyString(type_name)) {
+      Handle<String> type_string = Handle<String>::cast(type_name);
+      bool starts_with_type_name =
+          (StringIndexOf(isolate, function_string, type_string) == 0);
+      if (!starts_with_type_name) {
+        builder->AppendString(type_string);
+        builder->AppendCharacter('.');
+      }
+    }
+    builder->AppendString(function_string);
+
+    if (IsNonEmptyString(method_name)) {
+      Handle<String> method_string = Handle<String>::cast(method_name);
+      if (!StringEndsWithMethodName(isolate, function_string, method_string)) {
+        builder->AppendCString(" [as ");
+        builder->AppendString(method_string);
+        builder->AppendCharacter(']');
+      }
+    }
+  } else {
+    builder->AppendString(Handle<String>::cast(type_name));
+    builder->AppendCharacter('.');
+    if (IsNonEmptyString(method_name)) {
+      builder->AppendString(Handle<String>::cast(method_name));
+    } else {
+      builder->AppendCString("<anonymous>");
+    }
+  }
+
+  return recv;
+}
+
+}  // namespace
+
+MaybeHandle<String> CallSiteUtils::ToString(Isolate* isolate,
+                                            Handle<Object> receiver) {
+  if (!receiver->IsJSObject()) {
+    THROW_NEW_ERROR(
+        isolate,
+        NewTypeError(MessageTemplate::kIncompatibleMethodReceiver,
+                     isolate->factory()->NewStringFromAsciiChecked("toString"),
+                     receiver),
+        String);
+  }
+  Handle<JSObject> recv = Handle<JSObject>::cast(receiver);
+
+  if (!JSReceiver::HasOwnProperty(
+           recv, isolate->factory()->call_site_position_symbol())
+           .FromMaybe(false)) {
+    THROW_NEW_ERROR(
+        isolate,
+        NewTypeError(MessageTemplate::kCallSiteMethod,
+                     isolate->factory()->NewStringFromAsciiChecked("toString")),
+        String);
+  }
+
+  IncrementalStringBuilder builder(isolate);
+
+  CallSite call_site(isolate, recv);
+  if (call_site.IsWasm()) {
+    RETURN_ON_EXCEPTION(isolate,
+                        AppendWasmToString(isolate, recv, &call_site, &builder),
+                        String);
+    RETURN_RESULT(isolate, builder.Finish(), String);
+  }
+
+  DCHECK(!call_site.IsWasm());
+  Handle<Object> function_name = call_site.GetFunctionName();
+
+  const bool is_toplevel = call_site.IsToplevel();
+  const bool is_constructor = call_site.IsConstructor();
+  const bool is_method_call = !(is_toplevel || is_constructor);
+
+  if (is_method_call) {
+    RETURN_ON_EXCEPTION(
+        isolate, AppendMethodCall(isolate, recv, &call_site, &builder), String);
+  } else if (is_constructor) {
+    builder.AppendCString("new ");
+    if (IsNonEmptyString(function_name)) {
+      builder.AppendString(Handle<String>::cast(function_name));
+    } else {
+      builder.AppendCString("<anonymous>");
+    }
+  } else if (IsNonEmptyString(function_name)) {
+    builder.AppendString(Handle<String>::cast(function_name));
+  } else {
+    RETURN_ON_EXCEPTION(isolate,
+                        AppendFileLocation(isolate, recv, &call_site, &builder),
+                        String);
+    RETURN_RESULT(isolate, builder.Finish(), String);
+  }
+
+  builder.AppendCString(" (");
+  RETURN_ON_EXCEPTION(
+      isolate, AppendFileLocation(isolate, recv, &call_site, &builder), String);
+  builder.AppendCString(")");
+
+  RETURN_RESULT(isolate, builder.Finish(), String);
+}
+
 }  // namespace internal
 }  // namespace v8