Move FormatStackTrace to C++

src/messages.cc

 // Copyright 2011 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/messages.h"
 
 #include <memory>
 
 #include "src/api.h"
-#include "src/bootstrapper.h"
 #include "src/execution.h"
 #include "src/isolate-inl.h"
 #include "src/keys.h"
 #include "src/string-builder.h"
 #include "src/wasm/wasm-module.h"
 
 namespace v8 {
 namespace internal {
 
 MessageLocation::MessageLocation(Handle<Script> script, int start_pos,
@@ skipping 276 matching lines @@
       // 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 {
+
+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;
@@ skipping 41 matching lines @@
   // 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<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();
+
+  Handle<JSFunction> callsite_ctor =
+      handle(isolate->native_context()->callsite_function(), isolate);
+
+  int dst_ix = 0;
+  Handle<FixedArray> frames = isolate->factory()->NewFixedArray(frame_count);
+  for (int i = 1; i < raw_stack_len; i += 4) {

[Yang, 2016/08/01 06:49:18]

I wonder whether allocating CallSite objects is more expensive than the internal
array. If it's not significantly more expensive, maybe we should just allocate
CallSite objects in CaptureSimpleStackTrace directly and avoid this conversion
here.

But let's not do that in this CL.

[jgruber, 2016/08/01 10:52:55]

Acknowledged.

+    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, callsite_ctor, callsite_ctor, 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,
+                                      IncrementalStringBuilder* builder) {
+  MaybeHandle<String> err_str =
+      ErrorToString(isolate, Handle<Object>::cast(error));
+  if (err_str.is_null()) {
+    // Error.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();
+
+    err_str = ErrorToString(isolate, pending_exception);
+    if (err_str.is_null()) {
+      // Formatting the thrown exception threw again, give up.
+      DCHECK(isolate->has_pending_exception());
+      isolate->clear_pending_exception();
+
+      builder->AppendCString("<error>");
+    } else {
+      // Formatted thrown exception successfully, append it.
+      builder->AppendCString("<error: ");
+      builder->AppendString(err_str.ToHandleChecked());
+      builder->AppendCharacter('>');
+    }
+  } else {
+    builder->AppendString(err_str.ToHandleChecked());
+  }
+
+  return error;
+}
+
+}  // namespace
+
 MaybeHandle<Object> FormatStackTrace(Isolate* isolate, Handle<JSObject> error,
-                                     Handle<Object> stack_trace) {
-  // TODO(jgruber): Port FormatStackTrace from JS.
-  Handle<JSFunction> fun = isolate->error_format_stack_trace();
+                                     Handle<Object> raw_stack) {
+  Zone zone(isolate->allocator());
 
-  int argc = 2;
-  ScopedVector<Handle<Object>> argv(argc);
-  argv[0] = error;
-  argv[1] = stack_trace;
+  // Create JS CallSite objects from the raw stack frame array.
 
-  Handle<Object> formatted_stack_trace;
+  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.
+
+  Handle<JSFunction> global_error = isolate->error_function();
+  Handle<Object> prepare_stack_trace;
   ASSIGN_RETURN_ON_EXCEPTION(
-      isolate, formatted_stack_trace,
-      Execution::Call(isolate, fun, error, argc, argv.start()), Object);
+      isolate, prepare_stack_trace,
+      JSFunction::GetProperty(isolate, global_error, "prepareStackTrace"),
+      Object);
 
-  return formatted_stack_trace;
+  // TODO(jgruber): Handle recursive calls.

[jgruber, 2016/07/29 11:54:37]

Is this still needed? And if so, how do we want to track it? Setting a flag on
isolate?

[jgruber, 2016/07/29 11:56:06]

Recursion handling was introduced in a3f16f8e650.

[Yang, 2016/08/01 06:49:18]

I thought we had a test case covering this. Does this work?

Error.prepareStackTrace = function() {
  return new Error().stack;
}
new Error().stack;

[jgruber, 2016/08/01 10:52:55]

It worked, but more or less accidentally since the second stack overflow
exception was swallowed. Adding a flag to isolate as discussed.

+  if (prepare_stack_trace->IsJSFunction()) {
+    Handle<JSArray> array = isolate->factory()->NewJSArrayWithElements(frames);
+
+    const int argc = 2;
+    ScopedVector<Handle<Object>> argv(argc);
+    argv[0] = error;
+    argv[1] = array;
+
+    Handle<Object> result;
+    ASSIGN_RETURN_ON_EXCEPTION(
+        isolate, result, Execution::Call(isolate, prepare_stack_trace,
+                                         global_error, argc, argv.start()),
+        Object);
+
+    return result;
+  }
+
+  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 = CallSiteToString(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 = ErrorToString(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,
                                               int template_index,
                                               Handle<Object> arg) {
   Factory* factory = isolate->factory();
   Handle<String> result_string;
   if (arg->IsString()) {
     result_string = Handle<String>::cast(arg);
   } else {
@@ skipping 120 matching lines @@
   }
 
   // Capture a simple stack trace for the stack property.
   RETURN_ON_EXCEPTION(isolate,
                       isolate->CaptureAndSetSimpleStackTrace(err, mode, caller),
                       Object);
 
   return err;
 }
 
+namespace {
+
+MaybeHandle<String> GetStringPropertyOrDefault(Isolate* isolate,
+                                               Handle<JSReceiver> recv,
+                                               Handle<String> key,
+                                               Handle<String> default_str) {
+  Handle<Object> obj;
+  ASSIGN_RETURN_ON_EXCEPTION(isolate, obj, JSObject::GetProperty(recv, key),
+                             String);
+
+  Handle<String> str;
+  if (obj->IsUndefined(isolate)) {
+    str = default_str;
+  } else {
+    ASSIGN_RETURN_ON_EXCEPTION(isolate, str, Object::ToString(isolate, obj),
+                               String);
+  }
+
+  return str;
+}
+
+}  // namespace
+
+// ES6 section 19.5.3.4 Error.prototype.toString ( )
+MaybeHandle<String> ErrorToString(Isolate* isolate, Handle<Object> receiver) {
+  // 1. Let O be the this value.
+  // 2. If Type(O) is not Object, throw a TypeError exception.
+  if (!receiver->IsJSReceiver()) {
+    return isolate->Throw<String>(isolate->factory()->NewTypeError(
+        MessageTemplate::kIncompatibleMethodReceiver,
+        isolate->factory()->NewStringFromAsciiChecked(
+            "Error.prototype.toString"),
+        receiver));
+  }
+  Handle<JSReceiver> recv = Handle<JSReceiver>::cast(receiver);
+
+  // 3. Let name be ? Get(O, "name").
+  // 4. If name is undefined, let name be "Error"; otherwise let name be
+  // ? ToString(name).
+  Handle<String> name_key = isolate->factory()->name_string();
+  Handle<String> name_default = isolate->factory()->Error_string();
+  Handle<String> name;
+  ASSIGN_RETURN_ON_EXCEPTION(
+      isolate, name,
+      GetStringPropertyOrDefault(isolate, recv, name_key, name_default),
+      String);
+
+  // 5. Let msg be ? Get(O, "message").
+  // 6. If msg is undefined, let msg be the empty String; otherwise let msg be
+  // ? ToString(msg).
+  Handle<String> msg_key = isolate->factory()->message_string();
+  Handle<String> msg_default = isolate->factory()->empty_string();
+  Handle<String> msg;
+  ASSIGN_RETURN_ON_EXCEPTION(
+      isolate, msg,
+      GetStringPropertyOrDefault(isolate, recv, msg_key, msg_default), String);
+
+  // 7. If name is the empty String, return msg.
+  // 8. If msg is the empty String, return name.
+  if (name->length() == 0) return msg;
+  if (msg->length() == 0) return name;
+
+  // 9. Return the result of concatenating name, the code unit 0x003A (COLON),
+  // the code unit 0x0020 (SPACE), and msg.
+  IncrementalStringBuilder builder(isolate);
+  builder.AppendString(name);
+  builder.AppendCString(": ");
+  builder.AppendString(msg);
+
+  Handle<String> result;
+  ASSIGN_RETURN_ON_EXCEPTION(isolate, result, builder.Finish(), String);
+  return result;
+}
+
+#define SET_CALLSITE_PROPERTY(target, key, value)                        \
+  RETURN_ON_EXCEPTION(                                                   \
+      isolate, JSObject::SetOwnPropertyIgnoreAttributes(                 \
+                   target, isolate->factory()->key(), value, DONT_ENUM), \
+      Object)
+
+MaybeHandle<Object> ConstructCallSite(Isolate* isolate,
+                                      Handle<JSFunction> target,
+                                      Handle<Object> new_target,
+                                      Handle<Object> receiver,
+                                      Handle<Object> fun, Handle<Object> pos,
+                                      Handle<Object> strict_mode) {
+  // Create the JS object.
+
+  Handle<JSReceiver> new_target_recv =
+      new_target->IsJSReceiver() ? Handle<JSReceiver>::cast(new_target)
+                                 : Handle<JSReceiver>::cast(target);
+
+  Handle<JSObject> obj;
+  ASSIGN_RETURN_ON_EXCEPTION(isolate, obj,
+                             JSObject::New(target, new_target_recv), 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->IsJSFunction());
+    SET_CALLSITE_PROPERTY(obj, call_site_wasm_obj_symbol, receiver);
+
+    Handle<Object> fun_index;
+    ASSIGN_RETURN_ON_EXCEPTION(isolate, fun_index,
+                               Object::ToUint32(isolate, fun), Object);
+    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);
+  }
+
+  Handle<Object> pos_int32;
+  ASSIGN_RETURN_ON_EXCEPTION(isolate, pos_int32, Object::ToInt32(isolate, pos),
+                             Object);
+  SET_CALLSITE_PROPERTY(obj, call_site_position_symbol, pos_int32);
+  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> CallSiteToString(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