Update ObjectToString to Harmony-draft algorithm

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 0c78b5f27058f923fc02ccd2b9b6dc6e53c8bca7..512593014ec3b8bf74ead50ad125abe72f3d85ab 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -46,6 +46,7 @@
 #include "src/snapshot.h"
 #include "src/unicode-inl.h"
 #include "src/v8threads.h"
+#include "src/vector.h"
 #include "src/version.h"
 #include "src/vm-state-inl.h"
 
@@ -3379,6 +3380,7 @@ Local<String> v8::Object::ObjectProtoToString() {
   i::Handle<i::JSObject> self = Utils::OpenHandle(this);
 
   i::Handle<i::Object> name(self->class_name(), i_isolate);
+  i::Handle<i::Object> tag;
 
   // Native implementation of Object.prototype.toString (v8natives.js):
   //   var c = %_ClassOf(this);
@@ -3393,6 +3395,44 @@ Local<String> v8::Object::ObjectProtoToString() {
                           i_isolate->factory()->Arguments_string())) {
       return v8::String::NewFromUtf8(isolate, "[object Object]");
     } else {
+      if (internal::FLAG_harmony_tostring) {
+        i::Handle<i::Symbol> toStringTag = Utils::OpenHandle(
+            *Symbol::GetToStringTag(isolate));
+        tag = i::Runtime::GetObjectProperty(
+            i_isolate, self, toStringTag).ToHandleChecked();
+
+        if (!tag->IsUndefined()) {
+          if (!tag->IsString()) {
+            return v8::String::NewFromUtf8(isolate, "[object ???]");
+          } else {
+            i::Handle<i::String> tag_name = i::Handle<i::String>::cast(tag);
+            using namespace internal;
+            if (!i::String::Equals(class_name, tag_name)) {
+              if (tag_name->IsUtf8EqualTo(CStrVector("Arguments"))) {
+                return v8::String::NewFromUtf8(isolate, "[object ~Arguments]");

[caitp (gmail), 2014/10/17 22:00:49]

I'm not sure if it's worth doing this linearly, or creating a way to do an O(1)
lookup instead --- I feel like creating tons of string handles + vectors is
probably not very good.

Let me know if theres's a better way to do this, please~

[Dmitry Lomov (no reviews), 2014/10/18 08:41:49]

Instead of IsUtf8EqualTo with a new string constant (this creates a new string
constant every time and does a real compare) you should do the same as above for
comparison with Arguments (line 3394): use i::String::Equals and internalized
strings.

+              } else if (tag_name->IsUtf8EqualTo(CStrVector("Array"))) {
+                return v8::String::NewFromUtf8(isolate, "[object ~Array]");
+              } else if (tag_name->IsUtf8EqualTo(CStrVector("Boolean"))) {
+                return v8::String::NewFromUtf8(isolate, "[object ~Boolean]");
+              } else if (tag_name->IsUtf8EqualTo(CStrVector("Date"))) {
+                return v8::String::NewFromUtf8(isolate, "[object ~Date]");
+              } else if (tag_name->IsUtf8EqualTo(CStrVector("Error"))) {
+                return v8::String::NewFromUtf8(isolate, "[object ~Error]");
+              } else if (tag_name->IsUtf8EqualTo(CStrVector("Function"))) {
+                return v8::String::NewFromUtf8(isolate, "[object ~Function]");
+              } else if (tag_name->IsUtf8EqualTo(CStrVector("Number"))) {
+                return v8::String::NewFromUtf8(isolate, "[object ~Number]");
+              } else if (tag_name->IsUtf8EqualTo(CStrVector("RegExp"))) {
+                return v8::String::NewFromUtf8(isolate, "[object ~RegExp]");
+              } else if (tag_name->IsUtf8EqualTo(CStrVector("String"))) {
+                return v8::String::NewFromUtf8(isolate, "[object ~String]");
+              } else {
+                class_name = tag_name;
+              }
+            }
+          }
+        }
+      }
       const char* prefix = "[object ";
       Local<String> str = Utils::ToLocal(class_name);
       const char* postfix = "]";
@@ -6199,6 +6239,11 @@ Local<Symbol> v8::Symbol::GetUnscopables(Isolate* isolate) {
 }
 
 
+Local<Symbol> v8::Symbol::GetToStringTag(Isolate* isolate) {
+  return GetWellKnownSymbol(isolate, "Symbol.toStringTag");
+}
+
+
 Local<Private> v8::Private::New(Isolate* isolate, Local<String> name) {
   i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
   LOG_API(i_isolate, "Private::New()");