Rewrite Error.prototype.toString in C++.

src/messages.cc

Index: src/messages.cc
diff --git a/src/messages.cc b/src/messages.cc
index ebec3532fe2a4ca9b1505af9e0bc35281dd95a88..767781913ed60b8bf949fdf55f948bb97ec84ad7 100644
--- a/src/messages.cc
+++ b/src/messages.cc
@@ -368,5 +368,98 @@ MaybeHandle<String> MessageTemplate::FormatMessage(int template_index,
 
   return builder.Finish();
 }
+
+
+MaybeHandle<String> ErrorToStringHelper::Stringify(Isolate* isolate,
+                                                   Handle<JSObject> error) {
+  VisitedScope scope(this, error);
+  if (scope.HasVisited()) return isolate->factory()->empty_string();
+
+  Handle<String> name;
+  Handle<String> message;
+  Handle<Name> internal_key = isolate->factory()->internal_error_symbol();
+  Handle<String> message_string =
+      isolate->factory()->NewStringFromStaticChars("message");
+  Handle<String> name_string =
+      isolate->factory()->NewStringFromStaticChars("name");

[Jakob Kummerow, 2015/08/08 21:56:09]

we already have isolate->factory()->name_string() ;-)

+  LookupIterator internal_error_lookup(
+      error, internal_key, LookupIterator::PROTOTYPE_CHAIN_SKIP_INTERCEPTOR);
+  LookupIterator message_lookup(
+      error, message_string, LookupIterator::PROTOTYPE_CHAIN_SKIP_INTERCEPTOR);
+  LookupIterator name_lookup(error, name_string,
+                             LookupIterator::PROTOTYPE_CHAIN_SKIP_INTERCEPTOR);
+
+  // Find out whether an internally created error object is on the prototype
+  // chain. If the name property is found on a holder prior to the internally
+  // created error object, use that name property. Otherwise just use the
+  // constructor name to avoid triggering possible side effects.
+  // Similar for the message property. If the message property shadows the
+  // internally created error object, use that message property. Otherwise
+  // use empty string as message.
+  if (internal_error_lookup.IsFound()) {
+    if (!ShadowsInternalError(isolate, &name_lookup, &internal_error_lookup)) {
+      Handle<JSObject> holder = internal_error_lookup.GetHolder<JSObject>();
+      name = Handle<String>(holder->constructor_name());
+    }
+    if (!ShadowsInternalError(isolate, &message_lookup,
+                              &internal_error_lookup)) {
+      message = isolate->factory()->empty_string();
+    }
+  }
+  if (name.is_null()) {
+    ASSIGN_RETURN_ON_EXCEPTION(
+        isolate, name,
+        GetStringifiedProperty(isolate, &name_lookup,
+                               isolate->factory()->Error_string()),
+        String);
+  }
+  if (message.is_null()) {
+    ASSIGN_RETURN_ON_EXCEPTION(
+        isolate, message,
+        GetStringifiedProperty(isolate, &message_lookup,
+                               isolate->factory()->empty_string()),
+        String);
+  }
+
+  if (name->length() == 0) return message;
+  if (message->length() == 0) return name;
+  IncrementalStringBuilder builder(isolate);
+  builder.AppendString(name);
+  builder.AppendCString(": ");
+  builder.AppendString(message);
+  return builder.Finish();
+}
+
+
+bool ErrorToStringHelper::ShadowsInternalError(
+    Isolate* isolate, LookupIterator* property_lookup,
+    LookupIterator* internal_error_lookup) {
+  Handle<JSObject> holder = property_lookup->GetHolder<JSObject>();
+  // It's fine if the property is defined on the error itself.
+  if (holder.is_identical_to(property_lookup->GetReceiver())) return true;
+  PrototypeIterator it(isolate, holder, PrototypeIterator::START_AT_RECEIVER);
+  while (true) {
+    if (it.IsAtEnd()) return false;
+    if (it.IsAtEnd(internal_error_lookup->GetHolder<JSObject>())) return true;
+    it.AdvanceIgnoringProxies();
+  }
+}
+
+
+MaybeHandle<String> ErrorToStringHelper::GetStringifiedProperty(
+    Isolate* isolate, LookupIterator* property_lookup,
+    Handle<String> default_value) {
+  if (!property_lookup->IsFound()) return default_value;
+  Handle<Object> obj;
+  ASSIGN_RETURN_ON_EXCEPTION(isolate, obj, Object::GetProperty(property_lookup),
+                             String);
+  if (obj->IsUndefined()) return default_value;
+  if (!obj->IsString()) {
+    ASSIGN_RETURN_ON_EXCEPTION(isolate, obj, Execution::ToString(isolate, obj),
+                               String);
+  }
+  return Handle<String>::cast(obj);
+}
+
 }  // namespace internal
 }  // namespace v8