ES6: Make function name configurable

src/accessors.cc

Index: src/accessors.cc
diff --git a/src/accessors.cc b/src/accessors.cc
index 052108a9b065feba47aa9ae907d55a9f33d092ab..1f5729ef741aa7b6f08e1ed4d47cb3f686df6353 100644
--- a/src/accessors.cc
+++ b/src/accessors.cc
@@ -1135,8 +1135,20 @@ void Accessors::FunctionNameSetter(
     v8::Local<v8::Name> name,
     v8::Local<v8::Value> val,
     const v8::PropertyCallbackInfo<void>& info) {
-  // Function name is non writable, non configurable.
-  UNREACHABLE();
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(info.GetIsolate());
+  HandleScope scope(isolate);
+  Handle<Object> value = Utils::OpenHandle(*val);
+
+  if (SetPropertyOnInstanceIfInherited(isolate, info, name, value)) return;
+
+  Handle<JSObject> object = Utils::OpenHandle(*info.This());
+  LookupIterator it(object, Utils::OpenHandle(*name));
+  CHECK_EQ(LookupIterator::ACCESSOR, it.state());
+  DCHECK(it.HolderIsReceiverOrHiddenPrototype());
+
+  if (Object::SetDataProperty(&it, value).is_null()) {
+    isolate->OptionalRescheduleException(false);
+  }
 }