proto3 with arena crashes with segfault in Clear() method in C++

[romange]

Sample code:

TEST_F(ProtoTest, Clear) {
  Arena arena;
  Person* person = Arena::CreateMessage<Person>(&arena);
  person->mutable_account()->set_bank_name("Foo");
  person->Clear();
}

The code below is generated with proto3 mode and it fails at the marked line because account_ was not allocated with new but with arena.

void Person::Clear() {
  name_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),     GetArenaNoVirtual());
  id_ = GOOGLE_LONGLONG(0);
  email_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),     GetArenaNoVirtual());
  if (account_ != NULL) delete account_;            // ************
  account_ = NULL;
  phone_.Clear();
  phone2_.Clear();
  tag_.Clear();
}

[xfxyjwf]

@cfallin, could you take a look?

[cfallin]

@romange, thanks for the report! I've reproduced the bug and it's an unfortunate interaction of the removal of field presence with arena support.

@xfxyjwf, I've sent you a change internally. @romange, it should appear in our GitHub repo once reviewed internally and on our next GitHub sync. Alternately, I can cherry-pick if critical.

[romange]

Thanks, it's not urgent