def_property doesn't seems to keep parent alive when the return object is a py::array

[zhqrbitee]

Hi,
I have a use case that have some internal C++ vectors and want to return to python side as numpy array. To avoid copy, we only return a view on a C++ vector. It works OK in most of times, but I'm now hitting below corner case:

#include <vector>
#include <pybind11/pybind11.h>
#include <pybind11/numpy.h>

struct Wrapper1 {
  Wrapper1(const std::vector<double> &values): values{values} {};
  std::vector<double> values;
};

struct Wrapper2 {
  Wrapper2(const std::vector<double> &values): values{values} {};

  std::shared_ptr<Wrapper1> wrapper1() const { return std::make_shared<Wrapper1>(values); };

  std::vector<double> values;
};

namespace py = pybind11;
using namespace pybind11::literals;

PYBIND11_MODULE(test_return_numpy_array_no_copy_helper, m) {
  py::class_<Wrapper1, std::shared_ptr<Wrapper1>>(m, "Wrapper1")
      .def(py::init<const std::vector<double> &>(), "values"_a)
      .def_property_readonly("values", [](const Wrapper1& self) {
        // https://github.com/pybind/pybind11/issues/1042#issuecomment-325941022
        auto array = pybind11::array(self.values.size(), self.values.data(),
                                     // the base of the numpy array, as long as it is set to a python object, it won't do copy
                                     pybind11::handle{Py_None});
        // https://github.com/pybind/pybind11/issues/481, make numpy array read-only
        reinterpret_cast<pybind11::detail::PyArray_Proxy*>(array.ptr())->flags &=
            ~pybind11::detail::npy_api::NPY_ARRAY_WRITEABLE_;
        return array;
      });

  py::class_<Wrapper2, std::shared_ptr<Wrapper2>>(m, "Wrapper2")
      .def(py::init<const std::vector<double> &>(), "values"_a)
      .def_property_readonly("wrapper1", &Wrapper2::wrapper1);
}

Wrapper2 create a new instance of std::shared_ptr<Wrapper1> which contains a C++ std::vector values. The values is then return to python as a numpy array view.
From the docs: https://pybind11.readthedocs.io/en/stable/advanced/functions.html, def_property_readonly will use return_value_policy::reference_internal and thus keep the parent object alive. So I expect the values returned will keep its parent, i.e. the new instance of std::shared_ptr<Wrapper1> alive and the underlying memory will be valid as long as values is alive in Python.

However, below test case shows it is not the case

def test_return_np_array_with_no_copy():
    vec = [0.0, 0.5, 1.3, 2.2]
    wrapper2 = Wrapper2(vec)
    values = wrapper2.wrapper1.values
    # in some cases, you will see values be something like
    # array([1.08885983e-309, 5.00000000e-001, 1.30000000e+000, 2.20000000e+000])).
    # It means the underlying memory is destroyed
    assert np.all(values == vec), f"{values}"

I also try to manually to use keep_alive<0, 1> in the values binding of Wrapper1, but that doesn't seem to help.
So is the keep_alive system not supposed to work with an existing python object, e.g. py::array? If so, what should I do to make above test case work?