[BUG]: function with argument type `std::optional<std::reference_wrapper<Eigen::...>>` gives segmentation fault

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What version (or hash if on master) of pybind11 are you using?

2.13.6

Problem description

Due to https://github.com/pybind/pybind11/issues/5635 I started using std::optional<std::reference_wrapper<...>> and this works fine when I use it as a return value, but crashes when I accept it as an argument to a function.

Reproducible example code

#include <pybind11/pybind11.h>
#include <pybind11/eigen.h>
#include <pybind11/stl.h>
#include <iostream>

#include <Eigen/Eigen>

void print1(std::optional<std::reference_wrapper<Eigen::MatrixXd>> x)
{
    std::cout << x.value().get() << std::endl;
}

void print2(std::optional<Eigen::MatrixXd> x)
{
    std::cout << x.value() << std::endl;
}

void print3(std::reference_wrapper<Eigen::MatrixXd> x)
{
    std::cout << x.get() << std::endl;
}

void print4(Eigen::MatrixXd x)
{
    std::cout << x << std::endl;
}


PYBIND11_MODULE(tsting, m)
{
    m.def("print1", print1);
    m.def("print2", print2);
    m.def("print3", print3);
    m.def("print4", print4);
}

sin3point14@DESKTOP-D97C2FN:~/random/cpp/pybind11-test$ python3
Python 3.12.3 (main, Feb  4 2025, 14:48:35) [GCC 13.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import tsting
>>> import numpy as np
>>> a = np.ones((2,2))
>>> a
array([[1., 1.],
       [1., 1.]])
>>> tsting.print4(a)
1 1
1 1
>>> tsting.print3(a)
1 1
1 1
>>> tsting.print2(a)
1 1
1 1
>>> tsting.print1(a)
Segmentation fault (core dumped)

Is this a regression? Put the last known working version here if it is.

Not a regression

Start by reproducing the crash with the provided bindings and NumPy example, then read pybind11/eigen.h, pybind11/stl.h, and pybind11/pybind11.h around argument conversion for std::optional and std::reference_wrapper. Done means print1(a) no longer segfaults while the existing print2, print3, and print4 behavior remains intact.