[BUG]: Tried to call pure virtual function

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Problem description

Hi, I am trying to create a Python wrapper for a C++ class wrapped with pybind.
However, this class inherits from an abstract class and calling the foo method results in calling the abstract method instead.

The code was compiled with

g++ -O3 -Wall -shared -std=c++11 -fPIC $(python3 -m pybind11 --includes) test.cpp -o test$(python3-config --extension-suffix)

which results in

Traceback (most recent call last):
  File "/user/files/test.py", line 12, in <module>
    c.foo()
RuntimeError: Tried to call pure virtual function "parent::foo"

This behaviour feels quite strange; I would expect B::foo to be called.

Reproducible example code

#include <pybind11/pybind11.h>
namespace py = pybind11;

class A{

  public:
    A( int x ): m_x( x ){}
    virtual int foo() = 0;

  protected:
    int m_x;
};

class B: public A{

  public:
    B( int x ): A( x ){}
    virtual int foo(){ return m_x + 1; }
};

template <class parent = A>
class Py_A : public parent{

  public:
    using parent::parent;
    int foo() override{
      PYBIND11_OVERRIDE_PURE( int, parent, foo );
    }
};

PYBIND11_MODULE( test, m ){

  py::class_<A, Py_A<>>( m, "A" )
    .def(py::init<int>());

  py::class_<B, A, Py_A<B>>( m, "B" )
    .def(py::init<int>())
    .def("foo", &B::foo);
}

#!/usr/bin/env python3
from test import B

class C( B ):
  def __init__( self, *args, **kwargs ):
    super().__init__( *args, **kwargs )

if __name__ == "__main__":

  c = C( 1 )
  # RuntimeError: Tried to call pure virtual function "parent::foo"
  c.foo()

Reproduce the failure using the C++ example and Python script in the issue, built with the shown g++ command. Start by tracing the B::foo binding and PYBIND11_OVERRIDE_PURE behavior, then determine whether the observed dispatch should be corrected or documented; done means the example no longer raises unexpectedly or the expected behavior is clearly explained.