[QUESTION] Pybind11 undefined classes. Can't bind to object with definition unavailable at compile time.

Hello,

I'm having issues where my classes are undefined. I figured this is a pretty basic use case, but I couldn't find anything relevant when I searched for a solution. So I could use some help. Anyways, my PYBIND11_MODULE looks like this:

    py::class_<PDPage>(m, "PDPage");

    py::class_<APDFLDoc>(m, "APDFLDoc")
        .def(py::init<const char*, bool>())
        .def("getPage", &APDFLDoc::getPage);

I have this class called APDFLDoc and I want to create a binding for one of its methods, getPage. But when I try to build it in VS, I get this error message:

Error    C2139    '_t_PDPage': an undefined class is not allowed as an argument to compiler intrinsic type trait '__is_base_of'    RenderPage    C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30037\include\type_traits    1185

Now I think I know why this is happening. getPage is trying to create an object, a PDPage, from a class/struct that has no definition at compile-time because it is coming from a .dll. I raised the same question on Gitter, and I was told that Pybind11 has no support for this out of the box. I am wondering if you have a better solution than the one proposed there, which seems highly risky and time consuming. When I started using Pybind11, I assumed this was a basic use case and am surprised to have found no clear answer.

I also have a gist here.

Start with the PYBIND11_MODULE snippet, the linked gist, and the Visual Studio C2139 diagnostic in the issue. Reproduce the reported binding scenario and determine whether the undefined PDPage type is supported; done requires a confirmed solution or a clear statement of the supported approach.