[BUG]: Pure virtual method overriding using mixin class gives: Tried to call pure virtual function …

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

2.13.5

Problem description

I cant override pure virtual functions using mixin classes. Pybind does not realize that the function in question does exist but is provided by the mixin class.

Reproducible example code

struct M {
    int f() { return 1; }
};

struct A {
    virtual int f() = 0;
};

// Imagine a trampoline class AT for A here

PYBIND11_MODULE(example, m) {
    pybind11::class_<M>(m, "Mixin")
        .def("f", &M::f);
    pybind11::class_<A, AT>(m, "Abstract")
        .def("f", &A::f);
}

class Derived(M, A):
    ...

d = D()
d.foo()

The last statement throws "Tried to call pure virtual function". For example in plain Python this works as expected:

class A():
    def f(self):
        pass

class M:
    def f(self):
        return "mixed in"

class D(M, A):
     pass

d = D()
print(d.f())

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

Not a regression

Start with the C++ mixin, abstract class, and trampoline setup in the reproducible example, then run the corresponding Python multiple-inheritance case. Trace how the pure virtual call is dispatched; done when the mixin-provided f() implementation is used instead of raising the pure-virtual error.