Make `init_holder` do registration, and rename to `init_instance`
The instance registration for offset base types fails (under macOS, with
a segfault) in the presense of virtual base types. The issue occurs
when trying to `static_cast<Base *>(derived_ptr)` when `derived_ptr` has
been allocated (via `operator new`) but not initialized.
This commit fixes the issue by moving the addition to
`registered_instances` into `init_holder` rather than immediately after
value pointer allocation.
This also renames it to `init_instance` since it does more than holder
initialization now. (I also further renamed `init_holder_helper` to
`init_holder` since `init_holder` isn't used anymore).
Fixes #959.
diff --git a/tests/test_multiple_inheritance.cpp b/tests/test_multiple_inheritance.cpp
index c52b991..35f9d9c 100644
--- a/tests/test_multiple_inheritance.cpp
+++ b/tests/test_multiple_inheritance.cpp
@@ -201,4 +201,20 @@
py::class_<VanillaDictMix1, Vanilla, WithDict>(m, "VanillaDictMix1").def(py::init<>());
py::class_<VanillaDictMix2, WithDict, Vanilla>(m, "VanillaDictMix2").def(py::init<>());
#endif
+
+ // test_diamond_inheritance
+ // Issue #959: segfault when constructing diamond inheritance instance
+ // All of these have int members so that there will be various unequal pointers involved.
+ struct B { int b; virtual ~B() = default; };
+ struct C0 : public virtual B { int c0; };
+ struct C1 : public virtual B { int c1; };
+ struct D : public C0, public C1 { int d; };
+ py::class_<B>(m, "B")
+ .def("b", [](B *self) { return self; });
+ py::class_<C0, B>(m, "C0")
+ .def("c0", [](C0 *self) { return self; });
+ py::class_<C1, B>(m, "C1")
+ .def("c1", [](C1 *self) { return self; });
+ py::class_<D, C0, C1>(m, "D")
+ .def(py::init<>());
}