Adding smart_holder_type_caster_load::loaded_as_shared_ptr, currently bypassing smart_holder shared_ptr tracking completely, but the tests pass and are sanitizer clean.

include/pybind11/detail/classh_type_casters.h

@@ -231,7 +231,8 @@ struct smart_holder_type_caster_load {
         return true;
     }
 
-    T *as_raw_ptr_unowned() {
+    T *loaded_as_raw_ptr_unowned() {
+        // BYPASSES smart_holder type checking completely.
         if (load_impl.loaded_v_h_cpptype != nullptr) {
             if (load_impl.reinterpret_cast_deemed_ok) {
                 return static_cast<T *>(loaded_smhldr_ptr->vptr.get());
@@ -241,7 +242,13 @@ struct smart_holder_type_caster_load {
                 return static_cast<T *>(implicit_casted);
             }
         }
-        return loaded_smhldr_ptr->as_raw_ptr_unowned<T>();
+        return static_cast<T *>(loaded_smhldr_ptr->vptr.get());
+    }
+
+    std::shared_ptr<T> loaded_as_shared_ptr() {
+        T *raw_ptr = loaded_as_raw_ptr_unowned();
+        // BYPASSES smart_holder shared_ptr tracking completely.
+        return std::shared_ptr<T>(loaded_smhldr_ptr->vptr, raw_ptr);
     }
 
     std::unique_ptr<T> loaded_as_unique_ptr() {
@@ -350,8 +357,8 @@ struct classh_type_caster : smart_holder_type_caster_load<T> {
     operator T&&() &&   { return this->loaded_smhldr_ptr->template rvalue_ref<T>(); }
     operator T const&() { return this->loaded_smhldr_ptr->template lvalue_ref<T>(); }
     operator T&()       { return this->loaded_smhldr_ptr->template lvalue_ref<T>(); }
-    operator T const*() { return this->as_raw_ptr_unowned(); }
+    operator T const*() { return this->loaded_as_raw_ptr_unowned(); }
-    operator T*()       { return this->as_raw_ptr_unowned(); }
+    operator T*()       { return this->loaded_as_raw_ptr_unowned(); }
 
     // clang-format on
 
@@ -487,7 +494,7 @@ struct classh_type_caster<std::shared_ptr<T>> : smart_holder_type_caster_load<T>
     template <typename>
     using cast_op_type = std::shared_ptr<T>;
 
-    operator std::shared_ptr<T>() { return this->loaded_smhldr_ptr->template as_shared_ptr<T>(); }
+    operator std::shared_ptr<T>() { return this->loaded_as_shared_ptr(); }
 };
 
 template <typename T>
@@ -505,9 +512,7 @@ struct classh_type_caster<std::shared_ptr<T const>> : smart_holder_type_caster_l
     template <typename>
     using cast_op_type = std::shared_ptr<T const>;
 
-    operator std::shared_ptr<T const>() {
+    operator std::shared_ptr<T const>() { return this->loaded_as_shared_ptr(); } // Mutbl2Const
-        return this->loaded_smhldr_ptr->template as_shared_ptr<T>();
-    }
 };
 
 template <typename T>

tests/test_classh_inheritance.cpp

@@ -2,6 +2,8 @@
 
 #include <pybind11/classh.h>
 
+#include <memory>
+
 namespace pybind11_tests {
 namespace classh_inheritance {
 
@@ -25,6 +27,12 @@ inline base *rtrn_mptr_drvd_up_cast() { return new drvd; }
 
 inline int pass_cptr_base(base const *b) { return b->id() + 11; }
 inline int pass_cptr_drvd(drvd const *d) { return d->id() + 12; }
+
+inline std::shared_ptr<drvd> rtrn_shmp_drvd()         { return std::shared_ptr<drvd>(new drvd); }
+inline std::shared_ptr<base> rtrn_shmp_drvd_up_cast() { return std::shared_ptr<drvd>(new drvd); }
+
+inline int pass_shcp_base(std::shared_ptr<base const> b) { return b->id() + 21; }
+inline int pass_shcp_drvd(std::shared_ptr<drvd const> d) { return d->id() + 22; }
 // clang-format on
 
 using base1 = base_template<110>;
@@ -69,6 +77,11 @@ TEST_SUBMODULE(classh_inheritance, m) {
     m.def("pass_cptr_base", pass_cptr_base);
     m.def("pass_cptr_drvd", pass_cptr_drvd);
 
+    m.def("rtrn_shmp_drvd", rtrn_shmp_drvd);
+    m.def("rtrn_shmp_drvd_up_cast", rtrn_shmp_drvd_up_cast);
+    m.def("pass_shcp_base", pass_shcp_base);
+    m.def("pass_shcp_drvd", pass_shcp_drvd);
+
     py::classh<base1>(m, "base1").def(py::init<>()); // __init__ needed for Python inheritance.
     py::classh<base2>(m, "base2").def(py::init<>());
     py::classh<drvd2, base1, base2>(m, "drvd2");

tests/test_classh_inheritance.py

@@ -9,6 +9,12 @@ def test_rtrn_mptr_drvd_pass_cptr_base():
     assert i == 2 * 100 + 11
 
 
+def test_rtrn_shmp_drvd_pass_shcp_base():
+    d = m.rtrn_shmp_drvd()
+    i = m.pass_shcp_base(d)  # load_impl Case 2a
+    assert i == 2 * 100 + 21
+
+
 def test_rtrn_mptr_drvd_up_cast_pass_cptr_drvd():
     b = m.rtrn_mptr_drvd_up_cast()
     # the base return is down-cast immediately.
@@ -17,6 +23,14 @@ def test_rtrn_mptr_drvd_up_cast_pass_cptr_drvd():
     assert i == 2 * 100 + 12
 
 
+def test_rtrn_shmp_drvd_up_cast_pass_shcp_drvd():
+    b = m.rtrn_shmp_drvd_up_cast()
+    # the base return is down-cast immediately.
+    assert b.__class__.__name__ == "drvd"
+    i = m.pass_shcp_drvd(b)
+    assert i == 2 * 100 + 22
+
+
 def test_rtrn_mptr_drvd2_pass_cptr_bases():
     d = m.rtrn_mptr_drvd2()
     i1 = m.pass_cptr_base1(d)  # load_impl Case 2c