Copying files as-is from branch test_unique_ptr_member (PR #2672).

tests/test_type_caster_bare_interface.cpp

+#include "pybind11_tests.h"
+
+#include <memory>
+
+namespace pybind11_tests {
+namespace type_caster_bare_interface {
+
+struct mpty {};
+
+// clang-format off
+
+mpty        rtrn_mpty_valu() { mpty obj; return obj; }
+mpty&&      rtrn_mpty_rref() { static mpty obj; return std::move(obj); }
+mpty const& rtrn_mpty_cref() { static mpty obj; return obj; }
+mpty&       rtrn_mpty_mref() { static mpty obj; return obj; }
+mpty const* rtrn_mpty_cptr() { return new mpty; }
+mpty*       rtrn_mpty_mptr() { return new mpty; }
+
+const char* pass_mpty_valu(mpty)        { return "load_valu"; }
+const char* pass_mpty_rref(mpty&&)      { return "load_rref"; }
+const char* pass_mpty_cref(mpty const&) { return "load_cref"; }
+const char* pass_mpty_mref(mpty&)       { return "load_mref"; }
+const char* pass_mpty_cptr(mpty const*) { return "load_cptr"; }
+const char* pass_mpty_mptr(mpty*)       { return "load_mptr"; }
+
+std::shared_ptr<mpty>       rtrn_mpty_shmp() { return std::shared_ptr<mpty      >(new mpty); }
+std::shared_ptr<mpty const> rtrn_mpty_shcp() { return std::shared_ptr<mpty const>(new mpty); }
+
+const char* pass_mpty_shmp(std::shared_ptr<mpty>)       { return "load_shmp"; }
+const char* pass_mpty_shcp(std::shared_ptr<mpty const>) { return "load_shcp"; }
+
+std::unique_ptr<mpty>       rtrn_mpty_uqmp() { return std::unique_ptr<mpty      >(new mpty); }
+std::unique_ptr<mpty const> rtrn_mpty_uqcp() { return std::unique_ptr<mpty const>(new mpty); }
+
+const char* pass_mpty_uqmp(std::unique_ptr<mpty>)       { return "load_uqmp"; }
+const char* pass_mpty_uqcp(std::unique_ptr<mpty const>) { return "load_uqcp"; }
+
+// clang-format on
+
+} // namespace type_caster_bare_interface
+} // namespace pybind11_tests
+
+namespace pybind11 {
+namespace detail {
+
+using namespace pybind11_tests::type_caster_bare_interface;
+
+template <>
+struct type_caster<mpty> {
+    static constexpr auto name = _<mpty>();
+
+    // static handle cast(mpty, ...)
+    // is redundant (leads to ambiguous overloads).
+
+    static handle cast(mpty && /*src*/, return_value_policy /*policy*/, handle /*parent*/) {
+        return str("cast_rref").release();
+    }
+
+    static handle cast(mpty const & /*src*/, return_value_policy /*policy*/, handle /*parent*/) {
+        return str("cast_cref").release();
+    }
+
+    static handle cast(mpty & /*src*/, return_value_policy /*policy*/, handle /*parent*/) {
+        return str("cast_mref").release();
+    }
+
+    static handle cast(mpty const *src, return_value_policy /*policy*/, handle /*parent*/) {
+        delete src;
+        return str("cast_cptr").release();
+    }
+
+    static handle cast(mpty *src, return_value_policy /*policy*/, handle /*parent*/) {
+        delete src;
+        return str("cast_mptr").release();
+    }
+
+    template <typename T_>
+    using cast_op_type = conditional_t<
+        std::is_same<remove_reference_t<T_>, mpty const *>::value,
+        mpty const *,
+        conditional_t<
+            std::is_same<remove_reference_t<T_>, mpty *>::value,
+            mpty *,
+            conditional_t<
+                std::is_same<T_, mpty const &>::value,
+                mpty const &,
+                conditional_t<std::is_same<T_, mpty &>::value,
+                              mpty &,
+                              conditional_t<std::is_same<T_, mpty &&>::value, mpty &&, mpty>>>>>;
+
+    // clang-format off
+
+    operator mpty()        { return rtrn_mpty_valu(); }
+    operator mpty&&() &&   { return rtrn_mpty_rref(); }
+    operator mpty const&() { return rtrn_mpty_cref(); }
+    operator mpty&()       { return rtrn_mpty_mref(); }
+    operator mpty const*() { static mpty obj; return &obj; }
+    operator mpty*()       { static mpty obj; return &obj; }
+
+    // clang-format on
+
+    bool load(handle /*src*/, bool /*convert*/) { return true; }
+};
+
+template <>
+struct type_caster<std::shared_ptr<mpty>> {
+    static constexpr auto name = _<std::shared_ptr<mpty>>();
+
+    static handle cast(const std::shared_ptr<mpty> & /*src*/,
+                       return_value_policy /*policy*/,
+                       handle /*parent*/) {
+        return str("cast_shmp").release();
+    }
+
+    template <typename>
+    using cast_op_type = std::shared_ptr<mpty>;
+
+    operator std::shared_ptr<mpty>() { return rtrn_mpty_shmp(); }
+
+    bool load(handle /*src*/, bool /*convert*/) { return true; }
+};
+
+template <>
+struct type_caster<std::shared_ptr<mpty const>> {
+    static constexpr auto name = _<std::shared_ptr<mpty const>>();
+
+    static handle cast(const std::shared_ptr<mpty const> & /*src*/,
+                       return_value_policy /*policy*/,
+                       handle /*parent*/) {
+        return str("cast_shcp").release();
+    }
+
+    template <typename>
+    using cast_op_type = std::shared_ptr<mpty const>;
+
+    operator std::shared_ptr<mpty const>() { return rtrn_mpty_shcp(); }
+
+    bool load(handle /*src*/, bool /*convert*/) { return true; }
+};
+
+template <>
+struct type_caster<std::unique_ptr<mpty>> {
+    static constexpr auto name = _<std::unique_ptr<mpty>>();
+
+    static handle
+    cast(std::unique_ptr<mpty> && /*src*/, return_value_policy /*policy*/, handle /*parent*/) {
+        return str("cast_uqmp").release();
+    }
+
+    template <typename>
+    using cast_op_type = std::unique_ptr<mpty>;
+
+    operator std::unique_ptr<mpty>() { return rtrn_mpty_uqmp(); }
+
+    bool load(handle /*src*/, bool /*convert*/) { return true; }
+};
+
+template <>
+struct type_caster<std::unique_ptr<mpty const>> {
+    static constexpr auto name = _<std::unique_ptr<mpty const>>();
+
+    static handle cast(std::unique_ptr<mpty const> && /*src*/,
+                       return_value_policy /*policy*/,
+                       handle /*parent*/) {
+        return str("cast_uqcp").release();
+    }
+
+    template <typename>
+    using cast_op_type = std::unique_ptr<mpty const>;
+
+    operator std::unique_ptr<mpty const>() { return rtrn_mpty_uqcp(); }
+
+    bool load(handle /*src*/, bool /*convert*/) { return true; }
+};
+
+} // namespace detail
+} // namespace pybind11
+
+namespace pybind11_tests {
+namespace type_caster_bare_interface {
+
+TEST_SUBMODULE(type_caster_bare_interface, m) {
+    m.def("rtrn_mpty_valu", rtrn_mpty_valu);
+    m.def("rtrn_mpty_rref", rtrn_mpty_rref);
+    m.def("rtrn_mpty_cref", rtrn_mpty_cref);
+    m.def("rtrn_mpty_mref", rtrn_mpty_mref);
+    m.def("rtrn_mpty_cptr", rtrn_mpty_cptr);
+    m.def("rtrn_mpty_mptr", rtrn_mpty_mptr);
+
+    m.def("pass_mpty_valu", pass_mpty_valu);
+    m.def("pass_mpty_rref", pass_mpty_rref);
+    m.def("pass_mpty_cref", pass_mpty_cref);
+    m.def("pass_mpty_mref", pass_mpty_mref);
+    m.def("pass_mpty_cptr", pass_mpty_cptr);
+    m.def("pass_mpty_mptr", pass_mpty_mptr);
+
+    m.def("rtrn_mpty_shmp", rtrn_mpty_shmp);
+    m.def("rtrn_mpty_shcp", rtrn_mpty_shcp);
+
+    m.def("pass_mpty_shmp", pass_mpty_shmp);
+    m.def("pass_mpty_shcp", pass_mpty_shcp);
+
+    m.def("rtrn_mpty_uqmp", rtrn_mpty_uqmp);
+    m.def("rtrn_mpty_uqcp", rtrn_mpty_uqcp);
+
+    m.def("pass_mpty_uqmp", pass_mpty_uqmp);
+    m.def("pass_mpty_uqcp", pass_mpty_uqcp);
+}
+
+} // namespace type_caster_bare_interface
+} // namespace pybind11_tests

tests/test_type_caster_bare_interface.py

+# -*- coding: utf-8 -*-
+
+from pybind11_tests import type_caster_bare_interface as m
+
+
+def test_cast():
+    assert m.rtrn_mpty_valu() == "cast_rref"
+    assert m.rtrn_mpty_rref() == "cast_rref"
+    assert m.rtrn_mpty_cref() == "cast_cref"
+    assert m.rtrn_mpty_mref() == "cast_mref"
+    assert m.rtrn_mpty_cptr() == "cast_cptr"
+    assert m.rtrn_mpty_mptr() == "cast_mptr"
+
+
+def test_load():
+    assert m.pass_mpty_valu(None) == "load_valu"
+    assert m.pass_mpty_rref(None) == "load_rref"
+    assert m.pass_mpty_cref(None) == "load_cref"
+    assert m.pass_mpty_mref(None) == "load_mref"
+    assert m.pass_mpty_cptr(None) == "load_cptr"
+    assert m.pass_mpty_mptr(None) == "load_mptr"
+
+
+def test_cast_shared_ptr():
+    assert m.rtrn_mpty_shmp() == "cast_shmp"
+    assert m.rtrn_mpty_shcp() == "cast_shcp"
+
+
+def test_load_shared_ptr():
+    assert m.pass_mpty_shmp(None) == "load_shmp"
+    assert m.pass_mpty_shcp(None) == "load_shcp"
+
+
+def test_cast_unique_ptr():
+    assert m.rtrn_mpty_uqmp() == "cast_uqmp"
+    assert m.rtrn_mpty_uqcp() == "cast_uqcp"
+
+
+def test_load_unique_ptr():
+    assert m.pass_mpty_uqmp(None) == "load_uqmp"
+    assert m.pass_mpty_uqcp(None) == "load_uqcp"