[smart_holder] Simplification: Enable smart_holder functionality unconditionally. (#5531)

* git merge --squash purge_internals_versions_4_5

* Remove PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT, set PYBIND11_INTERNALS_VERSION 7

* Remove all uses of PYBIND11_SMART_HOLDER_ENABLED under include/pybind11

* Remove obsolete PYBIND11_ACTUALLY_USING_SMART_HOLDER_AS_DEFAULT macro.

* Remove PYBIND11_SMART_HOLDER_ENABLED in ubench/holder_comparison.cpp

* Remove all uses of PYBIND11_SMART_HOLDER_ENABLED under tests/

* Remove `#define PYBIND11_SMART_HOLDER_ENABLED`

* Remove all uses of PYBIND11_SMART_HOLDER_TYPE_CASTERS under tests/

* Remove all uses of PYBIND11_TYPE_CASTER_BASE_HOLDER under tests/

* Add missing `#include <cstdint>`

Example error message (🐍 3.11 • ubuntu-latest • x64, GNU 13.3.0):

```
include/pybind11/detail/value_and_holder.h:56:52: error: ‘uint8_t’ is not a member of ‘std’; did you mean ‘wint_t’?
   56 |             inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_holder_constructed;
      |                                                    ^~~~~~~
```

* Change PYBIND11_INTERNALS_VERSION to 106: It will be changed to 7 in a follow-on PR that actually changes the internals.

.github/workflows/ci.yml

@@ -102,20 +102,6 @@ jobs:
             python: '3.12'
             args: >
               -DCMAKE_CXX_FLAGS="/DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT /GR /EHsc"
-          # Exercise PYBIND11_SMART_HOLDER_DISABLE
-          # with recent (or ideally latest) released Python version.
-          - runs-on: ubuntu-latest
-            python: '3.12'
-            args: >
-              -DCMAKE_CXX_FLAGS="-DPYBIND11_SMART_HOLDER_DISABLE"
-          - runs-on: macos-13
-            python: '3.12'
-            args: >
-              -DCMAKE_CXX_FLAGS="-DPYBIND11_SMART_HOLDER_DISABLE"
-          - runs-on: windows-2022
-            python: '3.12'
-            args: >
-              -DCMAKE_CXX_FLAGS="/DPYBIND11_SMART_HOLDER_DISABLE /GR /EHsc"
         exclude:
           # The setup-python action currently doesn't have graalpy for windows
           - python: 'graalpy-24.1'

include/pybind11/attr.h

@@ -339,9 +339,7 @@ struct type_record {
     /// Solves pybind/pybind11#1446
     bool release_gil_before_calling_cpp_dtor : 1;
 
-#ifdef PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
     holder_enum_t holder_enum_v = holder_enum_t::undefined;
-#endif
 
     PYBIND11_NOINLINE void add_base(const std::type_info &base, void *(*caster)(void *) ) {
         auto *base_info = detail::get_type_info(base, false);

include/pybind11/cast.h

@@ -836,8 +836,6 @@ protected:
     holder_type holder;
 };
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
 template <typename, typename SFINAE = void>
 struct copyable_holder_caster_shared_ptr_with_smart_holder_support_enabled : std::true_type {};
 
@@ -928,13 +926,13 @@ protected:
             return;
         }
         throw cast_error("Unable to cast from non-held to held instance (T& to Holder<T>) "
-#    if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
+#if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
                          "(#define PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for "
                          "type information)");
-#    else
+#else
                          "of type '"
                          + type_id<std::shared_ptr<type>>() + "''");
-#    endif
+#endif
     }
 
     template <typename T = std::shared_ptr<type>,
@@ -968,8 +966,6 @@ protected:
     std::shared_ptr<type> shared_ptr_storage;
 };
 
-#endif // PYBIND11_SMART_HOLDER_ENABLED
-
 /// Specialize for the common std::shared_ptr, so users don't need to
 template <typename T>
 class type_caster<std::shared_ptr<T>> : public copyable_holder_caster<T, std::shared_ptr<T>> {};
@@ -990,8 +986,6 @@ struct move_only_holder_caster {
     static constexpr auto name = type_caster_base<type>::name;
 };
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
 template <typename, typename SFINAE = void>
 struct move_only_holder_caster_unique_ptr_with_smart_holder_support_enabled : std::true_type {};
 
@@ -1129,8 +1123,6 @@ public:
     std::shared_ptr<std::unique_ptr<type, deleter>> unique_ptr_storage;
 };
 
-#endif // PYBIND11_SMART_HOLDER_ENABLED
-
 template <typename type, typename deleter>
 class type_caster<std::unique_ptr<type, deleter>>
     : public move_only_holder_caster<type, std::unique_ptr<type, deleter>> {};
@@ -1169,10 +1161,8 @@ struct is_holder_type
 template <typename base, typename deleter>
 struct is_holder_type<base, std::unique_ptr<base, deleter>> : std::true_type {};
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
 template <typename base>
 struct is_holder_type<base, smart_holder> : std::true_type {};
-#endif
 
 #ifdef PYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION // See PR #4888
 

include/pybind11/detail/common.h

@@ -605,11 +605,8 @@ struct instance {
     bool simple_instance_registered : 1;
     /// If true, get_internals().patients has an entry for this object
     bool has_patients : 1;
-// Cannot use PYBIND11_INTERNALS_VERSION >= 106 here without refactoring.
-#if PYBIND11_VERSION_MAJOR >= 3
     /// If true, this Python object needs to be kept alive for the lifetime of the C++ value.
     bool is_alias : 1;
-#endif
 
     /// Initializes all of the above type/values/holders data (but not the instance values
     /// themselves)

include/pybind11/detail/init.h

@@ -198,8 +198,6 @@ void construct(value_and_holder &v_h, Alias<Class> &&result, bool) {
     v_h.value_ptr() = new Alias<Class>(std::move(result));
 }
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
 template <typename T, typename D>
 smart_holder init_smart_holder_from_unique_ptr(std::unique_ptr<T, D> &&unq_ptr,
                                                bool void_cast_raw_ptr) {
@@ -268,8 +266,6 @@ void construct(value_and_holder &v_h,
     v_h.type->init_instance(v_h.inst, &smhldr);
 }
 
-#endif // PYBIND11_SMART_HOLDER_ENABLED
-
 // Implementing class for py::init<...>()
 template <typename... Args>
 struct constructor {

include/pybind11/detail/internals.h

@@ -37,15 +37,11 @@
 /// further ABI-incompatible changes may be made before the ABI is officially
 /// changed to the new version.
 #ifndef PYBIND11_INTERNALS_VERSION
-#    if PYBIND11_VERSION_MAJOR >= 3
 #    define PYBIND11_INTERNALS_VERSION 106
-#    else
-#        define PYBIND11_INTERNALS_VERSION 6
-#    endif
 #endif
 
-#if PYBIND11_INTERNALS_VERSION < 6
+#if PYBIND11_INTERNALS_VERSION < 106
-#    error "PYBIND11_INTERNALS_VERSION 6 is the minimum for all platforms for pybind11v3."
+#    error "PYBIND11_INTERNALS_VERSION 106 is the minimum (SPECIAL SITUATION)."
 #endif
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
@@ -215,10 +211,6 @@ struct internals {
     }
 };
 
-#if PYBIND11_INTERNALS_VERSION >= 106
-
-#    define PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-
 enum class holder_enum_t : uint8_t {
     undefined,
     std_unique_ptr, // Default, lacking interop with std::shared_ptr.
@@ -227,13 +219,6 @@ enum class holder_enum_t : uint8_t {
     custom_holder,
 };
 
-#endif
-
-#if defined(PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT)                                     \
-    && !defined(PYBIND11_SMART_HOLDER_DISABLE)
-#    define PYBIND11_SMART_HOLDER_ENABLED
-#endif
-
 /// Additional type information which does not fit into the PyTypeObject.
 /// Changes to this struct also require bumping `PYBIND11_INTERNALS_VERSION`.
 struct type_info {
@@ -262,9 +247,7 @@ struct type_info {
     bool default_holder : 1;
     /* true if this is a type registered with py::module_local */
     bool module_local : 1;
-#ifdef PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
     holder_enum_t holder_enum_v = holder_enum_t::undefined;
-#endif
 };
 
 #define PYBIND11_INTERNALS_ID                                                                     \

include/pybind11/detail/type_caster_base.h

@@ -511,8 +511,6 @@ inline PyThreadState *get_thread_state_unchecked() {
 void keep_alive_impl(handle nurse, handle patient);
 inline PyObject *make_new_instance(PyTypeObject *type);
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
 // PYBIND11:REMINDER: Needs refactoring of existing pybind11 code.
 inline bool deregister_instance(instance *self, void *valptr, const type_info *tinfo);
 
@@ -868,8 +866,6 @@ struct load_helper : value_and_holder_helper {
 
 PYBIND11_NAMESPACE_END(smart_holder_type_caster_support)
 
-#endif // PYBIND11_SMART_HOLDER_ENABLED
-
 class type_caster_generic {
 public:
     PYBIND11_NOINLINE explicit type_caster_generic(const std::type_info &type_info)
@@ -974,7 +970,6 @@ public:
 
     // Base methods for generic caster; there are overridden in copyable_holder_caster
     void load_value(value_and_holder &&v_h) {
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
         if (typeinfo->holder_enum_v == detail::holder_enum_t::smart_holder) {
             smart_holder_type_caster_support::value_and_holder_helper v_h_helper;
             v_h_helper.loaded_v_h = v_h;
@@ -984,7 +979,6 @@ public:
                 return;
             }
         }
-#endif
         auto *&vptr = v_h.value_ptr();
         // Lazy allocation for unallocated values:
         if (vptr == nullptr) {

include/pybind11/detail/using_smart_holder.h

@@ -5,29 +5,18 @@
 #pragma once
 
 #include "common.h"
-#include "internals.h"
+#include "struct_smart_holder.h"
 
 #include <type_traits>
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-#    include "struct_smart_holder.h"
-#endif
-
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
 using pybindit::memory::smart_holder;
-#endif
 
 PYBIND11_NAMESPACE_BEGIN(detail)
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
 template <typename H>
 using is_smart_holder = std::is_same<H, smart_holder>;
-#else
-template <typename>
-struct is_smart_holder : std::false_type {};
-#endif
 
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

include/pybind11/detail/value_and_holder.h

@@ -7,6 +7,7 @@
 #include "common.h"
 
 #include <cstddef>
+#include <cstdint>
 #include <typeinfo>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)

include/pybind11/pybind11.h

@@ -1448,9 +1448,7 @@ protected:
         tinfo->simple_ancestors = true;
         tinfo->default_holder = rec.default_holder;
         tinfo->module_local = rec.module_local;
-#ifdef PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
         tinfo->holder_enum_v = rec.holder_enum_v;
-#endif
 
         with_internals([&](internals &internals) {
             auto tindex = std::type_index(*rec.type);
@@ -1665,8 +1663,6 @@ PYBIND11_NAMESPACE_END(detail)
 template <typename T, typename D, typename SFINAE = void>
 struct property_cpp_function : detail::property_cpp_function_classic<T, D> {};
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
 PYBIND11_NAMESPACE_BEGIN(detail)
 
 template <typename T, typename D, typename SFINAE = void>
@@ -1844,9 +1840,7 @@ struct property_cpp_function<
         detail::both_t_and_d_use_type_caster_base<T, typename D::element_type>>::value>>
     : detail::property_cpp_function_sh_unique_ptr_member<T, D> {};
 
-#endif // PYBIND11_SMART_HOLDER_ENABLED
+#if defined(PYBIND11_USE_SMART_HOLDER_AS_DEFAULT)
-
-#if defined(PYBIND11_USE_SMART_HOLDER_AS_DEFAULT) && defined(PYBIND11_SMART_HOLDER_ENABLED)
 // NOTE: THIS IS MEANT FOR STRESS-TESTING ONLY!
 //       As of PR #5257, for production use, there is no longer a strong reason to make
 //       smart_holder the default holder:
@@ -1854,7 +1848,6 @@ struct property_cpp_function<
 //       Running the pybind11 unit tests with smart_holder as the default holder is to ensure
 //       that `py::smart_holder` / `py::classh` is backward-compatible with all pre-existing
 //       functionality.
-#    define PYBIND11_ACTUALLY_USING_SMART_HOLDER_AS_DEFAULT
 template <typename>
 using default_holder_type = smart_holder;
 #else
@@ -1913,7 +1906,6 @@ public:
         // A more fitting name would be uses_unique_ptr_holder.
         record.default_holder = detail::is_instantiation<std::unique_ptr, holder_type>::value;
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
         if (detail::is_instantiation<std::unique_ptr, holder_type>::value) {
             record.holder_enum_v = detail::holder_enum_t::std_unique_ptr;
         } else if (detail::is_instantiation<std::shared_ptr, holder_type>::value) {
@@ -1923,7 +1915,6 @@ public:
         } else {
             record.holder_enum_v = detail::holder_enum_t::custom_holder;
         }
-#endif
 
         set_operator_new<type>(&record);
 
@@ -2265,8 +2256,6 @@ private:
         init_holder(inst, v_h, (const holder_type *) holder_ptr, v_h.value_ptr<type>());
     }
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
     template <typename WrappedType>
     static bool try_initialization_using_shared_from_this(holder_type *, WrappedType *, ...) {
         return false;
@@ -2326,8 +2315,6 @@ private:
         v_h.set_holder_constructed();
     }
 
-#endif // PYBIND11_SMART_HOLDER_ENABLED
-
     // Deallocates an instance; via holder, if constructed; otherwise via operator delete.
     // NOTE: The Python error indicator needs to cleared BEFORE this function is called.
     // This is because we could be deallocating while cleaning up after a Python exception.
@@ -2393,8 +2380,6 @@ private:
     }
 };
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
 // Supports easier switching between py::class_<T> and py::class_<T, py::smart_holder>:
 // users can simply replace the `_` in `class_` with `h` or vice versa.
 template <typename type_, typename... options>
@@ -2403,8 +2388,6 @@ public:
     using class_<type_, smart_holder, options...>::class_;
 };
 
-#endif
-
 /// Binds an existing constructor taking arguments Args...
 template <typename... Args>
 detail::initimpl::constructor<Args...> init() {

include/pybind11/trampoline_self_life_support.h

@@ -4,13 +4,9 @@
 
 #pragma once
 
-#include "detail/internals.h"
+#include "detail/common.h"
-
+#include "detail/using_smart_holder.h"
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
+#include "detail/value_and_holder.h"
-
-#    include "detail/common.h"
-#    include "detail/using_smart_holder.h"
-#    include "detail/value_and_holder.h"
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
@@ -62,5 +58,3 @@ struct trampoline_self_life_support {
 };
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#endif // PYBIND11_SMART_HOLDER_ENABLED

tests/test_class.cpp

@@ -109,11 +109,7 @@ TEST_SUBMODULE(class_, m) {
     struct ToBeHeldByUniquePtr {};
     py::class_<ToBeHeldByUniquePtr, std::unique_ptr<ToBeHeldByUniquePtr>>(m, "ToBeHeldByUniquePtr")
         .def(py::init<>());
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
     m.def("pass_unique_ptr", [](std::unique_ptr<ToBeHeldByUniquePtr> &&) {});
-#else
-    m.attr("pass_unique_ptr") = py::none();
-#endif
 
     // test_inheritance
     class Pet {
@@ -636,7 +632,7 @@ CHECK_NOALIAS(8);
 CHECK_HOLDER(1, unique);
 CHECK_HOLDER(2, unique);
 CHECK_HOLDER(3, unique);
-#ifndef PYBIND11_ACTUALLY_USING_SMART_HOLDER_AS_DEFAULT
+#ifndef PYBIND11_USE_SMART_HOLDER_AS_DEFAULT
 CHECK_HOLDER(4, unique);
 CHECK_HOLDER(5, unique);
 #endif

tests/test_class.py

@@ -51,8 +51,6 @@ def test_instance_new():
 
 def test_pass_unique_ptr():
     obj = m.ToBeHeldByUniquePtr()
-    if m.pass_unique_ptr is None:
-        pytest.skip("smart_holder not available.")
     with pytest.raises(RuntimeError) as execinfo:
         m.pass_unique_ptr(obj)
     assert str(execinfo.value).startswith(

tests/test_class_sh_basic.cpp

@@ -144,24 +144,7 @@ class LocalUnusualOpRef : UnusualOpRef {}; // To avoid clashing with `py::class_
 py::object CastUnusualOpRefConstRef(const LocalUnusualOpRef &cref) { return py::cast(cref); }
 py::object CastUnusualOpRefMovable(LocalUnusualOpRef &&mvbl) { return py::cast(std::move(mvbl)); }
 
-} // namespace class_sh_basic
-} // namespace pybind11_tests
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_basic::atyp)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_basic::uconsumer)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_basic::SharedPtrStash)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_basic::LocalUnusualOpRef)
-
-namespace pybind11_tests {
-namespace class_sh_basic {
-
 TEST_SUBMODULE(class_sh_basic, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     namespace py = pybind11;
 
     py::classh<atyp>(m, "atyp").def(py::init<>()).def(py::init([](const std::string &mtxt) {
@@ -260,7 +243,6 @@ TEST_SUBMODULE(class_sh_basic, m) {
           []() { return CastUnusualOpRefConstRef(LocalUnusualOpRef()); });
     m.def("CallCastUnusualOpRefMovable",
           []() { return CastUnusualOpRefMovable(LocalUnusualOpRef()); });
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }
 
 } // namespace class_sh_basic

tests/test_class_sh_basic.py

@@ -7,9 +7,6 @@ import pytest
 
 from pybind11_tests import class_sh_basic as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 def test_atyp_constructors():
     obj = m.atyp()

tests/test_class_sh_disowning.cpp

@@ -28,16 +28,7 @@ int overloaded(std::unique_ptr<Atype<2>> at2, int i) { return at2->get() * 40 +
 } // namespace class_sh_disowning
 } // namespace pybind11_tests
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_disowning::Atype<1>)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_disowning::Atype<2>)
-
 TEST_SUBMODULE(class_sh_disowning, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     using namespace pybind11_tests::class_sh_disowning;
 
     py::classh<Atype<1>>(m, "Atype1").def(py::init<int>()).def("get", &Atype<1>::get);
@@ -49,5 +40,4 @@ TEST_SUBMODULE(class_sh_disowning, m) {
 
     m.def("overloaded", (int (*)(std::unique_ptr<Atype<1>>, int)) &overloaded);
     m.def("overloaded", (int (*)(std::unique_ptr<Atype<2>>, int)) &overloaded);
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_disowning.py

@@ -4,9 +4,6 @@ import pytest
 
 from pybind11_tests import class_sh_disowning as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 def is_disowned(obj):
     try:

tests/test_class_sh_disowning_mi.cpp

@@ -48,21 +48,7 @@ int disown_base2(std::unique_ptr<Base2> b2) { return b2->j * 2000 + 2; }
 } // namespace class_sh_disowning_mi
 } // namespace pybind11_tests
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_disowning_mi::B)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_disowning_mi::C0)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_disowning_mi::C1)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_disowning_mi::D)
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_disowning_mi::Base1)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_disowning_mi::Base2)
-
 TEST_SUBMODULE(class_sh_disowning_mi, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     using namespace pybind11_tests::class_sh_disowning_mi;
 
     py::classh<B>(m, "B")
@@ -98,5 +84,4 @@ TEST_SUBMODULE(class_sh_disowning_mi, m) {
     py::classh<Base2>(m, "Base2").def(py::init<int>()).def("bar", &Base2::bar);
     m.def("disown_base1", disown_base1);
     m.def("disown_base2", disown_base2);
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_disowning_mi.py

@@ -5,9 +5,6 @@ import pytest
 import env  # noqa: F401
 from pybind11_tests import class_sh_disowning_mi as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 def test_diamond_inheritance():
     # Very similar to test_multiple_inheritance.py:test_diamond_inheritance.

tests/test_class_sh_factory_constructors.cpp

@@ -72,27 +72,7 @@ struct sddwaa : std::default_delete<with_alias_alias> {};
 } // namespace class_sh_factory_constructors
 } // namespace pybind11_tests
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_valu)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_rref)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_cref)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_mref)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_cptr)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_mptr)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_shmp)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_shcp)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_uqmp)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_uqcp)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_udmp)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::atyp_udcp)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_factory_constructors::with_alias)
-
 TEST_SUBMODULE(class_sh_factory_constructors, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     using namespace pybind11_tests::class_sh_factory_constructors;
 
     py::classh<atyp_valu>(m, "atyp_valu")
@@ -183,5 +163,4 @@ TEST_SUBMODULE(class_sh_factory_constructors, m) {
                       [](int, int, int, int, int) {
                           return std::make_shared<with_alias>(); // Invalid alias factory.
                       }));
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_factory_constructors.py

@@ -4,9 +4,6 @@ import pytest
 
 from pybind11_tests import class_sh_factory_constructors as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 def test_atyp_factories():
     assert m.atyp_valu().get_mtxt() == "Valu"

tests/test_class_sh_inheritance.cpp

@@ -59,26 +59,7 @@ inline int pass_cptr_base2(base2 const *b) { return b->id() + 22; }
 inline int pass_cptr_drvd2(drvd2 const *d) { return d->id() + 23; }
 // clang-format on
 
-} // namespace class_sh_inheritance
-} // namespace pybind11_tests
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_inheritance::base)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_inheritance::drvd)
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_inheritance::base1)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_inheritance::base2)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_inheritance::drvd2)
-
-namespace pybind11_tests {
-namespace class_sh_inheritance {
-
 TEST_SUBMODULE(class_sh_inheritance, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     py::classh<base>(m, "base");
     py::classh<drvd, base>(m, "drvd");
 
@@ -105,7 +86,6 @@ TEST_SUBMODULE(class_sh_inheritance, m) {
     m.def("pass_cptr_base1", pass_cptr_base1);
     m.def("pass_cptr_base2", pass_cptr_base2);
     m.def("pass_cptr_drvd2", pass_cptr_drvd2);
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }
 
 } // namespace class_sh_inheritance

tests/test_class_sh_inheritance.py

@@ -1,12 +1,7 @@
 from __future__ import annotations
 
-import pytest
-
 from pybind11_tests import class_sh_inheritance as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 def test_rtrn_mptr_drvd_pass_cptr_base():
     d = m.rtrn_mptr_drvd()

tests/test_class_sh_mi_thunks.cpp

@@ -35,17 +35,7 @@ struct Derived : Base1, Base0 {
 
 } // namespace test_class_sh_mi_thunks
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(test_class_sh_mi_thunks::Base0)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(test_class_sh_mi_thunks::Base1)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(test_class_sh_mi_thunks::Derived)
-
 TEST_SUBMODULE(class_sh_mi_thunks, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     using namespace test_class_sh_mi_thunks;
 
     m.def("ptrdiff_drvd_base0", []() {
@@ -103,5 +93,4 @@ TEST_SUBMODULE(class_sh_mi_thunks, m) {
         }
         return obj_der->vec.size();
     });
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_mi_thunks.py

@@ -4,9 +4,6 @@ import pytest
 
 from pybind11_tests import class_sh_mi_thunks as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 def test_ptrdiff_drvd_base0():
     ptrdiff = m.ptrdiff_drvd_base0()

tests/test_class_sh_property.cpp

@@ -46,24 +46,7 @@ struct WithConstCharPtrMember {
 
 } // namespace test_class_sh_property
 
-PYBIND11_TYPE_CASTER_BASE_HOLDER(test_class_sh_property::ClassicField,
-                                 std::unique_ptr<test_class_sh_property::ClassicField>)
-PYBIND11_TYPE_CASTER_BASE_HOLDER(test_class_sh_property::ClassicOuter,
-                                 std::unique_ptr<test_class_sh_property::ClassicOuter>)
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(test_class_sh_property::Field)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(test_class_sh_property::Outer)
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(test_class_sh_property::WithCharArrayMember)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(test_class_sh_property::WithConstCharPtrMember)
-
 TEST_SUBMODULE(class_sh_property, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     using namespace test_class_sh_property;
 
     py::class_<ClassicField, std::unique_ptr<ClassicField>>(m, "ClassicField")
@@ -109,5 +92,4 @@ TEST_SUBMODULE(class_sh_property, m) {
     py::classh<WithConstCharPtrMember>(m, "WithConstCharPtrMember")
         .def(py::init<>())
         .def_readonly("const_char_ptr_member", &WithConstCharPtrMember::const_char_ptr_member);
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_property.py

@@ -7,9 +7,6 @@ import pytest
 import env  # noqa: F401
 from pybind11_tests import class_sh_property as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 @pytest.mark.skipif(
     "env.PYPY or env.GRAALPY", reason="gc after `del field` is apparently deferred"

tests/test_class_sh_property_non_owning.cpp

@@ -46,17 +46,7 @@ public:
 
 using namespace test_class_sh_property_non_owning;
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(CoreField)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(DataField)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(DataFieldsHolder)
-
 TEST_SUBMODULE(class_sh_property_non_owning, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     py::classh<CoreField>(m, "CoreField").def_readwrite("int_value", &CoreField::int_value);
 
     py::classh<DataField>(m, "DataField")
@@ -71,5 +61,4 @@ TEST_SUBMODULE(class_sh_property_non_owning, m) {
     py::classh<DataFieldsHolder>(m, "DataFieldsHolder")
         .def(py::init<std::size_t>())
         .def("vec_at", &DataFieldsHolder::vec_at, py::return_value_policy::reference_internal);
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_property_non_owning.py

@@ -4,9 +4,6 @@ import pytest
 
 from pybind11_tests import class_sh_property_non_owning as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 @pytest.mark.parametrize("persistent_holder", [True, False])
 @pytest.mark.parametrize(

tests/test_class_sh_shared_ptr_copy_move.cpp

@@ -41,21 +41,8 @@ struct Outer {
 };
 
 } // namespace
-} // namespace pybind11_tests
-
-PYBIND11_TYPE_CASTER_BASE_HOLDER(pybind11_tests::FooShPtr,
-                                 std::shared_ptr<pybind11_tests::FooShPtr>)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::FooSmHld)
-
-namespace pybind11_tests {
 
 TEST_SUBMODULE(class_sh_shared_ptr_copy_move, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     namespace py = pybind11;
 
     py::class_<FooShPtr, std::shared_ptr<FooShPtr>>(m, "FooShPtr")
@@ -63,20 +50,20 @@ TEST_SUBMODULE(class_sh_shared_ptr_copy_move, m) {
     py::classh<FooSmHld>(m, "FooSmHld").def("get_history", &FooSmHld::get_history);
 
     auto outer = py::class_<Outer>(m, "Outer").def(py::init());
-#    define MAKE_PROP(PropTyp)                                                                    \
+#define MAKE_PROP(PropTyp)                                                                        \
     MAKE_PROP_FOO(ShPtr, PropTyp)                                                                 \
     MAKE_PROP_FOO(SmHld, PropTyp)
 
-#    define MAKE_PROP_FOO(FooTyp, PropTyp)                                                        \
+#define MAKE_PROP_FOO(FooTyp, PropTyp)                                                            \
     .def_##PropTyp(#FooTyp "_" #PropTyp "_default", &Outer::FooTyp)                               \
         .def_##PropTyp(                                                                           \
             #FooTyp "_" #PropTyp "_copy", &Outer::FooTyp, py::return_value_policy::copy)          \
         .def_##PropTyp(                                                                           \
             #FooTyp "_" #PropTyp "_move", &Outer::FooTyp, py::return_value_policy::move)
     outer MAKE_PROP(readonly) MAKE_PROP(readwrite);
-#    undef MAKE_PROP_FOO
+#undef MAKE_PROP_FOO
 
-#    define MAKE_PROP_FOO(FooTyp, PropTyp)                                                        \
+#define MAKE_PROP_FOO(FooTyp, PropTyp)                                                            \
     .def_##PropTyp(#FooTyp "_property_" #PropTyp "_default", &Outer::FooTyp)                      \
         .def_property_##PropTyp(#FooTyp "_property_" #PropTyp "_copy",                            \
                                 &Outer::get##FooTyp,                                              \
@@ -85,8 +72,8 @@ TEST_SUBMODULE(class_sh_shared_ptr_copy_move, m) {
                                 &Outer::get##FooTyp,                                              \
                                 py::return_value_policy::move)
     outer MAKE_PROP(readonly);
-#    undef MAKE_PROP_FOO
+#undef MAKE_PROP_FOO
-#    undef MAKE_PROP
+#undef MAKE_PROP
 
     m.def("test_ShPtr_copy", []() {
         auto o = std::make_shared<FooShPtr>("copy");
@@ -113,7 +100,6 @@ TEST_SUBMODULE(class_sh_shared_ptr_copy_move, m) {
         l.append(std::move(o));
         return l;
     });
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }
 
 } // namespace pybind11_tests

tests/test_class_sh_shared_ptr_copy_move.py

@@ -1,12 +1,7 @@
 from __future__ import annotations
 
-import pytest
-
 from pybind11_tests import class_sh_shared_ptr_copy_move as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 def test_shptr_copy():
     txt = m.test_ShPtr_copy()[0].get_history()

tests/test_class_sh_trampoline_basic.cpp

@@ -34,7 +34,6 @@ struct AbaseAlias : Abase<SerNo> {
     }
 };
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
 template <>
 struct AbaseAlias<1> : Abase<1>, py::trampoline_self_life_support {
     using Abase<1>::Abase;
@@ -46,7 +45,6 @@ struct AbaseAlias<1> : Abase<1>, py::trampoline_self_life_support {
                                other_val);
     }
 };
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 
 template <int SerNo>
 int AddInCppRawPtr(const Abase<SerNo> *obj, int other_val) {
@@ -63,7 +61,6 @@ int AddInCppUniquePtr(std::unique_ptr<Abase<SerNo>> obj, int other_val) {
     return obj->Add(other_val) * 100 + 13;
 }
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
 template <int SerNo>
 void wrap(py::module_ m, const char *py_class_name) {
     py::classh<Abase<SerNo>, AbaseAlias<SerNo>>(m, py_class_name)
@@ -75,24 +72,13 @@ void wrap(py::module_ m, const char *py_class_name) {
     m.def("AddInCppSharedPtr", AddInCppSharedPtr<SerNo>, py::arg("obj"), py::arg("other_val"));
     m.def("AddInCppUniquePtr", AddInCppUniquePtr<SerNo>, py::arg("obj"), py::arg("other_val"));
 }
-#endif
 
 } // namespace class_sh_trampoline_basic
 } // namespace pybind11_tests
 
 using namespace pybind11_tests::class_sh_trampoline_basic;
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(Abase<0>)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(Abase<1>)
-
 TEST_SUBMODULE(class_sh_trampoline_basic, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     wrap<0>(m, "Abase0");
     wrap<1>(m, "Abase1");
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_trampoline_basic.py

@@ -4,9 +4,6 @@ import pytest
 
 from pybind11_tests import class_sh_trampoline_basic as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 class PyDrvd0(m.Abase0):
     def __init__(self, val):

tests/test_class_sh_trampoline_self_life_support.cpp

@@ -38,26 +38,16 @@ protected:
     Big5() : history{"DefaultConstructor"} {}
 };
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
 struct Big5Trampoline : Big5, py::trampoline_self_life_support {
     using Big5::Big5;
 };
-#endif
 
 } // namespace class_sh_trampoline_self_life_support
 } // namespace pybind11_tests
 
 using namespace pybind11_tests::class_sh_trampoline_self_life_support;
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(Big5)
-
 TEST_SUBMODULE(class_sh_trampoline_self_life_support, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     py::classh<Big5, Big5Trampoline>(m, "Big5")
         .def(py::init<std::string>())
         .def_readonly("history", &Big5::history);
@@ -94,5 +84,4 @@ TEST_SUBMODULE(class_sh_trampoline_self_life_support, m) {
         py::object o1 = py::cast(std::move(obj));
         return py::make_tuple(o1, o2);
     });
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_trampoline_self_life_support.py

@@ -4,9 +4,6 @@ import pytest
 
 import pybind11_tests.class_sh_trampoline_self_life_support as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 class PyBig5(m.Big5):
     pass

tests/test_class_sh_trampoline_shared_from_this.cpp

@@ -71,11 +71,9 @@ struct SftSharedPtrStash {
     }
 };
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
 struct SftTrampoline : Sft, py::trampoline_self_life_support {
     using Sft::Sft;
 };
-#endif
 
 long use_count(const std::shared_ptr<Sft> &obj) { return obj.use_count(); }
 
@@ -111,16 +109,7 @@ std::shared_ptr<Sft> pass_through_shd_ptr(const std::shared_ptr<Sft> &obj) { ret
 
 using namespace pybind11_tests::class_sh_trampoline_shared_from_this;
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(Sft)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(SftSharedPtrStash)
-
 TEST_SUBMODULE(class_sh_trampoline_shared_from_this, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     py::classh<Sft, SftTrampoline>(m, "Sft")
         .def(py::init<const std::string &>())
         .def(py::init([](const std::string &history, int) {
@@ -146,5 +135,4 @@ TEST_SUBMODULE(class_sh_trampoline_shared_from_this, m) {
     m.def("make_pure_cpp_sft_unq_ptr", make_pure_cpp_sft_unq_ptr);
     m.def("make_pure_cpp_sft_shd_ptr", make_pure_cpp_sft_shd_ptr);
     m.def("pass_through_shd_ptr", pass_through_shd_ptr);
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_trampoline_shared_from_this.py

@@ -8,9 +8,6 @@ import pytest
 import env
 import pybind11_tests.class_sh_trampoline_shared_from_this as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 class PySft(m.Sft):
     pass

tests/test_class_sh_trampoline_shared_ptr_cpp_arg.cpp

@@ -57,18 +57,7 @@ struct SpGoAwayTester {
 
 using namespace pybind11_tests::class_sh_trampoline_shared_ptr_cpp_arg;
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(SpBase)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(SpBaseTester)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(SpGoAway)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(SpGoAwayTester)
-
 TEST_SUBMODULE(class_sh_trampoline_shared_ptr_cpp_arg, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     // For testing whether a python subclass of a C++ object dies when the
     // last python reference is lost
 
@@ -101,5 +90,4 @@ TEST_SUBMODULE(class_sh_trampoline_shared_ptr_cpp_arg, m) {
     py::classh<SpGoAwayTester>(m, "SpGoAwayTester")
         .def(py::init<>())
         .def_readwrite("obj", &SpGoAwayTester::m_obj);
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_trampoline_shared_ptr_cpp_arg.py

@@ -5,9 +5,6 @@ import pytest
 import env  # noqa: F401
 import pybind11_tests.class_sh_trampoline_shared_ptr_cpp_arg as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 @pytest.mark.skipif("env.GRAALPY", reason="Cannot reliably trigger GC")
 def test_shared_ptr_cpp_arg():

tests/test_class_sh_trampoline_unique_ptr.cpp

@@ -34,12 +34,9 @@ private:
 } // namespace class_sh_trampoline_unique_ptr
 } // namespace pybind11_tests
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_trampoline_unique_ptr::Class)
-
 namespace pybind11_tests {
 namespace class_sh_trampoline_unique_ptr {
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
 class PyClass : public Class, public py::trampoline_self_life_support {
 public:
     std::unique_ptr<Class> clone() const override {
@@ -48,18 +45,11 @@ public:
 
     int foo() const override { PYBIND11_OVERRIDE_PURE(int, Class, foo); }
 };
-#endif
 
 } // namespace class_sh_trampoline_unique_ptr
 } // namespace pybind11_tests
 
 TEST_SUBMODULE(class_sh_trampoline_unique_ptr, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     using namespace pybind11_tests::class_sh_trampoline_unique_ptr;
 
     py::classh<Class, PyClass>(m, "Class")
@@ -71,5 +61,4 @@ TEST_SUBMODULE(class_sh_trampoline_unique_ptr, m) {
 
     m.def("clone", [](const Class &obj) { return obj.clone(); });
     m.def("clone_and_foo", [](const Class &obj) { return obj.clone()->foo(); });
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_trampoline_unique_ptr.py

@@ -1,12 +1,7 @@
 from __future__ import annotations
 
-import pytest
-
 import pybind11_tests.class_sh_trampoline_unique_ptr as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 class MyClass(m.Class):
     def foo(self):

tests/test_class_sh_unique_ptr_custom_deleter.cpp

@@ -22,25 +22,10 @@ private:
     explicit Pet(const std::string &name) : name(name) {}
 };
 
-} // namespace class_sh_unique_ptr_custom_deleter
-} // namespace pybind11_tests
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_unique_ptr_custom_deleter::Pet)
-
-namespace pybind11_tests {
-namespace class_sh_unique_ptr_custom_deleter {
-
 TEST_SUBMODULE(class_sh_unique_ptr_custom_deleter, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     py::classh<Pet>(m, "Pet").def_readwrite("name", &Pet::name);
 
     m.def("create", &Pet::New);
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }
 
 } // namespace class_sh_unique_ptr_custom_deleter

tests/test_class_sh_unique_ptr_custom_deleter.py

@@ -1,12 +1,7 @@
 from __future__ import annotations
 
-import pytest
-
 from pybind11_tests import class_sh_unique_ptr_custom_deleter as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 def test_create():
     pet = m.create("abc")

tests/test_class_sh_unique_ptr_member.cpp

@@ -36,21 +36,7 @@ private:
     std::unique_ptr<pointee> ptr_;
 };
 
-} // namespace class_sh_unique_ptr_member
-} // namespace pybind11_tests
-
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(pybind11_tests::class_sh_unique_ptr_member::pointee)
-
-namespace pybind11_tests {
-namespace class_sh_unique_ptr_member {
-
 TEST_SUBMODULE(class_sh_unique_ptr_member, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     py::classh<pointee>(m, "pointee").def(py::init<>()).def("get_int", &pointee::get_int);
 
     m.def("make_unique_pointee", make_unique_pointee);
@@ -60,7 +46,6 @@ TEST_SUBMODULE(class_sh_unique_ptr_member, m) {
         .def("is_owner", &ptr_owner::is_owner)
         .def("give_up_ownership_via_unique_ptr", &ptr_owner::give_up_ownership_via_unique_ptr)
         .def("give_up_ownership_via_shared_ptr", &ptr_owner::give_up_ownership_via_shared_ptr);
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }
 
 } // namespace class_sh_unique_ptr_member

tests/test_class_sh_unique_ptr_member.py

@@ -4,9 +4,6 @@ import pytest
 
 from pybind11_tests import class_sh_unique_ptr_member as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 def test_make_unique_pointee():
     obj = m.make_unique_pointee()

tests/test_class_sh_virtual_py_cpp_mix.cpp

@@ -31,8 +31,6 @@ int get_from_cpp_plainc_ptr(const Base *b) { return b->get() + 4000; }
 
 int get_from_cpp_unique_ptr(std::unique_ptr<Base> b) { return b->get() + 5000; }
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
 struct BaseVirtualOverrider : Base, py::trampoline_self_life_support {
     using Base::Base;
 
@@ -45,24 +43,12 @@ struct CppDerivedVirtualOverrider : CppDerived, py::trampoline_self_life_support
     int get() const override { PYBIND11_OVERRIDE(int, CppDerived, get); }
 };
 
-#endif
-
 } // namespace class_sh_virtual_py_cpp_mix
 } // namespace pybind11_tests
 
 using namespace pybind11_tests::class_sh_virtual_py_cpp_mix;
 
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(Base)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(CppDerivedPlain)
-PYBIND11_SMART_HOLDER_TYPE_CASTERS(CppDerived)
-
 TEST_SUBMODULE(class_sh_virtual_py_cpp_mix, m) {
-    m.attr("defined_PYBIND11_SMART_HOLDER_ENABLED") =
-#ifndef PYBIND11_SMART_HOLDER_ENABLED
-        false;
-#else
-        true;
-
     py::classh<Base, BaseVirtualOverrider>(m, "Base").def(py::init<>()).def("get", &Base::get);
 
     py::classh<CppDerivedPlain, Base>(m, "CppDerivedPlain").def(py::init<>());
@@ -71,5 +57,4 @@ TEST_SUBMODULE(class_sh_virtual_py_cpp_mix, m) {
 
     m.def("get_from_cpp_plainc_ptr", get_from_cpp_plainc_ptr, py::arg("b"));
     m.def("get_from_cpp_unique_ptr", get_from_cpp_unique_ptr, py::arg("b"));
-#endif // PYBIND11_SMART_HOLDER_ENABLED
 }

tests/test_class_sh_virtual_py_cpp_mix.py

@@ -4,9 +4,6 @@ import pytest
 
 from pybind11_tests import class_sh_virtual_py_cpp_mix as m
 
-if not m.defined_PYBIND11_SMART_HOLDER_ENABLED:
-    pytest.skip("smart_holder not available.", allow_module_level=True)
-
 
 class PyBase(m.Base):  # Avoiding name PyDerived, for more systematic naming.
     def __init__(self):

ubench/holder_comparison.cpp

@@ -22,8 +22,6 @@ void wrap_number_bucket(py::module m, const char *class_name) {
         .def("add", &WrappedType::add, py::arg("other"));
 }
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
 template <typename T>
 class padded_unique_ptr {
     std::unique_ptr<T> ptr;
@@ -37,21 +35,15 @@ public:
 static_assert(sizeof(padded_unique_ptr<nb_pu>) == sizeof(py::smart_holder),
               "Unexpected sizeof mismatch.");
 
-#endif
-
 } // namespace hc
 
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
 PYBIND11_DECLARE_HOLDER_TYPE(T, hc::padded_unique_ptr<T>);
-#endif
 
 PYBIND11_MODULE(pybind11_ubench_holder_comparison, m) {
     using namespace hc;
     wrap_number_bucket<nb_up, std::unique_ptr<nb_up>>(m, "number_bucket_up");
     wrap_number_bucket<nb_sp, std::shared_ptr<nb_sp>>(m, "number_bucket_sp");
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
     m.def("sizeof_smart_holder", []() { return sizeof(py::smart_holder); });
     wrap_number_bucket<nb_pu, padded_unique_ptr<nb_pu>>(m, "number_bucket_pu");
     wrap_number_bucket<nb_sh, py::smart_holder>(m, "number_bucket_sh");
-#endif
 }