[smart_holder] Simplification: Enable smart_holder functionality unco…

…nditionally. (#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 @@ struct copyable_holder_caster : public type_caster_base<type> {
     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 @@ struct copyable_holder_caster<
             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 @@ struct copyable_holder_caster<
     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 @@ struct move_only_holder_caster<
     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
+#    define PYBIND11_INTERNALS_VERSION 106
 #endif
 
-#if PYBIND11_INTERNALS_VERSION < 6
-#    error "PYBIND11_INTERNALS_VERSION 6 is the minimum for all platforms for pybind11v3."
+#if PYBIND11_INTERNALS_VERSION < 106
+#    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 @@ class type_caster_generic {
 
     // 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 @@ class type_caster_generic {
                 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 @@ class generic_type : public object {
         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>
@@ -1844,17 +1840,14 @@ 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) && defined(PYBIND11_SMART_HOLDER_ENABLED)
+#if defined(PYBIND11_USE_SMART_HOLDER_AS_DEFAULT)
 // 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:
 //           Simply use `py::classh` (see below) instead of `py::class_` as needed.
 //       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 @@ class class_ : public detail::generic_type {
         // 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 @@ class class_ : public detail::generic_type {
         } else {
             record.holder_enum_v = detail::holder_enum_t::custom_holder;
         }
-#endif
 
         set_operator_new<type>(&record);
 
@@ -2265,8 +2256,6 @@ class class_ : public detail::generic_type {
         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 @@ class class_ : public detail::generic_type {
         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 @@ class class_ : public detail::generic_type {
     }
 };
 
-#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 @@ class classh : public class_<type_, smart_holder, options...> {
     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"
-
-#ifdef PYBIND11_SMART_HOLDER_ENABLED
-
-#    include "detail/common.h"
-#    include "detail/using_smart_holder.h"
-#    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(