The patch .rej below are resolved, but THIS STATE DOES NOT BUILD:

```
clang++ -o pybind11/tests/test_constants_and_functions.os -c -std=c++17 -fPIC -fvisibility=hidden -O0 -g -Wall -Wextra -Wconversion -Wcast-qual -Wdeprecated -Wundef -Wnon-virtual-dtor -Wunused-result -Werror -isystem /usr/include/python3.10 -isystem /usr/include/eigen3 -DPYBIND11_STRICT_ASSERTS_CLASS_HOLDER_VS_TYPE_CASTER_MIX -DPYBIND11_ENABLE_TYPE_CASTER_ODR_GUARD_IF_AVAILABLE -DPYBIND11_TEST_BOOST -Ipybind11/include -I/usr/local/google/home/rwgk/forked/pybind11/include -I/usr/local/google/home/rwgk/clone/pybind11/include /usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp
In file included from /usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp:11:
In file included from /usr/local/google/home/rwgk/forked/pybind11/tests/pybind11_tests.h:3:
In file included from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/eval.h:14:
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:1781:9: error: static_assert failed due to requirement '!holder_is_smart_holder == type_caster_type_is_type_caster_base_subtype' "py::class_ holder vs type_caster mismatch: missing PYBIND11_TYPE_CASTER_BASE_HOLDER(T, ...) or collision with custom py::detail::type_caster<T>?"
        static_assert(!holder_is_smart_holder == type_caster_type_is_type_caster_base_subtype,
        ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:2460:11: note: in instantiation of function template specialization 'pybind11::class_<MyEnum>::class_<>' requested here
        : class_<Type>(scope, name, extra...), m_base(*this, scope) {
          ^
/usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp:106:5: note: in instantiation of function template specialization 'pybind11::enum_<MyEnum>::enum_<>' requested here
    py::enum_<MyEnum>(m, "MyEnum")
    ^
1 error generated.
```

________

```
rwgk.c.googlers.com:~/forked/pybind11 $ patch -p 1 < ~/native_enum_git_diff_master_2022-11-19+131942.patch
patching file .github/workflows/python312.yml
patching file CMakeLists.txt
Hunk #1 FAILED at 111.
Hunk #2 succeeded at 138 (offset 5 lines).
1 out of 2 hunks FAILED -- saving rejects to file CMakeLists.txt.rej
patching file include/pybind11/cast.h
Hunk #1 FAILED at 12.
Hunk #2 succeeded at 78 (offset 30 lines).
Hunk #3 succeeded at 1173 (offset 41 lines).
1 out of 3 hunks FAILED -- saving rejects to file include/pybind11/cast.h.rej
patching file include/pybind11/detail/abi_platform_id.h
patching file include/pybind11/detail/cross_extension_shared_state.h
patching file include/pybind11/detail/internals.h
Hunk #1 FAILED at 16.
Hunk #2 succeeded at 109 (offset 1 line).
Hunk #3 FAILED at 203.
Hunk #4 succeeded at 398 (offset 11 lines).
Hunk #5 succeeded at 457 (offset 11 lines).
2 out of 5 hunks FAILED -- saving rejects to file include/pybind11/detail/internals.h.rej
patching file include/pybind11/detail/native_enum_data.h
patching file include/pybind11/detail/type_map.h
patching file include/pybind11/embed.h
patching file include/pybind11/native_enum.h
patching file include/pybind11/pybind11.h
Hunk #1 FAILED at 12.
Hunk #2 succeeded at 1269 (offset 1 line).
Hunk #3 succeeded at 2457 (offset 255 lines).
1 out of 3 hunks FAILED -- saving rejects to file include/pybind11/pybind11.h.rej
patching file include/pybind11/pytypes.h
patching file tests/CMakeLists.txt
Hunk #1 succeeded at 160 (offset 18 lines).
patching file tests/conftest.py
patching file tests/extra_python_package/test_files.py
Hunk #2 FAILED at 47.
1 out of 2 hunks FAILED -- saving rejects to file tests/extra_python_package/test_files.py.rej
patching file tests/test_embed/test_interpreter.cpp
patching file tests/test_enum.cpp
patching file tests/test_enum.py
patching file tests/test_native_enum.cpp
patching file tests/test_native_enum.py
```

* Transfer PR pybind#4329 from master to smart_holder branch, STEP 1.

The patch .rej below are resolved, but THIS STATE DOES NOT BUILD:

```
clang++ -o pybind11/tests/test_constants_and_functions.os -c -std=c++17 -fPIC -fvisibility=hidden -O0 -g -Wall -Wextra -Wconversion -Wcast-qual -Wdeprecated -Wundef -Wnon-virtual-dtor -Wunused-result -Werror -isystem /usr/include/python3.10 -isystem /usr/include/eigen3 -DPYBIND11_STRICT_ASSERTS_CLASS_HOLDER_VS_TYPE_CASTER_MIX -DPYBIND11_ENABLE_TYPE_CASTER_ODR_GUARD_IF_AVAILABLE -DPYBIND11_TEST_BOOST -Ipybind11/include -I/usr/local/google/home/rwgk/forked/pybind11/include -I/usr/local/google/home/rwgk/clone/pybind11/include /usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp
In file included from /usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp:11:
In file included from /usr/local/google/home/rwgk/forked/pybind11/tests/pybind11_tests.h:3:
In file included from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/eval.h:14:
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:1781:9: error: static_assert failed due to requirement '!holder_is_smart_holder == type_caster_type_is_type_caster_base_subtype' "py::class_ holder vs type_caster mismatch: missing PYBIND11_TYPE_CASTER_BASE_HOLDER(T, ...) or collision with custom py::detail::type_caster<T>?"
        static_assert(!holder_is_smart_holder == type_caster_type_is_type_caster_base_subtype,
        ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:2460:11: note: in instantiation of function template specialization 'pybind11::class_<MyEnum>::class_<>' requested here
        : class_<Type>(scope, name, extra...), m_base(*this, scope) {
          ^
/usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp:106:5: note: in instantiation of function template specialization 'pybind11::enum_<MyEnum>::enum_<>' requested here
    py::enum_<MyEnum>(m, "MyEnum")
    ^
1 error generated.
```

________

```
rwgk.c.googlers.com:~/forked/pybind11 $ patch -p 1 < ~/native_enum_git_diff_master_2022-11-19+131942.patch
patching file .github/workflows/python312.yml
patching file CMakeLists.txt
Hunk #1 FAILED at 111.
Hunk #2 succeeded at 138 (offset 5 lines).
1 out of 2 hunks FAILED -- saving rejects to file CMakeLists.txt.rej
patching file include/pybind11/cast.h
Hunk #1 FAILED at 12.
Hunk #2 succeeded at 78 (offset 30 lines).
Hunk #3 succeeded at 1173 (offset 41 lines).
1 out of 3 hunks FAILED -- saving rejects to file include/pybind11/cast.h.rej
patching file include/pybind11/detail/abi_platform_id.h
patching file include/pybind11/detail/cross_extension_shared_state.h
patching file include/pybind11/detail/internals.h
Hunk #1 FAILED at 16.
Hunk #2 succeeded at 109 (offset 1 line).
Hunk #3 FAILED at 203.
Hunk #4 succeeded at 398 (offset 11 lines).
Hunk #5 succeeded at 457 (offset 11 lines).
2 out of 5 hunks FAILED -- saving rejects to file include/pybind11/detail/internals.h.rej
patching file include/pybind11/detail/native_enum_data.h
patching file include/pybind11/detail/type_map.h
patching file include/pybind11/embed.h
patching file include/pybind11/native_enum.h
patching file include/pybind11/pybind11.h
Hunk #1 FAILED at 12.
Hunk #2 succeeded at 1269 (offset 1 line).
Hunk #3 succeeded at 2457 (offset 255 lines).
1 out of 3 hunks FAILED -- saving rejects to file include/pybind11/pybind11.h.rej
patching file include/pybind11/pytypes.h
patching file tests/CMakeLists.txt
Hunk #1 succeeded at 160 (offset 18 lines).
patching file tests/conftest.py
patching file tests/extra_python_package/test_files.py
Hunk #2 FAILED at 47.
1 out of 2 hunks FAILED -- saving rejects to file tests/extra_python_package/test_files.py.rej
patching file tests/test_embed/test_interpreter.cpp
patching file tests/test_enum.cpp
patching file tests/test_enum.py
patching file tests/test_native_enum.cpp
patching file tests/test_native_enum.py
```

* Make `smart_holder` code compatible with `type_caster_enum_type`

* Fix `if` condition guarding `Unable to cast native enum type to reference`

* WIP native_enum_add_to_parent

* PYBIND11_SILENCE_MSVC_C4127

* Transfer upstream.yml/python312.yml changes from PR pybind#4397

* clang-tidy (clang 15) auto-fix

* Remove python312.yml: this is handled separately under PR #30006

* Fixes for ruff

* Replace `PyEval_GetBuiltins()` in `finalize_interpreter()` with `get_python_state_dict()`

* Bug fix: Ensure `state_dict` is destroyed before `Py_Finalize()`

* Restore tests/test_embed/test_interpreter.cpp from google_pywrapcc_main

* Restore include/pybind11/embed.h from google_pywrapcc_main

* Back out all native_enum changes, leaving only the cross_extension_shared_state changes.

* Undo unrelated one-line change (from `auto` to `internals`).

…. (#30005)

* Transfer PR pybind#4329 from master to smart_holder branch, STEP 1.

The patch .rej below are resolved, but THIS STATE DOES NOT BUILD:

```
clang++ -o pybind11/tests/test_constants_and_functions.os -c -std=c++17 -fPIC -fvisibility=hidden -O0 -g -Wall -Wextra -Wconversion -Wcast-qual -Wdeprecated -Wundef -Wnon-virtual-dtor -Wunused-result -Werror -isystem /usr/include/python3.10 -isystem /usr/include/eigen3 -DPYBIND11_STRICT_ASSERTS_CLASS_HOLDER_VS_TYPE_CASTER_MIX -DPYBIND11_ENABLE_TYPE_CASTER_ODR_GUARD_IF_AVAILABLE -DPYBIND11_TEST_BOOST -Ipybind11/include -I/usr/local/google/home/rwgk/forked/pybind11/include -I/usr/local/google/home/rwgk/clone/pybind11/include /usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp
In file included from /usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp:11:
In file included from /usr/local/google/home/rwgk/forked/pybind11/tests/pybind11_tests.h:3:
In file included from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/eval.h:14:
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:1781:9: error: static_assert failed due to requirement '!holder_is_smart_holder == type_caster_type_is_type_caster_base_subtype' "py::class_ holder vs type_caster mismatch: missing PYBIND11_TYPE_CASTER_BASE_HOLDER(T, ...) or collision with custom py::detail::type_caster<T>?"
        static_assert(!holder_is_smart_holder == type_caster_type_is_type_caster_base_subtype,
        ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:2460:11: note: in instantiation of function template specialization 'pybind11::class_<MyEnum>::class_<>' requested here
        : class_<Type>(scope, name, extra...), m_base(*this, scope) {
          ^
/usr/local/google/home/rwgk/forked/pybind11/tests/test_constants_and_functions.cpp:106:5: note: in instantiation of function template specialization 'pybind11::enum_<MyEnum>::enum_<>' requested here
    py::enum_<MyEnum>(m, "MyEnum")
    ^
1 error generated.
```

________

```
rwgk.c.googlers.com:~/forked/pybind11 $ patch -p 1 < ~/native_enum_git_diff_master_2022-11-19+131942.patch
patching file .github/workflows/python312.yml
patching file CMakeLists.txt
Hunk #1 FAILED at 111.
Hunk #2 succeeded at 138 (offset 5 lines).
1 out of 2 hunks FAILED -- saving rejects to file CMakeLists.txt.rej
patching file include/pybind11/cast.h
Hunk #1 FAILED at 12.
Hunk #2 succeeded at 78 (offset 30 lines).
Hunk #3 succeeded at 1173 (offset 41 lines).
1 out of 3 hunks FAILED -- saving rejects to file include/pybind11/cast.h.rej
patching file include/pybind11/detail/abi_platform_id.h
patching file include/pybind11/detail/cross_extension_shared_state.h
patching file include/pybind11/detail/internals.h
Hunk #1 FAILED at 16.
Hunk #2 succeeded at 109 (offset 1 line).
Hunk #3 FAILED at 203.
Hunk #4 succeeded at 398 (offset 11 lines).
Hunk #5 succeeded at 457 (offset 11 lines).
2 out of 5 hunks FAILED -- saving rejects to file include/pybind11/detail/internals.h.rej
patching file include/pybind11/detail/native_enum_data.h
patching file include/pybind11/detail/type_map.h
patching file include/pybind11/embed.h
patching file include/pybind11/native_enum.h
patching file include/pybind11/pybind11.h
Hunk #1 FAILED at 12.
Hunk #2 succeeded at 1269 (offset 1 line).
Hunk #3 succeeded at 2457 (offset 255 lines).
1 out of 3 hunks FAILED -- saving rejects to file include/pybind11/pybind11.h.rej
patching file include/pybind11/pytypes.h
patching file tests/CMakeLists.txt
Hunk #1 succeeded at 160 (offset 18 lines).
patching file tests/conftest.py
patching file tests/extra_python_package/test_files.py
Hunk #2 FAILED at 47.
1 out of 2 hunks FAILED -- saving rejects to file tests/extra_python_package/test_files.py.rej
patching file tests/test_embed/test_interpreter.cpp
patching file tests/test_enum.cpp
patching file tests/test_enum.py
patching file tests/test_native_enum.cpp
patching file tests/test_native_enum.py
```

* Make `smart_holder` code compatible with `type_caster_enum_type`

* Fix `if` condition guarding `Unable to cast native enum type to reference`

* WIP native_enum_add_to_parent

* PYBIND11_SILENCE_MSVC_C4127

* Transfer upstream.yml/python312.yml changes from PR pybind#4397

* clang-tidy (clang 15) auto-fix

* Remove python312.yml: this is handled separately under PR #30006

* Fixes for ruff

* Replace `PyEval_GetBuiltins()` in `finalize_interpreter()` with `get_python_state_dict()`

* Bug fix: Ensure `state_dict` is destroyed before `Py_Finalize()`

* Restore tests/test_embed/test_interpreter.cpp from google_pywrapcc_main

* Restore include/pybind11/embed.h from google_pywrapcc_main

* Undo unrelated one-line change (from `auto` to `internals`).

* Add missing `test_class_with_enum`

* Add note to docs/classes.rst pointing to PR #30005

…ng __init__` safety feature to work for any metaclass. (#30095)

* Also wrap with `py::metaclass((PyObject *) &PyType_Type)`

* Transfer additional tests from PyCLIF python_multiple_inheritance_test.py

* Expand tests to fully cover wrapping with alternative metaclasses.

* * Factor out `ensure_base_init_functions_were_called()`.

* Call from new `tp_init_intercepted()` (adopting mechanism first added in PyCLIF: google/clif@7cba87d).

* Remove `pybind11_meta_call()` (which was added with pybind#2152).

* Bug fix (maybe actually two bugs?): simplify condition to `type->tp_init != tp_init_intercepted`

* Removing `Py_DECREF(self)` that leads to MSAN failure (Google toolchain).

```
==6380==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x5611589c9a58 in Py_DECREF third_party/python_runtime/v3_11/Include/object.h:537:9
...

  Uninitialized value was created by a heap deallocation
    #0 0x5611552757b0 in free third_party/llvm/llvm-project/compiler-rt/lib/msan/msan_interceptors.cpp:218:3
    #1 0x56115898e06b in _PyMem_RawFree third_party/python_runtime/v3_11/Objects/obmalloc.c:154:5
    #2 0x56115898f6ad in PyObject_Free third_party/python_runtime/v3_11/Objects/obmalloc.c:769:5
    #3 0x561158271bcc in PyObject_GC_Del third_party/python_runtime/v3_11/Modules/gcmodule.c:2407:5
    #4 0x7f21224b070c in pybind11_object_dealloc third_party/pybind11/include/pybind11/detail/class.h:483:5
    #5 0x5611589c2ed0 in subtype_dealloc third_party/python_runtime/v3_11/Objects/typeobject.c:1463:5
...
```

* IncludeCleaner fixes (Google toolchain).

* Restore `type->tp_call = pybind11_meta_call;` for PyPy only.

* pytest.skip("ensure_base_init_functions_were_called() does not work with PyPy and Python `type` as metaclass")

* Do not intercept our own `tp_init` function (`pybind11_object_init`).

* Add `derived_tp_init_registry` weakref-based cleanup.

* Replace `assert()` with `if` to resolve erroneous `lambda capture 'type' is not used` diagnostics (many CI jobs; seems to be a clang issue).

* Add `derived_tp_init_registry()->count(type) == 0` condition.

* Changes based on feedback from @rainwoodman

* Use PYBIND11_INIT_SAFETY_CHECKS_VIA_* macros, based on suggestion from @rainwoodman