```
test_type_caster_pyobject_ptr.cpp:8:23: error: variable templates only available with ‘-std=c++14’ or ‘-std=gnu++14’ [-Werror]
    8 | static constexpr bool is_same_ignoring_cvref = std::is_same<detail::remove_cvref_t<T>, U>::value;
      |                       ^~~~~~~~~~~~~~~~~~~~~~
```

… (because of doubts about it actually being useful).

…ious cosmetic changes.

…caster_pyobject_ptr.h)

…test_files.py

…d add a related comment in cast.h.

No production code changes.

Make tests more sensitive by using `ValueHolder` instead of empty tuples and dicts.

Manual leak checks with `while True:` & top command repeated for all tests.

(No production code changes.)

…ylion007

…bject *`]

The original suggestion leads to `error: call to 'cast' is ambiguous` (full error message below), therefore SFINAE guarding is needed.

```
clang++ -o pybind11/tests/test_type_caster_pyobject_ptr.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_type_caster_pyobject_ptr.cpp
In file included from /usr/local/google/home/rwgk/forked/pybind11/tests/test_type_caster_pyobject_ptr.cpp:1:
In file included from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/functional.h:12:
In file included from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:13:
In file included from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/class.h:12:
In file included from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/attr.h:14:
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/cast.h:1165:12: error: call to 'cast' is ambiguous
    return pybind11::cast<T>(std::move(*this));
           ^~~~~~~~~~~~~~~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/functional.h:109:70: note: in instantiation of function template specialization 'pybind11::object::cast<_object *>' requested here
                return hfunc.f(std::forward<Args>(args)...).template cast<Return>();
                                                                     ^
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/functional.h:103:16: note: in instantiation of member function 'pybind11::detail::type_caster<std::function<_object *(int)>>::load(pybind11::handle, bool)::func_wrapper::operator()' requested here
        struct func_wrapper {
               ^
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/cast.h:1456:47: note: in instantiation of member function 'pybind11::detail::type_caster<std::function<_object *(int)>>::load' requested here
        if ((... || !std::get<Is>(argcasters).load(call.args[Is], call.args_convert[Is]))) {
                                              ^
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/cast.h:1434:50: note: in instantiation of function template specialization 'pybind11::detail::argument_loader<const std::function<_object *(int)> &, int>::load_impl_sequence<0UL, 1UL>' requested here
    bool load_args(function_call &call) { return load_impl_sequence(call, indices{}); }
                                                 ^
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:227:33: note: in instantiation of member function 'pybind11::detail::argument_loader<const std::function<_object *(int)> &, int>::load_args' requested here
            if (!args_converter.load_args(call)) {
                                ^
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:101:9: note: in instantiation of function template specialization 'pybind11::cpp_function::initialize<(lambda at /usr/local/google/home/rwgk/forked/pybind11/tests/test_type_caster_pyobject_ptr.cpp:50:9), _object *, const std::function<_object *(int)> &, int, pybind11::name, pybind11::scope, pybind11::sibling, pybind11::return_value_policy>' requested here
        initialize(
        ^
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:1163:22: note: in instantiation of function template specialization 'pybind11::cpp_function::cpp_function<(lambda at /usr/local/google/home/rwgk/forked/pybind11/tests/test_type_caster_pyobject_ptr.cpp:50:9), pybind11::name, pybind11::scope, pybind11::sibling, pybind11::return_value_policy, void>' requested here
        cpp_function func(std::forward<Func>(f),
                     ^
/usr/local/google/home/rwgk/forked/pybind11/tests/test_type_caster_pyobject_ptr.cpp:48:7: note: in instantiation of function template specialization 'pybind11::module_::def<(lambda at /usr/local/google/home/rwgk/forked/pybind11/tests/test_type_caster_pyobject_ptr.cpp:50:9), pybind11::return_value_policy>' requested here
    m.def(
      ^
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/cast.h:1077:3: note: candidate function [with T = _object *, $1 = 0]
T cast(object &&obj) {
  ^
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/cast.h:1149:1: note: candidate function [with T = _object *]
cast(object &&object) {
^
1 error generated.
```