* Using new smart_holder::reclaim_disowned in smart_holder_type_caster for unique_ptr.

* Systematically renaming was_disowned to is_disowned (because disowning is now reversible: reclaim_disowned).

* Systematically renaming virtual_overrider_self_life_support to trampoline_self_life_support (to reuse existing terminology instead of introducing new one).

* Systematically renaming test_class_sh_with_alias to test_class_sh_trampoline_basic.

* Adding a Trampolines and std::unique_ptr section to README_smart_holder.rst.

* MSVC compatibility.

* Porting subset of absltest code from reproducer provided by @elkhrt. Baseline for debugging ASAN heap-use-after-free.

* Moving Py_DECREF to resolve ASAN heap-use-after-free failure.

* Fixing trivial formatting issue.

* Workaround for clang 3.6 and 3.7.

It was only useful for easily harvest this from the GitHub Actions CI results, mostly out of curiosity:

52 C++ function argument 1 is evaluated first.
90 C++ function argument 2 is evaluated first.

These results came for the final CI run for PR #2936; that PR has nothing else to do with the results.

Pushing directly. This tiny change is not worth a PR.

[skip actions]

Fixing very minor oversights discovered while proof-reading the initial version for the first time on GitHub. Pushing directly. Not worth a PR.

* Adding initial README_smart_holder.rst.

* Adding README_smart_holder.rst to MANIFEST.in and test_files.py.

* Adding PyGILState_Check() in object_api<>::operator().

* Enabling PyGILState_Check() for Python >= 3.6 only.

Possibly, this explains why PyGILState_Check() cannot safely be used with Python 3.4 and 3.5:

https://github.com/python/cpython/pull/10267#issuecomment-434881587

* Adding simple micro benchmark.

* Reducing test time to minimum (purely for coverage, not for accurate results).

* Fixing silly oversight.

* Minor code organization improvement in test.

* Adding example runtimes.

* Removing capsys (just run with `-k test_callback_num_times -s` and using `.format()`.

env: Add surrogate for pytest.deprecated_call for ptyest<3.9

* Pybind11Extension add the "/EHsc /bigobj /std:c++14" flags on Windows.
  This is good for Visual C++ but not for Mingw.
* According
  https://github.com/msys2/MINGW-packages/blob/master/mingw-w64-python2/0410-MINGW-build-extensions-with-GCC.patch
  sysconfig.get_platform() is the way to check for a Mingw64

* Adding tests to test_class_sh_disowning_mi for expanded coverage.

* Setting @pytest.mark.xfail strict=False (some tests pass with PyPy, some don't).

* Adding test_class_sh_disowning.

* Fixing minor namespace naming inconsistency between test_class_sh_*.cpp files.

* Replacing py::overload_cast with plain cast for C++11 compatibility.

* Accommodate that the C++ order of evaluation of function arguments is unspecified.

* Adaption of PyCLIF virtual_py_cpp_mix test.

* Removing ValueError: Ownership of instance with virtual overrides in Python cannot be transferred to C++. TODO: static_assert alias class needs to inherit from virtual_overrider_self_life_support.

* Bringing back ValueError: "... instance cannot safely be transferred to C++.", but based on dynamic_cast<AliasType>.

* Fixing oversight: adding test_class_sh_virtual_py_cpp_mix.cpp to cmake file.

* clang <= 3.6 compatibility.

* Fixing oversight: dynamic_raw_ptr_cast_if_possible needs special handling for To = void. Adding corresponding missing test in test_class_sh_virtual_py_cpp_mix. Moving dynamic_raw_ptr_cast_if_possible to separate header.

* Changing py::detail::virtual_overrider_self_life_support to py::virtual_overrider_self_life_support.

* Add roundtrip tests for unique_ptr

* Implementation for casting from const std::unique_ptr&

... forwarding to smart_holder_type_caster<T>::cast(T*)

* Initial version of virtual_overrider_self_life_support (enables safely passing unique_ptr to C++).

* Clang 3.6, 3.7 compatibility.

* Adding missing default constructor.

* Restoring test for exception for the case that virtual_overrider_self_life_support is not used.

* Fixing oversight: Adding missing holder().ensure_was_not_disowned().

* Adding unit tests for new `struct smart_holder` member functions.

* Moving virtual_overrider_self_life_support to separate include file, with iwyu cleanup.

* Adding suppression for pypocketfft.

* Generalize existing pypocketfft Valgrind suppression

Co-authored-by: Yannick Jadoul <yannick.jadoul@belgacom.net>

Use correct duration representation when casting from datetime.timdelta to std::chrono::duration (#2870)

* Use correct duration representation when casting from datetime.timdelta to std::chrono::duration

* When asserting datetime/timedelta/date/time we can equality-compare whole objects

Shuffling code in test_multiple_inheritance.cpp to separate struct/class definitions from bindings code. (#2890)

* WIP: test setup complete, AddInCppUniquePtr failing (reproduces PyCLIF smart_ptrs_test failure).

* Fully tested locally.

* Adding new tests to cmake file.

Changing all but one std::runtime_error to std::invalid_argument, which appears as ValueError in the Python interpreter. Adding `test_cannot_disown_use_count_ne_1`. (#2883)

* shared_ptr<bool> vptr_deleter_armed_flag_ptr (instead of unique_ptr), to fix heap-use-after-free bug.

* Fixing  generated by some compilers in the pybind11 CI suite.

Revert "WIP: test setup complete, AddInCppUniquePtr failing (reproduces PyCLIF smart_ptrs_test failure)."

This reverts commit 20107030.

Changing cast_error("... Python instance was disowned.") to value_error (which changes RuntimeError to ValueError). (#2880)

* Enabling use of smart_holder for types with non-public destructors.

* Resolving clang-tidy error (GitHub CI).