* Adding ci_sh_def.yml, based on PR #2930.

* Adding exludes for .patch files.

* Bug fix: adding back `!is_alias<Class>(ptr)` that were accidentally omitted.

* Introducing PYBIND11_SH_AVL, PYBIND11_SH_DEF macros. Applying PYBIND11_SH_DEF to test_factory_constructors.py to complete test coverage.

* Using PYBIND11_SH_DEF in test_methods_and_attributes.cpp, for more complete test coverage.

* Using PYBIND11_SH_DEF in test_multiple_inheritance.cpp, for more complete test coverage.

* Cleaning up test_classh_mock.cpp.

* Better explanations for PYBIND11_SH_AVL, PYBIND11_SH_DEF.

* Disabling 3.10-dev builds.

When the user defines _GLIBCXX_USE_CXX11_ABI=0 to force the pre-c++11 ABI, numpy.h assumes that is_trivially_copyable is available.
It is not necessarily the case. This patch uses clang's feature detection instead.
The workaround is for certain libstdc++ versions, so the test should target these particular versions.

* Connecting PYBIND11_INTERNALS_VERSION to PYBIND11_USE_SMART_HOLDER_AS_DEFAULT.

* Adding section: Classic / Conservative / Progressive cross-module compatibility

Revert "Adding documentation with associated test: Using py::classh but with fallback to classic pybind11"

This reverts commit 49f8f60e.

The direct commit was accidental. I meant to create a PR.

* correcting Werror for Intel

* adding ward for Intel

* adding wards for intel

* another ward for Intel

* missed one intel ward

* exact match for intel compiler

* removing inline limits

* disable warnings about inline limits

* formatter suggestion

* more indent

* hopefully make formatter happy

* addressed review

* fix &&

* Update tests/CMakeLists.txt

Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>

Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>

* Add a failure test for overloaded functions

* Allow function pointer extraction from overloaded functions

* chore: add myself to CODEOWNERS

This will ensure I get notified about pull requests where these files change.

* Update .github/CODEOWNERS

* 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.