* Download catch for MinGw

* Fix rest of MinGW

* fix: update catch to 2.13.5 to fix glibc 2.34 failures

Update the downloaded Catch version to 2.13.5, in order to fix build
failure on glibc 2.34:

```
In file included from /usr/include/signal.h:328,
                 from /tmp/pybind11/.nox/tests-3-9/tmp/tests/catch/catch.hpp:8030,
                 from /tmp/pybind11/tests/test_embed/catch.cpp:13:
/tmp/pybind11/.nox/tests-3-9/tmp/tests/catch/catch.hpp:10818:58: error: call to non-‘constexpr’ function ‘long int sysconf(int)’
10818 |     static constexpr std::size_t sigStackSize = 32768 >= MINSIGSTKSZ ? 32768 : MINSIGSTKSZ;
      |                                                          ^~~~~~~~~~~
In file included from /usr/include/python3.9/Python.h:36,
                 from /tmp/pybind11/include/pybind11/detail/common.h:215,
                 from /tmp/pybind11/include/pybind11/pytypes.h:12,
                 from /tmp/pybind11/include/pybind11/cast.h:13,
                 from /tmp/pybind11/include/pybind11/attr.h:13,
                 from /tmp/pybind11/include/pybind11/pybind11.h:13,
                 from /tmp/pybind11/include/pybind11/embed.h:12,
                 from /tmp/pybind11/tests/test_embed/catch.cpp:4:
/usr/include/unistd.h:640:17: note: ‘long int sysconf(int)’ declared here
  640 | extern long int sysconf (int __name) __THROW;
      |                 ^~~~~~~
In file included from /tmp/pybind11/tests/test_embed/catch.cpp:13:
/tmp/pybind11/.nox/tests-3-9/tmp/tests/catch/catch.hpp:10877:45: error: size of array ‘altStackMem’ is not an integral constant-expression
10877 |     char FatalConditionHandler::altStackMem[sigStackSize] = {};
      |                                             ^~~~~~~~~~~~
```

The newest Catch version cannot be used yet because of regression:
catchorg/Catch2#2364

* fix: add option for _ check, only define on pybind11

* Revert "fix: add option for _ check, only define on pybind11"

This reverts commit 86817db.

* fix: only undef _ for catch cpp creation.

Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>

* chore: minor odd py version cleanup

* Update include/pybind11/pybind11.h

* fix: always make __index__ available

…d-statements.

Informed by experiments under PR pybind#3698.

clang-tidy automatic changes. NO manual changes.

Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>

* Adding readability-qualified-auto to .clang-tidy

Ported from @henryiii's pybind@287527f

* fix: support Python < 3.6

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

…g-tidy. (pybind#3705)

…nd#3709)

* Enable static downcast check

* Add inconsistent declaration naming check

…d optin.performance.Padding (pybind#3716)

* Add clang-tidy prefer-member-initializer

* Fix clang-tdy config

* Fix incorrect change

* Fix sorting of .clang-tidy

…bind#3712)

* Manual line breaks to pre-empt undesired `clang-format`ing.

Informed by work under pybind#3683:

pybind@60b7eb4

pybind@59572e6

* Manual curation of clang-format diffs involving source code comments.

Very labor-intensive and dull.

* Pulling .clang-format change from @henryiii's pybind@9057962

* Adding commonly used .clang-format `CommentPragmas:`

* Ensure short lambdas are allowed

Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>

* chore: add clang-format

* Removing check-style (Classic check-style)

Ported from @henryiii's pybind@53056b1

* Automatic clang-format changes (NO manual changes).

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

…pybind#3688)

* `#error BYE_BYE_GOLDEN_SNAKE`

* Removing everything related to 2.7 from ci.yml

* Commenting-out Centos7

* Removing `PYTHON: 27` from .appveyor.yml

* "PY2" removal, mainly from tests. C++ code is not touched.

* Systematic removal of `u` prefix from `u"..."` and `u'...'` literals. Collateral cleanup of a couple minor other things.

* Cleaning up around case-insensitive hits for `[^a-z]py.*2` in tests/.

* Removing obsolete Python 2 mention in compiling.rst

* Proper `#error` for Python 2.

* Using PY_VERSION_HEX to guard `#error "PYTHON 2 IS NO LONGER SUPPORTED.`

* chore: bump pre-commit

* style: run pre-commit for pyupgrade 3+

* tests: use sys.version_info, not PY

* chore: more Python 2 removal

* Uncommenting Centos7 block (PR pybind#3691 showed that it is working again).

* Update pre-commit hooks

* Fix pre-commit hook

* refactor: remove Python 2 from CMake

* refactor: remove Python 2 from setup code

* refactor: simplify, better static typing

* feat: fail with nice messages

* refactor: drop Python 2 C++ code

* docs: cleanup for Python 3

* revert: intree

revert: intree

* docs: minor touchup to py2 statement

Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>

* chore: drop Python 3.5 support

* chore: more fstrings with flynt's help

* ci: drop Python 3.5

* chore: bump dependency versions

* docs: touch up py::args

* tests: remove deprecation warning

* Ban smartquotes

* Very minor tweaks (by-product of reviewing PR pybind#3719).

Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>
Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>

* Trying another way of adding windows-2022 C++20

* ci: try merging 2019 & 2022

* Revert "ci: try merging 2019 & 2022"

This reverts commit b158a1b.

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

* Changing `_MSC_VER` guard to `< 1910` (dropping MSVC 2015).

* Removing MSVC 2015 from ci.yml, and .appveyor.yml entirely.

* Bringing back .appveyor.yml from master.

* appveyor Visual Studio 2017

* 1st manual pass, builds & tests with unix_clang, before pre-commit.

* After clang-format (via pre-commit).

* Manual pass looking for "2015", builds & tests with unix_clang, before pre-commit.

* Backtracking for include/pybind11 changes in previous commit.

git checkout d078658 include/pybind11/attr.h include/pybind11/detail/common.h include/pybind11/functional.h

--------------------

CI pybind#4160 errors observed:

pybind@2a26873
https://github.com/pybind/pybind11/runs/5168332130?check_suite_focus=true

$ grep ' error C' *.txt | sed 's/2022-02-12[^ ]*//' | sed 's/^[0-9][0-9]*//' | sed 's/^.*\.txt: //' | sort | uniqD:\a\pybind11\pybind11\include\pybind11\cast.h(1364,1): error C2752: 'pybind11::detail::type_caster<Eigen::Ref<Eigen::Vector3f,0,pybind11::EigenDStride>,void>': more than one partial specialization matches the template argument list [D:\a\pybind11\pybind11\build\tests\pybind11_tests.vcxproj]

d:\a\pybind11\pybind11\include\pybind11\detail/common.h(1023): error C2737: 'pybind11::overload_cast': 'constexpr' object must be initialized [D:\a\pybind11\pybind11\build\tests\cross_module_gil_utils.vcxproj]
d:\a\pybind11\pybind11\include\pybind11\detail/common.h(1023): error C2737: 'pybind11::overload_cast': 'constexpr' object must be initialized [D:\a\pybind11\pybind11\build\tests\pybind11_cross_module_tests.vcxproj]
d:\a\pybind11\pybind11\include\pybind11\detail/common.h(1023): error C2737: 'pybind11::overload_cast': 'constexpr' object must be initialized [D:\a\pybind11\pybind11\build\tests\pybind11_tests.vcxproj]
d:\a\pybind11\pybind11\include\pybind11\detail/common.h(1023): error C2737: 'pybind11::overload_cast': 'constexpr' object must be initialized [D:\a\pybind11\pybind11\build\tests\test_embed\external_module.vcxproj]
D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\build\tests\pybind11_tests.vcxproj]
D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\tests\pybind11_tests.vcxproj]

$ grep ': error C2737' *.txt | sed 's/^.*MSVC//' | sed 's/___.*//' | sort | uniq

_2017

$ grep ': error C2752' *.txt

3______3.8_____MSVC_2019_____x86_-DCMAKE_CXX_STANDARD=17.txt:2022-02-12T16:12:45.9921122Z D:\a\pybind11\pybind11\include\pybind11\cast.h(1364,1): error C2752: 'pybind11::detail::type_caster<Eigen::Ref<Eigen::Vector3f,0,pybind11::EigenDStride>,void>': more than one partial specialization matches the template argument list [D:\a\pybind11\pybind11\build\tests\pybind11_tests.vcxproj]

$ grep ': fatal error C1001:' *.txt

10______pypy-3.8-v7.3.7_____windows-2022_____x64.txt:2022-02-12T16:12:56.3163683Z D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\tests\pybind11_tests.vcxproj]
1______3.6_____MSVC_2019_____x86.txt:2022-02-12T16:12:47.6774625Z D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\build\tests\pybind11_tests.vcxproj]
16______3.6_____windows-latest_____x64_-DPYBIND11_FINDPYTHON=ON.txt:2022-02-12T16:12:27.0556151Z D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\tests\pybind11_tests.vcxproj]
17______3.9_____windows-2019_____x64.txt:2022-02-12T16:12:30.3822566Z D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\tests\pybind11_tests.vcxproj]
2______3.7_____MSVC_2019_____x86.txt:2022-02-12T16:12:38.7018911Z D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\build\tests\pybind11_tests.vcxproj]
6______3.6_____windows-2022_____x64.txt:2022-02-12T16:12:00.4513642Z D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\tests\pybind11_tests.vcxproj]
7______3.9_____windows-2022_____x64.txt:2022-02-12T16:11:43.6306160Z D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\tests\pybind11_tests.vcxproj]
8______3.10_____windows-2022_____x64.txt:2022-02-12T16:11:49.9589644Z D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\tests\pybind11_tests.vcxproj]
9______pypy-3.7-v7.3.7_____windows-2022_____x64.txt:2022-02-12T16:11:53.7912112Z D:\a\pybind11\pybind11\include\pybind11\detail/common.h(624): fatal error C1001: Internal compiler error. [D:\a\pybind11\pybind11\tests\pybind11_tests.vcxproj]

* common.h: is_template_base_of

* Re-applying 4 changes from 2a26873 that work universally.

* `overload_cast = {};` only for MSVC 2017 and Clang 5

* Refining condition for using is_template_base_of workaround.

* Undoing MSVC 2015 workaround in test_constants_and_functions.cpp

* CentOS7: silence_unused_warnings

* Tweaks in response to reviews.

* Adding windows-2022 C++20

* Trying another way of adding windows-2022 C++20

First pass manually resolving the many merge conflicts.

Mostly automatic, except for mypy type annotations in ubench/*.py

Only 1 manual line break. All other changes are automatically generated.