Merge branch 'master' into stable

e315e1fe · Henry Schreiner · 71fd5241 · 97976c16 · e315e1fe · e315e1fe
Commit e315e1fe authored Oct 04, 2021 by Henry Schreiner
143 changed files
--- a/.clang-tidy
+++ b/.clang-tidy
 FormatStyle: file
 Checks: '
+*bugprone*,
 cppcoreguidelines-init-variables,
+cppcoreguidelines-slicing,
 clang-analyzer-optin.cplusplus.VirtualCall,
+google-explicit-constructor,
 llvm-namespace-comment,
 misc-misplaced-const,
 misc-non-copyable-objects,
@@ -28,9 +31,10 @@ modernize-use-override,
 modernize-use-using,
 *performance*,
 readability-avoid-const-params-in-decls,
+readability-const-return-type,
 readability-container-size-empty,
-readability-else-after-return,
 readability-delete-null-pointer,
+readability-else-after-return,
 readability-implicit-bool-conversion,
 readability-make-member-function-const,
 readability-misplaced-array-index,
@@ -43,6 +47,9 @@ readability-static-accessed-through-instance,
 readability-static-definition-in-anonymous-namespace,
 readability-string-compare,
 readability-uniqueptr-delete-release,
+-bugprone-exception-escape,
+-bugprone-reserved-identifier,
+-bugprone-unused-raii,
 '
 CheckOptions:

--- a/.github/CONTRIBUTING.md
+++ b/.github/CONTRIBUTING.md
@@ -68,8 +68,8 @@ nox -l
 # Run linters
 nox -s lint
-# Run tests
+# Run tests on Python 3.9
-nox -s tests
+nox -s tests-3.9
 # Build and preview docs
 nox -s docs -- serve

--- a/.github/ISSUE_TEMPLATE/bug-report.md
+++ b/.github/ISSUE_TEMPLATE/bug-report.md
---
-name: Bug Report
-about: File an issue about a bug
-title: "[BUG] "
---
-Make sure you've completed the following steps before submitting your issue -- thank you!
-1. Make sure you've read the [documentation][]. Your issue may be addressed there.
-2. Search the [issue tracker][] to verify that this hasn't already been reported. +1 or comment there if it has.
-3. Consider asking first in the [Gitter chat room][].
-4. Include a self-contained and minimal piece of code that reproduces the problem. If that's not possible, try to make the description as clear as possible.
-    a. If possible, make a PR with a new, failing test to give us a starting point to work on!
-[documentation]: https://pybind11.readthedocs.io
-[issue tracker]: https://github.com/pybind/pybind11/issues
-[Gitter chat room]: https://gitter.im/pybind/Lobby
-*After reading, remove this checklist and the template text in parentheses below.*
-## Issue description
-(Provide a short description, state the expected behavior and what actually happens.)
-## Reproducible example code
-(The code should be minimal, have no external dependencies, isolate the function(s) that cause breakage. Submit matched and complete C++ and Python snippets that can be easily compiled and run to diagnose the issue.)
--- a/.github/ISSUE_TEMPLATE/bug-report.yml
+++ b/.github/ISSUE_TEMPLATE/bug-report.yml
+name: Bug Report
+description: File an issue about a bug
+title: "[BUG]: "
+labels: [triage]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Maintainers will only make a best effort to triage PRs. Please do your best to make the issue as easy to act on as possible, and only open if clearly a problem with pybind11 (ask first if unsure).
+  - type: checkboxes
+    id: steps
+    attributes:
+      label: Required prerequisites
+      description: Make sure you've completed the following steps before submitting your issue -- thank you!
+      options:
+        - label: Make sure you've read the [documentation](https://pybind11.readthedocs.io). Your issue may be addressed there.
+          required: true
+        - label: Search the [issue tracker](https://github.com/pybind/pybind11/issues) and [Discussions](https:/pybind/pybind11/discussions) to verify that this hasn't already been reported. +1 or comment there if it has.
+          required: true
+        - label: Consider asking first in the [Gitter chat room](https://gitter.im/pybind/Lobby) or in a [Discussion](https:/pybind/pybind11/discussions/new).
+          required: false
+  - type: textarea
+    id: description
+    attributes:
+      label: Problem description
+      placeholder: >-
+        Provide a short description, state the expected behavior and what
+        actually happens. Include relevant information like what version of
+        pybind11 you are using, what system you are on, and any useful commands
+        / output.
+    validations:
+      required: true
+  - type: textarea
+    id: code
+    attributes:
+      label: Reproducible example code
+      placeholder: >-
+        The code should be minimal, have no external dependencies, isolate the
+        function(s) that cause breakage. Submit matched and complete C++ and
+        Python snippets that can be easily compiled and run to diagnose the
+        issue. If possible, make a PR with a new, failing test to give us a
+        starting point to work on!
+      render: text
--- a/.github/ISSUE_TEMPLATE/config.yml
+++ b/.github/ISSUE_TEMPLATE/config.yml
 blank_issues_enabled: false
 contact_links:
+  - name: Ask a question
+    url: https://github.com/pybind/pybind11/discussions/new
+    about: Please ask and answer questions here, or propose new ideas.
  - name: Gitter room
    url: https://gitter.im/pybind/Lobby
    about: A room for discussing pybind11 with an active community
--- a/.github/ISSUE_TEMPLATE/feature-request.md
+++ b/.github/ISSUE_TEMPLATE/feature-request.md
---
-name: Feature Request
-about: File an issue about adding a feature
-title: "[FEAT] "
---
-Make sure you've completed the following steps before submitting your issue -- thank you!
-1. Check if your feature has already been mentioned / rejected / planned in other issues.
-2. If those resources didn't help, consider asking in the [Gitter chat room][] to see if this is interesting / useful to a larger audience and possible to implement reasonably,
-4. If you have a useful feature that passes the previous items (or not suitable for chat), please fill in the details below.
-[Gitter chat room]: https://gitter.im/pybind/Lobby
-*After reading, remove this checklist.*
--- a/.github/ISSUE_TEMPLATE/question.md
+++ b/.github/ISSUE_TEMPLATE/question.md
---
-name: Question
-about: File an issue about unexplained behavior
-title: "[QUESTION] "
---
-If you have a question, please check the following first:
-1. Check if your question has already been answered in the [FAQ][] section.
-2. Make sure you've read the [documentation][]. Your issue may be addressed there.
-3. If those resources didn't help and you only have a short question (not a bug report), consider asking in the [Gitter chat room][]
-4. Search the [issue tracker][], including the closed issues, to see if your question has already been asked/answered. +1 or comment if it has been asked but has no answer.
-5. If you have a more complex question which is not answered in the previous items (or not suitable for chat), please fill in the details below.
-6. Include a self-contained and minimal piece of code that illustrates your question. If that's not possible, try to make the description as clear as possible.
-[FAQ]: http://pybind11.readthedocs.io/en/latest/faq.html
-[documentation]: https://pybind11.readthedocs.io
-[issue tracker]: https://github.com/pybind/pybind11/issues
-[Gitter chat room]: https://gitter.im/pybind/Lobby
-*After reading, remove this checklist.*
--- a/.github/pull_request_template.md
+++ b/.github/pull_request_template.md
+<!--
+Title (above): please place [branch_name] at the beginning if you are targeting a branch other than master. *Do not target stable*.
+It is recommended to use conventional commit format, see conventionalcommits.org, but not required.
+-->
 ## Description
 <!-- Include relevant issues or PRs here, describe what changed and why -->

--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -75,7 +75,7 @@ jobs:
      run: brew install boost
    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.9
+      uses: jwlawson/actions-setup-cmake@v1.11
    - name: Cache wheels
      if: runner.os == 'macOS'
@@ -144,6 +144,24 @@ jobs:
      if: "!(runner.os == 'Windows' && (matrix.python == 3.8 || matrix.python == 3.9 || matrix.python == '3.10-dev'))"
      run: cmake --build build2 --target cpptest
+    # Third build - C++17 mode with unstable ABI
+    - name: Configure (unstable ABI)
+      run: >
+        cmake -S . -B build3
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DDOWNLOAD_EIGEN=ON
+        -DCMAKE_CXX_STANDARD=17
+        -DPYBIND11_INTERNALS_VERSION=10000000
+        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
+        ${{ matrix.args }}
+    - name: Build (unstable ABI)
+      run: cmake --build build3 -j 2
+    - name: Python tests (unstable ABI)
+      run: cmake --build build3 --target pytest
    - name: Interface test
      run: cmake --build build2 --target test_cmake_build
@@ -193,7 +211,7 @@ jobs:
        debug: ${{ matrix.python-debug }}
    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.9
+      uses: jwlawson/actions-setup-cmake@v1.11
    - name: Valgrind cache
      if: matrix.valgrind
@@ -445,7 +463,7 @@ jobs:
      run: python3 -m pip install --upgrade pip
    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.9
+      uses: jwlawson/actions-setup-cmake@v1.11
    - name: Configure
      shell: bash
@@ -594,14 +612,15 @@ jobs:
    - name: VAR_BUILD_TYPE 7
      if: matrix.centos == 7
-      run: echo Release > VAR_BUILD_TYPE
+      run: echo MinSizeRel > VAR_BUILD_TYPE
-    # Using Debug to avoid segfault that appeared around 2021-06-04,
+    # Using Release to avoid segfault that appeared around 2021-06-04,
    # apparently when the gcc version changed from 8.3 to 8.4.
    - name: VAR_BUILD_TYPE 8
      if: matrix.centos == 8
-      run: echo Debug > VAR_BUILD_TYPE
+      run: echo Release > VAR_BUILD_TYPE
+    # Temporally disabling EIGEN due to SSL issue in CentOS 7
    - name: Configure
      shell: bash
      run: >
@@ -664,7 +683,7 @@ jobs:
        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
      working-directory: /build-tests
-    - name: Run tests
+    - name: Python tests
      run: make pytest -j 2
      working-directory: /build-tests
@@ -738,7 +757,7 @@ jobs:
        architecture: x86
    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.9
+      uses: jwlawson/actions-setup-cmake@v1.11
    - name: Prepare MSVC
      uses: ilammy/msvc-dev-cmd@v1.9.0
@@ -760,7 +779,7 @@ jobs:
    - name: Build C++11
      run: cmake --build build -j 2
-    - name: Run tests
+    - name: Python tests
      run: cmake --build build -t pytest
  win32-msvc2015:
@@ -784,7 +803,7 @@ jobs:
        python-version: ${{ matrix.python }}
    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.9
+      uses: jwlawson/actions-setup-cmake@v1.11
    - name: Prepare MSVC
      uses: ilammy/msvc-dev-cmd@v1.9.0
@@ -838,7 +857,7 @@ jobs:
        python-version: ${{ matrix.python }}
    - name: Update CMake
-      uses: jwlawson/actions-setup-cmake@v1.9
+      uses: jwlawson/actions-setup-cmake@v1.11
    - name: Prepare env
      run: python -m pip install -r tests/requirements.txt --prefer-binary
@@ -861,32 +880,85 @@ jobs:
      run: cmake --build build -t check
  mingw:
+    name: "🐍 3 • windows-latest • ${{ matrix.sys }}"
    runs-on: windows-latest
    defaults:
      run:
        shell: msys2 {0}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - { sys: mingw64, env: x86_64 }
+          - { sys: mingw32, env: i686 }
    steps:
    - uses: msys2/setup-msys2@v2
      with:
+        msystem: ${{matrix.sys}}
        install: >-
-          mingw-w64-x86_64-gcc
+          git
-          mingw-w64-x86_64-python-pip
+          mingw-w64-${{matrix.env}}-gcc
-          mingw-w64-x86_64-cmake
+          mingw-w64-${{matrix.env}}-python-pip
-          mingw-w64-x86_64-make
+          mingw-w64-${{matrix.env}}-python-numpy
-          mingw-w64-x86_64-python-pytest
+          mingw-w64-${{matrix.env}}-python-scipy
-          mingw-w64-x86_64-eigen3
+          mingw-w64-${{matrix.env}}-cmake
-          mingw-w64-x86_64-boost
+          mingw-w64-${{matrix.env}}-make
-          mingw-w64-x86_64-catch
+          mingw-w64-${{matrix.env}}-python-pytest
+          mingw-w64-${{matrix.env}}-eigen3
+          mingw-w64-${{matrix.env}}-boost
+          mingw-w64-${{matrix.env}}-catch
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
-    - name: Configure
+    - name: Configure C++11
      # LTO leads to many undefined reference like
      # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
-      run: cmake -G "MinGW Makefiles" -S . -B build
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -S . -B build
-    - name: Build
+    - name: Build C++11
      run: cmake --build build -j 2
-    - name: Python tests
+    - name: Python tests C++11
-      run: cmake --build build --target pytest
+      run: cmake --build build --target pytest -j 2
+    - name: C++11 tests
+      run: cmake --build build --target cpptest -j 2
+    - name: Interface test C++11
+      run: cmake --build build --target test_cmake_build
+    - name: Clean directory
+      run: git clean -fdx
+    - name: Configure C++14
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -S . -B build2
+    - name: Build C++14
+      run: cmake --build build2 -j 2
+    - name: Python tests C++14
+      run: cmake --build build2 --target pytest -j 2
+    - name: C++14 tests
+      run: cmake --build build2 --target cpptest -j 2
+    - name: Interface test C++14
+      run: cmake --build build2 --target test_cmake_build
+    - name: Clean directory
+      run: git clean -fdx
+    - name: Configure C++17
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -S . -B build3
+    - name: Build C++17
+      run: cmake --build build3 -j 2
+    - name: Python tests C++17
+      run: cmake --build build3 --target pytest -j 2
+    - name: C++17 tests
+      run: cmake --build build3 --target cpptest -j 2
+    - name: Interface test C++17
+      run: cmake --build build3 --target test_cmake_build
--- a/.github/workflows/configure.yml
+++ b/.github/workflows/configure.yml
@@ -18,7 +18,7 @@ jobs:
      matrix:
        runs-on: [ubuntu-latest, macos-latest, windows-latest]
        arch: [x64]
-        cmake: [3.18]
+        cmake: ["3.21"]
        include:
        - runs-on: ubuntu-latest
@@ -55,7 +55,7 @@ jobs:
    # An action for adding a specific version of CMake:
    #   https://github.com/jwlawson/actions-setup-cmake
    - name: Setup CMake ${{ matrix.cmake }}
-      uses: jwlawson/actions-setup-cmake@v1.9
+      uses: jwlawson/actions-setup-cmake@v1.11
      with:
        cmake-version: ${{ matrix.cmake }}

--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -19,8 +19,10 @@ repos:
  hooks:
  - id: check-added-large-files
  - id: check-case-conflict
+  - id: check-docstring-first
  - id: check-merge-conflict
  - id: check-symlinks
+  - id: check-toml
  - id: check-yaml
  - id: debug-statements
  - id: end-of-file-fixer
@@ -31,18 +33,27 @@ repos:
    exclude: ^noxfile.py$
 - repo: https://github.com/asottile/pyupgrade
-  rev: v2.23.1
+  rev: v2.29.0
  hooks:
  - id: pyupgrade
+- repo: https://github.com/PyCQA/isort
+  rev: 5.9.3
+  hooks:
+  - id: isort
 # Black, the code formatter, natively supports pre-commit
 - repo: https://github.com/psf/black
-  rev: 21.7b0
+  rev: 21.9b0 # Keep in sync with blacken-docs
  hooks:
  - id: black
-    # By default, this ignores pyi files, though black supports them
-    types: [text]
+- repo: https://github.com/asottile/blacken-docs
-    files: \.pyi?$
+  rev: v1.11.0
+  hooks:
+  - id: blacken-docs
+    additional_dependencies:
+    - black==21.9b0 # keep in sync with black hook
 # Changes tabs to spaces
 - repo: https://github.com/Lucas-C/pre-commit-hooks
@@ -50,6 +61,12 @@ repos:
  hooks:
  - id: remove-tabs
+# Autoremoves unused imports
+- repo: https://github.com/hadialqattan/pycln
+  rev: v1.0.3
+  hooks:
+  - id: pycln
 # Flake8 also supports pre-commit natively (same author)
 - repo: https://github.com/PyCQA/flake8
  rev: 3.9.2
@@ -81,7 +98,7 @@ repos:
 # Checks the manifest for missing files (native support)
 - repo: https://github.com/mgedmin/check-manifest
-  rev: "0.46"
+  rev: "0.47"
  hooks:
  - id: check-manifest
    # This is a slow hook, so only run this if --hook-stage manual is passed
@@ -95,10 +112,10 @@ repos:
    exclude: ".supp$"
    args: ["-L", "nd,ot,thist"]
-   repo: https://github.com/shellcheck-py/shellcheck-py
+- repo: https://github.com/shellcheck-py/shellcheck-py
-    rev: v0.7.2.1
+  rev: v0.7.2.1
-    hooks:
+  hooks:
-    -   id: shellcheck
+  - id: shellcheck
 # The original pybind11 checks for a few C++ style items
 - repo: local

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,13 +7,13 @@
 cmake_minimum_required(VERSION 3.4)
-# The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
+# The `cmake_minimum_required(VERSION 3.4...3.21)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.21)
  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.21)
 endif()
 # Extract project version from source
@@ -89,6 +89,9 @@ endif()
 option(PYBIND11_INSTALL "Install pybind11 header files?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_TEST "Build pybind11 test suite?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_NOPYTHON "Disable search for Python" OFF)
+set(PYBIND11_INTERNALS_VERSION
+    ""
+    CACHE STRING "Override the ABI version, may be used to enable the unstable ABI.")
 cmake_dependent_option(
  USE_PYTHON_INCLUDE_DIR
@@ -183,6 +186,10 @@ if(NOT TARGET pybind11_headers)
  target_compile_features(pybind11_headers INTERFACE cxx_inheriting_constructors cxx_user_literals
                                                     cxx_right_angle_brackets)
+  if(NOT "${PYBIND11_INTERNALS_VERSION}" STREQUAL "")
+    target_compile_definitions(
+      pybind11_headers INTERFACE "PYBIND11_INTERNALS_VERSION=${PYBIND11_INTERNALS_VERSION}")
+  endif()
 else()
  # It is invalid to install a target twice, too.
  set(PYBIND11_INSTALL OFF)

--- a/README.rst
+++ b/README.rst
@@ -3,7 +3,7 @@
 **pybind11 — Seamless operability between C++11 and Python**
-|Latest Documentation Status| |Stable Documentation Status| |Gitter chat| |CI| |Build status|
+|Latest Documentation Status| |Stable Documentation Status| |Gitter chat| |GitHub Discussions| |CI| |Build status|
 |Repology| |PyPI package| |Conda-forge| |Python Versions|
@@ -134,9 +134,9 @@ About
 This project was created by `Wenzel
 Jakob <http://rgl.epfl.ch/people/wjakob>`_. Significant features and/or
 improvements to the code were contributed by Jonas Adler, Lori A. Burns,
-Sylvain Corlay, Eric Cousineau, Ralf Grosse-Kunstleve, Trent Houliston, Axel
+Sylvain Corlay, Eric Cousineau, Aaron Gokaslan, Ralf Grosse-Kunstleve, Trent Houliston, Axel
 Huebl, @hulucc, Yannick Jadoul, Sergey Lyskov Johan Mabille, Tomasz Miąsko,
-Dean Moldovan, Ben Pritchard, Jason Rhinelander, Boris Schäling,  Pim
+Dean Moldovan, Ben Pritchard, Jason Rhinelander, Boris Schäling, Pim
 Schellart, Henry Schreiner, Ivan Smirnov, Boris Staletic, and Patrick Stewart.
 We thank Google for a generous financial contribution to the continuous
@@ -176,3 +176,5 @@ to the terms and conditions of this license.
   :target: https://repology.org/project/python:pybind11/versions
 .. |Python Versions| image:: https://img.shields.io/pypi/pyversions/pybind11.svg
   :target: https://pypi.org/project/pybind11/
+.. |GitHub Discussions| image:: https://img.shields.io/static/v1?label=Discussions&message=Ask&color=blue&logo=github
+   :target: https://github.com/pybind/pybind11/discussions
--- a/docs/advanced/cast/custom.rst
+++ b/docs/advanced/cast/custom.rst
@@ -26,7 +26,9 @@ The following Python snippet demonstrates the intended usage from the Python sid
        def __int__(self):
            return 123
    from example import print
    print(A())
 To register the necessary conversion routines, it is necessary to add an

--- a/docs/advanced/cast/eigen.rst
+++ b/docs/advanced/cast/eigen.rst
@@ -112,7 +112,7 @@ example:
 .. code-block:: python
    a = MyClass()
-    m = a.get_matrix()   # flags.writeable = True,  flags.owndata = False
+    m = a.get_matrix()  # flags.writeable = True,  flags.owndata = False
    v = a.view_matrix()  # flags.writeable = False, flags.owndata = False
    c = a.copy_matrix()  # flags.writeable = True,  flags.owndata = True
    # m[5,6] and v[5,6] refer to the same element, c[5,6] does not.
@@ -203,7 +203,7 @@ adding the ``order='F'`` option when creating an array:
 .. code-block:: python
-    myarray = np.array(source, order='F')
+    myarray = np.array(source, order="F")
 Such an object will be passable to a bound function accepting an
 ``Eigen::Ref<MatrixXd>`` (or similar column-major Eigen type).

--- a/docs/advanced/cast/strings.rst
+++ b/docs/advanced/cast/strings.rst
@@ -36,13 +36,13 @@ everywhere <http://utf8everywhere.org/>`_.
        }
    );
-.. code-block:: python
+.. code-block:: pycon
-    >>> utf8_test('🎂')
+    >>> utf8_test("🎂")
    utf-8 is icing on the cake.
    🎂
-    >>> utf8_charptr('🍕')
+    >>> utf8_charptr("🍕")
    My favorite food is
    🍕
@@ -80,7 +80,7 @@ raise a ``UnicodeDecodeError``.
        }
    );
-.. code-block:: python
+.. code-block:: pycon
    >>> isinstance(example.std_string_return(), str)
    True
@@ -114,7 +114,7 @@ conversion has the same overhead as implicit conversion.
        }
    );
-.. code-block:: python
+.. code-block:: pycon
    >>> str_output()
    'Send your résumé to Alice in HR'
@@ -143,7 +143,7 @@ returned to Python as ``bytes``, then one can return the data as a
        }
    );
-.. code-block:: python
+.. code-block:: pycon
    >>> example.return_bytes()
    b'\xba\xd0\xba\xd0'
@@ -160,7 +160,7 @@ encoding, but cannot convert ``std::string`` back to ``bytes`` implicitly.
        }
    );
-.. code-block:: python
+.. code-block:: pycon
    >>> isinstance(example.asymmetry(b"have some bytes"), str)
    True
@@ -229,16 +229,16 @@ character.
    m.def("pass_char", [](char c) { return c; });
    m.def("pass_wchar", [](wchar_t w) { return w; });
-.. code-block:: python
+.. code-block:: pycon
-    >>> example.pass_char('A')
+    >>> example.pass_char("A")
    'A'
 While C++ will cast integers to character types (``char c = 0x65;``), pybind11
 does not convert Python integers to characters implicitly. The Python function
 ``chr()`` can be used to convert integers to characters.
-.. code-block:: python
+.. code-block:: pycon
    >>> example.pass_char(0x65)
    TypeError
@@ -259,17 +259,17 @@ a combining acute accent). The combining character will be lost if the
 two-character sequence is passed as an argument, even though it renders as a
 single grapheme.
-.. code-block:: python
+.. code-block:: pycon
-    >>> example.pass_wchar('é')
+    >>> example.pass_wchar("é")
    'é'
-    >>> combining_e_acute = 'e' + '\u0301'
+    >>> combining_e_acute = "e" + "\u0301"
    >>> combining_e_acute
    'é'
-    >>> combining_e_acute == 'é'
+    >>> combining_e_acute == "é"
    False
    >>> example.pass_wchar(combining_e_acute)
@@ -278,9 +278,9 @@ single grapheme.
 Normalizing combining characters before passing the character literal to C++
 may resolve *some* of these issues:
-.. code-block:: python
+.. code-block:: pycon
-    >>> example.pass_wchar(unicodedata.normalize('NFC', combining_e_acute))
+    >>> example.pass_wchar(unicodedata.normalize("NFC", combining_e_acute))
    'é'
 In some languages (Thai for example), there are `graphemes that cannot be

--- a/docs/advanced/classes.rst
+++ b/docs/advanced/classes.rst
@@ -136,7 +136,7 @@ a virtual method call.
    u'woof! woof! woof! '
    >>> class Cat(Animal):
    ...     def go(self, n_times):
-    ...             return "meow! " * n_times
+    ...         return "meow! " * n_times
    ...
    >>> c = Cat()
    >>> call_go(c)
@@ -159,8 +159,9 @@ Here is an example:
    class Dachshund(Dog):
        def __init__(self, name):
-            Dog.__init__(self) # Without this, a TypeError is raised.
+            Dog.__init__(self)  # Without this, a TypeError is raised.
            self.name = name
        def bark(self):
            return "yap!"
@@ -1153,6 +1154,7 @@ error:
    >>> class PyFinalChild(IsFinal):
    ...     pass
+    ...
    TypeError: type 'IsFinal' is not an acceptable base type
 .. note:: This attribute is currently ignored on PyPy
@@ -1247,7 +1249,7 @@ Accessing the type object
 You can get the type object from a C++ class that has already been registered using:
-.. code-block:: python
+.. code-block:: cpp
    py::type T_py = py::type::of<T>();
@@ -1259,3 +1261,37 @@ object, just like ``type(ob)`` in Python.
    Other types, like ``py::type::of<int>()``, do not work, see :ref:`type-conversions`.
 .. versionadded:: 2.6
+Custom type setup
+=================
+For advanced use cases, such as enabling garbage collection support, you may
+wish to directly manipulate the `PyHeapTypeObject` corresponding to a
+``py::class_`` definition.
+You can do that using ``py::custom_type_setup``:
+.. code-block:: cpp
+   struct OwnsPythonObjects {
+       py::object value = py::none();
+   };
+   py::class_<OwnsPythonObjects> cls(
+       m, "OwnsPythonObjects", py::custom_type_setup([](PyHeapTypeObject *heap_type) {
+           auto *type = &heap_type->ht_type;
+           type->tp_flags |= Py_TPFLAGS_HAVE_GC;
+           type->tp_traverse = [](PyObject *self_base, visitproc visit, void *arg) {
+               auto &self = py::cast<OwnsPythonObjects&>(py::handle(self_base));
+               Py_VISIT(self.value.ptr());
+               return 0;
+           };
+           type->tp_clear = [](PyObject *self_base) {
+               auto &self = py::cast<OwnsPythonObjects&>(py::handle(self_base));
+               self.value = py::none();
+               return 0;
+           };
+       }));
+   cls.def(py::init<>());
+   cls.def_readwrite("value", &OwnsPythonObjects::value);
+.. versionadded:: 2.8
--- a/docs/advanced/embedding.rst
+++ b/docs/advanced/embedding.rst
@@ -122,6 +122,7 @@ embedding the interpreter. This makes it easy to import local Python files:
    """calc.py located in the working directory"""
    def add(i, j):
        return i + j

--- a/docs/advanced/exceptions.rst
+++ b/docs/advanced/exceptions.rst
@@ -75,9 +75,10 @@ Registering custom translators
 If the default exception conversion policy described above is insufficient,
 pybind11 also provides support for registering custom exception translators.
-To register a simple exception conversion that translates a C++ exception into
+Similar to pybind11 classes, exception translators can be local to the module
-a new Python exception using the C++ exception's ``what()`` method, a helper
+they are defined in or global to the entire python session.  To register a simple
-function is available:
+exception conversion that translates a C++ exception into a new Python exception
+using the C++ exception's ``what()`` method, a helper function is available:
 .. code-block:: cpp
@@ -87,12 +88,20 @@ This call creates a Python exception class with the name ``PyExp`` in the given
 module and automatically converts any encountered exceptions of type ``CppExp``
 into Python exceptions of type ``PyExp``.
+A matching function is available for registering a local exception translator:
+.. code-block:: cpp
+    py::register_local_exception<CppExp>(module, "PyExp");
 It is possible to specify base class for the exception using the third
 parameter, a `handle`:
 .. code-block:: cpp
    py::register_exception<CppExp>(module, "PyExp", PyExc_RuntimeError);
+    py::register_local_exception<CppExp>(module, "PyExp", PyExc_RuntimeError);
 Then `PyExp` can be caught both as `PyExp` and `RuntimeError`.
@@ -100,16 +109,18 @@ The class objects of the built-in Python exceptions are listed in the Python
 documentation on `Standard Exceptions <https://docs.python.org/3/c-api/exceptions.html#standard-exceptions>`_.
 The default base class is `PyExc_Exception`.
-When more advanced exception translation is needed, the function
+When more advanced exception translation is needed, the functions
-``py::register_exception_translator(translator)`` can be used to register
+``py::register_exception_translator(translator)`` and
+``py::register_local_exception_translator(translator)`` can be used to register
 functions that can translate arbitrary exception types (and which may include
-additional logic to do so).  The function takes a stateless callable (e.g.  a
+additional logic to do so).  The functions takes a stateless callable (e.g. a
 function pointer or a lambda function without captured variables) with the call
 signature ``void(std::exception_ptr)``.
 When a C++ exception is thrown, the registered exception translators are tried
 in reverse order of registration (i.e. the last registered translator gets the
-first shot at handling the exception).
+first shot at handling the exception). All local translators will be tried
+before a global translator is tried.
 Inside the translator, ``std::rethrow_exception`` should be used within
 a try block to re-throw the exception.  One or more catch clauses to catch
@@ -168,6 +179,53 @@ section.
    with ``-fvisibility=hidden``. Therefore exceptions that are used across ABI boundaries need to be explicitly exported, as exercised in ``tests/test_exceptions.h``.
    See also: "Problems with C++ exceptions" under `GCC Wiki <https://gcc.gnu.org/wiki/Visibility>`_.
+Local vs Global Exception Translators
+=====================================
+When a global exception translator is registered, it will be applied across all
+modules in the reverse order of registration. This can create behavior where the
+order of module import influences how exceptions are translated.
+If module1 has the following translator:
+.. code-block:: cpp
+      py::register_exception_translator([](std::exception_ptr p) {
+        try {
+            if (p) std::rethrow_exception(p);
+        } catch (const std::invalid_argument &e) {
+            PyErr_SetString("module1 handled this")
+        }
+      }
+and module2 has the following similar translator:
+.. code-block:: cpp
+      py::register_exception_translator([](std::exception_ptr p) {
+        try {
+            if (p) std::rethrow_exception(p);
+        } catch (const std::invalid_argument &e) {
+            PyErr_SetString("module2 handled this")
+        }
+      }
+then which translator handles the invalid_argument will be determined by the
+order that module1 and module2 are imported. Since exception translators are
+applied in the reverse order of registration, which ever module was imported
+last will "win" and that translator will be applied.
+If there are multiple pybind11 modules that share exception types (either
+standard built-in or custom) loaded into a single python instance and
+consistent error handling behavior is needed, then local translators should be
+used.
+Changing the previous example to use ``register_local_exception_translator``
+would mean that when invalid_argument is thrown in the module2 code, the
+module2 translator will always handle it, while in module1, the module1
+translator will do the same.
 .. _handling_python_exceptions_cpp:
 Handling exceptions from Python in C++
@@ -265,6 +323,34 @@ Alternately, to ignore the error, call `PyErr_Clear
 Any Python error must be thrown or cleared, or Python/pybind11 will be left in
 an invalid state.
+Chaining exceptions ('raise from')
+==================================
+In Python 3.3 a mechanism for indicating that exceptions were caused by other
+exceptions was introduced:
+.. code-block:: py
+    try:
+        print(1 / 0)
+    except Exception as exc:
+        raise RuntimeError("could not divide by zero") from exc
+To do a similar thing in pybind11, you can use the ``py::raise_from`` function. It
+sets the current python error indicator, so to continue propagating the exception
+you should ``throw py::error_already_set()`` (Python 3 only).
+.. code-block:: cpp
+    try {
+        py::eval("print(1 / 0"));
+    } catch (py::error_already_set &e) {
+        py::raise_from(e, PyExc_RuntimeError, "could not divide by zero");
+        throw py::error_already_set();
+    }
+.. versionadded:: 2.8
 .. _unraisable_exceptions:
 Handling unraisable exceptions

--- a/docs/advanced/functions.rst
+++ b/docs/advanced/functions.rst
@@ -272,7 +272,7 @@ And used in Python as usual:
 .. code-block:: pycon
-    >>> print_dict({'foo': 123, 'bar': 'hello'})
+    >>> print_dict({"foo": 123, "bar": "hello"})
    key=foo, value=123
    key=bar, value=hello
@@ -377,10 +377,11 @@ argument in a function definition:
    def f(a, *, b):  # a can be positional or via keyword; b must be via keyword
        pass
    f(a=1, b=2)  # good
    f(b=2, a=1)  # good
-    f(1, b=2)    # good
+    f(1, b=2)  # good
-    f(1, 2)      # TypeError: f() takes 1 positional argument but 2 were given
+    f(1, 2)  # TypeError: f() takes 1 positional argument but 2 were given
 Pybind11 provides a ``py::kw_only`` object that allows you to implement
 the same behaviour by specifying the object between positional and keyword-only

--- a/docs/advanced/pycpp/numpy.rst
+++ b/docs/advanced/pycpp/numpy.rst
@@ -171,6 +171,31 @@ template parameter, and it ensures that non-conforming arguments are converted
 into an array satisfying the specified requirements instead of trying the next
 function overload.
+There are several methods on arrays; the methods listed below under references
+work, as well as the following functions based on the NumPy API:
+- ``.dtype()`` returns the type of the contained values.
+- ``.strides()`` returns a pointer to the strides of the array (optionally pass
+  an integer axis to get a number).
+- ``.flags()`` returns the flag settings. ``.writable()`` and ``.owndata()``
+  are directly available.
+- ``.offset_at()`` returns the offset (optionally pass indices).
+- ``.squeeze()`` returns a view with length-1 axes removed.
+- ``.view(dtype)`` returns a view of the array with a different dtype.
+- ``.reshape({i, j, ...})`` returns a view of the array with a different shape.
+  ``.resize({...})`` is also available.
+- ``.index_at(i, j, ...)`` gets the count from the beginning to a given index.
+There are also several methods for getting references (described below).
 Structured types
 ================
@@ -233,8 +258,8 @@ by the compiler. The result is returned as a NumPy array of type
 .. code-block:: pycon
-    >>> x = np.array([[1, 3],[5, 7]])
+    >>> x = np.array([[1, 3], [5, 7]])
-    >>> y = np.array([[2, 4],[6, 8]])
+    >>> y = np.array([[2, 4], [6, 8]])
    >>> z = 3
    >>> result = vectorized_func(x, y, z)
@@ -345,21 +370,21 @@ The returned proxy object supports some of the same methods as ``py::array`` so
 that it can be used as a drop-in replacement for some existing, index-checked
 uses of ``py::array``:
- ``r.ndim()`` returns the number of dimensions
+- ``.ndim()`` returns the number of dimensions
- ``r.data(1, 2, ...)`` and ``r.mutable_data(1, 2, ...)``` returns a pointer to
+- ``.data(1, 2, ...)`` and ``r.mutable_data(1, 2, ...)``` returns a pointer to
  the ``const T`` or ``T`` data, respectively, at the given indices.  The
  latter is only available to proxies obtained via ``a.mutable_unchecked()``.
- ``itemsize()`` returns the size of an item in bytes, i.e. ``sizeof(T)``.
+- ``.itemsize()`` returns the size of an item in bytes, i.e. ``sizeof(T)``.
- ``ndim()`` returns the number of dimensions.
+- ``.ndim()`` returns the number of dimensions.
- ``shape(n)`` returns the size of dimension ``n``
+- ``.shape(n)`` returns the size of dimension ``n``
- ``size()`` returns the total number of elements (i.e. the product of the shapes).
+- ``.size()`` returns the total number of elements (i.e. the product of the shapes).
- ``nbytes()`` returns the number of bytes used by the referenced elements
+- ``.nbytes()`` returns the number of bytes used by the referenced elements
  (i.e. ``itemsize()`` times ``size()``).
 .. seealso::
@@ -378,7 +403,7 @@ In Python 2, the syntactic sugar ``...`` is not available, but the singleton
 .. code-block:: python
-   a = # a NumPy array
+   a = ...  # a NumPy array
   b = a[0, ..., 0]
 The function ``py::ellipsis()`` function can be used to perform the same

--- a/docs/advanced/pycpp/object.rst
+++ b/docs/advanced/pycpp/object.rst
@@ -20,6 +20,47 @@ Available types include :class:`handle`, :class:`object`, :class:`bool_`,
    Be sure to review the :ref:`pytypes_gotchas` before using this heavily in
    your C++ API.
+.. _instantiating_compound_types:
+Instantiating compound Python types from C++
+============================================
+Dictionaries can be initialized in the :class:`dict` constructor:
+.. code-block:: cpp
+    using namespace pybind11::literals; // to bring in the `_a` literal
+    py::dict d("spam"_a=py::none(), "eggs"_a=42);
+A tuple of python objects can be instantiated using :func:`py::make_tuple`:
+.. code-block:: cpp
+    py::tuple tup = py::make_tuple(42, py::none(), "spam");
+Each element is converted to a supported Python type.
+A `simple namespace`_ can be instantiated using
+:func:`py::make_simple_namespace`:
+.. code-block:: cpp
+    using namespace pybind11::literals; // to bring in the `_a` literal
+    py::object ns = py::make_simple_namespace("spam"_a=py::none(), "eggs"_a=42);
+Attributes on a namespace can be modified with the :func:`py::delattr`,
+:func:`py::getattr`, and :func:`py::setattr` functions. Simple namespaces can
+be useful as lightweight stand-ins for class instances.
+.. note::
+    ``make_simple_namespace`` is not available in Python 2.
+.. versionchanged:: 2.8
+    ``make_simple_namespace`` added.
+.. _simple namespace: https://docs.python.org/3/library/types.html#types.SimpleNamespace
 .. _casting_back_and_forth:
 Casting back and forth
@@ -30,7 +71,7 @@ types to Python, which can be done using :func:`py::cast`:
 .. code-block:: cpp
-    MyClass *cls = ..;
+    MyClass *cls = ...;
    py::object obj = py::cast(cls);
 The reverse direction uses the following syntax:
@@ -132,6 +173,7 @@ Keyword arguments are also supported. In Python, there is the usual call syntax:
    def f(number, say, to):
        ...  # function code
    f(1234, say="hello", to=some_instance)  # keyword call in Python
 In C++, the same call can be made using:

--- a/docs/advanced/pycpp/utilities.rst
+++ b/docs/advanced/pycpp/utilities.rst
@@ -66,7 +66,7 @@ extra type, `py::scoped_estream_redirect <scoped_estream_redirect>`, is identica
 except for defaulting to ``std::cerr`` and ``sys.stderr``; this can be useful with
 `py::call_guard`, which allows multiple items, but uses the default constructor:
-.. code-block:: py
+.. code-block:: cpp
    // Alternative: Call single function using call guard
    m.def("noisy_func", &call_noisy_function,

--- a/docs/advanced/smart_ptrs.rst
+++ b/docs/advanced/smart_ptrs.rst
@@ -77,6 +77,7 @@ segmentation fault).
 .. code-block:: python
   from example import Parent
   print(Parent().get_child())
 The problem is that ``Parent::get_child()`` returns a pointer to an instance of

--- a/docs/benchmark.py
+++ b/docs/benchmark.py
 # -*- coding: utf-8 -*-
-import random
-import os
-import time
 import datetime as dt
+import os
+import random
 nfns = 4  # Functions per class
 nargs = 4  # Arguments per function

--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -6,8 +6,13 @@ Changelog
 Starting with version 1.8.0, pybind11 releases use a `semantic versioning
 <http://semver.org>`_ policy.
-v2.8.0 (WIP)
+v2.8.0 (Oct 4, 2021)
------------
+--------------------
+New features:
+* Added ``py::raise_from`` to enable chaining exceptions.
+  `#3215 <https://github.com/pybind/pybind11/pull/3215>`_
 * Allow exception translators to be optionally registered local to a module
  instead of applying globally across all pybind11 modules. Use
@@ -16,6 +21,158 @@ v2.8.0 (WIP)
  translator)`` to keep your exception remapping code local to the module.
  `#2650 <https://github.com/pybind/pybind11/pull/2650>`_
+* Add ``make_simple_namespace`` function for instantiating Python
+  ``SimpleNamespace`` objects.
+  `#2840 <https://github.com/pybind/pybind11/pull/2840>`_
+* ``pybind11::scoped_interpreter`` and ``initialize_interpreter`` have new
+  arguments to allow ``sys.argv`` initialization.
+  `#2341 <https://github.com/pybind/pybind11/pull/2341>`_
+* Allow Python builtins to be used as callbacks in CPython.
+  `#1413 <https://github.com/pybind/pybind11/pull/1413>`_
+* Added ``view`` to view arrays with a different datatype.
+  `#987 <https://github.com/pybind/pybind11/pull/987>`_
+* Implemented ``reshape`` on arrays.
+  `#984 <https://github.com/pybind/pybind11/pull/984>`_
+* Enable defining custom ``__new__`` methods on classes by fixing bug
+  preventing overriding methods if they have non-pybind11 siblings.
+  `#3265 <https://github.com/pybind/pybind11/pull/3265>`_
+* Add ``make_value_iterator()``, and fix ``make_key_iterator()`` to return
+  references instead of copies.
+  `#3293 <https://github.com/pybind/pybind11/pull/3293>`_
+* Improve the classes generated by ``bind_map``: `#3310 <https://github.com/pybind/pybind11/pull/3310>`_
+    * Change ``.items`` from an iterator to a dictionary view.
+    * Add ``.keys`` and ``.values`` (both dictionary views).
+    * Allow ``__contains__`` to take any object.
+* ``pybind11::custom_type_setup`` was added, for customizing the
+  ``PyHeapTypeObject`` corresponding to a class, which may be useful for
+  enabling garbage collection support, among other things.
+  `#3287 <https://github.com/pybind/pybind11/pull/3287>`_
+Changes:
+* Set ``__file__`` constant when running ``eval_file`` in an embedded interpreter.
+  `#3233 <https://github.com/pybind/pybind11/pull/3233>`_
+* Python objects and (C++17) ``std::optional`` now accepted in ``py::slice``
+  constructor.
+  `#1101 <https://github.com/pybind/pybind11/pull/1101>`_
+* The pybind11 proxy types ``str``, ``bytes``, ``bytearray``, ``tuple``,
+  ``list`` now consistently support passing ``ssize_t`` values for sizes and
+  indexes. Previously, only ``size_t`` was accepted in several interfaces.
+  `#3219 <https://github.com/pybind/pybind11/pull/3219>`_
+* Avoid evaluating ``PYBIND11_TLS_REPLACE_VALUE`` arguments more than once.
+  `#3290 <https://github.com/pybind/pybind11/pull/3290>`_
+Fixes:
+* Bug fix: enum value's ``__int__`` returning non-int when underlying type is
+  bool or of char type.
+  `#1334 <https://github.com/pybind/pybind11/pull/1334>`_
+* Fixes bug in setting error state in Capsule's pointer methods.
+  `#3261 <https://github.com/pybind/pybind11/pull/3261>`_
+* A long-standing memory leak in ``py::cpp_function::initialize`` was fixed.
+  `#3229 <https://github.com/pybind/pybind11/pull/3229>`_
+* Fixes thread safety for some ``pybind11::type_caster`` which require lifetime
+  extension, such as for ``std::string_view``.
+  `#3237 <https://github.com/pybind/pybind11/pull/3237>`_
+* Restore compatibility with gcc 4.8.4 as distributed by ubuntu-trusty, linuxmint-17.
+  `#3270 <https://github.com/pybind/pybind11/pull/3270>`_
+Build system improvements:
+* Fix regression in CMake Python package config: improper use of absolute path.
+  `#3144 <https://github.com/pybind/pybind11/pull/3144>`_
+* Cached Python version information could become stale when CMake was re-run
+  with a different Python version. The build system now detects this and
+  updates this information.
+  `#3299 <https://github.com/pybind/pybind11/pull/3299>`_
+* Specified UTF8-encoding in setup.py calls of open().
+  `#3137 <https://github.com/pybind/pybind11/pull/3137>`_
+* Fix a harmless warning from CMake 3.21 with the classic Python discovery.
+  `#3220 <https://github.com/pybind/pybind11/pull/3220>`_
+* Eigen repo and version can now be specified as cmake options.
+  `#3324 <https://github.com/pybind/pybind11/pull/3324>`_
+Backend and tidying up:
+* Reduced thread-local storage required for keeping alive temporary data for
+  type conversion to one key per ABI version, rather than one key per extension
+  module.  This makes the total thread-local storage required by pybind11 2
+  keys per ABI version.
+  `#3275 <https://github.com/pybind/pybind11/pull/3275>`_
+* Optimize NumPy array construction with additional moves.
+  `#3183 <https://github.com/pybind/pybind11/pull/3183>`_
+* Conversion to ``std::string`` and ``std::string_view`` now avoids making an
+  extra copy of the data on Python >= 3.3.
+  `#3257 <https://github.com/pybind/pybind11/pull/3257>`_
+* Remove const modifier from certain C++ methods on Python collections
+  (``list``, ``set``, ``dict``) such as (``clear()``, ``append()``,
+  ``insert()``, etc...) and annotated them with ``py-non-const``.
+* Enable readability ``clang-tidy-const-return`` and remove useless consts.
+  `#3254 <https://github.com/pybind/pybind11/pull/3254>`_
+  `#3194 <https://github.com/pybind/pybind11/pull/3194>`_
+* The clang-tidy ``google-explicit-constructor`` option was enabled.
+  `#3250 <https://github.com/pybind/pybind11/pull/3250>`_
+* Mark a pytype move constructor as noexcept (perf).
+  `#3236 <https://github.com/pybind/pybind11/pull/3236>`_
+* Enable clang-tidy check to guard against inheritance slicing.
+  `#3210 <https://github.com/pybind/pybind11/pull/3210>`_
+* Legacy warning suppression pragma were removed from eigen.h. On Unix
+  platforms, please use -isystem for Eigen include directories, to suppress
+  compiler warnings originating from Eigen headers. Note that CMake does this
+  by default. No adjustments are needed for Windows.
+  `#3198 <https://github.com/pybind/pybind11/pull/3198>`_
+* Format pybind11 with isort consistent ordering of imports
+  `#3195 <https://github.com/pybind/pybind11/pull/3195>`_
+* The warnings-suppression "pragma clamp" at the top/bottom of pybind11 was
+  removed, clearing the path to refactoring and IWYU cleanup.
+  `#3186 <https://github.com/pybind/pybind11/pull/3186>`_
+* Enable most bugprone checks in clang-tidy and fix the found potential bugs
+  and poor coding styles.
+  `#3166 <https://github.com/pybind/pybind11/pull/3166>`_
+* Add ``clang-tidy-readability`` rules to make boolean casts explicit improving
+  code readability. Also enabled other misc and readability clang-tidy checks.
+  `#3148 <https://github.com/pybind/pybind11/pull/3148>`_
+* Move object in ``.pop()`` for list.
+  `#3116 <https://github.com/pybind/pybind11/pull/3116>`_
 v2.7.1 (Aug 3, 2021)
 ---------------------
@@ -1028,6 +1185,7 @@ v2.2.0 (August 31, 2017)
      from cpp_module import CppBase1, CppBase2
      class PyDerived(CppBase1, CppBase2):
          def __init__(self):
              CppBase1.__init__(self)  # C++ bases must be initialized explicitly

--- a/docs/classes.rst
+++ b/docs/classes.rst
@@ -44,12 +44,12 @@ interactive Python session demonstrating this example is shown below:
    % python
    >>> import example
-    >>> p = example.Pet('Molly')
+    >>> p = example.Pet("Molly")
    >>> print(p)
    <example.Pet object at 0x10cd98060>
    >>> p.getName()
    u'Molly'
-    >>> p.setName('Charly')
+    >>> p.setName("Charly")
    >>> p.getName()
    u'Charly'
@@ -122,10 +122,10 @@ This makes it possible to write
 .. code-block:: pycon
-    >>> p = example.Pet('Molly')
+    >>> p = example.Pet("Molly")
    >>> p.name
    u'Molly'
-    >>> p.name = 'Charly'
+    >>> p.name = "Charly"
    >>> p.name
    u'Charly'
@@ -174,10 +174,10 @@ Native Python classes can pick up new attributes dynamically:
 .. code-block:: pycon
    >>> class Pet:
-    ...     name = 'Molly'
+    ...     name = "Molly"
    ...
    >>> p = Pet()
-    >>> p.name = 'Charly'  # overwrite existing
+    >>> p.name = "Charly"  # overwrite existing
    >>> p.age = 2  # dynamically add a new attribute
 By default, classes exported from C++ do not support this and the only writable
@@ -195,7 +195,7 @@ Trying to set any other attribute results in an error:
 .. code-block:: pycon
    >>> p = example.Pet()
-    >>> p.name = 'Charly'  # OK, attribute defined in C++
+    >>> p.name = "Charly"  # OK, attribute defined in C++
    >>> p.age = 2  # fail
    AttributeError: 'Pet' object has no attribute 'age'
@@ -213,7 +213,7 @@ Now everything works as expected:
 .. code-block:: pycon
    >>> p = example.Pet()
-    >>> p.name = 'Charly'  # OK, overwrite value in C++
+    >>> p.name = "Charly"  # OK, overwrite value in C++
    >>> p.age = 2  # OK, dynamically add a new attribute
    >>> p.__dict__  # just like a native Python class
    {'age': 2}
@@ -280,7 +280,7 @@ expose fields and methods of both types:
 .. code-block:: pycon
-    >>> p = example.Dog('Molly')
+    >>> p = example.Dog("Molly")
    >>> p.name
    u'Molly'
    >>> p.bark()
@@ -446,8 +446,7 @@ you can use ``py::detail::overload_cast_impl`` with an additional set of parenth
 Enumerations and internal types
 ===============================
-Let's now suppose that the example class contains an internal enumeration type,
+Let's now suppose that the example class contains internal types like enumerations, e.g.:
-e.g.:
 .. code-block:: cpp
@@ -457,10 +456,15 @@ e.g.:
            Cat
        };
+        struct Attributes {
+            float age = 0;
+        };
        Pet(const std::string &name, Kind type) : name(name), type(type) { }
        std::string name;
        Kind type;
+        Attributes attr;
    };
 The binding code for this example looks as follows:
@@ -471,22 +475,28 @@ The binding code for this example looks as follows:
    pet.def(py::init<const std::string &, Pet::Kind>())
        .def_readwrite("name", &Pet::name)
-        .def_readwrite("type", &Pet::type);
+        .def_readwrite("type", &Pet::type)
+        .def_readwrite("attr", &Pet::attr);
    py::enum_<Pet::Kind>(pet, "Kind")
        .value("Dog", Pet::Kind::Dog)
        .value("Cat", Pet::Kind::Cat)
        .export_values();
-To ensure that the ``Kind`` type is created within the scope of ``Pet``, the
+    py::class_<Pet::Attributes> attributes(pet, "Attributes")
-``pet`` :class:`class_` instance must be supplied to the :class:`enum_`.
+        .def(py::init<>())
+        .def_readwrite("age", &Pet::Attributes::age);
+To ensure that the nested types ``Kind`` and ``Attributes`` are created within the scope of ``Pet``, the
+``pet`` :class:`class_` instance must be supplied to the :class:`enum_` and :class:`class_`
 constructor. The :func:`enum_::export_values` function exports the enum entries
 into the parent scope, which should be skipped for newer C++11-style strongly
 typed enums.
 .. code-block:: pycon
-    >>> p = Pet('Lucy', Pet.Cat)
+    >>> p = Pet("Lucy", Pet.Cat)
    >>> p.type
    Kind.Cat
    >>> int(p.type)
@@ -508,7 +518,7 @@ The ``name`` property returns the name of the enum value as a unicode string.
    .. code-block:: pycon
-        >>> p = Pet( "Lucy", Pet.Cat )
+        >>> p = Pet("Lucy", Pet.Cat)
        >>> pet_type = p.type
        >>> pet_type
        Pet.Cat

--- a/docs/compiling.rst
+++ b/docs/compiling.rst
@@ -42,10 +42,7 @@ An example of a ``setup.py`` using pybind11's helpers:
        ),
    ]
-    setup(
+    setup(..., ext_modules=ext_modules)
-        ...,
-        ext_modules=ext_modules
-    )
 If you want to do an automatic search for the highest supported C++ standard,
 that is supported via a ``build_ext`` command override; it will only affect
@@ -64,11 +61,7 @@ that is supported via a ``build_ext`` command override; it will only affect
        ),
    ]
-    setup(
+    setup(..., cmdclass={"build_ext": build_ext}, ext_modules=ext_modules)
-        ...,
-        cmdclass={"build_ext": build_ext},
-        ext_modules=ext_modules
-    )
 If you have single-file extension modules that are directly stored in the
 Python source tree (``foo.cpp`` in the same directory as where a ``foo.py``
@@ -113,7 +106,7 @@ with the following:
    from pybind11.setup_helpers import ParallelCompile, naive_recompile
-    SmartCompile("NPY_NUM_BUILD_JOBS", needs_recompile=naive_recompile).install()
+    ParallelCompile("NPY_NUM_BUILD_JOBS", needs_recompile=naive_recompile).install()
 If you have a more complex build, you can implement a smarter function and pass

--- a/docs/conf.py
+++ b/docs/conf.py
@@ -13,12 +13,11 @@
 # All configuration values have a default; values that are commented out
 # serve to show the default.
-import sys
 import os
-import shlex
+import re
 import subprocess
+import sys
 from pathlib import Path
-import re
 DIR = Path(__file__).parent.resolve()

--- a/docs/faq.rst
+++ b/docs/faq.rst
@@ -54,7 +54,7 @@ provided by the caller -- in fact, it does nothing at all.
 .. code-block:: python
    def increment(i):
-        i += 1 # nope..
+        i += 1  # nope..
 pybind11 is also affected by such language-level conventions, which means that
 binding ``increment`` or ``increment_ptr`` will also create Python functions

--- a/docs/reference.rst
+++ b/docs/reference.rst
@@ -63,6 +63,9 @@ Convenience functions converting to Python types
 .. doxygenfunction:: make_key_iterator(Iterator, Sentinel, Extra &&...)
 .. doxygenfunction:: make_key_iterator(Type &, Extra&&...)
+.. doxygenfunction:: make_value_iterator(Iterator, Sentinel, Extra &&...)
+.. doxygenfunction:: make_value_iterator(Type &, Extra&&...)
 .. _extras:
 Passing extra arguments to ``def`` or ``class_``

--- a/include/pybind11/attr.h
+++ b/include/pybind11/attr.h
@@ -12,13 +12,17 @@
 #include "cast.h"
+#include <functional>
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 /// \addtogroup annotations
 /// @{
 /// Annotation for methods
-struct is_method { handle class_; is_method(const handle &c) : class_(c) { } };
+struct is_method { handle class_;
+    explicit is_method(const handle &c) : class_(c) {}
+};
 /// Annotation for operators
 struct is_operator { };
@@ -27,16 +31,24 @@ struct is_operator { };
 struct is_final { };
 /// Annotation for parent scope
-struct scope { handle value; scope(const handle &s) : value(s) { } };
+struct scope { handle value;
+    explicit scope(const handle &s) : value(s) {}
+};
 /// Annotation for documentation
-struct doc { const char *value; doc(const char *value) : value(value) { } };
+struct doc { const char *value;
+    explicit doc(const char *value) : value(value) {}
+};
 /// Annotation for function names
-struct name { const char *value; name(const char *value) : value(value) { } };
+struct name { const char *value;
+    explicit name(const char *value) : value(value) {}
+};
 /// Annotation indicating that a function is an overload associated with a given "sibling"
-struct sibling { handle value; sibling(const handle &value) : value(value.ptr()) { } };
+struct sibling { handle value;
+    explicit sibling(const handle &value) : value(value.ptr()) {}
+};
 /// Annotation indicating that a class derives from another given type
 template <typename T> struct base {
@@ -69,8 +81,27 @@ struct metaclass {
    explicit metaclass(handle value) : value(value) { }
 };
+/// Specifies a custom callback with signature `void (PyHeapTypeObject*)` that
+/// may be used to customize the Python type.
+///
+/// The callback is invoked immediately before `PyType_Ready`.
+///
+/// Note: This is an advanced interface, and uses of it may require changes to
+/// work with later versions of pybind11.  You may wish to consult the
+/// implementation of `make_new_python_type` in `detail/classes.h` to understand
+/// the context in which the callback will be run.
+struct custom_type_setup {
+    using callback = std::function<void(PyHeapTypeObject *heap_type)>;
+    explicit custom_type_setup(callback value) : value(std::move(value)) {}
+    callback value;
+};
 /// Annotation that marks a class as local to the module:
-struct module_local { const bool value; constexpr module_local(bool v = true) : value(v) { } };
+struct module_local { const bool value;
+    constexpr explicit module_local(bool v = true) : value(v) {}
+};
 /// Annotation to mark enums as an arithmetic type
 struct arithmetic { };
@@ -124,7 +155,7 @@ enum op_id : int;
 enum op_type : int;
 struct undefined_t;
 template <op_id id, op_type ot, typename L = undefined_t, typename R = undefined_t> struct op_;
-inline void keep_alive_impl(size_t Nurse, size_t Patient, function_call &call, handle ret);
+void keep_alive_impl(size_t Nurse, size_t Patient, function_call &call, handle ret);
 /// Internal data structure which holds metadata about a keyword argument
 struct argument_record {
@@ -260,6 +291,9 @@ struct type_record {
    /// Custom metaclass (optional)
    handle metaclass;
+    /// Custom type setup.
+    custom_type_setup::callback custom_type_setup_callback;
    /// Multiple inheritance marker
    bool multiple_inheritance : 1;
@@ -465,6 +499,13 @@ struct process_attribute<dynamic_attr> : process_attribute_default<dynamic_attr>
 };
 template <>
+struct process_attribute<custom_type_setup> {
+    static void init(const custom_type_setup &value, type_record *r) {
+        r->custom_type_setup_callback = value.value;
+    }
+};
+template <>
 struct process_attribute<is_final> : process_attribute_default<is_final> {
    static void init(const is_final &, type_record *r) { r->is_final = true; }
 };
@@ -516,20 +557,31 @@ template <size_t Nurse, size_t Patient> struct process_attribute<keep_alive<Nurs
 /// Recursively iterate over variadic template arguments
 template <typename... Args> struct process_attributes {
    static void init(const Args&... args, function_record *r) {
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::init(args, r), 0) ... };
+        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(r);
-        ignore_unused(unused);
+        PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(r);
+        using expander = int[];
+        (void) expander{
+            0, ((void) process_attribute<typename std::decay<Args>::type>::init(args, r), 0)...};
    }
    static void init(const Args&... args, type_record *r) {
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::init(args, r), 0) ... };
+        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(r);
-        ignore_unused(unused);
+        PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(r);
+        using expander = int[];
+        (void) expander{0,
+                        (process_attribute<typename std::decay<Args>::type>::init(args, r), 0)...};
    }
    static void precall(function_call &call) {
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::precall(call), 0) ... };
+        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(call);
-        ignore_unused(unused);
+        using expander = int[];
+        (void) expander{0,
+                        (process_attribute<typename std::decay<Args>::type>::precall(call), 0)...};
    }
    static void postcall(function_call &call, handle fn_ret) {
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::postcall(call, fn_ret), 0) ... };
+        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(call, fn_ret);
-        ignore_unused(unused);
+        PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(fn_ret);
+        using expander = int[];
+        (void) expander{
+            0, (process_attribute<typename std::decay<Args>::type>::postcall(call, fn_ret), 0)...};
    }
 };
@@ -545,6 +597,7 @@ template <typename... Extra,
          size_t named = constexpr_sum(std::is_base_of<arg, Extra>::value...),
          size_t self  = constexpr_sum(std::is_same<is_method, Extra>::value...)>
 constexpr bool expected_num_args(size_t nargs, bool has_args, bool has_kwargs) {
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(nargs, has_args, has_kwargs);
    return named == 0 || (self + named + size_t(has_args) + size_t(has_kwargs)) == nargs;
 }

--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -82,7 +82,7 @@ public:
        return caster_t::cast(&src.get(), policy, parent);
    }
    template <typename T> using cast_op_type = std::reference_wrapper<type>;
-    operator std::reference_wrapper<type>() { return cast_op<type &>(subcaster); }
+    explicit operator std::reference_wrapper<type>() { return cast_op<type &>(subcaster); }
 };
 #define PYBIND11_TYPE_CASTER(type, py_name)                                                       \
@@ -102,9 +102,9 @@ public:                                                                         
        }                                                                                         \
        return cast(*src, policy, parent);                                                        \
    }                                                                                             \
-    operator type *() { return &value; }                                                          \
+    operator type *() { return &value; }               /* NOLINT(bugprone-macro-parentheses) */   \
-    operator type &() { return value; }                                                           \
+    operator type &() { return value; }                /* NOLINT(bugprone-macro-parentheses) */   \
-    operator type &&() && { return std::move(value); }                                            \
+    operator type &&() && { return std::move(value); } /* NOLINT(bugprone-macro-parentheses) */   \
    template <typename T_>                                                                        \
    using cast_op_type = pybind11::detail::movable_cast_op_type<T_>
@@ -145,9 +145,8 @@ public:
                py_value = (py_type) PyFloat_AsDouble(src.ptr());
            else
                return false;
-        } else if (PyFloat_Check(src.ptr())) {
+        } else if (PyFloat_Check(src.ptr())
-            return false;
+                   || (!convert && !PYBIND11_LONG_CHECK(src.ptr()) && !index_check(src.ptr()))) {
-        } else if (!convert && !PYBIND11_LONG_CHECK(src.ptr()) && !index_check(src.ptr())) {
            return false;
        } else {
            handle src_or_index = src;
@@ -280,7 +279,7 @@ public:
    }
    template <typename T> using cast_op_type = void*&;
-    operator void *&() { return value; }
+    explicit operator void *&() { return value; }
    static constexpr auto name = _("capsule");
 private:
    void *value = nullptr;
@@ -378,13 +377,33 @@ template <typename StringType, bool IsView = false> struct string_caster {
 #endif
        }
+#if PY_VERSION_HEX >= 0x03030000
+        // On Python >= 3.3, for UTF-8 we avoid the need for a temporary `bytes`
+        // object by using `PyUnicode_AsUTF8AndSize`.
+        if (PYBIND11_SILENCE_MSVC_C4127(UTF_N == 8)) {
+            Py_ssize_t size = -1;
+            const auto *buffer
+                = reinterpret_cast<const CharT *>(PyUnicode_AsUTF8AndSize(load_src.ptr(), &size));
+            if (!buffer) {
+                PyErr_Clear();
+                return false;
+            }
+            value = StringType(buffer, static_cast<size_t>(size));
+            return true;
+        }
+#endif
        auto utfNbytes = reinterpret_steal<object>(PyUnicode_AsEncodedString(
            load_src.ptr(), UTF_N == 8 ? "utf-8" : UTF_N == 16 ? "utf-16" : "utf-32", nullptr));
        if (!utfNbytes) { PyErr_Clear(); return false; }
        const auto *buffer = reinterpret_cast<const CharT *>(PYBIND11_BYTES_AS_STRING(utfNbytes.ptr()));
        size_t length = (size_t) PYBIND11_BYTES_SIZE(utfNbytes.ptr()) / sizeof(CharT);
-        if (UTF_N > 8) { buffer++; length--; } // Skip BOM for UTF-16/32
+        // Skip BOM for UTF-16/32
+        if (PYBIND11_SILENCE_MSVC_C4127(UTF_N > 8)) {
+            buffer++;
+            length--;
+        }
        value = StringType(buffer, length);
        // If we're loading a string_view we need to keep the encoded Python object alive:
@@ -484,8 +503,10 @@ public:
        return StringCaster::cast(StringType(1, src), policy, parent);
    }
-    operator CharT*() { return none ? nullptr : const_cast<CharT *>(static_cast<StringType &>(str_caster).c_str()); }
+    explicit operator CharT *() {
-    operator CharT&() {
+        return none ? nullptr : const_cast<CharT *>(static_cast<StringType &>(str_caster).c_str());
+    }
+    explicit operator CharT &() {
        if (none)
            throw value_error("Cannot convert None to a character");
@@ -499,7 +520,7 @@ public:
        // out how long the first encoded character is in bytes to distinguish between these two
        // errors.  We also allow want to allow unicode characters U+0080 through U+00FF, as those
        // can fit into a single char value.
-        if (StringCaster::UTF_N == 8 && str_len > 1 && str_len <= 4) {
+        if (PYBIND11_SILENCE_MSVC_C4127(StringCaster::UTF_N == 8) && str_len > 1 && str_len <= 4) {
            auto v0 = static_cast<unsigned char>(value[0]);
            // low bits only: 0-127
            // 0b110xxxxx - start of 2-byte sequence
@@ -524,7 +545,7 @@ public:
        // UTF-16 is much easier: we can only have a surrogate pair for values above U+FFFF, thus a
        // surrogate pair with total length 2 instantly indicates a range error (but not a "your
        // string was too long" error).
-        else if (StringCaster::UTF_N == 16 && str_len == 2) {
+        else if (PYBIND11_SILENCE_MSVC_C4127(StringCaster::UTF_N == 16) && str_len == 2) {
            one_char = static_cast<CharT>(value[0]);
            if (one_char >= 0xD800 && one_char < 0xE000)
                throw value_error("Character code point not in range(0x10000)");
@@ -578,8 +599,8 @@ public:
    template <typename T> using cast_op_type = type;
-    operator type() & { return implicit_cast(indices{}); }
+    explicit operator type() & { return implicit_cast(indices{}); }
-    operator type() && { return std::move(*this).implicit_cast(indices{}); }
+    explicit operator type() && { return std::move(*this).implicit_cast(indices{}); }
 protected:
    template <size_t... Is>
@@ -605,6 +626,8 @@ protected:
    /* Implementation: Convert a C++ tuple into a Python tuple */
    template <typename T, size_t... Is>
    static handle cast_impl(T &&src, return_value_policy policy, handle parent, index_sequence<Is...>) {
+        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(src, policy, parent);
+        PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(policy, parent);
        std::array<object, size> entries{{
            reinterpret_steal<object>(make_caster<Ts>::cast(std::get<Is>(std::forward<T>(src)), policy, parent))...
        }};
@@ -777,7 +800,7 @@ struct pyobject_caster {
        // For Python 2, without this implicit conversion, Python code would
        // need to be cluttered with six.ensure_text() or similar, only to be
        // un-cluttered later after Python 2 support is dropped.
-        if (std::is_same<T, str>::value && isinstance<bytes>(src)) {
+        if (PYBIND11_SILENCE_MSVC_C4127(std::is_same<T, str>::value) && isinstance<bytes>(src)) {
            PyObject *str_from_bytes = PyUnicode_FromEncodedObject(src.ptr(), "utf-8", nullptr);
            if (!str_from_bytes) throw error_already_set();
            value = reinterpret_steal<type>(str_from_bytes);
@@ -1013,6 +1036,16 @@ template <return_value_policy policy = return_value_policy::automatic_reference,
    return result;
 }
+#if PY_VERSION_HEX >= 0x03030000
+template <typename... Args,
+          typename = detail::enable_if_t<args_are_all_keyword_or_ds<Args...>()>>
+object make_simple_namespace(Args&&... args_) {
+    PyObject *ns = _PyNamespace_New(dict(std::forward<Args>(args_)...).ptr());
+    if (!ns) throw error_already_set();
+    return reinterpret_steal<object>(ns);
+}
+#endif
 /// \ingroup annotations
 /// Annotation for arguments
 struct arg {
@@ -1161,13 +1194,14 @@ public:
    }
    template <typename Return, typename Guard, typename Func>
+    // NOLINTNEXTLINE(readability-const-return-type)
    enable_if_t<!std::is_void<Return>::value, Return> call(Func &&f) && {
-        return std::move(*this).template call_impl<Return>(std::forward<Func>(f), indices{}, Guard{});
+        return std::move(*this).template call_impl<remove_cv_t<Return>>(std::forward<Func>(f), indices{}, Guard{});
    }
    template <typename Return, typename Guard, typename Func>
    enable_if_t<std::is_void<Return>::value, void_type> call(Func &&f) && {
-        std::move(*this).template call_impl<Return>(std::forward<Func>(f), indices{}, Guard{});
+        std::move(*this).template call_impl<remove_cv_t<Return>>(std::forward<Func>(f), indices{}, Guard{});
        return void_type();
    }
@@ -1231,8 +1265,8 @@ public:
        // Tuples aren't (easily) resizable so a list is needed for collection,
        // but the actual function call strictly requires a tuple.
        auto args_list = list();
-        int _[] = { 0, (process(args_list, std::forward<Ts>(values)), 0)... };
+        using expander = int[];
-        ignore_unused(_);
+        (void) expander{0, (process(args_list, std::forward<Ts>(values)), 0)...};
        m_args = std::move(args_list);
    }

--- a/include/pybind11/detail/class.h
+++ b/include/pybind11/detail/class.h
@@ -210,7 +210,7 @@ extern "C" inline void pybind11_meta_dealloc(PyObject *obj) {
        internals.direct_conversions.erase(tindex);
        if (tinfo->module_local)
-            registered_local_types_cpp().erase(tindex);
+            get_local_internals().registered_types_cpp.erase(tindex);
        else
            internals.registered_types_cpp.erase(tindex);
        internals.registered_types_py.erase(tinfo->type);
@@ -683,11 +683,13 @@ inline PyObject* make_new_python_type(const type_record &rec) {
    if (rec.buffer_protocol)
        enable_buffer_protocol(heap_type);
+    if (rec.custom_type_setup_callback)
+        rec.custom_type_setup_callback(heap_type);
    if (PyType_Ready(type) < 0)
        pybind11_fail(std::string(rec.name) + ": PyType_Ready failed (" + error_string() + ")!");
-    assert(rec.dynamic_attr ? PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC)
+    assert(!rec.dynamic_attr || PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC));
-                            : !PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC));
    /* Register type with the parent scope */
    if (rec.scope)

--- a/include/pybind11/detail/common.h
+++ b/include/pybind11/detail/common.h
--- a/include/pybind11/detail/descr.h
+++ b/include/pybind11/detail/descr.h
@@ -26,12 +26,14 @@ struct descr {
    char text[N + 1]{'\0'};
    constexpr descr() = default;
+    // NOLINTNEXTLINE(google-explicit-constructor)
    constexpr descr(char const (&s)[N+1]) : descr(s, make_index_sequence<N>()) { }
    template <size_t... Is>
    constexpr descr(char const (&s)[N+1], index_sequence<Is...>) : text{s[Is]..., '\0'} { }
    template <typename... Chars>
+    // NOLINTNEXTLINE(google-explicit-constructor)
    constexpr descr(char c, Chars... cs) : text{c, static_cast<char>(cs)..., '\0'} { }
    static constexpr std::array<const std::type_info *, sizeof...(Ts) + 1> types() {
@@ -42,6 +44,7 @@ struct descr {
 template <size_t N1, size_t N2, typename... Ts1, typename... Ts2, size_t... Is1, size_t... Is2>
 constexpr descr<N1 + N2, Ts1..., Ts2...> plus_impl(const descr<N1, Ts1...> &a, const descr<N2, Ts2...> &b,
                                                   index_sequence<Is1...>, index_sequence<Is2...>) {
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(b);
    return {a.text[Is1]..., b.text[Is2]...};
 }
@@ -74,7 +77,8 @@ constexpr enable_if_t<B, T1> _(const T1 &d, const T2 &) { return d; }
 template <bool B, typename T1, typename T2>
 constexpr enable_if_t<!B, T2> _(const T1 &, const T2 &d) { return d; }
-template <size_t Size> auto constexpr _() -> decltype(int_to_str<Size / 10, Size % 10>::digits) {
+template <size_t Size>
+auto constexpr _() -> remove_cv_t<decltype(int_to_str<Size / 10, Size % 10>::digits)> {
    return int_to_str<Size / 10, Size % 10>::digits;
 }

--- a/include/pybind11/detail/init.h
+++ b/include/pybind11/detail/init.h
@@ -23,7 +23,7 @@ public:
    }
    template <typename> using cast_op_type = value_and_holder &;
-    operator value_and_holder &() { return *value; }
+    explicit operator value_and_holder &() { return *value; }
    static constexpr auto name = _<value_and_holder>();
 private:
@@ -94,8 +94,9 @@ void construct(...) {
 // construct an Alias from the returned base instance.
 template <typename Class>
 void construct(value_and_holder &v_h, Cpp<Class> *ptr, bool need_alias) {
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
    no_nullptr(ptr);
-    if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr)) {
        // We're going to try to construct an alias by moving the cpp type.  Whether or not
        // that succeeds, we still need to destroy the original cpp pointer (either the
        // moved away leftover, if the alias construction works, or the value itself if we
@@ -131,10 +132,11 @@ void construct(value_and_holder &v_h, Alias<Class> *alias_ptr, bool) {
 // derived type (through those holder's implicit conversion from derived class holder constructors).
 template <typename Class>
 void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
    auto *ptr = holder_helper<Holder<Class>>::get(holder);
    no_nullptr(ptr);
    // If we need an alias, check that the held pointer is actually an alias instance
-    if (Class::has_alias && need_alias && !is_alias<Class>(ptr))
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr))
        throw type_error("pybind11::init(): construction failed: returned holder-wrapped instance "
                         "is not an alias instance");
@@ -148,9 +150,10 @@ void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
 // need it, we simply move-construct the cpp value into a new instance.
 template <typename Class>
 void construct(value_and_holder &v_h, Cpp<Class> &&result, bool need_alias) {
+    PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
    static_assert(std::is_move_constructible<Cpp<Class>>::value,
        "pybind11::init() return-by-value factory function requires a movable class");
-    if (Class::has_alias && need_alias)
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias)
        construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(result));
    else
        v_h.value_ptr() = new Cpp<Class>(std::move(result));
@@ -219,7 +222,8 @@ template <typename Func, typename Return, typename... Args>
 struct factory<Func, void_type (*)(), Return(Args...)> {
    remove_reference_t<Func> class_factory;
-    factory(Func &&f) : class_factory(std::forward<Func>(f)) { }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    factory(Func &&f) : class_factory(std::forward<Func>(f)) {}
    // The given class either has no alias or has no separate alias factory;
    // this always constructs the class itself.  If the class is registered with an alias

--- a/include/pybind11/detail/internals.h
+++ b/include/pybind11/detail/internals.h
--- a/include/pybind11/detail/type_caster_base.h
+++ b/include/pybind11/detail/type_caster_base.h
--- a/include/pybind11/detail/typeid.h
+++ b/include/pybind11/detail/typeid.h
@@ -29,7 +29,7 @@ inline void erase_all(std::string &string, const std::string &search) {
    }
 }
-PYBIND11_NOINLINE inline void clean_type_id(std::string &name) {
+PYBIND11_NOINLINE void clean_type_id(std::string &name) {
 #if defined(__GNUG__)
    int status = 0;
    std::unique_ptr<char, void (*)(void *)> res {

--- a/include/pybind11/eigen.h
+++ b/include/pybind11/eigen.h
@@ -9,29 +9,13 @@
 #pragma once
-#include "numpy.h"
+/* HINT: To suppress warnings originating from the Eigen headers, use -isystem.
+   See also:
-#if defined(__INTEL_COMPILER)
+       https://stackoverflow.com/questions/2579576/i-dir-vs-isystem-dir
-#  pragma warning(disable: 1682) // implicit conversion of a 64-bit integral type to a smaller integral type (potential portability problem)
+       https://stackoverflow.com/questions/1741816/isystem-for-ms-visual-studio-c-compiler
-#elif defined(__GNUG__) || defined(__clang__)
+*/
-#  pragma GCC diagnostic push
-#  pragma GCC diagnostic ignored "-Wconversion"
-#  pragma GCC diagnostic ignored "-Wdeprecated-declarations"
-#  ifdef __clang__
-//   Eigen generates a bunch of implicit-copy-constructor-is-deprecated warnings with -Wdeprecated
-//   under Clang, so disable that warning here:
-#    pragma GCC diagnostic ignored "-Wdeprecated"
-#  endif
-#  if __GNUC__ >= 7
-#    pragma GCC diagnostic ignored "-Wint-in-bool-context"
-#  endif
-#endif
-#if defined(_MSC_VER)
+#include "numpy.h"
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#  pragma warning(disable: 4996) // warning C4996: std::unary_negate is deprecated in C++17
-#endif
 #include <Eigen/Core>
 #include <Eigen/SparseCore>
@@ -77,6 +61,7 @@ template <bool EigenRowMajor> struct EigenConformable {
    EigenDStride stride{0, 0};      // Only valid if negativestrides is false!
    bool negativestrides = false;   // If true, do not use stride!
+    // NOLINTNEXTLINE(google-explicit-constructor)
    EigenConformable(bool fits = false) : conformable{fits} {}
    // Matrix type:
    EigenConformable(EigenIndex r, EigenIndex c,
@@ -104,6 +89,7 @@ template <bool EigenRowMajor> struct EigenConformable {
            (props::outer_stride == Eigen::Dynamic || props::outer_stride == stride.outer() ||
                (EigenRowMajor ? rows : cols) == 1);
    }
+    // NOLINTNEXTLINE(google-explicit-constructor)
    operator bool() const { return conformable; }
 };
@@ -153,7 +139,8 @@ template <typename Type_> struct EigenProps {
                np_cols = a.shape(1),
                np_rstride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar)),
                np_cstride = a.strides(1) / static_cast<ssize_t>(sizeof(Scalar));
-            if ((fixed_rows && np_rows != rows) || (fixed_cols && np_cols != cols))
+            if ((PYBIND11_SILENCE_MSVC_C4127(fixed_rows) && np_rows != rows) ||
+                (PYBIND11_SILENCE_MSVC_C4127(fixed_cols) && np_cols != cols))
                return false;
            return {np_rows, np_cols, np_rstride, np_cstride};
@@ -165,7 +152,7 @@ template <typename Type_> struct EigenProps {
              stride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar));
        if (vector) { // Eigen type is a compile-time vector
-            if (fixed && size != n)
+            if (PYBIND11_SILENCE_MSVC_C4127(fixed) && size != n)
                return false; // Vector size mismatch
            return {rows == 1 ? 1 : n, cols == 1 ? 1 : n, stride};
        }
@@ -179,7 +166,7 @@ template <typename Type_> struct EigenProps {
            if (cols != n) return false;
            return {1, n, stride};
        } // Otherwise it's either fully dynamic, or column dynamic; both become a column vector
-            if (fixed_rows && rows != n) return false;
+            if (PYBIND11_SILENCE_MSVC_C4127(fixed_rows) && rows != n) return false;
            return {n, 1, stride};
    }
@@ -341,8 +328,11 @@ public:
    static constexpr auto name = props::descriptor;
+    // NOLINTNEXTLINE(google-explicit-constructor)
    operator Type*() { return &value; }
+    // NOLINTNEXTLINE(google-explicit-constructor)
    operator Type&() { return value; }
+    // NOLINTNEXTLINE(google-explicit-constructor)
    operator Type&&() && { return std::move(value); }
    template <typename T> using cast_op_type = movable_cast_op_type<T>;
@@ -466,7 +456,9 @@ public:
        return true;
    }
+    // NOLINTNEXTLINE(google-explicit-constructor)
    operator Type*() { return ref.get(); }
+    // NOLINTNEXTLINE(google-explicit-constructor)
    operator Type&() { return *ref; }
    template <typename _T> using cast_op_type = pybind11::detail::cast_op_type<_T>;
@@ -596,9 +588,3 @@ struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-#if defined(__GNUG__) || defined(__clang__)
-#  pragma GCC diagnostic pop
-#elif defined(_MSC_VER)
-#  pragma warning(pop)
-#endif
--- a/include/pybind11/embed.h
+++ b/include/pybind11/embed.h
@@ -12,6 +12,9 @@
 #include "pybind11.h"
 #include "eval.h"
+#include <memory>
+#include <vector>
 #if defined(PYPY_VERSION)
 #  error Embedding the interpreter is not supported with PyPy
 #endif
@@ -45,25 +48,23 @@
            });
        }
 \endrst */
-#define PYBIND11_EMBEDDED_MODULE(name, variable)                                \
+#define PYBIND11_EMBEDDED_MODULE(name, variable)                                                  \
-    static ::pybind11::module_::module_def                                      \
+    static ::pybind11::module_::module_def PYBIND11_CONCAT(pybind11_module_def_, name);           \
-        PYBIND11_CONCAT(pybind11_module_def_, name);                            \
+    static void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_ &);                     \
-    static void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_ &);   \
+    static PyObject PYBIND11_CONCAT(*pybind11_init_wrapper_, name)() {                            \
-    static PyObject PYBIND11_CONCAT(*pybind11_init_wrapper_, name)() {          \
+        auto m = ::pybind11::module_::create_extension_module(                                    \
-        auto m = ::pybind11::module_::create_extension_module(                  \
+            PYBIND11_TOSTRING(name), nullptr, &PYBIND11_CONCAT(pybind11_module_def_, name));      \
-            PYBIND11_TOSTRING(name), nullptr,                                   \
+        try {                                                                                     \
-            &PYBIND11_CONCAT(pybind11_module_def_, name));                      \
+            PYBIND11_CONCAT(pybind11_init_, name)(m);                                             \
-        try {                                                                   \
+            return m.ptr();                                                                       \
-            PYBIND11_CONCAT(pybind11_init_, name)(m);                           \
+        }                                                                                         \
-            return m.ptr();                                                     \
+        PYBIND11_CATCH_INIT_EXCEPTIONS                                                            \
-        } PYBIND11_CATCH_INIT_EXCEPTIONS                                        \
+    }                                                                                             \
-    }                                                                           \
+    PYBIND11_EMBEDDED_MODULE_IMPL(name)                                                           \
-    PYBIND11_EMBEDDED_MODULE_IMPL(name)                                         \
+    ::pybind11::detail::embedded_module PYBIND11_CONCAT(pybind11_module_, name)(                  \
-    ::pybind11::detail::embedded_module PYBIND11_CONCAT(pybind11_module_, name) \
+        PYBIND11_TOSTRING(name), PYBIND11_CONCAT(pybind11_init_impl_, name));                     \
-                              (PYBIND11_TOSTRING(name),                         \
+    void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_                                \
-                               PYBIND11_CONCAT(pybind11_init_impl_, name));     \
+                                               & variable) // NOLINT(bugprone-macro-parentheses)
-    void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_ &variable)
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -85,29 +86,106 @@ struct embedded_module {
    }
 };
+struct wide_char_arg_deleter {
+    void operator()(wchar_t *ptr) const {
+#if PY_VERSION_HEX >= 0x030500f0
+        // API docs: https://docs.python.org/3/c-api/sys.html#c.Py_DecodeLocale
+        PyMem_RawFree(ptr);
+#else
+        delete[] ptr;
+#endif
+    }
+};
+inline wchar_t *widen_chars(const char *safe_arg) {
+#if PY_VERSION_HEX >= 0x030500f0
+    wchar_t *widened_arg = Py_DecodeLocale(safe_arg, nullptr);
+#else
+    wchar_t *widened_arg = nullptr;
+#    if defined(HAVE_BROKEN_MBSTOWCS) && HAVE_BROKEN_MBSTOWCS
+    size_t count = strlen(safe_arg);
+#    else
+    size_t count = mbstowcs(nullptr, safe_arg, 0);
+#    endif
+    if (count != static_cast<size_t>(-1)) {
+        widened_arg = new wchar_t[count + 1];
+        mbstowcs(widened_arg, safe_arg, count + 1);
+    }
+#endif
+    return widened_arg;
+}
+/// Python 2.x/3.x-compatible version of `PySys_SetArgv`
+inline void set_interpreter_argv(int argc, const char *const *argv, bool add_program_dir_to_path) {
+    // Before it was special-cased in python 3.8, passing an empty or null argv
+    // caused a segfault, so we have to reimplement the special case ourselves.
+    bool special_case = (argv == nullptr || argc <= 0);
+    const char *const empty_argv[]{"\0"};
+    const char *const *safe_argv = special_case ? empty_argv : argv;
+    if (special_case)
+        argc = 1;
+    auto argv_size = static_cast<size_t>(argc);
+#if PY_MAJOR_VERSION >= 3
+    // SetArgv* on python 3 takes wchar_t, so we have to convert.
+    std::unique_ptr<wchar_t *[]> widened_argv(new wchar_t *[argv_size]);
+    std::vector<std::unique_ptr<wchar_t[], wide_char_arg_deleter>> widened_argv_entries;
+    widened_argv_entries.reserve(argv_size);
+    for (size_t ii = 0; ii < argv_size; ++ii) {
+        widened_argv_entries.emplace_back(widen_chars(safe_argv[ii]));
+        if (!widened_argv_entries.back()) {
+            // A null here indicates a character-encoding failure or the python
+            // interpreter out of memory. Give up.
+            return;
+        }
+        widened_argv[ii] = widened_argv_entries.back().get();
+    }
+    auto pysys_argv = widened_argv.get();
+#else
+    // python 2.x
+    std::vector<std::string> strings{safe_argv, safe_argv + argv_size};
+    std::vector<char *> char_strings{argv_size};
+    for (std::size_t i = 0; i < argv_size; ++i)
+        char_strings[i] = &strings[i][0];
+    char **pysys_argv = char_strings.data();
+#endif
+    PySys_SetArgvEx(argc, pysys_argv, static_cast<int>(add_program_dir_to_path));
+}
 PYBIND11_NAMESPACE_END(detail)
 /** \rst
    Initialize the Python interpreter. No other pybind11 or CPython API functions can be
    called before this is done; with the exception of `PYBIND11_EMBEDDED_MODULE`. The
-    optional parameter can be used to skip the registration of signal handlers (see the
+    optional `init_signal_handlers` parameter can be used to skip the registration of
-    `Python documentation`_ for details). Calling this function again after the interpreter
+    signal handlers (see the `Python documentation`_ for details). Calling this function
-    has already been initialized is a fatal error.
+    again after the interpreter has already been initialized is a fatal error.
    If initializing the Python interpreter fails, then the program is terminated.  (This
    is controlled by the CPython runtime and is an exception to pybind11's normal behavior
    of throwing exceptions on errors.)
+    The remaining optional parameters, `argc`, `argv`, and `add_program_dir_to_path` are
+    used to populate ``sys.argv`` and ``sys.path``.
+    See the |PySys_SetArgvEx documentation|_ for details.
    .. _Python documentation: https://docs.python.org/3/c-api/init.html#c.Py_InitializeEx
+    .. |PySys_SetArgvEx documentation| replace:: ``PySys_SetArgvEx`` documentation
+    .. _PySys_SetArgvEx documentation: https://docs.python.org/3/c-api/init.html#c.PySys_SetArgvEx
 \endrst */
-inline void initialize_interpreter(bool init_signal_handlers = true) {
+inline void initialize_interpreter(bool init_signal_handlers = true,
+                                   int argc = 0,
+                                   const char *const *argv = nullptr,
+                                   bool add_program_dir_to_path = true) {
    if (Py_IsInitialized() != 0)
        pybind11_fail("The interpreter is already running");
    Py_InitializeEx(init_signal_handlers ? 1 : 0);
-    // Make .py files in the working directory available by default
+    detail::set_interpreter_argv(argc, argv, add_program_dir_to_path);
-    module_::import("sys").attr("path").cast<list>().append(".");
 }
 /** \rst
@@ -169,6 +247,8 @@ inline void finalize_interpreter() {
    Scope guard version of `initialize_interpreter` and `finalize_interpreter`.
    This a move-only guard and only a single instance can exist.
+    See `initialize_interpreter` for a discussion of its constructor arguments.
    .. code-block:: cpp
        #include <pybind11/embed.h>
@@ -180,8 +260,11 @@ inline void finalize_interpreter() {
 \endrst */
 class scoped_interpreter {
 public:
-    scoped_interpreter(bool init_signal_handlers = true) {
+    explicit scoped_interpreter(bool init_signal_handlers = true,
-        initialize_interpreter(init_signal_handlers);
+                                int argc = 0,
+                                const char *const *argv = nullptr,
+                                bool add_program_dir_to_path = true) {
+        initialize_interpreter(init_signal_handlers, argc, argv, add_program_dir_to_path);
    }
    scoped_interpreter(const scoped_interpreter &) = delete;

--- a/include/pybind11/eval.h
+++ b/include/pybind11/eval.h
@@ -136,6 +136,15 @@ object eval_file(str fname, object global = globals(), object local = object()) 
        pybind11_fail("File \"" + fname_str + "\" could not be opened!");
    }
+    // In Python2, this should be encoded by getfilesystemencoding.
+    // We don't boher setting it since Python2 is past EOL anyway.
+    // See PR#3233
+#if PY_VERSION_HEX >= 0x03000000
+    if (!global.contains("__file__")) {
+        global["__file__"] = std::move(fname);
+    }
+#endif
 #if PY_VERSION_HEX < 0x03000000 && defined(PYPY_VERSION)
    PyObject *result = PyRun_File(f, fname_str.c_str(), start, global.ptr(),
                                  local.ptr());

--- a/include/pybind11/functional.h
+++ b/include/pybind11/functional.h
@@ -69,6 +69,10 @@ public:
        // ensure GIL is held during functor destruction
        struct func_handle {
            function f;
+#if !(defined(_MSC_VER) && _MSC_VER == 1916 && defined(PYBIND11_CPP17) && PY_MAJOR_VERSION < 3)
+            // This triggers a syntax error under very special conditions (very weird indeed).
+            explicit
+#endif
            func_handle(function &&f_) noexcept : f(std::move(f_)) {}
            func_handle(const func_handle &f_) { operator=(f_); }
            func_handle &operator=(const func_handle &f_) {
@@ -85,7 +89,7 @@ public:
        // to emulate 'move initialization capture' in C++11
        struct func_wrapper {
            func_handle hfunc;
-            func_wrapper(func_handle &&hf) noexcept : hfunc(std::move(hf)) {}
+            explicit func_wrapper(func_handle &&hf) noexcept : hfunc(std::move(hf)) {}
            Return operator()(Args... args) const {
                gil_scoped_acquire acq;
                object retval(hfunc.f(std::forward<Args>(args)...));

--- a/include/pybind11/gil.h
+++ b/include/pybind11/gil.h
@@ -50,7 +50,7 @@ PYBIND11_NAMESPACE_END(detail)
 class gil_scoped_acquire {
 public:
    PYBIND11_NOINLINE gil_scoped_acquire() {
-        auto const &internals = detail::get_internals();
+        auto &internals = detail::get_internals();
        tstate = (PyThreadState *) PYBIND11_TLS_GET_VALUE(internals.tstate);
        if (!tstate) {
@@ -132,7 +132,7 @@ public:
        // `get_internals()` must be called here unconditionally in order to initialize
        // `internals.tstate` for subsequent `gil_scoped_acquire` calls. Otherwise, an
        // initialization race could occur as multiple threads try `gil_scoped_acquire`.
-        const auto &internals = detail::get_internals();
+        auto &internals = detail::get_internals();
        tstate = PyEval_SaveThread();
        if (disassoc) {
            auto key = internals.tstate;

--- a/include/pybind11/iostream.h
+++ b/include/pybind11/iostream.h
@@ -123,7 +123,7 @@ private:
    }
 public:
-    pythonbuf(const object &pyostream, size_t buffer_size = 1024)
+    explicit pythonbuf(const object &pyostream, size_t buffer_size = 1024)
        : buf_size(buffer_size), d_buffer(new char[buf_size]), pywrite(pyostream.attr("write")),
          pyflush(pyostream.attr("flush")) {
        setp(d_buffer.get(), d_buffer.get() + buf_size - 1);
@@ -171,8 +171,9 @@ protected:
    detail::pythonbuf buffer;
 public:
-    scoped_ostream_redirect(std::ostream &costream  = std::cout,
+    explicit scoped_ostream_redirect(std::ostream &costream = std::cout,
-                            const object &pyostream = module_::import("sys").attr("stdout"))
+                                     const object &pyostream
+                                     = module_::import("sys").attr("stdout"))
        : costream(costream), buffer(pyostream) {
        old = costream.rdbuf(&buffer);
    }
@@ -201,8 +202,9 @@ public:
 \endrst */
 class scoped_estream_redirect : public scoped_ostream_redirect {
 public:
-    scoped_estream_redirect(std::ostream &costream  = std::cerr,
+    explicit scoped_estream_redirect(std::ostream &costream = std::cerr,
-                            const object &pyostream = module_::import("sys").attr("stderr"))
+                                     const object &pyostream
+                                     = module_::import("sys").attr("stderr"))
        : scoped_ostream_redirect(costream, pyostream) {}
 };
@@ -217,7 +219,7 @@ class OstreamRedirect {
    std::unique_ptr<scoped_estream_redirect> redirect_stderr;
 public:
-    OstreamRedirect(bool do_stdout = true, bool do_stderr = true)
+    explicit OstreamRedirect(bool do_stdout = true, bool do_stderr = true)
        : do_stdout_(do_stdout), do_stderr_(do_stderr) {}
    void enter() {

--- a/include/pybind11/numpy.h
+++ b/include/pybind11/numpy.h
@@ -25,11 +25,6 @@
 #include <vector>
 #include <typeindex>
-#if defined(_MSC_VER)
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#endif
 /* This will be true on all flat address space platforms and allows us to reduce the
   whole npy_intp / ssize_t / Py_intptr_t business down to just ssize_t for all size
   and dimension types (e.g. shape, strides, indexing), instead of inflicting this
@@ -104,7 +99,7 @@ struct numpy_internals {
    }
 };
-inline PYBIND11_NOINLINE void load_numpy_internals(numpy_internals* &ptr) {
+PYBIND11_NOINLINE void load_numpy_internals(numpy_internals* &ptr) {
    ptr = &get_or_create_shared_data<numpy_internals>("_numpy_internals");
 }
@@ -203,6 +198,9 @@ struct npy_api {
    // Unused. Not removed because that affects ABI of the class.
    int (*PyArray_SetBaseObject_)(PyObject *, PyObject *);
    PyObject* (*PyArray_Resize_)(PyObject*, PyArray_Dims*, int, int);
+    PyObject* (*PyArray_Newshape_)(PyObject*, PyArray_Dims*, int);
+    PyObject* (*PyArray_View_)(PyObject*, PyObject*, PyObject*);
 private:
    enum functions {
        API_PyArray_GetNDArrayCFeatureVersion = 211,
@@ -217,10 +215,12 @@ private:
        API_PyArray_NewCopy = 85,
        API_PyArray_NewFromDescr = 94,
        API_PyArray_DescrNewFromType = 96,
+        API_PyArray_Newshape = 135,
+        API_PyArray_Squeeze = 136,
+        API_PyArray_View = 137,
        API_PyArray_DescrConverter = 174,
        API_PyArray_EquivTypes = 182,
        API_PyArray_GetArrayParamsFromObject = 278,
-        API_PyArray_Squeeze = 136,
        API_PyArray_SetBaseObject = 282
    };
@@ -248,11 +248,14 @@ private:
        DECL_NPY_API(PyArray_NewCopy);
        DECL_NPY_API(PyArray_NewFromDescr);
        DECL_NPY_API(PyArray_DescrNewFromType);
+        DECL_NPY_API(PyArray_Newshape);
+        DECL_NPY_API(PyArray_Squeeze);
+        DECL_NPY_API(PyArray_View);
        DECL_NPY_API(PyArray_DescrConverter);
        DECL_NPY_API(PyArray_EquivTypes);
        DECL_NPY_API(PyArray_GetArrayParamsFromObject);
-        DECL_NPY_API(PyArray_Squeeze);
        DECL_NPY_API(PyArray_SetBaseObject);
 #undef DECL_NPY_API
        return api;
    }
@@ -319,7 +322,7 @@ template <typename T> using remove_all_extents_t = typename array_info<T>::type;
 template <typename T> using is_pod_struct = all_of<
    std::is_standard_layout<T>,     // since we're accessing directly in memory we need a standard layout type
-#if defined(__GLIBCXX__) && (__GLIBCXX__ < 20150422 || __GLIBCXX__ == 20150623 || __GLIBCXX__ == 20150626 || __GLIBCXX__ == 20160803)
+#if defined(__GLIBCXX__) && (__GLIBCXX__ < 20150422 || __GLIBCXX__ == 20150426 || __GLIBCXX__ == 20150623 || __GLIBCXX__ == 20150626 || __GLIBCXX__ == 20160803)
    // libstdc++ < 5 (including versions 4.8.5, 4.9.3 and 4.9.4 which were released after 5)
    // don't implement is_trivially_copyable, so approximate it
    std::is_trivially_destructible<T>,
@@ -474,15 +477,15 @@ public:
        m_ptr = from_args(pybind11::str(format)).release().ptr();
    }
-    dtype(const char *format) : dtype(std::string(format)) { }
+    explicit dtype(const char *format) : dtype(std::string(format)) {}
    dtype(list names, list formats, list offsets, ssize_t itemsize) {
        dict args;
-        args["names"] = names;
+        args["names"] = std::move(names);
-        args["formats"] = formats;
+        args["formats"] = std::move(formats);
-        args["offsets"] = offsets;
+        args["offsets"] = std::move(offsets);
        args["itemsize"] = pybind11::int_(itemsize);
-        m_ptr = from_args(args).release().ptr();
+        m_ptr = from_args(std::move(args)).release().ptr();
    }
    /// This is essentially the same as calling numpy.dtype(args) in Python.
@@ -560,7 +563,7 @@ private:
            formats.append(descr.format);
            offsets.append(descr.offset);
        }
-        return dtype(names, formats, offsets, itemsize);
+        return dtype(std::move(names), std::move(formats), std::move(offsets), itemsize);
    }
 };
@@ -747,7 +750,7 @@ public:
     * and the caller must take care not to access invalid dimensions or dimension indices.
     */
    template <typename T, ssize_t Dims = -1> detail::unchecked_mutable_reference<T, Dims> mutable_unchecked() & {
-        if (Dims >= 0 && ndim() != Dims)
+        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims)
            throw std::domain_error("array has incorrect number of dimensions: " + std::to_string(ndim()) +
                    "; expected " + std::to_string(Dims));
        return detail::unchecked_mutable_reference<T, Dims>(mutable_data(), shape(), strides(), ndim());
@@ -761,7 +764,7 @@ public:
     * invalid dimensions or dimension indices.
     */
    template <typename T, ssize_t Dims = -1> detail::unchecked_reference<T, Dims> unchecked() const & {
-        if (Dims >= 0 && ndim() != Dims)
+        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims)
            throw std::domain_error("array has incorrect number of dimensions: " + std::to_string(ndim()) +
                    "; expected " + std::to_string(Dims));
        return detail::unchecked_reference<T, Dims>(data(), shape(), strides(), ndim());
@@ -790,6 +793,33 @@ public:
        if (isinstance<array>(new_array)) { *this = std::move(new_array); }
    }
+    /// Optional `order` parameter omitted, to be added as needed.
+    array reshape(ShapeContainer new_shape) {
+        detail::npy_api::PyArray_Dims d
+            = {reinterpret_cast<Py_intptr_t *>(new_shape->data()), int(new_shape->size())};
+        auto new_array
+            = reinterpret_steal<array>(detail::npy_api::get().PyArray_Newshape_(m_ptr, &d, 0));
+        if (!new_array) {
+            throw error_already_set();
+        }
+        return new_array;
+    }
+    /// Create a view of an array in a different data type.
+    /// This function may fundamentally reinterpret the data in the array.
+    /// It is the responsibility of the caller to ensure that this is safe.
+    /// Only supports the `dtype` argument, the `type` argument is omitted,
+    /// to be added as needed.
+    array view(const std::string &dtype) {
+        auto &api = detail::npy_api::get();
+        auto new_view = reinterpret_steal<array>(api.PyArray_View_(
+            m_ptr, dtype::from_args(pybind11::str(dtype)).release().ptr(), nullptr));
+        if (!new_view) {
+            throw error_already_set();
+        }
+        return new_view;
+    }
    /// Ensure that the argument is a NumPy array
    /// In case of an error, nullptr is returned and the Python error is cleared.
    static array ensure(handle h, int ExtraFlags = 0) {
@@ -864,6 +894,7 @@ public:
        if (!is_borrowed) Py_XDECREF(h.ptr());
    }
+    // NOLINTNEXTLINE(google-explicit-constructor)
    array_t(const object &o) : array(raw_array_t(o.ptr()), stolen_t{}) {
        if (!m_ptr) throw error_already_set();
    }
@@ -1110,7 +1141,7 @@ struct field_descriptor {
    dtype descr;
 };
-inline PYBIND11_NOINLINE void register_structured_dtype(
+PYBIND11_NOINLINE void register_structured_dtype(
    any_container<field_descriptor> fields,
    const std::type_info& tinfo, ssize_t itemsize,
    bool (*direct_converter)(PyObject *, void *&)) {
@@ -1134,7 +1165,10 @@ inline PYBIND11_NOINLINE void register_structured_dtype(
        formats.append(field.descr);
        offsets.append(pybind11::int_(field.offset));
    }
-    auto dtype_ptr = pybind11::dtype(names, formats, offsets, itemsize).release().ptr();
+    auto dtype_ptr
+        = pybind11::dtype(std::move(names), std::move(formats), std::move(offsets), itemsize)
+              .release()
+              .ptr();
    // There is an existing bug in NumPy (as of v1.11): trailing bytes are
    // not encoded explicitly into the format string. This will supposedly
@@ -1551,8 +1585,11 @@ private:
            "pybind11::vectorize(...) requires a function with at least one vectorizable argument");
 public:
-    template <typename T>
+    template <typename T,
-    explicit vectorize_helper(T &&f) : f(std::forward<T>(f)) { }
+              // SFINAE to prevent shadowing the copy constructor.
+              typename = detail::enable_if_t<
+                  !std::is_same<vectorize_helper, typename std::decay<T>::type>::value>>
+    explicit vectorize_helper(T &&f) : f(std::forward<T>(f)) {}
    object operator()(typename vectorize_arg<Args>::type... args) {
        return run(args...,
@@ -1702,7 +1739,3 @@ Helper vectorize(Return (Class::*f)(Args...) const) {
 }
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-#if defined(_MSC_VER)
-#pragma warning(pop)
-#endif
--- a/include/pybind11/operators.h
+++ b/include/pybind11/operators.h
@@ -11,13 +11,6 @@
 #include "pybind11.h"
-#if defined(__clang__) && !defined(__INTEL_COMPILER)
-#  pragma clang diagnostic ignored "-Wunsequenced" // multiple unsequenced modifications to 'self' (when using def(py::self OP Type()))
-#elif defined(_MSC_VER)
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#endif
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -58,7 +51,8 @@ template <op_id id, op_type ot, typename L, typename R> struct op_ {
        using op = op_impl<id, ot, Base, L_type, R_type>;
        cl.def(op::name(), &op::execute, is_operator(), extra...);
        #if PY_MAJOR_VERSION < 3
-        if (id == op_truediv || id == op_itruediv)
+        if (PYBIND11_SILENCE_MSVC_C4127(id == op_truediv) ||
+            PYBIND11_SILENCE_MSVC_C4127(id == op_itruediv))
            cl.def(id == op_itruediv ? "__idiv__" : ot == op_l ? "__div__" : "__rdiv__",
                    &op::execute, is_operator(), extra...);
        #endif
@@ -167,7 +161,3 @@ using detail::self;
 using detail::hash;
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-#if defined(_MSC_VER)
-#  pragma warning(pop)
-#endif
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
--- a/include/pybind11/pytypes.h
+++ b/include/pybind11/pytypes.h
--- a/include/pybind11/stl.h
+++ b/include/pybind11/stl.h
@@ -9,6 +9,7 @@
 #pragma once
+#include "detail/common.h"
 #include "pybind11.h"
 #include <set>
 #include <unordered_set>
@@ -19,33 +20,15 @@
 #include <deque>
 #include <valarray>
-#if defined(_MSC_VER)
+// See `detail/common.h` for implementation of these guards.
-#pragma warning(push)
+#if defined(PYBIND11_HAS_OPTIONAL)
-#pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
+#  include <optional>
+#elif defined(PYBIND11_HAS_EXP_OPTIONAL)
+#  include <experimental/optional>
 #endif
-#ifdef __has_include
+#if defined(PYBIND11_HAS_VARIANT)
-// std::optional (but including it in c++14 mode isn't allowed)
-#  if defined(PYBIND11_CPP17) && __has_include(<optional>)
-#    include <optional>
-#    define PYBIND11_HAS_OPTIONAL 1
-#  endif
-// std::experimental::optional (but not allowed in c++11 mode)
-#  if defined(PYBIND11_CPP14) && (__has_include(<experimental/optional>) && \
-                                 !__has_include(<optional>))
-#    include <experimental/optional>
-#    define PYBIND11_HAS_EXP_OPTIONAL 1
-#  endif
-// std::variant
-#  if defined(PYBIND11_CPP17) && __has_include(<variant>)
-#    include <variant>
-#    define PYBIND11_HAS_VARIANT 1
-#  endif
-#elif defined(_MSC_VER) && defined(PYBIND11_CPP17)
-#  include <optional>
 #  include <variant>
-#  define PYBIND11_HAS_OPTIONAL 1
-#  define PYBIND11_HAS_VARIANT 1
 #endif
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
@@ -173,12 +156,12 @@ public:
        if (!std::is_lvalue_reference<T>::value)
            policy = return_value_policy_override<Value>::policy(policy);
        list l(src.size());
-        size_t index = 0;
+        ssize_t index = 0;
        for (auto &&value : src) {
            auto value_ = reinterpret_steal<object>(value_conv::cast(forward_like<T>(value), policy, parent));
            if (!value_)
                return handle();
-            PyList_SET_ITEM(l.ptr(), (ssize_t) index++, value_.release().ptr()); // steals a reference
+            PyList_SET_ITEM(l.ptr(), index++, value_.release().ptr()); // steals a reference
        }
        return l.release();
    }
@@ -230,12 +213,12 @@ public:
    template <typename T>
    static handle cast(T &&src, return_value_policy policy, handle parent) {
        list l(src.size());
-        size_t index = 0;
+        ssize_t index = 0;
        for (auto &&value : src) {
            auto value_ = reinterpret_steal<object>(value_conv::cast(forward_like<T>(value), policy, parent));
            if (!value_)
                return handle();
-            PyList_SET_ITEM(l.ptr(), (ssize_t) index++, value_.release().ptr()); // steals a reference
+            PyList_SET_ITEM(l.ptr(), index++, value_.release().ptr()); // steals a reference
        }
        return l.release();
    }
@@ -390,7 +373,3 @@ inline std::ostream &operator<<(std::ostream &os, const handle &obj) {
 }
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-#if defined(_MSC_VER)
-#pragma warning(pop)
-#endif
--- a/include/pybind11/stl_bind.h
+++ b/include/pybind11/stl_bind.h
@@ -595,6 +595,23 @@ template <typename Map, typename Class_> auto map_if_insertion_operator(Class_ &
    );
 }
+template<typename Map>
+struct keys_view
+{
+    Map &map;
+};
+template<typename Map>
+struct values_view
+{
+    Map &map;
+};
+template<typename Map>
+struct items_view
+{
+    Map &map;
+};
 PYBIND11_NAMESPACE_END(detail)
@@ -602,6 +619,9 @@ template <typename Map, typename holder_type = std::unique_ptr<Map>, typename...
 class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&... args) {
    using KeyType = typename Map::key_type;
    using MappedType = typename Map::mapped_type;
+    using KeysView = detail::keys_view<Map>;
+    using ValuesView = detail::values_view<Map>;
+    using ItemsView = detail::items_view<Map>;
    using Class_ = class_<Map, holder_type>;
    // If either type is a non-module-local bound type then make the map binding non-local as well;
@@ -615,6 +635,12 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&.
    }
    Class_ cl(scope, name.c_str(), pybind11::module_local(local), std::forward<Args>(args)...);
+    class_<KeysView> keys_view(
+        scope, ("KeysView[" + name + "]").c_str(), pybind11::module_local(local));
+    class_<ValuesView> values_view(
+        scope, ("ValuesView[" + name + "]").c_str(), pybind11::module_local(local));
+    class_<ItemsView> items_view(
+        scope, ("ItemsView[" + name + "]").c_str(), pybind11::module_local(local));
    cl.def(init<>());
@@ -628,12 +654,22 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&.
    cl.def("__iter__",
           [](Map &m) { return make_key_iterator(m.begin(), m.end()); },
-           keep_alive<0, 1>() /* Essential: keep list alive while iterator exists */
+           keep_alive<0, 1>() /* Essential: keep map alive while iterator exists */
+    );
+    cl.def("keys",
+           [](Map &m) { return KeysView{m}; },
+           keep_alive<0, 1>() /* Essential: keep map alive while view exists */
+    );
+    cl.def("values",
+           [](Map &m) { return ValuesView{m}; },
+           keep_alive<0, 1>() /* Essential: keep map alive while view exists */
    );
    cl.def("items",
-           [](Map &m) { return make_iterator(m.begin(), m.end()); },
+           [](Map &m) { return ItemsView{m}; },
-           keep_alive<0, 1>() /* Essential: keep list alive while iterator exists */
+           keep_alive<0, 1>() /* Essential: keep map alive while view exists */
    );
    cl.def("__getitem__",
@@ -654,6 +690,8 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&.
           return true;
        }
    );
+    // Fallback for when the object is not of the key type
+    cl.def("__contains__", [](Map &, const object &) -> bool { return false; });
    // Assignment provided only if the type is copyable
    detail::map_assignment<Map, Class_>(cl);
@@ -669,6 +707,40 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args&&.
    cl.def("__len__", &Map::size);
+    keys_view.def("__len__", [](KeysView &view) { return view.map.size(); });
+    keys_view.def("__iter__",
+        [](KeysView &view) {
+            return make_key_iterator(view.map.begin(), view.map.end());
+        },
+        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+    );
+    keys_view.def("__contains__",
+        [](KeysView &view, const KeyType &k) -> bool {
+            auto it = view.map.find(k);
+            if (it == view.map.end())
+                return false;
+            return true;
+        }
+    );
+    // Fallback for when the object is not of the key type
+    keys_view.def("__contains__", [](KeysView &, const object &) -> bool { return false; });
+    values_view.def("__len__", [](ValuesView &view) { return view.map.size(); });
+    values_view.def("__iter__",
+        [](ValuesView &view) {
+            return make_value_iterator(view.map.begin(), view.map.end());
+        },
+        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+    );
+    items_view.def("__len__", [](ItemsView &view) { return view.map.size(); });
+    items_view.def("__iter__",
+        [](ItemsView &view) {
+            return make_iterator(view.map.begin(), view.map.end());
+        },
+        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+    );
    return cl;
 }

--- a/noxfile.py
+++ b/noxfile.py
 import nox
 nox.options.sessions = ["lint", "tests", "tests_packaging"]
+PYTHON_VERISONS = ["2.7", "3.5", "3.6", "3.7", "3.8", "3.9", "3.10"]
 @nox.session(reuse_venv=True)
 def lint(session: nox.Session) -> None:
@@ -13,7 +14,7 @@ def lint(session: nox.Session) -> None:
    session.run("pre-commit", "run", "-a")
-@nox.session
+@nox.session(python=PYTHON_VERISONS)
 def tests(session: nox.Session) -> None:
    """
    Run the tests (requires a compiler).

--- a/pybind11/__init__.py
+++ b/pybind11/__init__.py
 # -*- coding: utf-8 -*-
-from ._version import version_info, __version__
+from ._version import __version__, version_info
-from .commands import get_include, get_cmake_dir
+from .commands import get_cmake_dir, get_include
 __all__ = (
    "version_info",

--- a/pybind11/__main__.py
+++ b/pybind11/__main__.py
@@ -5,7 +5,7 @@ import argparse
 import sys
 import sysconfig
-from .commands import get_include, get_cmake_dir
+from .commands import get_cmake_dir, get_include
 def print_includes():

--- a/pybind11/_version.py
+++ b/pybind11/_version.py
@@ -8,5 +8,5 @@ def _to_int(s):
        return s
-__version__ = "2.7.1"
+__version__ = "2.8.0"
 version_info = tuple(_to_int(s) for s in __version__.split("."))
--- a/pybind11/_version.pyi
+++ b/pybind11/_version.pyi
-from typing import Union, Tuple
+from typing import Tuple, Union
 def _to_int(s: str) -> Union[int, str]: ...

--- a/pybind11/commands.py
+++ b/pybind11/commands.py
 # -*- coding: utf-8 -*-
 import os
 DIR = os.path.abspath(os.path.dirname(__file__))

--- a/pybind11/setup_helpers.py
+++ b/pybind11/setup_helpers.py
@@ -41,23 +41,23 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 import contextlib
 import os
+import platform
 import shutil
 import sys
+import sysconfig
 import tempfile
 import threading
-import platform
 import warnings
-import sysconfig
 try:
-    from setuptools.command.build_ext import build_ext as _build_ext
    from setuptools import Extension as _Extension
+    from setuptools.command.build_ext import build_ext as _build_ext
 except ImportError:
    from distutils.command.build_ext import build_ext as _build_ext
    from distutils.extension import Extension as _Extension
-import distutils.errors
 import distutils.ccompiler
+import distutils.errors
 WIN = sys.platform.startswith("win32") and "mingw" not in sysconfig.get_platform()
 PY2 = sys.version_info[0] < 3

--- a/pybind11/setup_helpers.pyi
+++ b/pybind11/setup_helpers.pyi
 # IMPORTANT: Should stay in sync with setup_helpers.py (mostly checked by CI /
 # pre-commit).
-from typing import Any, Callable, Dict, Iterator, List, Optional, Type, TypeVar, Union
+import contextlib
-from types import TracebackType
+import distutils.ccompiler
 from distutils.command.build_ext import build_ext as _build_ext  # type: ignore
 from distutils.extension import Extension as _Extension
-import distutils.ccompiler
+from types import TracebackType
-import contextlib
+from typing import Any, Callable, Dict, Iterator, List, Optional, Type, TypeVar, Union
 WIN: bool
 PY2: bool

--- a/pyproject.toml
+++ b/pyproject.toml
@@ -15,6 +15,12 @@ ignore = [
    "noxfile.py",
 ]
+[tool.isort]
+# Needs the compiled .so modules and env.py from tests
+known_first_party = "env,pybind11_cross_module_tests,pybind11_tests,"
+# For black compatibility
+profile = "black"
 [tool.mypy]
 files = "pybind11"
 python_version = "2.7"

--- a/setup.py
+++ b/setup.py
@@ -4,6 +4,7 @@
 # Setup script for PyPI; use CMakeFile.txt to build extension modules
 import contextlib
+import io
 import os
 import re
 import shutil
@@ -11,7 +12,6 @@ import string
 import subprocess
 import sys
 import tempfile
-import io
 import setuptools.command.sdist

--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -10,10 +10,10 @@ cmake_minimum_required(VERSION 3.4)
 # The `cmake_minimum_required(VERSION 3.4...3.18)` syntax does not work with
 # some versions of VS that have a patched CMake 3.11. This forces us to emulate
 # the behavior using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
+if(${CMAKE_VERSION} VERSION_LESS 3.21)
  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-  cmake_policy(VERSION 3.18)
+  cmake_policy(VERSION 3.21)
 endif()
 # Only needed for CMake < 3.5 support
@@ -104,6 +104,7 @@ set(PYBIND11_TEST_FILES
    test_constants_and_functions.cpp
    test_copy_move.cpp
    test_custom_type_casters.cpp
+    test_custom_type_setup.cpp
    test_docstring_options.cpp
    test_eigen.cpp
    test_enum.cpp
@@ -129,6 +130,7 @@ set(PYBIND11_TEST_FILES
    test_stl.cpp
    test_stl_binders.cpp
    test_tagbased_polymorphic.cpp
+    test_thread.cpp
    test_union.cpp
    test_virtual_functions.cpp)
@@ -169,6 +171,14 @@ set(PYBIND11_CROSS_MODULE_TESTS test_exceptions.py test_local_bindings.py test_s
 set(PYBIND11_CROSS_MODULE_GIL_TESTS test_gil_scoped.py)
+set(PYBIND11_EIGEN_REPO
+    "https://gitlab.com/libeigen/eigen.git"
+    CACHE STRING "Eigen repository to use for tests")
+# This hash is for 3.3.8, using a hash for security reasons
+set(PYBIND11_EIGEN_VERSION
+    "dc252fbf00079ccab57948a164b1421703fe4361"
+    CACHE STRING "Eigen version to use for tests")
 # Check if Eigen is available; if not, remove from PYBIND11_TEST_FILES (but
 # keep it in PYBIND11_PYTEST_FILES, so that we get the "eigen is not installed"
 # skip message).
@@ -182,13 +192,11 @@ if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
      message(FATAL_ERROR "CMake 3.11+ required when using DOWNLOAD_EIGEN")
    endif()
-    set(EIGEN3_VERSION_STRING "3.3.8")
    include(FetchContent)
    FetchContent_Declare(
      eigen
-      GIT_REPOSITORY https://gitlab.com/libeigen/eigen.git
+      GIT_REPOSITORY "${PYBIND11_EIGEN_REPO}"
-      GIT_TAG ${EIGEN3_VERSION_STRING})
+      GIT_TAG "${PYBIND11_EIGEN_VERSION}")
    FetchContent_GetProperties(eigen)
    if(NOT eigen_POPULATED)

--- a/tests/extra_setuptools/test_setuphelper.py
+++ b/tests/extra_setuptools/test_setuphelper.py
 # -*- coding: utf-8 -*-
 import os
-import sys
 import subprocess
+import sys
 from textwrap import dedent
 import pytest

--- a/tests/local_bindings.h
+++ b/tests/local_bindings.h
@@ -6,7 +6,7 @@
 /// Simple class used to test py::local:
 template <int> class LocalBase {
 public:
-    LocalBase(int i) : i(i) { }
+    explicit LocalBase(int i) : i(i) { }
    int i = -1;
 };
@@ -35,6 +35,25 @@ using NonLocalVec2 = std::vector<NonLocal2>;
 using NonLocalMap = std::unordered_map<std::string, NonLocalType>;
 using NonLocalMap2 = std::unordered_map<std::string, uint8_t>;
+// Exception that will be caught via the module local translator.
+class LocalException : public std::exception {
+public:
+    explicit LocalException(const char * m) : message{m} {}
+    const char * what() const noexcept override {return message.c_str();}
+private:
+    std::string message = "";
+};
+// Exception that will be registered with register_local_exception_translator
+class LocalSimpleException : public std::exception {
+public:
+    explicit LocalSimpleException(const char * m) : message{m} {}
+    const char * what() const noexcept override {return message.c_str();}
+private:
+    std::string message = "";
+};
 PYBIND11_MAKE_OPAQUE(LocalVec);
 PYBIND11_MAKE_OPAQUE(LocalVec2);
 PYBIND11_MAKE_OPAQUE(LocalMap);
@@ -56,11 +75,11 @@ py::class_<T> bind_local(Args && ...args) {
 namespace pets {
 class Pet {
 public:
-    Pet(std::string name) : name_(std::move(name)) {}
+    explicit Pet(std::string name) : name_(std::move(name)) {}
    std::string name_;
    const std::string &name() const { return name_; }
 };
 } // namespace pets
-struct MixGL { int i; MixGL(int i) : i{i} {} };
+struct MixGL { int i; explicit MixGL(int i) : i{i} {} };
-struct MixGL2 { int i; MixGL2(int i) : i{i} {} };
+struct MixGL2 { int i; explicit MixGL2(int i) : i{i} {} };
--- a/tests/object.h
+++ b/tests/object.h
@@ -65,7 +65,7 @@ public:
    ref() : m_ptr(nullptr) { print_default_created(this); track_default_created((ref_tag*) this); }
    /// Construct a reference from a pointer
-    ref(T *ptr) : m_ptr(ptr) {
+    explicit ref(T *ptr) : m_ptr(ptr) {
        if (m_ptr) ((Object *) m_ptr)->incRef();
        print_created(this, "from pointer", m_ptr); track_created((ref_tag*) this, "from pointer");
@@ -110,7 +110,11 @@ public:
    /// Overwrite this reference with another reference
    ref& operator=(const ref& r) {
-        print_copy_assigned(this, "pointer", r.m_ptr); track_copy_assigned((ref_tag*) this);
+        if (this == &r) {
+            return *this;
+        }
+        print_copy_assigned(this, "pointer", r.m_ptr);
+        track_copy_assigned((ref_tag *) this);
        if (m_ptr == r.m_ptr)
            return *this;
@@ -161,7 +165,7 @@ public:
    const T& operator*() const { return *m_ptr; }
    /// Return a pointer to the referenced object
-    operator T* () { return m_ptr; }
+    explicit operator T* () { return m_ptr; }
    /// Return a const pointer to the referenced object
    T* get_ptr() { return m_ptr; }

--- a/tests/pybind11_cross_module_tests.cpp
+++ b/tests/pybind11_cross_module_tests.cpp
@@ -29,11 +29,14 @@ PYBIND11_MODULE(pybind11_cross_module_tests, m) {
    bind_local<ExternalType2>(m, "ExternalType2", py::module_local());
    // test_exceptions.py
+    py::register_local_exception<LocalSimpleException>(m, "LocalSimpleException");
    m.def("raise_runtime_error", []() { PyErr_SetString(PyExc_RuntimeError, "My runtime error"); throw py::error_already_set(); });
    m.def("raise_value_error", []() { PyErr_SetString(PyExc_ValueError, "My value error"); throw py::error_already_set(); });
    m.def("throw_pybind_value_error", []() { throw py::value_error("pybind11 value error"); });
    m.def("throw_pybind_type_error", []() { throw py::type_error("pybind11 type error"); });
    m.def("throw_stop_iteration", []() { throw py::stop_iteration(); });
+    m.def("throw_local_error", []() { throw LocalException("just local"); });
+    m.def("throw_local_simple_error", []() { throw LocalSimpleException("external mod"); });
    py::register_exception_translator([](std::exception_ptr p) {
      try {
          if (p) std::rethrow_exception(p);
@@ -42,6 +45,17 @@ PYBIND11_MODULE(pybind11_cross_module_tests, m) {
      }
    });
+    // translate the local exception into a key error but only in this module
+    py::register_local_exception_translator([](std::exception_ptr p) {
+      try {
+          if (p) {
+            std::rethrow_exception(p);
+          }
+      } catch (const LocalException &e) {
+        PyErr_SetString(PyExc_KeyError, e.what());
+      }
+    });
    // test_local_bindings.py
    // Local to both:
    bind_local<LocalType, 1>(m, "LocalType", py::module_local())
@@ -94,7 +108,7 @@ PYBIND11_MODULE(pybind11_cross_module_tests, m) {
    m.def("get_mixed_lg", [](int i) { return MixedLocalGlobal(i); });
    // test_internal_locals_differ
-    m.def("local_cpp_types_addr", []() { return (uintptr_t) &py::detail::registered_local_types_cpp(); });
+    m.def("local_cpp_types_addr", []() { return (uintptr_t) &py::detail::get_local_internals().registered_types_cpp; });
    // test_stl_caster_vs_stl_bind
    py::bind_vector<std::vector<int>>(m, "VectorInt");
@@ -109,7 +123,7 @@ PYBIND11_MODULE(pybind11_cross_module_tests, m) {
    class Dog : public pets::Pet {
    public:
-        Dog(std::string name) : Pet(std::move(name)) {}
+        explicit Dog(std::string name) : Pet(std::move(name)) {}
    };
    py::class_<pets::Pet>(m, "Pet", py::module_local())
        .def("name", &pets::Pet::name);

--- a/tests/pybind11_tests.h
+++ b/tests/pybind11_tests.h
 #pragma once
-// This must be kept first for MSVC 2015.
-// Do not remove the empty line between the #includes.
 #include <pybind11/pybind11.h>
 #include <pybind11/eval.h>
 #if defined(_MSC_VER) && _MSC_VER < 1910
@@ -19,15 +16,14 @@ class test_initializer {
    using Initializer = void (*)(py::module_ &);
 public:
-    test_initializer(Initializer init);
+    explicit test_initializer(Initializer init);
    test_initializer(const char *submodule_name, Initializer init);
 };
-#define TEST_SUBMODULE(name, variable)                   \
+#define TEST_SUBMODULE(name, variable)                                                            \
-    void test_submodule_##name(py::module_ &);            \
+    void test_submodule_##name(py::module_ &);                                                    \
-    test_initializer name(#name, test_submodule_##name); \
+    test_initializer name(#name, test_submodule_##name);                                          \
-    void test_submodule_##name(py::module_ &variable)
+    void test_submodule_##name(py::module_ &(variable))
 /// Dummy type which is not exported anywhere -- something to trigger a conversion error
 struct UnregisteredType { };
@@ -36,7 +32,7 @@ struct UnregisteredType { };
 class UserType {
 public:
    UserType() = default;
-    UserType(int i) : i(i) { }
+    explicit UserType(int i) : i(i) { }
    int value() const { return i; }
    void set(int set) { i = set; }

--- a/tests/requirements.txt
+++ b/tests/requirements.txt
@@ -2,11 +2,11 @@
 numpy==1.16.6; python_version<"3.6" and sys_platform!="win32"
 numpy==1.18.0; platform_python_implementation=="PyPy" and sys_platform=="darwin" and python_version>="3.6"
 numpy==1.19.3; (platform_python_implementation!="PyPy" or sys_platform=="linux") and python_version=="3.6"
-numpy==1.20.0; (platform_python_implementation!="PyPy" or sys_platform=="linux") and python_version>="3.7" and python_version<"3.10"
+numpy==1.21.2; (platform_python_implementation!="PyPy" or sys_platform=="linux") and python_version>="3.7" and python_version<"3.10"
+numpy==1.21.2; platform_python_implementation!="PyPy" and sys_platform=="linux" and python_version=="3.10"
 pytest==4.6.9; python_version<"3.5"
 pytest==6.1.2; python_version=="3.5"
-pytest==6.2.1; python_version>="3.6" and python_version<="3.9"
+pytest==6.2.4; python_version>="3.6"
-pytest @ git+https://github.com/pytest-dev/pytest@c117bc350ec1e570672fda3b2ad234fd52e72b53; python_version>="3.10"
 pytest-timeout
 scipy==1.2.3; (platform_python_implementation!="PyPy" or sys_platform=="linux") and python_version<"3.6"
 scipy==1.5.4; (platform_python_implementation!="PyPy" or sys_platform=="linux") and python_version>="3.6" and python_version<"3.10"
--- a/tests/test_buffers.cpp
+++ b/tests/test_buffers.cpp
@@ -40,7 +40,11 @@ TEST_SUBMODULE(buffers, m) {
        }
        Matrix &operator=(const Matrix &s) {
-            print_copy_assigned(this, std::to_string(m_rows) + "x" + std::to_string(m_cols) + " matrix");
+            if (this == &s) {
+                return *this;
+            }
+            print_copy_assigned(this,
+                                std::to_string(m_rows) + "x" + std::to_string(m_cols) + " matrix");
            delete[] m_data;
            m_rows = s.m_rows;
            m_cols = s.m_cols;
@@ -118,7 +122,7 @@ TEST_SUBMODULE(buffers, m) {
    // test_inherited_protocol
    class SquareMatrix : public Matrix {
    public:
-        SquareMatrix(py::ssize_t n) : Matrix(n, n) { }
+        explicit SquareMatrix(py::ssize_t n) : Matrix(n, n) {}
    };
    // Derived classes inherit the buffer protocol and the buffer access function
    py::class_<SquareMatrix, Matrix>(m, "SquareMatrix")
@@ -169,7 +173,7 @@ TEST_SUBMODULE(buffers, m) {
    struct BufferReadOnly {
        const uint8_t value = 0;
-        BufferReadOnly(uint8_t value): value(value) {}
+        explicit BufferReadOnly(uint8_t value) : value(value) {}
        py::buffer_info get_buffer_info() {
            return py::buffer_info(&value, 1);

--- a/tests/test_buffers.py
+++ b/tests/test_buffers.py
 # -*- coding: utf-8 -*-
+import ctypes
 import io
 import struct
-import ctypes
 import pytest
 import env  # noqa: F401
-from pybind11_tests import buffers as m
 from pybind11_tests import ConstructorStats
+from pybind11_tests import buffers as m
 np = pytest.importorskip("numpy")

--- a/tests/test_builtin_casters.cpp
+++ b/tests/test_builtin_casters.cpp
@@ -10,11 +10,6 @@
 #include "pybind11_tests.h"
 #include <pybind11/complex.h>
-#if defined(_MSC_VER)
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#endif
 struct ConstRefCasted {
  int tag;
 };
@@ -30,16 +25,28 @@ class type_caster<ConstRefCasted> {
  // cast operator.
  bool load(handle, bool) { return true; }
-  operator ConstRefCasted &&() {
+  explicit operator ConstRefCasted &&() {
      value = {1};
      // NOLINTNEXTLINE(performance-move-const-arg)
      return std::move(value);
  }
-  operator ConstRefCasted&() { value = {2}; return value; }
+  explicit operator ConstRefCasted &() {
-  operator ConstRefCasted*() { value = {3}; return &value; }
+      value = {2};
+      return value;
+  }
+  explicit operator ConstRefCasted *() {
+      value = {3};
+      return &value;
+  }
-  operator const ConstRefCasted&() { value = {4}; return value; }
+  explicit operator const ConstRefCasted &() {
-  operator const ConstRefCasted*() { value = {5}; return &value; }
+      value = {4};
+      return value;
+  }
+  explicit operator const ConstRefCasted *() {
+      value = {5};
+      return &value;
+  }
  // custom cast_op to explicitly propagate types to the conversion operators.
  template <typename T_>
@@ -73,7 +80,7 @@ TEST_SUBMODULE(builtin_casters, m) {
    std::wstring wstr;
    wstr.push_back(0x61); // a
    wstr.push_back(0x2e18); // ⸘
-    if (sizeof(wchar_t) == 2) { wstr.push_back(mathbfA16_1); wstr.push_back(mathbfA16_2); } // 𝐀, utf16
+    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(wchar_t) == 2)) { wstr.push_back(mathbfA16_1); wstr.push_back(mathbfA16_2); } // 𝐀, utf16
    else { wstr.push_back((wchar_t) mathbfA32); } // 𝐀, utf32
    wstr.push_back(0x7a); // z
@@ -83,11 +90,12 @@ TEST_SUBMODULE(builtin_casters, m) {
    m.def("good_wchar_string", [=]() { return wstr; }); // a‽𝐀z
    m.def("bad_utf8_string", []()  { return std::string("abc\xd0" "def"); });
    m.def("bad_utf16_string", [=]() { return std::u16string({ b16, char16_t(0xd800), z16 }); });
+#if PY_MAJOR_VERSION >= 3
    // Under Python 2.7, invalid unicode UTF-32 characters don't appear to trigger UnicodeDecodeError
-    if (PY_MAJOR_VERSION >= 3)
+    m.def("bad_utf32_string", [=]() { return std::u32string({ a32, char32_t(0xd800), z32 }); });
-        m.def("bad_utf32_string", [=]() { return std::u32string({ a32, char32_t(0xd800), z32 }); });
+    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(wchar_t) == 2))
-    if (PY_MAJOR_VERSION >= 3 || sizeof(wchar_t) == 2)
        m.def("bad_wchar_string", [=]() { return std::wstring({ wchar_t(0x61), wchar_t(0xd800) }); });
+#endif
    m.def("u8_Z", []() -> char { return 'Z'; });
    m.def("u8_eacute", []() -> char { return '\xe9'; });
    m.def("u16_ibang", [=]() -> char16_t { return ib16; });

--- a/tests/test_builtin_casters.py
+++ b/tests/test_builtin_casters.py
@@ -2,9 +2,8 @@
 import pytest
 import env  # noqa: F401
+from pybind11_tests import IncType, UserType
 from pybind11_tests import builtin_casters as m
-from pybind11_tests import UserType, IncType
 def test_simple_string():

--- a/tests/test_call_policies.py
+++ b/tests/test_call_policies.py
@@ -2,9 +2,8 @@
 import pytest
 import env  # noqa: F401
-from pybind11_tests import call_policies as m
 from pybind11_tests import ConstructorStats
+from pybind11_tests import call_policies as m
 @pytest.mark.xfail("env.PYPY", reason="sometimes comes out 1 off on PyPy", strict=False)

--- a/tests/test_callbacks.cpp
+++ b/tests/test_callbacks.cpp
@@ -81,16 +81,55 @@ TEST_SUBMODULE(callbacks, m) {
    };
    // Export the payload constructor statistics for testing purposes:
    m.def("payload_cstats", &ConstructorStats::get<Payload>);
-    /* Test cleanup of lambda closure */
+    m.def("test_lambda_closure_cleanup", []() -> std::function<void()> {
-    m.def("test_cleanup", []() -> std::function<void()> {
        Payload p;
+        // In this situation, `Func` in the implementation of
+        // `cpp_function::initialize` is NOT trivially destructible.
        return [p]() {
            /* p should be cleaned up when the returned function is garbage collected */
            (void) p;
        };
    });
+    class CppCallable {
+    public:
+        CppCallable() { track_default_created(this); }
+        ~CppCallable() { track_destroyed(this); }
+        CppCallable(const CppCallable &) { track_copy_created(this); }
+        CppCallable(CppCallable &&) noexcept { track_move_created(this); }
+        void operator()() {}
+    };
+    m.def("test_cpp_callable_cleanup", []() {
+        // Related issue: https://github.com/pybind/pybind11/issues/3228
+        // Related PR: https://github.com/pybind/pybind11/pull/3229
+        py::list alive_counts;
+        ConstructorStats &stat = ConstructorStats::get<CppCallable>();
+        alive_counts.append(stat.alive());
+        {
+            CppCallable cpp_callable;
+            alive_counts.append(stat.alive());
+            {
+                // In this situation, `Func` in the implementation of
+                // `cpp_function::initialize` IS trivially destructible,
+                // only `capture` is not.
+                py::cpp_function py_func(cpp_callable);
+                py::detail::silence_unused_warnings(py_func);
+                alive_counts.append(stat.alive());
+            }
+            alive_counts.append(stat.alive());
+            {
+                py::cpp_function py_func(std::move(cpp_callable));
+                py::detail::silence_unused_warnings(py_func);
+                alive_counts.append(stat.alive());
+            }
+            alive_counts.append(stat.alive());
+        }
+        alive_counts.append(stat.alive());
+        return alive_counts;
+    });
    // test_cpp_function_roundtrip
    /* Test if passing a function pointer from C++ -> Python -> C++ yields the original pointer */
    m.def("dummy_function", &dummy_function);

--- a/tests/test_callbacks.py
+++ b/tests/test_callbacks.py
 # -*- coding: utf-8 -*-
-import pytest
-from pybind11_tests import callbacks as m
-from threading import Thread
 import time
+from threading import Thread
+import pytest
 import env  # NOQA: F401
+from pybind11_tests import callbacks as m
 def test_callbacks():
@@ -77,13 +79,18 @@ def test_keyword_args_and_generalized_unpacking():
 def test_lambda_closure_cleanup():
-    m.test_cleanup()
+    m.test_lambda_closure_cleanup()
    cstats = m.payload_cstats()
    assert cstats.alive() == 0
    assert cstats.copy_constructions == 1
    assert cstats.move_constructions >= 1
+def test_cpp_callable_cleanup():
+    alive_counts = m.test_cpp_callable_cleanup()
+    assert alive_counts == [0, 1, 2, 1, 2, 1, 0]
 def test_cpp_function_roundtrip():
    """Test if passing a function pointer from C++ -> Python -> C++ yields the original pointer"""

--- a/tests/test_chrono.py
+++ b/tests/test_chrono.py
 # -*- coding: utf-8 -*-
-from pybind11_tests import chrono as m
 import datetime
 import pytest
 import env  # noqa: F401
+from pybind11_tests import chrono as m
 def test_chrono_system_clock():

--- a/tests/test_class.cpp
+++ b/tests/test_class.cpp
@@ -27,7 +27,7 @@
 // test_brace_initialization
 struct NoBraceInitialization {
-    NoBraceInitialization(std::vector<int> v) : vec{std::move(v)} {}
+    explicit NoBraceInitialization(std::vector<int> v) : vec{std::move(v)} {}
    template <typename T>
    NoBraceInitialization(std::initializer_list<T> l) : vec(l) {}
@@ -47,10 +47,26 @@ TEST_SUBMODULE(class_, m) {
        }
        ~NoConstructor() { print_destroyed(this); }
    };
+    struct NoConstructorNew {
+        NoConstructorNew() = default;
+        NoConstructorNew(const NoConstructorNew &) = default;
+        NoConstructorNew(NoConstructorNew &&) = default;
+        static NoConstructorNew *new_instance() {
+            auto *ptr = new NoConstructorNew();
+            print_created(ptr, "via new_instance");
+            return ptr;
+        }
+        ~NoConstructorNew() { print_destroyed(this); }
+    };
    py::class_<NoConstructor>(m, "NoConstructor")
        .def_static("new_instance", &NoConstructor::new_instance, "Return an instance");
+    py::class_<NoConstructorNew>(m, "NoConstructorNew")
+        .def(py::init([](const NoConstructorNew &self) { return self; })) // Need a NOOP __init__
+        .def_static("__new__",
+                    [](const py::object &) { return NoConstructorNew::new_instance(); });
    // test_inheritance
    class Pet {
    public:
@@ -65,18 +81,18 @@ TEST_SUBMODULE(class_, m) {
    class Dog : public Pet {
    public:
-        Dog(const std::string &name) : Pet(name, "dog") {}
+        explicit Dog(const std::string &name) : Pet(name, "dog") {}
        std::string bark() const { return "Woof!"; }
    };
    class Rabbit : public Pet {
    public:
-        Rabbit(const std::string &name) : Pet(name, "parrot") {}
+        explicit Rabbit(const std::string &name) : Pet(name, "parrot") {}
    };
    class Hamster : public Pet {
    public:
-        Hamster(const std::string &name) : Pet(name, "rodent") {}
+        explicit Hamster(const std::string &name) : Pet(name, "rodent") {}
    };
    class Chimera : public Pet {
@@ -208,7 +224,7 @@ TEST_SUBMODULE(class_, m) {
    struct ConvertibleFromUserType {
        int i;
-        ConvertibleFromUserType(UserType u) : i(u.value()) { }
+        explicit ConvertibleFromUserType(UserType u) : i(u.value()) {}
    };
    py::class_<ConvertibleFromUserType>(m, "AcceptsUserType")
@@ -263,7 +279,7 @@ TEST_SUBMODULE(class_, m) {
    };
    struct PyAliasedHasOpNewDelSize : AliasedHasOpNewDelSize {
        PyAliasedHasOpNewDelSize() = default;
-        PyAliasedHasOpNewDelSize(int) { }
+        explicit PyAliasedHasOpNewDelSize(int) {}
        std::uint64_t j;
    };
    struct HasOpNewDelBoth {
@@ -492,15 +508,15 @@ using DoesntBreak5 = py::class_<BreaksBase<5>>;
 using DoesntBreak6 = py::class_<BreaksBase<6>, std::shared_ptr<BreaksBase<6>>, BreaksTramp<6>>;
 using DoesntBreak7 = py::class_<BreaksBase<7>, BreaksTramp<7>, std::shared_ptr<BreaksBase<7>>>;
 using DoesntBreak8 = py::class_<BreaksBase<8>, std::shared_ptr<BreaksBase<8>>>;
-#define CHECK_BASE(N) static_assert(std::is_same<typename DoesntBreak##N::type, BreaksBase<N>>::value, \
+#define CHECK_BASE(N) static_assert(std::is_same<typename DoesntBreak##N::type, BreaksBase<(N)>>::value, \
        "DoesntBreak" #N " has wrong type!")
 CHECK_BASE(1); CHECK_BASE(2); CHECK_BASE(3); CHECK_BASE(4); CHECK_BASE(5); CHECK_BASE(6); CHECK_BASE(7); CHECK_BASE(8);
-#define CHECK_ALIAS(N) static_assert(DoesntBreak##N::has_alias && std::is_same<typename DoesntBreak##N::type_alias, BreaksTramp<N>>::value, \
+#define CHECK_ALIAS(N) static_assert(DoesntBreak##N::has_alias && std::is_same<typename DoesntBreak##N::type_alias, BreaksTramp<(N)>>::value, \
        "DoesntBreak" #N " has wrong type_alias!")
 #define CHECK_NOALIAS(N) static_assert(!DoesntBreak##N::has_alias && std::is_void<typename DoesntBreak##N::type_alias>::value, \
        "DoesntBreak" #N " has type alias, but shouldn't!")
 CHECK_ALIAS(1); CHECK_ALIAS(2); CHECK_NOALIAS(3); CHECK_ALIAS(4); CHECK_NOALIAS(5); CHECK_ALIAS(6); CHECK_ALIAS(7); CHECK_NOALIAS(8);
-#define CHECK_HOLDER(N, TYPE) static_assert(std::is_same<typename DoesntBreak##N::holder_type, std::TYPE##_ptr<BreaksBase<N>>>::value, \
+#define CHECK_HOLDER(N, TYPE) static_assert(std::is_same<typename DoesntBreak##N::holder_type, std::TYPE##_ptr<BreaksBase<(N)>>>::value, \
        "DoesntBreak" #N " has wrong holder_type!")
 CHECK_HOLDER(1, unique); CHECK_HOLDER(2, unique); CHECK_HOLDER(3, unique); CHECK_HOLDER(4, unique); CHECK_HOLDER(5, unique);
 CHECK_HOLDER(6, shared); CHECK_HOLDER(7, shared); CHECK_HOLDER(8, shared);
@@ -510,7 +526,7 @@ CHECK_HOLDER(6, shared); CHECK_HOLDER(7, shared); CHECK_HOLDER(8, shared);
 // failures occurs).
 // We have to actually look into the type: the typedef alone isn't enough to instantiate the type:
-#define CHECK_BROKEN(N) static_assert(std::is_same<typename Breaks##N::type, BreaksBase<-N>>::value, \
+#define CHECK_BROKEN(N) static_assert(std::is_same<typename Breaks##N::type, BreaksBase<-(N)>>::value, \
        "Breaks1 has wrong type!");
 //// Two holder classes:

--- a/tests/test_class.py
+++ b/tests/test_class.py
@@ -2,9 +2,8 @@
 import pytest
 import env  # noqa: F401
+from pybind11_tests import ConstructorStats, UserType
 from pybind11_tests import class_ as m
-from pybind11_tests import UserType, ConstructorStats
 def test_repr():
@@ -26,6 +25,14 @@ def test_instance(msg):
    assert cstats.alive() == 0
+def test_instance_new(msg):
+    instance = m.NoConstructorNew()  # .__new__(m.NoConstructor.__class__)
+    cstats = ConstructorStats.get(m.NoConstructorNew)
+    assert cstats.alive() == 1
+    del instance
+    assert cstats.alive() == 0
 def test_type():
    assert m.check_type(1) == m.DerivedClass1
    with pytest.raises(RuntimeError) as execinfo:

--- a/tests/test_cmake_build/installed_embed/CMakeLists.txt
+++ b/tests/test_cmake_build/installed_embed/CMakeLists.txt
@@ -22,5 +22,7 @@ set_target_properties(test_installed_embed PROPERTIES OUTPUT_NAME test_cmake_bui
 # This may be needed to resolve header conflicts, e.g. between Python release and debug headers.
 set_target_properties(test_installed_embed PROPERTIES NO_SYSTEM_FROM_IMPORTED ON)
-add_custom_target(check_installed_embed $<TARGET_FILE:test_installed_embed>
+add_custom_target(
-                                        ${PROJECT_SOURCE_DIR}/../test.py)
+  check_installed_embed
+  $<TARGET_FILE:test_installed_embed> ${PROJECT_SOURCE_DIR}/../test.py
+  DEPENDS test_installed_embed)
--- a/tests/test_cmake_build/installed_function/CMakeLists.txt
+++ b/tests/test_cmake_build/installed_function/CMakeLists.txt
@@ -35,4 +35,5 @@ add_custom_target(
  PYTHONPATH=$<TARGET_FILE_DIR:test_installed_function>
  ${_Python_EXECUTABLE}
  ${PROJECT_SOURCE_DIR}/../test.py
-  ${PROJECT_NAME})
+  ${PROJECT_NAME}
+  DEPENDS test_installed_function)
--- a/tests/test_cmake_build/installed_target/CMakeLists.txt
+++ b/tests/test_cmake_build/installed_target/CMakeLists.txt
@@ -42,4 +42,5 @@ add_custom_target(
  PYTHONPATH=$<TARGET_FILE_DIR:test_installed_target>
  ${_Python_EXECUTABLE}
  ${PROJECT_SOURCE_DIR}/../test.py
-  ${PROJECT_NAME})
+  ${PROJECT_NAME}
+  DEPENDS test_installed_target)
--- a/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt
+++ b/tests/test_cmake_build/subdirectory_embed/CMakeLists.txt
@@ -23,8 +23,10 @@ add_executable(test_subdirectory_embed ../embed.cpp)
 target_link_libraries(test_subdirectory_embed PRIVATE pybind11::embed)
 set_target_properties(test_subdirectory_embed PROPERTIES OUTPUT_NAME test_cmake_build)
-add_custom_target(check_subdirectory_embed $<TARGET_FILE:test_subdirectory_embed>
+add_custom_target(
-                                           "${PROJECT_SOURCE_DIR}/../test.py")
+  check_subdirectory_embed
+  $<TARGET_FILE:test_subdirectory_embed> "${PROJECT_SOURCE_DIR}/../test.py"
+  DEPENDS test_subdirectory_embed)
 # Test custom export group -- PYBIND11_EXPORT_NAME
 add_library(test_embed_lib ../embed.cpp)

--- a/tests/test_cmake_build/subdirectory_function/CMakeLists.txt
+++ b/tests/test_cmake_build/subdirectory_function/CMakeLists.txt
@@ -31,4 +31,5 @@ add_custom_target(
  PYTHONPATH=$<TARGET_FILE_DIR:test_subdirectory_function>
  ${_Python_EXECUTABLE}
  ${PROJECT_SOURCE_DIR}/../test.py
-  ${PROJECT_NAME})
+  ${PROJECT_NAME}
+  DEPENDS test_subdirectory_function)
--- a/tests/test_cmake_build/subdirectory_target/CMakeLists.txt
+++ b/tests/test_cmake_build/subdirectory_target/CMakeLists.txt
@@ -37,4 +37,5 @@ add_custom_target(
  PYTHONPATH=$<TARGET_FILE_DIR:test_subdirectory_target>
  ${_Python_EXECUTABLE}
  ${PROJECT_SOURCE_DIR}/../test.py
-  ${PROJECT_NAME})
+  ${PROJECT_NAME}
+  DEPENDS test_subdirectory_target)
--- a/tests/test_cmake_build/test.py
+++ b/tests/test_cmake_build/test.py
 # -*- coding: utf-8 -*-
 import sys
 import test_cmake_build
+if str is not bytes:  # If not Python2
+    assert isinstance(__file__, str)  # Test this is properly set
 assert test_cmake_build.add(1, 2) == 3
 print("{} imports, runs, and adds: 1 + 2 = 3".format(sys.argv[1]))
--- a/tests/test_copy_move.cpp
+++ b/tests/test_copy_move.cpp
@@ -37,7 +37,7 @@ template <> lacking_move_ctor empty<lacking_move_ctor>::instance_ = {};
 class MoveOnlyInt {
 public:
    MoveOnlyInt() { print_default_created(this); }
-    MoveOnlyInt(int v) : value{v} { print_created(this, value); }
+    explicit MoveOnlyInt(int v) : value{v} { print_created(this, value); }
    MoveOnlyInt(MoveOnlyInt &&m) noexcept {
        print_move_created(this, m.value);
        std::swap(value, m.value);
@@ -56,7 +56,7 @@ public:
 class MoveOrCopyInt {
 public:
    MoveOrCopyInt() { print_default_created(this); }
-    MoveOrCopyInt(int v) : value{v} { print_created(this, value); }
+    explicit MoveOrCopyInt(int v) : value{v} { print_created(this, value); }
    MoveOrCopyInt(MoveOrCopyInt &&m) noexcept {
        print_move_created(this, m.value);
        std::swap(value, m.value);
@@ -75,7 +75,7 @@ public:
 class CopyOnlyInt {
 public:
    CopyOnlyInt() { print_default_created(this); }
-    CopyOnlyInt(int v) : value{v} { print_created(this, value); }
+    explicit CopyOnlyInt(int v) : value{v} { print_created(this, value); }
    CopyOnlyInt(const CopyOnlyInt &c) { print_copy_created(this, c.value); value = c.value; }
    CopyOnlyInt &operator=(const CopyOnlyInt &c) { print_copy_assigned(this, c.value); value = c.value; return *this; }
    ~CopyOnlyInt() { print_destroyed(this); }
@@ -107,8 +107,8 @@ public:
        if (!src) return none().release();
        return cast(*src, policy, parent);
    }
-    operator CopyOnlyInt*() { return &value; }
+    explicit operator CopyOnlyInt *() { return &value; }
-    operator CopyOnlyInt&() { return value; }
+    explicit operator CopyOnlyInt &() { return value; }
    template <typename T> using cast_op_type = pybind11::detail::cast_op_type<T>;
 };
 PYBIND11_NAMESPACE_END(detail)
@@ -219,7 +219,7 @@ TEST_SUBMODULE(copy_move_policies, m) {
    // #389: rvp::move should fall-through to copy on non-movable objects
    struct MoveIssue1 {
        int v;
-        MoveIssue1(int v) : v{v} {}
+        explicit MoveIssue1(int v) : v{v} {}
        MoveIssue1(const MoveIssue1 &c) = default;
        MoveIssue1(MoveIssue1 &&) = delete;
    };
@@ -227,7 +227,7 @@ TEST_SUBMODULE(copy_move_policies, m) {
    struct MoveIssue2 {
        int v;
-        MoveIssue2(int v) : v{v} {}
+        explicit MoveIssue2(int v) : v{v} {}
        MoveIssue2(MoveIssue2 &&) = default;
    };
    py::class_<MoveIssue2>(m, "MoveIssue2").def(py::init<int>()).def_readwrite("value", &MoveIssue2::v);

--- a/tests/test_copy_move.py
+++ b/tests/test_copy_move.py
 # -*- coding: utf-8 -*-
 import pytest
 from pybind11_tests import copy_move_policies as m

--- a/tests/test_custom_type_casters.py
+++ b/tests/test_custom_type_casters.py
 # -*- coding: utf-8 -*-
 import pytest
 from pybind11_tests import custom_type_casters as m

--- a/tests/test_custom_type_setup.cpp
+++ b/tests/test_custom_type_setup.cpp
+/*
+    tests/test_custom_type_setup.cpp -- Tests `pybind11::custom_type_setup`
+    Copyright (c) Google LLC
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+#include <pybind11/pybind11.h>
+#include "pybind11_tests.h"
+namespace py = pybind11;
+namespace {
+struct OwnsPythonObjects {
+    py::object value = py::none();
+};
+} // namespace
+TEST_SUBMODULE(custom_type_setup, m) {
+    py::class_<OwnsPythonObjects> cls(
+        m, "OwnsPythonObjects", py::custom_type_setup([](PyHeapTypeObject *heap_type) {
+            auto *type = &heap_type->ht_type;
+            type->tp_flags |= Py_TPFLAGS_HAVE_GC;
+            type->tp_traverse = [](PyObject *self_base, visitproc visit, void *arg) {
+                auto &self = py::cast<OwnsPythonObjects &>(py::handle(self_base));
+                Py_VISIT(self.value.ptr());
+                return 0;
+            };
+            type->tp_clear = [](PyObject *self_base) {
+                auto &self = py::cast<OwnsPythonObjects &>(py::handle(self_base));
+                self.value = py::none();
+                return 0;
+            };
+        }));
+    cls.def(py::init<>());
+    cls.def_readwrite("value", &OwnsPythonObjects::value);
+}
--- a/tests/test_custom_type_setup.py
+++ b/tests/test_custom_type_setup.py
+# -*- coding: utf-8 -*-
+import gc
+import weakref
+import pytest
+import env  # noqa: F401
+from pybind11_tests import custom_type_setup as m
+@pytest.fixture
+def gc_tester():
+    """Tests that an object is garbage collected.
+    Assumes that any unreferenced objects are fully collected after calling
+    `gc.collect()`.  That is true on CPython, but does not appear to reliably
+    hold on PyPy.
+    """
+    weak_refs = []
+    def add_ref(obj):
+        # PyPy does not support `gc.is_tracked`.
+        if hasattr(gc, "is_tracked"):
+            assert gc.is_tracked(obj)
+        weak_refs.append(weakref.ref(obj))
+    yield add_ref
+    gc.collect()
+    for ref in weak_refs:
+        assert ref() is None
+# PyPy does not seem to reliably garbage collect.
+@pytest.mark.skipif("env.PYPY")
+def test_self_cycle(gc_tester):
+    obj = m.OwnsPythonObjects()
+    obj.value = obj
+    gc_tester(obj)
+# PyPy does not seem to reliably garbage collect.
+@pytest.mark.skipif("env.PYPY")
+def test_indirect_cycle(gc_tester):
+    obj = m.OwnsPythonObjects()
+    obj_list = [obj]
+    obj.value = obj_list
+    gc_tester(obj)
--- a/tests/test_eigen.cpp
+++ b/tests/test_eigen.cpp
@@ -178,6 +178,7 @@ TEST_SUBMODULE(eigen, m) {
        ReturnTester() { print_created(this); }
        ~ReturnTester() { print_destroyed(this); }
        static Eigen::MatrixXd create() { return Eigen::MatrixXd::Ones(10, 10); }
+        // NOLINTNEXTLINE(readability-const-return-type)
        static const Eigen::MatrixXd createConst() { return Eigen::MatrixXd::Ones(10, 10); }
        Eigen::MatrixXd &get() { return mat; }
        Eigen::MatrixXd *getPtr() { return &mat; }
@@ -244,6 +245,9 @@ TEST_SUBMODULE(eigen, m) {
    // test_fixed, and various other tests
    m.def("fixed_r", [mat]() -> FixedMatrixR { return FixedMatrixR(mat); });
+    // Our Eigen does a hack which respects constness through the numpy writeable flag.
+    // Therefore, the const return actually affects this type despite being an rvalue.
+    // NOLINTNEXTLINE(readability-const-return-type)
    m.def("fixed_r_const", [mat]() -> const FixedMatrixR { return FixedMatrixR(mat); });
    m.def("fixed_c", [mat]() -> FixedMatrixC { return FixedMatrixC(mat); });
    m.def("fixed_copy_r", [](const FixedMatrixR &m) -> FixedMatrixR { return m; });

--- a/tests/test_eigen.py
+++ b/tests/test_eigen.py
 # -*- coding: utf-8 -*-
 import pytest
 from pybind11_tests import ConstructorStats
 np = pytest.importorskip("numpy")

--- a/tests/test_embed/CMakeLists.txt
+++ b/tests/test_embed/CMakeLists.txt
@@ -31,6 +31,7 @@ endif()
 add_custom_target(
  cpptest
  COMMAND "$<TARGET_FILE:test_embed>"
+  DEPENDS test_embed
  WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}")
 pybind11_add_module(external_module THIN_LTO external_module.cpp)

--- a/tests/test_embed/external_module.cpp
+++ b/tests/test_embed/external_module.cpp
@@ -9,7 +9,7 @@ namespace py = pybind11;
 PYBIND11_MODULE(external_module, m) {
    class A {
    public:
-        A(int value) : v{value} {};
+        explicit A(int value) : v{value} {};
        int v;
    };

--- a/tests/test_embed/test_interpreter.cpp
+++ b/tests/test_embed/test_interpreter.cpp
@@ -8,6 +8,7 @@
 #include <catch.hpp>
+#include <cstdlib>
 #include <fstream>
 #include <functional>
 #include <thread>
@@ -18,11 +19,12 @@ using namespace py::literals;
 class Widget {
 public:
-    Widget(std::string message) : message(std::move(message)) {}
+    explicit Widget(std::string message) : message(std::move(message)) {}
    virtual ~Widget() = default;
    std::string the_message() const { return message; }
    virtual int the_answer() const = 0;
+    virtual std::string argv0() const = 0;
 private:
    std::string message;
@@ -32,6 +34,7 @@ class PyWidget final : public Widget {
    using Widget::Widget;
    int the_answer() const override { PYBIND11_OVERRIDE_PURE(int, Widget, the_answer); }
+    std::string argv0() const override { PYBIND11_OVERRIDE_PURE(std::string, Widget, argv0); }
 };
 PYBIND11_EMBEDDED_MODULE(widget_module, m) {
@@ -74,8 +77,24 @@ TEST_CASE("Import error handling") {
    REQUIRE_NOTHROW(py::module_::import("widget_module"));
    REQUIRE_THROWS_WITH(py::module_::import("throw_exception"),
                        "ImportError: C++ Error");
+#if PY_VERSION_HEX >= 0x03030000
+    REQUIRE_THROWS_WITH(py::module_::import("throw_error_already_set"),
+                        Catch::Contains("ImportError: initialization failed"));
+    auto locals = py::dict("is_keyerror"_a=false, "message"_a="not set");
+    py::exec(R"(
+        try:
+            import throw_error_already_set
+        except ImportError as e:
+            is_keyerror = type(e.__cause__) == KeyError
+            message = str(e.__cause__)
+    )", py::globals(), locals);
+    REQUIRE(locals["is_keyerror"].cast<bool>() == true);
+    REQUIRE(locals["message"].cast<std::string>() == "'missing'");
+#else
    REQUIRE_THROWS_WITH(py::module_::import("throw_error_already_set"),
                        Catch::Contains("ImportError: KeyError"));
+#endif
 }
 TEST_CASE("There can be only one interpreter") {
@@ -283,3 +302,25 @@ TEST_CASE("Reload module from file") {
    result = module_.attr("test")().cast<int>();
    REQUIRE(result == 2);
 }
+TEST_CASE("sys.argv gets initialized properly") {
+    py::finalize_interpreter();
+    {
+        py::scoped_interpreter default_scope;
+        auto module = py::module::import("test_interpreter");
+        auto py_widget = module.attr("DerivedWidget")("The question");
+        const auto &cpp_widget = py_widget.cast<const Widget &>();
+        REQUIRE(cpp_widget.argv0().empty());
+    }
+    {
+        char *argv[] = {strdup("a.out")};
+        py::scoped_interpreter argv_scope(true, 1, argv);
+        std::free(argv[0]);
+        auto module = py::module::import("test_interpreter");
+        auto py_widget = module.attr("DerivedWidget")("The question");
+        const auto &cpp_widget = py_widget.cast<const Widget &>();
+        REQUIRE(cpp_widget.argv0() == "a.out");
+    }
+    py::initialize_interpreter();
+}
--- a/tests/test_embed/test_interpreter.py
+++ b/tests/test_embed/test_interpreter.py
 # -*- coding: utf-8 -*-
+import sys
 from widget_module import Widget
@@ -8,3 +10,6 @@ class DerivedWidget(Widget):
    def the_answer(self):
        return 42
+    def argv0(self):
+        return sys.argv[0]
--- a/tests/test_enum.cpp
+++ b/tests/test_enum.cpp
@@ -84,4 +84,65 @@ TEST_SUBMODULE(enums, m) {
            .value("ONE", SimpleEnum::THREE)
            .export_values();
    });
+    // test_enum_scalar
+    enum UnscopedUCharEnum : unsigned char {};
+    enum class ScopedShortEnum : short {};
+    enum class ScopedLongEnum : long {};
+    enum UnscopedUInt64Enum : std::uint64_t {};
+    static_assert(py::detail::all_of<
+        std::is_same<py::enum_<UnscopedUCharEnum>::Scalar, unsigned char>,
+        std::is_same<py::enum_<ScopedShortEnum>::Scalar, short>,
+        std::is_same<py::enum_<ScopedLongEnum>::Scalar, long>,
+        std::is_same<py::enum_<UnscopedUInt64Enum>::Scalar, std::uint64_t>
+    >::value, "Error during the deduction of enum's scalar type with normal integer underlying");
+    // test_enum_scalar_with_char_underlying
+    enum class ScopedCharEnum   : char     { Zero, Positive };
+    enum class ScopedWCharEnum  : wchar_t  { Zero, Positive };
+    enum class ScopedChar32Enum : char32_t { Zero, Positive };
+    enum class ScopedChar16Enum : char16_t { Zero, Positive };
+    // test the scalar of char type enums according to chapter 'Character types'
+    // from https://en.cppreference.com/w/cpp/language/types
+    static_assert(py::detail::any_of<
+        std::is_same<py::enum_<ScopedCharEnum>::Scalar, signed char>, // e.g. gcc on x86
+        std::is_same<py::enum_<ScopedCharEnum>::Scalar, unsigned char>  // e.g. arm linux
+    >::value, "char should be cast to either signed char or unsigned char");
+    static_assert(
+        sizeof(py::enum_<ScopedWCharEnum>::Scalar) == 2 ||
+        sizeof(py::enum_<ScopedWCharEnum>::Scalar) == 4
+    , "wchar_t should be either 16 bits (Windows) or 32 (everywhere else)");
+    static_assert(py::detail::all_of<
+        std::is_same<py::enum_<ScopedChar32Enum>::Scalar, std::uint_least32_t>,
+        std::is_same<py::enum_<ScopedChar16Enum>::Scalar, std::uint_least16_t>
+    >::value, "char32_t, char16_t (and char8_t)'s size, signedness, and alignment is determined");
+#if defined(PYBIND11_HAS_U8STRING)
+    enum class ScopedChar8Enum : char8_t { Zero, Positive };
+    static_assert(std::is_same<py::enum_<ScopedChar8Enum>::Scalar, unsigned char>::value);
+#endif
+    // test_char_underlying_enum
+    py::enum_<ScopedCharEnum>(m, "ScopedCharEnum")
+        .value("Zero", ScopedCharEnum::Zero)
+        .value("Positive", ScopedCharEnum::Positive);
+    py::enum_<ScopedWCharEnum>(m, "ScopedWCharEnum")
+        .value("Zero", ScopedWCharEnum::Zero)
+        .value("Positive", ScopedWCharEnum::Positive);
+    py::enum_<ScopedChar32Enum>(m, "ScopedChar32Enum")
+        .value("Zero", ScopedChar32Enum::Zero)
+        .value("Positive", ScopedChar32Enum::Positive);
+    py::enum_<ScopedChar16Enum>(m, "ScopedChar16Enum")
+        .value("Zero", ScopedChar16Enum::Zero)
+        .value("Positive", ScopedChar16Enum::Positive);
+    // test_bool_underlying_enum
+    enum class ScopedBoolEnum : bool { FALSE, TRUE };
+    // bool is unsigned (std::is_signed returns false) and 1-byte long, so represented with u8
+    static_assert(std::is_same<py::enum_<ScopedBoolEnum>::Scalar, std::uint8_t>::value, "");
+    py::enum_<ScopedBoolEnum>(m, "ScopedBoolEnum")
+        .value("FALSE", ScopedBoolEnum::FALSE)
+        .value("TRUE", ScopedBoolEnum::TRUE);
 }
--- a/tests/test_enum.py
+++ b/tests/test_enum.py
 # -*- coding: utf-8 -*-
 import pytest
+import env
 from pybind11_tests import enums as m
@@ -217,10 +219,16 @@ def test_binary_operators():
 def test_enum_to_int():
    m.test_enum_to_int(m.Flags.Read)
    m.test_enum_to_int(m.ClassWithUnscopedEnum.EMode.EFirstMode)
+    m.test_enum_to_int(m.ScopedCharEnum.Positive)
+    m.test_enum_to_int(m.ScopedBoolEnum.TRUE)
    m.test_enum_to_uint(m.Flags.Read)
    m.test_enum_to_uint(m.ClassWithUnscopedEnum.EMode.EFirstMode)
+    m.test_enum_to_uint(m.ScopedCharEnum.Positive)
+    m.test_enum_to_uint(m.ScopedBoolEnum.TRUE)
    m.test_enum_to_long_long(m.Flags.Read)
    m.test_enum_to_long_long(m.ClassWithUnscopedEnum.EMode.EFirstMode)
+    m.test_enum_to_long_long(m.ScopedCharEnum.Positive)
+    m.test_enum_to_long_long(m.ScopedBoolEnum.TRUE)
 def test_duplicate_enum_name():
@@ -229,6 +237,34 @@ def test_duplicate_enum_name():
    assert str(excinfo.value) == 'SimpleEnum: element "ONE" already exists!'
+def test_char_underlying_enum():  # Issue #1331/PR #1334:
+    assert type(m.ScopedCharEnum.Positive.__int__()) is int
+    assert int(m.ScopedChar16Enum.Zero) == 0
+    assert hash(m.ScopedChar32Enum.Positive) == 1
+    if env.PY2:
+        assert m.ScopedCharEnum.Positive.__getstate__() == 1  # long
+    else:
+        assert type(m.ScopedCharEnum.Positive.__getstate__()) is int
+    assert m.ScopedWCharEnum(1) == m.ScopedWCharEnum.Positive
+    with pytest.raises(TypeError):
+        # Even if the underlying type is char, only an int can be used to construct the enum:
+        m.ScopedCharEnum("0")
+def test_bool_underlying_enum():
+    assert type(m.ScopedBoolEnum.TRUE.__int__()) is int
+    assert int(m.ScopedBoolEnum.FALSE) == 0
+    assert hash(m.ScopedBoolEnum.TRUE) == 1
+    if env.PY2:
+        assert m.ScopedBoolEnum.TRUE.__getstate__() == 1  # long
+    else:
+        assert type(m.ScopedBoolEnum.TRUE.__getstate__()) is int
+    assert m.ScopedBoolEnum(1) == m.ScopedBoolEnum.TRUE
+    # Enum could construct with a bool
+    # (bool is a strict subclass of int, and False will be converted to 0)
+    assert m.ScopedBoolEnum(False) == m.ScopedBoolEnum.FALSE
 def test_docstring_signatures():
    for enum_type in [m.ScopedEnum, m.UnscopedEnum]:
        for attr in enum_type.__dict__.values():

--- a/tests/test_eval.cpp
+++ b/tests/test_eval.cpp
@@ -98,4 +98,22 @@ TEST_SUBMODULE(eval_, m) {
        auto int_class = py::eval("isinstance(42, int)", global);
        return global;
    });
+    // test_eval_closure
+    m.def("test_eval_closure", []() {
+        py::dict global;
+        global["closure_value"] = 42;
+        py::dict local;
+        local["closure_value"] = 0;
+        py::exec(R"(
+            local_value = closure_value
+            def func_global():
+                return closure_value
+            def func_local():
+                return local_value
+            )", global, local);
+        return std::make_pair(global, local);
+    });
 }
--- a/tests/test_eval.py
+++ b/tests/test_eval.py
--- a/tests/test_exceptions.cpp
+++ b/tests/test_exceptions.cpp
--- a/tests/test_exceptions.py
+++ b/tests/test_exceptions.py
--- a/tests/test_factory_constructors.cpp
+++ b/tests/test_factory_constructors.cpp
--- a/tests/test_factory_constructors.py
+++ b/tests/test_factory_constructors.py
--- a/tests/test_iostream.py
+++ b/tests/test_iostream.py
--- a/tests/test_kwargs_and_defaults.py
+++ b/tests/test_kwargs_and_defaults.py
--- a/tests/test_local_bindings.cpp
+++ b/tests/test_local_bindings.cpp
--- a/tests/test_local_bindings.py
+++ b/tests/test_local_bindings.py
--- a/tests/test_methods_and_attributes.cpp
+++ b/tests/test_methods_and_attributes.cpp
--- a/tests/test_methods_and_attributes.py
+++ b/tests/test_methods_and_attributes.py
--- a/tests/test_modules.cpp
+++ b/tests/test_modules.cpp
--- a/tests/test_modules.py
+++ b/tests/test_modules.py
--- a/tests/test_multiple_inheritance.cpp
+++ b/tests/test_multiple_inheritance.cpp
--- a/tests/test_multiple_inheritance.py
+++ b/tests/test_multiple_inheritance.py
--- a/tests/test_numpy_array.cpp
+++ b/tests/test_numpy_array.cpp
--- a/tests/test_numpy_array.py
+++ b/tests/test_numpy_array.py
--- a/tests/test_numpy_dtypes.cpp
+++ b/tests/test_numpy_dtypes.cpp
--- a/tests/test_numpy_dtypes.py
+++ b/tests/test_numpy_dtypes.py
--- a/tests/test_numpy_vectorize.cpp
+++ b/tests/test_numpy_vectorize.cpp
--- a/tests/test_numpy_vectorize.py
+++ b/tests/test_numpy_vectorize.py
--- a/tests/test_opaque_types.py
+++ b/tests/test_opaque_types.py
--- a/tests/test_operator_overloading.py
+++ b/tests/test_operator_overloading.py
--- a/tests/test_pickling.cpp
+++ b/tests/test_pickling.cpp
--- a/tests/test_pickling.py
+++ b/tests/test_pickling.py
--- a/tests/test_pytypes.cpp
+++ b/tests/test_pytypes.cpp
--- a/tests/test_pytypes.py
+++ b/tests/test_pytypes.py
--- a/tests/test_sequences_and_iterators.cpp
+++ b/tests/test_sequences_and_iterators.cpp
--- a/tests/test_sequences_and_iterators.py
+++ b/tests/test_sequences_and_iterators.py
--- a/tests/test_smart_ptr.cpp
+++ b/tests/test_smart_ptr.cpp
--- a/tests/test_stl.cpp
+++ b/tests/test_stl.cpp
--- a/tests/test_stl.py
+++ b/tests/test_stl.py
--- a/tests/test_stl_binders.cpp
+++ b/tests/test_stl_binders.cpp
--- a/tests/test_stl_binders.py
+++ b/tests/test_stl_binders.py
--- a/tests/test_tagbased_polymorphic.cpp
+++ b/tests/test_tagbased_polymorphic.cpp
--- a/tests/test_thread.cpp
+++ b/tests/test_thread.cpp
--- a/tests/test_thread.py
+++ b/tests/test_thread.py
--- a/tests/test_virtual_functions.cpp
+++ b/tests/test_virtual_functions.cpp
--- a/tools/libsize.py
+++ b/tools/libsize.py
--- a/tools/make_changelog.py
+++ b/tools/make_changelog.py
--- a/tools/pybind11Config.cmake.in
+++ b/tools/pybind11Config.cmake.in
--- a/tools/pybind11NewTools.cmake
+++ b/tools/pybind11NewTools.cmake
--- a/tools/pybind11Tools.cmake
+++ b/tools/pybind11Tools.cmake