Merge branch 'master' into v2.10

.github/ISSUE_TEMPLATE/bug-report.yml

@@ -6,7 +6,8 @@ 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).
+        Please do your best to make the issue as easy to act on as possible, and only submit here if there is clearly a problem with pybind11 (ask first if unsure). **Note that a reproducer in a PR is much more likely to get immediate attention.**
+
   - type: checkboxes
     id: steps
     attributes:
@@ -20,6 +21,13 @@ body:
         - 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: input
+    id: version
+    attributes:
+      label: What version (or hash if on master) of pybind11 are you using?
+    validations:
+      required: true
+
   - type: textarea
     id: description
     attributes:
@@ -40,6 +48,14 @@ body:
         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!
+        issue. — Note that a reproducer in a PR is much more likely to get
+        immediate attention: failing tests in the pybind11 CI are the best
+        starting point for working out fixes.
       render: text
+
+  - type: input
+    id: regression
+    attributes:
+      label: Is this a regression? Put the last known working version here if it is.
+      description: Put the last known working version here if this is a regression.
+      value: Not a regression

.github/workflows/ci.yml

@@ -17,6 +17,8 @@ env:
   PIP_ONLY_BINARY: numpy
   FORCE_COLOR: 3
   PYTEST_TIMEOUT: 300
+  # For cmake:
+  VERBOSE: 1
 
 jobs:
   # This is the "main" test suite, which tests a large number of different
@@ -25,7 +27,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        runs-on: [ubuntu-latest, windows-2022, macos-latest]
+        runs-on: [ubuntu-20.04, windows-2022, macos-latest]
         python:
         - '3.6'
         - '3.9'
@@ -42,12 +44,12 @@ jobs:
         # We support an optional key: args, for cmake args
         include:
           # Just add a key
-          - runs-on: ubuntu-latest
+          - runs-on: ubuntu-20.04
             python: '3.6'
             args: >
               -DPYBIND11_FINDPYTHON=ON
               -DCMAKE_CXX_FLAGS="-D_=1"
-          - runs-on: ubuntu-latest
+          - runs-on: ubuntu-20.04
             python: 'pypy-3.8'
             args: >
               -DPYBIND11_FINDPYTHON=ON
@@ -194,13 +196,13 @@ jobs:
           python-debug: false
 
     name: "🐍 ${{ matrix.python-version }}${{ matrix.python-debug && '-dbg' || '' }} (deadsnakes)${{ matrix.valgrind && ' • Valgrind' || '' }} • x64"
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
     - uses: actions/checkout@v3
 
     - name: Setup Python ${{ matrix.python-version }} (deadsnakes)
-      uses: deadsnakes/action@v2.1.1
+      uses: deadsnakes/action@v3.0.0
       with:
         python-version: ${{ matrix.python-version }}
         debug: ${{ matrix.python-debug }}
@@ -918,7 +920,7 @@ jobs:
     - 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" -DCMAKE_CXX_STANDARD=11 -DCMAKE_VERBOSE_MAKEFILE=ON -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -S . -B build
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -S . -B build
 
     - name: Build C++11
       run: cmake --build build -j 2
@@ -936,7 +938,7 @@ jobs:
       run: git clean -fdx
 
     - name: Configure C++14
-      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -DCMAKE_VERBOSE_MAKEFILE=ON -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -S . -B build2
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -S . -B build2
 
     - name: Build C++14
       run: cmake --build build2 -j 2
@@ -954,7 +956,7 @@ jobs:
       run: git clean -fdx
 
     - name: Configure C++17
-      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DCMAKE_VERBOSE_MAKEFILE=ON -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -S . -B build3
+      run: cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON -S . -B build3
 
     - name: Build C++17
       run: cmake --build build3 -j 2
@@ -967,3 +969,138 @@ jobs:
 
     - name: Interface test C++17
       run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build3 --target test_cmake_build
+
+  windows_clang:
+
+    strategy:
+      matrix:
+        os: [windows-latest]
+        python: ['3.10']
+
+    runs-on: "${{ matrix.os }}"
+
+    name: "🐍 ${{ matrix.python }} • ${{ matrix.os }} • clang-latest"
+
+    steps:
+      - name: Show env
+        run: env
+
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Set up Clang
+        uses: egor-tensin/setup-clang@v1
+
+      - name: Setup Python ${{ matrix.python }}
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python }}
+
+      - name: Update CMake
+        uses: jwlawson/actions-setup-cmake@v1.13
+
+      - name: Install ninja-build tool
+        uses: seanmiddleditch/gha-setup-ninja@v3
+
+      - name: Run pip installs
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install -r tests/requirements.txt
+
+      - name: Show Clang++ version
+        run: clang++ --version
+
+      - name: Show CMake version
+        run: cmake --version
+
+      # TODO: WERROR=ON
+      - name: Configure Clang
+        run: >
+          cmake -G Ninja -S . -B .
+          -DPYBIND11_WERROR=OFF
+          -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
+          -DDOWNLOAD_CATCH=ON
+          -DDOWNLOAD_EIGEN=ON
+          -DCMAKE_CXX_COMPILER=clang++
+          -DCMAKE_CXX_STANDARD=17
+
+      - name: Build
+        run: cmake --build . -j 2
+
+      - name: Python tests
+        run: cmake --build . --target pytest -j 2
+
+      - name: C++ tests
+        run: cmake --build . --target cpptest -j 2
+
+      - name: Interface test
+        run: cmake --build . --target test_cmake_build -j 2
+
+      - name: Clean directory
+        run: git clean -fdx
+
+  macos_brew_install_llvm:
+    name: "macos-latest • brew install llvm"
+    runs-on: macos-latest
+
+    env:
+      # https://apple.stackexchange.com/questions/227026/how-to-install-recent-clang-with-homebrew
+      LDFLAGS: '-L/usr/local/opt/llvm/lib -Wl,-rpath,/usr/local/opt/llvm/lib'
+
+    steps:
+      - name: Update PATH
+        run: echo "/usr/local/opt/llvm/bin" >> $GITHUB_PATH
+
+      - name: Show env
+        run: env
+
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Show Clang++ version before brew install llvm
+        run: clang++ --version
+
+      - name: brew install llvm
+        run: brew install llvm
+
+      - name: Show Clang++ version after brew install llvm
+        run: clang++ --version
+
+      - name: Update CMake
+        uses: jwlawson/actions-setup-cmake@v1.13
+
+      - name: Run pip installs
+        run: |
+          python3 -m pip install --upgrade pip
+          python3 -m pip install -r tests/requirements.txt
+          python3 -m pip install numpy
+          python3 -m pip install scipy
+
+      - name: Show CMake version
+        run: cmake --version
+
+      - name: CMake Configure
+        run: >
+          cmake -S . -B .
+          -DPYBIND11_WERROR=ON
+          -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
+          -DDOWNLOAD_CATCH=ON
+          -DDOWNLOAD_EIGEN=ON
+          -DCMAKE_CXX_COMPILER=clang++
+          -DCMAKE_CXX_STANDARD=17
+          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
+
+      - name: Build
+        run: cmake --build . -j 2
+
+      - name: Python tests
+        run: cmake --build . --target pytest -j 2
+
+      - name: C++ tests
+        run: cmake --build . --target cpptest -j 2
+
+      - name: Interface test
+        run: cmake --build . --target test_cmake_build -j 2
+
+      - name: Clean directory
+        run: git clean -fdx

.github/workflows/configure.yml

@@ -9,6 +9,10 @@ on:
       - stable
       - v*
 
+env:
+  # For cmake:
+  VERBOSE: 1
+
 jobs:
   # This tests various versions of CMake in various combinations, to make sure
   # the configure step passes.
@@ -16,12 +20,12 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        runs-on: [ubuntu-latest, macos-latest, windows-latest]
+        runs-on: [ubuntu-20.04, macos-latest, windows-latest]
         arch: [x64]
         cmake: ["3.23"]
 
         include:
-        - runs-on: ubuntu-latest
+        - runs-on: ubuntu-20.04
           arch: x64
           cmake: 3.4
 

.github/workflows/format.yml

@@ -14,6 +14,8 @@ on:
 
 env:
   FORCE_COLOR: 3
+  # For cmake:
+  VERBOSE: 1
 
 jobs:
   pre-commit:

.github/workflows/labeler.yml

@@ -10,7 +10,11 @@ jobs:
     steps:
 
     - uses: actions/labeler@main
-      if: github.event.pull_request.merged == true
+      if: >
+        github.event.pull_request.merged == true &&
+        !startsWith(github.event.pull_request.title, 'chore(deps):') &&
+        !startsWith(github.event.pull_request.title, 'ci(fix):') &&
+        !startsWith(github.event.pull_request.title, 'docs(changelog):')
       with:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
         configuration-path: .github/labeler_merged.yml

.github/workflows/pip.yml

@@ -98,13 +98,13 @@ jobs:
     - uses: actions/download-artifact@v3
 
     - name: Publish standard package
-      uses: pypa/gh-action-pypi-publish@v1.5.1
+      uses: pypa/gh-action-pypi-publish@v1.6.4
       with:
         password: ${{ secrets.pypi_password }}
         packages_dir: standard/
 
     - name: Publish global package
-      uses: pypa/gh-action-pypi-publish@v1.5.1
+      uses: pypa/gh-action-pypi-publish@v1.6.4
       with:
         password: ${{ secrets.pypi_password_global }}
         packages_dir: global/

.github/workflows/upstream.yml

@@ -11,6 +11,8 @@ concurrency:
 
 env:
   PIP_ONLY_BINARY: numpy
+  # For cmake:
+  VERBOSE: 1
 
 jobs:
   standard:

.gitignore

@@ -43,3 +43,4 @@ pybind11Targets.cmake
 /pybind11/share/*
 /docs/_build/*
 .ipynb_checkpoints/
+tests/main.cpp

.pre-commit-config.yaml

@@ -24,7 +24,7 @@ exclude: ^tools/JoinPaths.cmake$
 repos:
 # Standard hooks
 - repo: https://github.com/pre-commit/pre-commit-hooks
-  rev: "v4.3.0"
+  rev: "v4.4.0"
   hooks:
   - id: check-added-large-files
   - id: check-case-conflict
@@ -41,7 +41,7 @@ repos:
 
 # Upgrade old Python syntax
 - repo: https://github.com/asottile/pyupgrade
-  rev: "v2.38.2"
+  rev: "v3.3.0"
   hooks:
   - id: pyupgrade
     args: [--py36-plus]
@@ -54,7 +54,7 @@ repos:
 
 # Black, the code formatter, natively supports pre-commit
 - repo: https://github.com/psf/black
-  rev: "22.8.0" # Keep in sync with blacken-docs
+  rev: "22.10.0" # Keep in sync with blacken-docs
   hooks:
   - id: black
 
@@ -64,7 +64,7 @@ repos:
   hooks:
   - id: blacken-docs
     additional_dependencies:
-    - black==22.8.0 # keep in sync with black hook
+    - black==22.10.0 # keep in sync with black hook
 
 # Changes tabs to spaces
 - repo: https://github.com/Lucas-C/pre-commit-hooks
@@ -80,7 +80,7 @@ repos:
 
 # Autoremoves unused imports
 - repo: https://github.com/hadialqattan/pycln
-  rev: "v2.1.1"
+  rev: "v2.1.2"
   hooks:
   - id: pycln
     stages: [manual]
@@ -108,7 +108,7 @@ repos:
 
 # Flake8 also supports pre-commit natively (same author)
 - repo: https://github.com/PyCQA/flake8
-  rev: "5.0.4"
+  rev: "6.0.0"
   hooks:
   - id: flake8
     exclude: ^(docs/.*|tools/.*)$
@@ -116,7 +116,7 @@ repos:
 
 # PyLint has native support - not always usable, but works for us
 - repo: https://github.com/PyCQA/pylint
-  rev: "v2.15.3"
+  rev: "v2.15.8"
   hooks:
   - id: pylint
     files: ^pybind11
@@ -132,7 +132,7 @@ repos:
 
 # Check static types with mypy
 - repo: https://github.com/pre-commit/mirrors-mypy
-  rev: "v0.981"
+  rev: "v0.991"
   hooks:
   - id: mypy
     args: []
@@ -141,7 +141,7 @@ repos:
 
 # Checks the manifest for missing files (native support)
 - repo: https://github.com/mgedmin/check-manifest
-  rev: "0.48"
+  rev: "0.49"
   hooks:
   - id: check-manifest
     # This is a slow hook, so only run this if --hook-stage manual is passed
@@ -152,7 +152,7 @@ repos:
 # Use tools/codespell_ignore_lines_from_errors.py
 # to rebuild .codespell-ignore-lines
 - repo: https://github.com/codespell-project/codespell
-  rev: "v2.2.1"
+  rev: "v2.2.2"
   hooks:
   - id: codespell
     exclude: ".supp$"
@@ -175,7 +175,7 @@ repos:
 
 # Clang format the codebase automatically
 - repo: https://github.com/pre-commit/mirrors-clang-format
-  rev: "v14.0.6"
+  rev: "v15.0.4"
   hooks:
   - id: clang-format
     types_or: [c++, c, cuda]

CMakeLists.txt

@@ -126,6 +126,8 @@ set(PYBIND11_HEADERS
     include/pybind11/complex.h
     include/pybind11/options.h
     include/pybind11/eigen.h
+    include/pybind11/eigen/matrix.h
+    include/pybind11/eigen/tensor.h
     include/pybind11/embed.h
     include/pybind11/eval.h
     include/pybind11/gil.h

docs/advanced/exceptions.rst

@@ -177,9 +177,12 @@ section.
     may be explicitly (re-)thrown to delegate it to the other,
     previously-declared existing exception translators.
 
-    Note that ``libc++`` and ``libstdc++`` `behave differently <https://stackoverflow.com/questions/19496643/using-clang-fvisibility-hidden-and-typeinfo-and-type-erasure/28827430>`_
-    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>`_.
+    Note that ``libc++`` and ``libstdc++`` `behave differently under macOS
+    <https://stackoverflow.com/questions/19496643/using-clang-fvisibility-hidden-and-typeinfo-and-type-erasure/28827430>`_
+    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

docs/advanced/misc.rst

@@ -324,6 +324,15 @@ The class ``options`` allows you to selectively suppress auto-generated signatur
         m.def("add", [](int a, int b) { return a + b; }, "A function which adds two numbers");
     }
 
+pybind11 also appends all members of an enum to the resulting enum docstring.
+This default behavior can be disabled by using the ``disable_enum_members_docstring()``
+function of the ``options`` class.
+
+With ``disable_user_defined_docstrings()`` all user defined docstrings of
+``module_::def()``, ``class_::def()`` and ``enum_()`` are disabled, but the
+function signatures and enum members are included in the docstring, unless they
+are disabled separately.
+
 Note that changes to the settings affect only function bindings created during the
 lifetime of the ``options`` instance. When it goes out of scope at the end of the module's init function,
 the default settings are restored to prevent unwanted side effects.

docs/changelog.rst

@@ -15,6 +15,60 @@ IN DEVELOPMENT
 
 Changes will be summarized here periodically.
 
+Version 2.10.2 (Dec 20, 2022)
+-----------------------------
+
+Changes:
+
+* ``scoped_interpreter`` constructor taking ``PyConfig``.
+  `#4330 <https://github.com/pybind/pybind11/pull/4330>`_
+
+* ``pybind11/eigen/tensor.h`` adds converters to and from ``Eigen::Tensor`` and
+  ``Eigen::TensorMap``.
+  `#4201 <https://github.com/pybind/pybind11/pull/4201>`_
+
+* ``PyGILState_Check()``'s  were integrated to ``pybind11::handle``
+  ``inc_ref()`` & ``dec_ref()``. The added GIL checks are guarded by
+  ``PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF``, which is the default only if
+  ``NDEBUG`` is not defined.
+  `#4246 <https://github.com/pybind/pybind11/pull/4246>`_
+
+* Add option for enable/disable enum members in docstring.
+  `#2768 <https://github.com/pybind/pybind11/pull/2768>`_
+
+* Fixed typing of ``KeysView``, ``ValuesView`` and ``ItemsView`` in ``bind_map``.
+  `#4353 <https://github.com/pybind/pybind11/pull/4353>`_
+
+Bug fixes:
+
+* Bug fix affecting only Python 3.6 under very specific, uncommon conditions:
+  move ``PyEval_InitThreads()`` call to the correct location.
+  `#4350 <https://github.com/pybind/pybind11/pull/4350>`_
+
+* Fix segfault bug when passing foreign native functions to functional.h.
+  `#4254 <https://github.com/pybind/pybind11/pull/4254>`_
+
+Build system improvements:
+
+* Support setting PYTHON_LIBRARIES manually for Windows ARM cross-compilation
+  (classic mode).
+  `#4406 <https://github.com/pybind/pybind11/pull/4406>`_
+
+* Extend IPO/LTO detection for ICX (a.k.a IntelLLVM) compiler.
+  `#4402 <https://github.com/pybind/pybind11/pull/4402>`_
+
+* Allow calling ``find_package(pybind11 CONFIG)`` multiple times from separate
+  directories in the same CMake project and properly link Python (new mode).
+  `#4401 <https://github.com/pybind/pybind11/pull/4401>`_
+
+* ``multiprocessing_set_spawn`` in pytest fixture for added safety.
+  `#4377 <https://github.com/pybind/pybind11/pull/4377>`_
+
+* Fixed a bug in two pybind11/tools cmake scripts causing "Unknown arguments specified" errors.
+  `#4327 <https://github.com/pybind/pybind11/pull/4327>`_
+
+
+
 Version 2.10.1 (Oct 31, 2022)
 -----------------------------
 
@@ -95,7 +149,6 @@ Bug fixes:
   finalization.
   `#4192 <https://github.com/pybind/pybind11/pull/4192>`_
 
-
 Performance and style:
 
 * Reserve space in set and STL map casters if possible. This will prevent

include/pybind11/cast.h

@@ -29,6 +29,9 @@
 #include <vector>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
 PYBIND11_NAMESPACE_BEGIN(detail)
 
 template <typename type, typename SFINAE = void>
@@ -88,7 +91,8 @@ public:
     template <typename T_,                                                                        \
               ::pybind11::detail::enable_if_t<                                                    \
                   std::is_same<type, ::pybind11::detail::remove_cv_t<T_>>::value,                 \
-                  int> = 0>                                                                       \
+                  int>                                                                            \
+              = 0>                                                                                \
     static ::pybind11::handle cast(                                                               \
         T_ *src, ::pybind11::return_value_policy policy, ::pybind11::handle parent) {             \
         if (!src)                                                                                 \
@@ -389,7 +393,7 @@ struct string_caster {
 
         // For UTF-8 we avoid the need for a temporary `bytes` object by using
         // `PyUnicode_AsUTF8AndSize`.
-        if (PYBIND11_SILENCE_MSVC_C4127(UTF_N == 8)) {
+        if (UTF_N == 8) {
             Py_ssize_t size = -1;
             const auto *buffer
                 = reinterpret_cast<const CharT *>(PyUnicode_AsUTF8AndSize(load_src.ptr(), &size));
@@ -416,7 +420,7 @@ struct string_caster {
             = reinterpret_cast<const CharT *>(PYBIND11_BYTES_AS_STRING(utfNbytes.ptr()));
         size_t length = (size_t) PYBIND11_BYTES_SIZE(utfNbytes.ptr()) / sizeof(CharT);
         // Skip BOM for UTF-16/32
-        if (PYBIND11_SILENCE_MSVC_C4127(UTF_N > 8)) {
+        if (UTF_N > 8) {
             buffer++;
             length--;
         }
@@ -572,7 +576,7 @@ public:
         // figure 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 (PYBIND11_SILENCE_MSVC_C4127(StringCaster::UTF_N == 8) && str_len > 1 && str_len <= 4) {
+        if (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
@@ -598,7 +602,7 @@ 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 (PYBIND11_SILENCE_MSVC_C4127(StringCaster::UTF_N == 16) && str_len == 2) {
+        else if (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)");

include/pybind11/detail/common.h

@@ -11,14 +11,75 @@
 
 #define PYBIND11_VERSION_MAJOR 2
 #define PYBIND11_VERSION_MINOR 10
-#define PYBIND11_VERSION_PATCH 1
+#define PYBIND11_VERSION_PATCH 2
 
 // Similar to Python's convention: https://docs.python.org/3/c-api/apiabiversion.html
 // Additional convention: 0xD = dev
-#define PYBIND11_VERSION_HEX 0x020A0100
+#define PYBIND11_VERSION_HEX 0x020A0200
 
-#define PYBIND11_NAMESPACE_BEGIN(name) namespace name {
-#define PYBIND11_NAMESPACE_END(name) }
+// Define some generic pybind11 helper macros for warning management.
+//
+// Note that compiler-specific push/pop pairs are baked into the
+// PYBIND11_NAMESPACE_BEGIN/PYBIND11_NAMESPACE_END pair of macros. Therefore manual
+// PYBIND11_WARNING_PUSH/PYBIND11_WARNING_POP are usually only needed in `#include` sections.
+//
+// If you find you need to suppress a warning, please try to make the suppression as local as
+// possible using these macros. Please also be sure to push/pop with the pybind11 macros. Please
+// only use compiler specifics if you need to check specific versions, e.g. Apple Clang vs. vanilla
+// Clang.
+#if defined(_MSC_VER)
+#    define PYBIND11_COMPILER_MSVC
+#    define PYBIND11_PRAGMA(...) __pragma(__VA_ARGS__)
+#    define PYBIND11_WARNING_PUSH PYBIND11_PRAGMA(warning(push))
+#    define PYBIND11_WARNING_POP PYBIND11_PRAGMA(warning(pop))
+#elif defined(__INTEL_COMPILER)
+#    define PYBIND11_COMPILER_INTEL
+#    define PYBIND11_PRAGMA(...) _Pragma(#__VA_ARGS__)
+#    define PYBIND11_WARNING_PUSH PYBIND11_PRAGMA(warning push)
+#    define PYBIND11_WARNING_POP PYBIND11_PRAGMA(warning pop)
+#elif defined(__clang__)
+#    define PYBIND11_COMPILER_CLANG
+#    define PYBIND11_PRAGMA(...) _Pragma(#__VA_ARGS__)
+#    define PYBIND11_WARNING_PUSH PYBIND11_PRAGMA(clang diagnostic push)
+#    define PYBIND11_WARNING_POP PYBIND11_PRAGMA(clang diagnostic push)
+#elif defined(__GNUC__)
+#    define PYBIND11_COMPILER_GCC
+#    define PYBIND11_PRAGMA(...) _Pragma(#__VA_ARGS__)
+#    define PYBIND11_WARNING_PUSH PYBIND11_PRAGMA(GCC diagnostic push)
+#    define PYBIND11_WARNING_POP PYBIND11_PRAGMA(GCC diagnostic pop)
+#endif
+
+#ifdef PYBIND11_COMPILER_MSVC
+#    define PYBIND11_WARNING_DISABLE_MSVC(name) PYBIND11_PRAGMA(warning(disable : name))
+#else
+#    define PYBIND11_WARNING_DISABLE_MSVC(name)
+#endif
+
+#ifdef PYBIND11_COMPILER_CLANG
+#    define PYBIND11_WARNING_DISABLE_CLANG(name) PYBIND11_PRAGMA(clang diagnostic ignored name)
+#else
+#    define PYBIND11_WARNING_DISABLE_CLANG(name)
+#endif
+
+#ifdef PYBIND11_COMPILER_GCC
+#    define PYBIND11_WARNING_DISABLE_GCC(name) PYBIND11_PRAGMA(GCC diagnostic ignored name)
+#else
+#    define PYBIND11_WARNING_DISABLE_GCC(name)
+#endif
+
+#ifdef PYBIND11_COMPILER_INTEL
+#    define PYBIND11_WARNING_DISABLE_INTEL(name) PYBIND11_PRAGMA(warning disable name)
+#else
+#    define PYBIND11_WARNING_DISABLE_INTEL(name)
+#endif
+
+#define PYBIND11_NAMESPACE_BEGIN(name)                                                            \
+    namespace name {                                                                              \
+    PYBIND11_WARNING_PUSH
+
+#define PYBIND11_NAMESPACE_END(name)                                                              \
+    PYBIND11_WARNING_POP                                                                          \
+    }
 
 // Robust support for some features and loading modules compiled against different pybind versions
 // requires forcing hidden visibility on pybind code, so we enforce this by setting the attribute
@@ -96,13 +157,10 @@
 #endif
 
 #if !defined(PYBIND11_EXPORT_EXCEPTION)
-#    ifdef __MINGW32__
-// workaround for:
-// error: 'dllexport' implies default visibility, but xxx has already been declared with a
-// different visibility
-#        define PYBIND11_EXPORT_EXCEPTION
-#    else
+#    if defined(__apple_build_version__)
 #        define PYBIND11_EXPORT_EXCEPTION PYBIND11_EXPORT
+#    else
+#        define PYBIND11_EXPORT_EXCEPTION
 #    endif
 #endif
 
@@ -154,9 +212,9 @@
 
 /// Include Python header, disable linking to pythonX_d.lib on Windows in debug mode
 #if defined(_MSC_VER)
-#    pragma warning(push)
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_MSVC(4505)
 // C4505: 'PySlice_GetIndicesEx': unreferenced local function has been removed (PyPy only)
-#    pragma warning(disable : 4505)
 #    if defined(_DEBUG) && !defined(Py_DEBUG)
 // Workaround for a VS 2022 issue.
 // NOTE: This workaround knowingly violates the Python.h include order requirement:
@@ -239,7 +297,7 @@
 #        define _DEBUG
 #        undef PYBIND11_DEBUG_MARKER
 #    endif
-#    pragma warning(pop)
+PYBIND11_WARNING_POP
 #endif
 
 #include <cstddef>
@@ -265,6 +323,15 @@
 #    define PYBIND11_HAS_U8STRING
 #endif
 
+// See description of PR #4246:
+#if !defined(NDEBUG) && !defined(PY_ASSERT_GIL_HELD_INCREF_DECREF)                                \
+    && !(defined(PYPY_VERSION)                                                                    \
+         && defined(_MSC_VER)) /* PyPy Windows: pytest hangs indefinitely at the end of the       \
+                                  process (see PR #4268) */                                       \
+    && !defined(PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF)
+#    define PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF
+#endif
+
 // #define PYBIND11_STR_LEGACY_PERMISSIVE
 // If DEFINED, pybind11::str can hold PyUnicodeObject or PyBytesObject
 //             (probably surprising and never documented, but this was the
@@ -904,12 +971,6 @@ using expand_side_effects = bool[];
 
 PYBIND11_NAMESPACE_END(detail)
 
-#if defined(_MSC_VER)
-#    pragma warning(push)
-#    pragma warning(disable : 4275)
-//     warning C4275: An exported class was derived from a class that wasn't exported.
-//     Can be ignored when derived from a STL class.
-#endif
 /// C++ bindings of builtin Python exceptions
 class PYBIND11_EXPORT_EXCEPTION builtin_exception : public std::runtime_error {
 public:
@@ -917,9 +978,6 @@ public:
     /// Set the error using the Python C API
     virtual void set_error() const = 0;
 };
-#if defined(_MSC_VER)
-#    pragma warning(pop)
-#endif
 
 #define PYBIND11_RUNTIME_EXCEPTION(name, type)                                                    \
     class PYBIND11_EXPORT_EXCEPTION name : public builtin_exception {                             \
@@ -1148,17 +1206,6 @@ constexpr
 #    define PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(...)
 #endif
 
-#if defined(_MSC_VER) // All versions (as of July 2021).
-
-// warning C4127: Conditional expression is constant
-constexpr inline bool silence_msvc_c4127(bool cond) { return cond; }
-
-#    define PYBIND11_SILENCE_MSVC_C4127(...) ::pybind11::detail::silence_msvc_c4127(__VA_ARGS__)
-
-#else
-#    define PYBIND11_SILENCE_MSVC_C4127(...) __VA_ARGS__
-#endif
-
 #if defined(__clang__)                                                                            \
     && (defined(__apple_build_version__) /* AppleClang 13.0.0.13000029 was the only data point    \
                                             available. */                                         \

include/pybind11/detail/init.h

@@ -12,6 +12,9 @@
 #include "class.h"
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
 PYBIND11_NAMESPACE_BEGIN(detail)
 
 template <>
@@ -115,7 +118,7 @@ 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 (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr)) {
+    if (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
@@ -156,7 +159,7 @@ void construct(value_and_holder &v_h, Holder<Class> holder, bool 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 (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr)) {
+    if (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");
     }
@@ -174,7 +177,7 @@ 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 (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias) {
+    if (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));
@@ -206,10 +209,11 @@ struct constructor {
             extra...);
     }
 
-    template <typename Class,
-              typename... Extra,
-              enable_if_t<Class::has_alias && std::is_constructible<Cpp<Class>, Args...>::value,
-                          int> = 0>
+    template <
+        typename Class,
+        typename... Extra,
+        enable_if_t<Class::has_alias && std::is_constructible<Cpp<Class>, Args...>::value, int>
+        = 0>
     static void execute(Class &cl, const Extra &...extra) {
         cl.def(
             "__init__",
@@ -226,10 +230,11 @@ struct constructor {
             extra...);
     }
 
-    template <typename Class,
-              typename... Extra,
-              enable_if_t<Class::has_alias && !std::is_constructible<Cpp<Class>, Args...>::value,
-                          int> = 0>
+    template <
+        typename Class,
+        typename... Extra,
+        enable_if_t<Class::has_alias && !std::is_constructible<Cpp<Class>, Args...>::value, int>
+        = 0>
     static void execute(Class &cl, const Extra &...extra) {
         cl.def(
             "__init__",
@@ -245,10 +250,11 @@ struct constructor {
 // Implementing class for py::init_alias<...>()
 template <typename... Args>
 struct alias_constructor {
-    template <typename Class,
-              typename... Extra,
-              enable_if_t<Class::has_alias && std::is_constructible<Alias<Class>, Args...>::value,
-                          int> = 0>
+    template <
+        typename Class,
+        typename... Extra,
+        enable_if_t<Class::has_alias && std::is_constructible<Alias<Class>, Args...>::value, int>
+        = 0>
     static void execute(Class &cl, const Extra &...extra) {
         cl.def(
             "__init__",

include/pybind11/detail/internals.h

@@ -43,6 +43,8 @@ using ExceptionTranslator = void (*)(std::exception_ptr);
 
 PYBIND11_NAMESPACE_BEGIN(detail)
 
+constexpr const char *internals_function_record_capsule_name = "pybind11_function_record_capsule";
+
 // Forward declarations
 inline PyTypeObject *make_static_property_type();
 inline PyTypeObject *make_default_metaclass();
@@ -182,6 +184,16 @@ struct internals {
 #    endif // PYBIND11_INTERNALS_VERSION > 4
     // Unused if PYBIND11_SIMPLE_GIL_MANAGEMENT is defined:
     PyInterpreterState *istate = nullptr;
+
+#    if PYBIND11_INTERNALS_VERSION > 4
+    // Note that we have to use a std::string to allocate memory to ensure a unique address
+    // We want unique addresses since we use pointer equality to compare function records
+    std::string function_record_capsule_name = internals_function_record_capsule_name;
+#    endif
+
+    internals() = default;
+    internals(const internals &other) = delete;
+    internals &operator=(const internals &other) = delete;
     ~internals() {
 #    if PYBIND11_INTERNALS_VERSION > 4
         PYBIND11_TLS_FREE(loader_life_support_tls_key);
@@ -456,9 +468,6 @@ PYBIND11_NOINLINE internals &get_internals() {
         internals_ptr = new internals();
 #if defined(WITH_THREAD)
 
-#    if PY_VERSION_HEX < 0x03090000
-        PyEval_InitThreads();
-#    endif
         PyThreadState *tstate = PyThreadState_Get();
         if (!PYBIND11_TLS_KEY_CREATE(internals_ptr->tstate)) {
             pybind11_fail("get_internals: could not successfully initialize the tstate TSS key!");
@@ -548,6 +557,25 @@ const char *c_str(Args &&...args) {
     return strings.front().c_str();
 }
 
+inline const char *get_function_record_capsule_name() {
+#if PYBIND11_INTERNALS_VERSION > 4
+    return get_internals().function_record_capsule_name.c_str();
+#else
+    return nullptr;
+#endif
+}
+
+// Determine whether or not the following capsule contains a pybind11 function record.
+// Note that we use `internals` to make sure that only ABI compatible records are touched.
+//
+// This check is currently used in two places:
+// - An important optimization in functional.h to avoid overhead in C++ -> Python -> C++
+// - The sibling feature of cpp_function to allow overloads
+inline bool is_function_record_capsule(const capsule &cap) {
+    // Pointer equality as we rely on internals() to ensure unique pointers
+    return cap.name() == get_function_record_capsule_name();
+}
+
 PYBIND11_NAMESPACE_END(detail)
 
 /// Returns a named pointer that is shared among all extension modules (using the same

include/pybind11/detail/type_caster_base.h

@@ -1006,5 +1006,14 @@ protected:
     static Constructor make_move_constructor(...) { return nullptr; }
 };
 
+PYBIND11_NOINLINE std::string type_info_description(const std::type_info &ti) {
+    if (auto *type_data = get_type_info(ti)) {
+        handle th((PyObject *) type_data->type);
+        return th.attr("__module__").cast<std::string>() + '.'
+               + th.attr("__qualname__").cast<std::string>();
+    }
+    return clean_type_id(ti.name());
+}
+
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

include/pybind11/eigen.h

@@ -9,705 +9,4 @@
 
 #pragma once
 
-/* HINT: To suppress warnings originating from the Eigen headers, use -isystem.
-   See also:
-       https://stackoverflow.com/questions/2579576/i-dir-vs-isystem-dir
-       https://stackoverflow.com/questions/1741816/isystem-for-ms-visual-studio-c-compiler
-*/
-
-#include "numpy.h"
-
-// The C4127 suppression was introduced for Eigen 3.4.0. In theory we could
-// make it version specific, or even remove it later, but considering that
-// 1. C4127 is generally far more distracting than useful for modern template code, and
-// 2. we definitely want to ignore any MSVC warnings originating from Eigen code,
-//    it is probably best to keep this around indefinitely.
-#if defined(_MSC_VER)
-#    pragma warning(push)
-#    pragma warning(disable : 4127) // C4127: conditional expression is constant
-#    pragma warning(disable : 5054) // https://github.com/pybind/pybind11/pull/3741
-//       C5054: operator '&': deprecated between enumerations of different types
-#elif defined(__MINGW32__)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
-#endif
-
-#include <Eigen/Core>
-#include <Eigen/SparseCore>
-
-#if defined(_MSC_VER)
-#    pragma warning(pop)
-#elif defined(__MINGW32__)
-#    pragma GCC diagnostic pop
-#endif
-
-// Eigen prior to 3.2.7 doesn't have proper move constructors--but worse, some classes get implicit
-// move constructors that break things.  We could detect this an explicitly copy, but an extra copy
-// of matrices seems highly undesirable.
-static_assert(EIGEN_VERSION_AT_LEAST(3, 2, 7),
-              "Eigen support in pybind11 requires Eigen >= 3.2.7");
-
-PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
-
-// Provide a convenience alias for easier pass-by-ref usage with fully dynamic strides:
-using EigenDStride = Eigen::Stride<Eigen::Dynamic, Eigen::Dynamic>;
-template <typename MatrixType>
-using EigenDRef = Eigen::Ref<MatrixType, 0, EigenDStride>;
-template <typename MatrixType>
-using EigenDMap = Eigen::Map<MatrixType, 0, EigenDStride>;
-
-PYBIND11_NAMESPACE_BEGIN(detail)
-
-#if EIGEN_VERSION_AT_LEAST(3, 3, 0)
-using EigenIndex = Eigen::Index;
-template <typename Scalar, int Flags, typename StorageIndex>
-using EigenMapSparseMatrix = Eigen::Map<Eigen::SparseMatrix<Scalar, Flags, StorageIndex>>;
-#else
-using EigenIndex = EIGEN_DEFAULT_DENSE_INDEX_TYPE;
-template <typename Scalar, int Flags, typename StorageIndex>
-using EigenMapSparseMatrix = Eigen::MappedSparseMatrix<Scalar, Flags, StorageIndex>;
-#endif
-
-// Matches Eigen::Map, Eigen::Ref, blocks, etc:
-template <typename T>
-using is_eigen_dense_map = all_of<is_template_base_of<Eigen::DenseBase, T>,
-                                  std::is_base_of<Eigen::MapBase<T, Eigen::ReadOnlyAccessors>, T>>;
-template <typename T>
-using is_eigen_mutable_map = std::is_base_of<Eigen::MapBase<T, Eigen::WriteAccessors>, T>;
-template <typename T>
-using is_eigen_dense_plain
-    = all_of<negation<is_eigen_dense_map<T>>, is_template_base_of<Eigen::PlainObjectBase, T>>;
-template <typename T>
-using is_eigen_sparse = is_template_base_of<Eigen::SparseMatrixBase, T>;
-// Test for objects inheriting from EigenBase<Derived> that aren't captured by the above.  This
-// basically covers anything that can be assigned to a dense matrix but that don't have a typical
-// matrix data layout that can be copied from their .data().  For example, DiagonalMatrix and
-// SelfAdjointView fall into this category.
-template <typename T>
-using is_eigen_other
-    = all_of<is_template_base_of<Eigen::EigenBase, T>,
-             negation<any_of<is_eigen_dense_map<T>, is_eigen_dense_plain<T>, is_eigen_sparse<T>>>>;
-
-// Captures numpy/eigen conformability status (returned by EigenProps::conformable()):
-template <bool EigenRowMajor>
-struct EigenConformable {
-    bool conformable = false;
-    EigenIndex rows = 0, cols = 0;
-    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, EigenIndex rstride, EigenIndex cstride)
-        : conformable{true}, rows{r}, cols{c},
-          // TODO: when Eigen bug #747 is fixed, remove the tests for non-negativity.
-          // http://eigen.tuxfamily.org/bz/show_bug.cgi?id=747
-          stride{EigenRowMajor ? (rstride > 0 ? rstride : 0)
-                               : (cstride > 0 ? cstride : 0) /* outer stride */,
-                 EigenRowMajor ? (cstride > 0 ? cstride : 0)
-                               : (rstride > 0 ? rstride : 0) /* inner stride */},
-          negativestrides{rstride < 0 || cstride < 0} {}
-    // Vector type:
-    EigenConformable(EigenIndex r, EigenIndex c, EigenIndex stride)
-        : EigenConformable(r, c, r == 1 ? c * stride : stride, c == 1 ? r : r * stride) {}
-
-    template <typename props>
-    bool stride_compatible() const {
-        // To have compatible strides, we need (on both dimensions) one of fully dynamic strides,
-        // matching strides, or a dimension size of 1 (in which case the stride value is
-        // irrelevant). Alternatively, if any dimension size is 0, the strides are not relevant
-        // (and numpy ≥ 1.23 sets the strides to 0 in that case, so we need to check explicitly).
-        if (negativestrides) {
-            return false;
-        }
-        if (rows == 0 || cols == 0) {
-            return true;
-        }
-        return (props::inner_stride == Eigen::Dynamic || props::inner_stride == stride.inner()
-                || (EigenRowMajor ? cols : rows) == 1)
-               && (props::outer_stride == Eigen::Dynamic || props::outer_stride == stride.outer()
-                   || (EigenRowMajor ? rows : cols) == 1);
-    }
-    // NOLINTNEXTLINE(google-explicit-constructor)
-    operator bool() const { return conformable; }
-};
-
-template <typename Type>
-struct eigen_extract_stride {
-    using type = Type;
-};
-template <typename PlainObjectType, int MapOptions, typename StrideType>
-struct eigen_extract_stride<Eigen::Map<PlainObjectType, MapOptions, StrideType>> {
-    using type = StrideType;
-};
-template <typename PlainObjectType, int Options, typename StrideType>
-struct eigen_extract_stride<Eigen::Ref<PlainObjectType, Options, StrideType>> {
-    using type = StrideType;
-};
-
-// Helper struct for extracting information from an Eigen type
-template <typename Type_>
-struct EigenProps {
-    using Type = Type_;
-    using Scalar = typename Type::Scalar;
-    using StrideType = typename eigen_extract_stride<Type>::type;
-    static constexpr EigenIndex rows = Type::RowsAtCompileTime, cols = Type::ColsAtCompileTime,
-                                size = Type::SizeAtCompileTime;
-    static constexpr bool row_major = Type::IsRowMajor,
-                          vector
-                          = Type::IsVectorAtCompileTime, // At least one dimension has fixed size 1
-        fixed_rows = rows != Eigen::Dynamic, fixed_cols = cols != Eigen::Dynamic,
-                          fixed = size != Eigen::Dynamic, // Fully-fixed size
-        dynamic = !fixed_rows && !fixed_cols;             // Fully-dynamic size
-
-    template <EigenIndex i, EigenIndex ifzero>
-    using if_zero = std::integral_constant<EigenIndex, i == 0 ? ifzero : i>;
-    static constexpr EigenIndex inner_stride
-        = if_zero<StrideType::InnerStrideAtCompileTime, 1>::value,
-        outer_stride = if_zero < StrideType::OuterStrideAtCompileTime,
-        vector      ? size
-        : row_major ? cols
-                    : rows > ::value;
-    static constexpr bool dynamic_stride
-        = inner_stride == Eigen::Dynamic && outer_stride == Eigen::Dynamic;
-    static constexpr bool requires_row_major
-        = !dynamic_stride && !vector && (row_major ? inner_stride : outer_stride) == 1;
-    static constexpr bool requires_col_major
-        = !dynamic_stride && !vector && (row_major ? outer_stride : inner_stride) == 1;
-
-    // Takes an input array and determines whether we can make it fit into the Eigen type.  If
-    // the array is a vector, we attempt to fit it into either an Eigen 1xN or Nx1 vector
-    // (preferring the latter if it will fit in either, i.e. for a fully dynamic matrix type).
-    static EigenConformable<row_major> conformable(const array &a) {
-        const auto dims = a.ndim();
-        if (dims < 1 || dims > 2) {
-            return false;
-        }
-
-        if (dims == 2) { // Matrix type: require exact match (or dynamic)
-
-            EigenIndex np_rows = a.shape(0), 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 ((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};
-        }
-
-        // Otherwise we're storing an n-vector.  Only one of the strides will be used, but
-        // whichever is used, we want the (single) numpy stride value.
-        const EigenIndex n = a.shape(0),
-                         stride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar));
-
-        if (vector) { // Eigen type is a compile-time vector
-            if (PYBIND11_SILENCE_MSVC_C4127(fixed) && size != n) {
-                return false; // Vector size mismatch
-            }
-            return {rows == 1 ? 1 : n, cols == 1 ? 1 : n, stride};
-        }
-        if (fixed) {
-            // The type has a fixed size, but is not a vector: abort
-            return false;
-        }
-        if (fixed_cols) {
-            // Since this isn't a vector, cols must be != 1.  We allow this only if it exactly
-            // equals the number of elements (rows is Dynamic, and so 1 row is allowed).
-            if (cols != n) {
-                return false;
-            }
-            return {1, n, stride};
-        } // Otherwise it's either fully dynamic, or column dynamic; both become a column vector
-        if (PYBIND11_SILENCE_MSVC_C4127(fixed_rows) && rows != n) {
-            return false;
-        }
-        return {n, 1, stride};
-    }
-
-    static constexpr bool show_writeable
-        = is_eigen_dense_map<Type>::value && is_eigen_mutable_map<Type>::value;
-    static constexpr bool show_order = is_eigen_dense_map<Type>::value;
-    static constexpr bool show_c_contiguous = show_order && requires_row_major;
-    static constexpr bool show_f_contiguous
-        = !show_c_contiguous && show_order && requires_col_major;
-
-    static constexpr auto descriptor
-        = const_name("numpy.ndarray[") + npy_format_descriptor<Scalar>::name + const_name("[")
-          + const_name<fixed_rows>(const_name<(size_t) rows>(), const_name("m")) + const_name(", ")
-          + const_name<fixed_cols>(const_name<(size_t) cols>(), const_name("n")) + const_name("]")
-          +
-          // For a reference type (e.g. Ref<MatrixXd>) we have other constraints that might need to
-          // be satisfied: writeable=True (for a mutable reference), and, depending on the map's
-          // stride options, possibly f_contiguous or c_contiguous.  We include them in the
-          // descriptor output to provide some hint as to why a TypeError is occurring (otherwise
-          // it can be confusing to see that a function accepts a 'numpy.ndarray[float64[3,2]]' and
-          // an error message that you *gave* a numpy.ndarray of the right type and dimensions.
-          const_name<show_writeable>(", flags.writeable", "")
-          + const_name<show_c_contiguous>(", flags.c_contiguous", "")
-          + const_name<show_f_contiguous>(", flags.f_contiguous", "") + const_name("]");
-};
-
-// Casts an Eigen type to numpy array.  If given a base, the numpy array references the src data,
-// otherwise it'll make a copy.  writeable lets you turn off the writeable flag for the array.
-template <typename props>
-handle
-eigen_array_cast(typename props::Type const &src, handle base = handle(), bool writeable = true) {
-    constexpr ssize_t elem_size = sizeof(typename props::Scalar);
-    array a;
-    if (props::vector) {
-        a = array({src.size()}, {elem_size * src.innerStride()}, src.data(), base);
-    } else {
-        a = array({src.rows(), src.cols()},
-                  {elem_size * src.rowStride(), elem_size * src.colStride()},
-                  src.data(),
-                  base);
-    }
-
-    if (!writeable) {
-        array_proxy(a.ptr())->flags &= ~detail::npy_api::NPY_ARRAY_WRITEABLE_;
-    }
-
-    return a.release();
-}
-
-// Takes an lvalue ref to some Eigen type and a (python) base object, creating a numpy array that
-// reference the Eigen object's data with `base` as the python-registered base class (if omitted,
-// the base will be set to None, and lifetime management is up to the caller).  The numpy array is
-// non-writeable if the given type is const.
-template <typename props, typename Type>
-handle eigen_ref_array(Type &src, handle parent = none()) {
-    // none here is to get past array's should-we-copy detection, which currently always
-    // copies when there is no base.  Setting the base to None should be harmless.
-    return eigen_array_cast<props>(src, parent, !std::is_const<Type>::value);
-}
-
-// Takes a pointer to some dense, plain Eigen type, builds a capsule around it, then returns a
-// numpy array that references the encapsulated data with a python-side reference to the capsule to
-// tie its destruction to that of any dependent python objects.  Const-ness is determined by
-// whether or not the Type of the pointer given is const.
-template <typename props, typename Type, typename = enable_if_t<is_eigen_dense_plain<Type>::value>>
-handle eigen_encapsulate(Type *src) {
-    capsule base(src, [](void *o) { delete static_cast<Type *>(o); });
-    return eigen_ref_array<props>(*src, base);
-}
-
-// Type caster for regular, dense matrix types (e.g. MatrixXd), but not maps/refs/etc. of dense
-// types.
-template <typename Type>
-struct type_caster<Type, enable_if_t<is_eigen_dense_plain<Type>::value>> {
-    using Scalar = typename Type::Scalar;
-    using props = EigenProps<Type>;
-
-    bool load(handle src, bool convert) {
-        // If we're in no-convert mode, only load if given an array of the correct type
-        if (!convert && !isinstance<array_t<Scalar>>(src)) {
-            return false;
-        }
-
-        // Coerce into an array, but don't do type conversion yet; the copy below handles it.
-        auto buf = array::ensure(src);
-
-        if (!buf) {
-            return false;
-        }
-
-        auto dims = buf.ndim();
-        if (dims < 1 || dims > 2) {
-            return false;
-        }
-
-        auto fits = props::conformable(buf);
-        if (!fits) {
-            return false;
-        }
-
-        // Allocate the new type, then build a numpy reference into it
-        value = Type(fits.rows, fits.cols);
-        auto ref = reinterpret_steal<array>(eigen_ref_array<props>(value));
-        if (dims == 1) {
-            ref = ref.squeeze();
-        } else if (ref.ndim() == 1) {
-            buf = buf.squeeze();
-        }
-
-        int result = detail::npy_api::get().PyArray_CopyInto_(ref.ptr(), buf.ptr());
-
-        if (result < 0) { // Copy failed!
-            PyErr_Clear();
-            return false;
-        }
-
-        return true;
-    }
-
-private:
-    // Cast implementation
-    template <typename CType>
-    static handle cast_impl(CType *src, return_value_policy policy, handle parent) {
-        switch (policy) {
-            case return_value_policy::take_ownership:
-            case return_value_policy::automatic:
-                return eigen_encapsulate<props>(src);
-            case return_value_policy::move:
-                return eigen_encapsulate<props>(new CType(std::move(*src)));
-            case return_value_policy::copy:
-                return eigen_array_cast<props>(*src);
-            case return_value_policy::reference:
-            case return_value_policy::automatic_reference:
-                return eigen_ref_array<props>(*src);
-            case return_value_policy::reference_internal:
-                return eigen_ref_array<props>(*src, parent);
-            default:
-                throw cast_error("unhandled return_value_policy: should not happen!");
-        };
-    }
-
-public:
-    // Normal returned non-reference, non-const value:
-    static handle cast(Type &&src, return_value_policy /* policy */, handle parent) {
-        return cast_impl(&src, return_value_policy::move, parent);
-    }
-    // If you return a non-reference const, we mark the numpy array readonly:
-    static handle cast(const Type &&src, return_value_policy /* policy */, handle parent) {
-        return cast_impl(&src, return_value_policy::move, parent);
-    }
-    // lvalue reference return; default (automatic) becomes copy
-    static handle cast(Type &src, return_value_policy policy, handle parent) {
-        if (policy == return_value_policy::automatic
-            || policy == return_value_policy::automatic_reference) {
-            policy = return_value_policy::copy;
-        }
-        return cast_impl(&src, policy, parent);
-    }
-    // const lvalue reference return; default (automatic) becomes copy
-    static handle cast(const Type &src, return_value_policy policy, handle parent) {
-        if (policy == return_value_policy::automatic
-            || policy == return_value_policy::automatic_reference) {
-            policy = return_value_policy::copy;
-        }
-        return cast(&src, policy, parent);
-    }
-    // non-const pointer return
-    static handle cast(Type *src, return_value_policy policy, handle parent) {
-        return cast_impl(src, policy, parent);
-    }
-    // const pointer return
-    static handle cast(const Type *src, return_value_policy policy, handle parent) {
-        return cast_impl(src, policy, parent);
-    }
-
-    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>;
-
-private:
-    Type value;
-};
-
-// Base class for casting reference/map/block/etc. objects back to python.
-template <typename MapType>
-struct eigen_map_caster {
-private:
-    using props = EigenProps<MapType>;
-
-public:
-    // Directly referencing a ref/map's data is a bit dangerous (whatever the map/ref points to has
-    // to stay around), but we'll allow it under the assumption that you know what you're doing
-    // (and have an appropriate keep_alive in place).  We return a numpy array pointing directly at
-    // the ref's data (The numpy array ends up read-only if the ref was to a const matrix type.)
-    // Note that this means you need to ensure you don't destroy the object in some other way (e.g.
-    // with an appropriate keep_alive, or with a reference to a statically allocated matrix).
-    static handle cast(const MapType &src, return_value_policy policy, handle parent) {
-        switch (policy) {
-            case return_value_policy::copy:
-                return eigen_array_cast<props>(src);
-            case return_value_policy::reference_internal:
-                return eigen_array_cast<props>(src, parent, is_eigen_mutable_map<MapType>::value);
-            case return_value_policy::reference:
-            case return_value_policy::automatic:
-            case return_value_policy::automatic_reference:
-                return eigen_array_cast<props>(src, none(), is_eigen_mutable_map<MapType>::value);
-            default:
-                // move, take_ownership don't make any sense for a ref/map:
-                pybind11_fail("Invalid return_value_policy for Eigen Map/Ref/Block type");
-        }
-    }
-
-    static constexpr auto name = props::descriptor;
-
-    // Explicitly delete these: support python -> C++ conversion on these (i.e. these can be return
-    // types but not bound arguments).  We still provide them (with an explicitly delete) so that
-    // you end up here if you try anyway.
-    bool load(handle, bool) = delete;
-    operator MapType() = delete;
-    template <typename>
-    using cast_op_type = MapType;
-};
-
-// We can return any map-like object (but can only load Refs, specialized next):
-template <typename Type>
-struct type_caster<Type, enable_if_t<is_eigen_dense_map<Type>::value>> : eigen_map_caster<Type> {};
-
-// Loader for Ref<...> arguments.  See the documentation for info on how to make this work without
-// copying (it requires some extra effort in many cases).
-template <typename PlainObjectType, typename StrideType>
-struct type_caster<
-    Eigen::Ref<PlainObjectType, 0, StrideType>,
-    enable_if_t<is_eigen_dense_map<Eigen::Ref<PlainObjectType, 0, StrideType>>::value>>
-    : public eigen_map_caster<Eigen::Ref<PlainObjectType, 0, StrideType>> {
-private:
-    using Type = Eigen::Ref<PlainObjectType, 0, StrideType>;
-    using props = EigenProps<Type>;
-    using Scalar = typename props::Scalar;
-    using MapType = Eigen::Map<PlainObjectType, 0, StrideType>;
-    using Array
-        = array_t<Scalar,
-                  array::forcecast
-                      | ((props::row_major ? props::inner_stride : props::outer_stride) == 1
-                             ? array::c_style
-                         : (props::row_major ? props::outer_stride : props::inner_stride) == 1
-                             ? array::f_style
-                             : 0)>;
-    static constexpr bool need_writeable = is_eigen_mutable_map<Type>::value;
-    // Delay construction (these have no default constructor)
-    std::unique_ptr<MapType> map;
-    std::unique_ptr<Type> ref;
-    // Our array.  When possible, this is just a numpy array pointing to the source data, but
-    // sometimes we can't avoid copying (e.g. input is not a numpy array at all, has an
-    // incompatible layout, or is an array of a type that needs to be converted).  Using a numpy
-    // temporary (rather than an Eigen temporary) saves an extra copy when we need both type
-    // conversion and storage order conversion.  (Note that we refuse to use this temporary copy
-    // when loading an argument for a Ref<M> with M non-const, i.e. a read-write reference).
-    Array copy_or_ref;
-
-public:
-    bool load(handle src, bool convert) {
-        // First check whether what we have is already an array of the right type.  If not, we
-        // can't avoid a copy (because the copy is also going to do type conversion).
-        bool need_copy = !isinstance<Array>(src);
-
-        EigenConformable<props::row_major> fits;
-        if (!need_copy) {
-            // We don't need a converting copy, but we also need to check whether the strides are
-            // compatible with the Ref's stride requirements
-            auto aref = reinterpret_borrow<Array>(src);
-
-            if (aref && (!need_writeable || aref.writeable())) {
-                fits = props::conformable(aref);
-                if (!fits) {
-                    return false; // Incompatible dimensions
-                }
-                if (!fits.template stride_compatible<props>()) {
-                    need_copy = true;
-                } else {
-                    copy_or_ref = std::move(aref);
-                }
-            } else {
-                need_copy = true;
-            }
-        }
-
-        if (need_copy) {
-            // We need to copy: If we need a mutable reference, or we're not supposed to convert
-            // (either because we're in the no-convert overload pass, or because we're explicitly
-            // instructed not to copy (via `py::arg().noconvert()`) we have to fail loading.
-            if (!convert || need_writeable) {
-                return false;
-            }
-
-            Array copy = Array::ensure(src);
-            if (!copy) {
-                return false;
-            }
-            fits = props::conformable(copy);
-            if (!fits || !fits.template stride_compatible<props>()) {
-                return false;
-            }
-            copy_or_ref = std::move(copy);
-            loader_life_support::add_patient(copy_or_ref);
-        }
-
-        ref.reset();
-        map.reset(new MapType(data(copy_or_ref),
-                              fits.rows,
-                              fits.cols,
-                              make_stride(fits.stride.outer(), fits.stride.inner())));
-        ref.reset(new Type(*map));
-
-        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>;
-
-private:
-    template <typename T = Type, enable_if_t<is_eigen_mutable_map<T>::value, int> = 0>
-    Scalar *data(Array &a) {
-        return a.mutable_data();
-    }
-
-    template <typename T = Type, enable_if_t<!is_eigen_mutable_map<T>::value, int> = 0>
-    const Scalar *data(Array &a) {
-        return a.data();
-    }
-
-    // Attempt to figure out a constructor of `Stride` that will work.
-    // If both strides are fixed, use a default constructor:
-    template <typename S>
-    using stride_ctor_default = bool_constant<S::InnerStrideAtCompileTime != Eigen::Dynamic
-                                              && S::OuterStrideAtCompileTime != Eigen::Dynamic
-                                              && std::is_default_constructible<S>::value>;
-    // Otherwise, if there is a two-index constructor, assume it is (outer,inner) like
-    // Eigen::Stride, and use it:
-    template <typename S>
-    using stride_ctor_dual
-        = bool_constant<!stride_ctor_default<S>::value
-                        && std::is_constructible<S, EigenIndex, EigenIndex>::value>;
-    // Otherwise, if there is a one-index constructor, and just one of the strides is dynamic, use
-    // it (passing whichever stride is dynamic).
-    template <typename S>
-    using stride_ctor_outer
-        = bool_constant<!any_of<stride_ctor_default<S>, stride_ctor_dual<S>>::value
-                        && S::OuterStrideAtCompileTime == Eigen::Dynamic
-                        && S::InnerStrideAtCompileTime != Eigen::Dynamic
-                        && std::is_constructible<S, EigenIndex>::value>;
-    template <typename S>
-    using stride_ctor_inner
-        = bool_constant<!any_of<stride_ctor_default<S>, stride_ctor_dual<S>>::value
-                        && S::InnerStrideAtCompileTime == Eigen::Dynamic
-                        && S::OuterStrideAtCompileTime != Eigen::Dynamic
-                        && std::is_constructible<S, EigenIndex>::value>;
-
-    template <typename S = StrideType, enable_if_t<stride_ctor_default<S>::value, int> = 0>
-    static S make_stride(EigenIndex, EigenIndex) {
-        return S();
-    }
-    template <typename S = StrideType, enable_if_t<stride_ctor_dual<S>::value, int> = 0>
-    static S make_stride(EigenIndex outer, EigenIndex inner) {
-        return S(outer, inner);
-    }
-    template <typename S = StrideType, enable_if_t<stride_ctor_outer<S>::value, int> = 0>
-    static S make_stride(EigenIndex outer, EigenIndex) {
-        return S(outer);
-    }
-    template <typename S = StrideType, enable_if_t<stride_ctor_inner<S>::value, int> = 0>
-    static S make_stride(EigenIndex, EigenIndex inner) {
-        return S(inner);
-    }
-};
-
-// type_caster for special matrix types (e.g. DiagonalMatrix), which are EigenBase, but not
-// EigenDense (i.e. they don't have a data(), at least not with the usual matrix layout).
-// load() is not supported, but we can cast them into the python domain by first copying to a
-// regular Eigen::Matrix, then casting that.
-template <typename Type>
-struct type_caster<Type, enable_if_t<is_eigen_other<Type>::value>> {
-protected:
-    using Matrix
-        = Eigen::Matrix<typename Type::Scalar, Type::RowsAtCompileTime, Type::ColsAtCompileTime>;
-    using props = EigenProps<Matrix>;
-
-public:
-    static handle cast(const Type &src, return_value_policy /* policy */, handle /* parent */) {
-        handle h = eigen_encapsulate<props>(new Matrix(src));
-        return h;
-    }
-    static handle cast(const Type *src, return_value_policy policy, handle parent) {
-        return cast(*src, policy, parent);
-    }
-
-    static constexpr auto name = props::descriptor;
-
-    // Explicitly delete these: support python -> C++ conversion on these (i.e. these can be return
-    // types but not bound arguments).  We still provide them (with an explicitly delete) so that
-    // you end up here if you try anyway.
-    bool load(handle, bool) = delete;
-    operator Type() = delete;
-    template <typename>
-    using cast_op_type = Type;
-};
-
-template <typename Type>
-struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
-    using Scalar = typename Type::Scalar;
-    using StorageIndex = remove_reference_t<decltype(*std::declval<Type>().outerIndexPtr())>;
-    using Index = typename Type::Index;
-    static constexpr bool rowMajor = Type::IsRowMajor;
-
-    bool load(handle src, bool) {
-        if (!src) {
-            return false;
-        }
-
-        auto obj = reinterpret_borrow<object>(src);
-        object sparse_module = module_::import("scipy.sparse");
-        object matrix_type = sparse_module.attr(rowMajor ? "csr_matrix" : "csc_matrix");
-
-        if (!type::handle_of(obj).is(matrix_type)) {
-            try {
-                obj = matrix_type(obj);
-            } catch (const error_already_set &) {
-                return false;
-            }
-        }
-
-        auto values = array_t<Scalar>((object) obj.attr("data"));
-        auto innerIndices = array_t<StorageIndex>((object) obj.attr("indices"));
-        auto outerIndices = array_t<StorageIndex>((object) obj.attr("indptr"));
-        auto shape = pybind11::tuple((pybind11::object) obj.attr("shape"));
-        auto nnz = obj.attr("nnz").cast<Index>();
-
-        if (!values || !innerIndices || !outerIndices) {
-            return false;
-        }
-
-        value = EigenMapSparseMatrix<Scalar,
-                                     Type::Flags &(Eigen::RowMajor | Eigen::ColMajor),
-                                     StorageIndex>(shape[0].cast<Index>(),
-                                                   shape[1].cast<Index>(),
-                                                   std::move(nnz),
-                                                   outerIndices.mutable_data(),
-                                                   innerIndices.mutable_data(),
-                                                   values.mutable_data());
-
-        return true;
-    }
-
-    static handle cast(const Type &src, return_value_policy /* policy */, handle /* parent */) {
-        const_cast<Type &>(src).makeCompressed();
-
-        object matrix_type
-            = module_::import("scipy.sparse").attr(rowMajor ? "csr_matrix" : "csc_matrix");
-
-        array data(src.nonZeros(), src.valuePtr());
-        array outerIndices((rowMajor ? src.rows() : src.cols()) + 1, src.outerIndexPtr());
-        array innerIndices(src.nonZeros(), src.innerIndexPtr());
-
-        return matrix_type(pybind11::make_tuple(
-                               std::move(data), std::move(innerIndices), std::move(outerIndices)),
-                           pybind11::make_tuple(src.rows(), src.cols()))
-            .release();
-    }
-
-    PYBIND11_TYPE_CASTER(Type,
-                         const_name<(Type::IsRowMajor) != 0>("scipy.sparse.csr_matrix[",
-                                                             "scipy.sparse.csc_matrix[")
-                             + npy_format_descriptor<Scalar>::name + const_name("]"));
-};
-
-PYBIND11_NAMESPACE_END(detail)
-PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
+#include "eigen/matrix.h"

include/pybind11/eigen/matrix.h

@@ -0,0 +1,699 @@
+/*
+    pybind11/eigen/matrix.h: Transparent conversion for dense and sparse Eigen matrices
+
+    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#pragma once
+
+#include "../numpy.h"
+
+/* HINT: To suppress warnings originating from the Eigen headers, use -isystem.
+   See also:
+       https://stackoverflow.com/questions/2579576/i-dir-vs-isystem-dir
+       https://stackoverflow.com/questions/1741816/isystem-for-ms-visual-studio-c-compiler
+*/
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_MSVC(5054) // https://github.com/pybind/pybind11/pull/3741
+//       C5054: operator '&': deprecated between enumerations of different types
+PYBIND11_WARNING_DISABLE_GCC("-Wmaybe-uninitialized")
+
+#include <Eigen/Core>
+#include <Eigen/SparseCore>
+
+PYBIND11_WARNING_POP
+
+// Eigen prior to 3.2.7 doesn't have proper move constructors--but worse, some classes get implicit
+// move constructors that break things.  We could detect this an explicitly copy, but an extra copy
+// of matrices seems highly undesirable.
+static_assert(EIGEN_VERSION_AT_LEAST(3, 2, 7),
+              "Eigen matrix support in pybind11 requires Eigen >= 3.2.7");
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
+// Provide a convenience alias for easier pass-by-ref usage with fully dynamic strides:
+using EigenDStride = Eigen::Stride<Eigen::Dynamic, Eigen::Dynamic>;
+template <typename MatrixType>
+using EigenDRef = Eigen::Ref<MatrixType, 0, EigenDStride>;
+template <typename MatrixType>
+using EigenDMap = Eigen::Map<MatrixType, 0, EigenDStride>;
+
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+#if EIGEN_VERSION_AT_LEAST(3, 3, 0)
+using EigenIndex = Eigen::Index;
+template <typename Scalar, int Flags, typename StorageIndex>
+using EigenMapSparseMatrix = Eigen::Map<Eigen::SparseMatrix<Scalar, Flags, StorageIndex>>;
+#else
+using EigenIndex = EIGEN_DEFAULT_DENSE_INDEX_TYPE;
+template <typename Scalar, int Flags, typename StorageIndex>
+using EigenMapSparseMatrix = Eigen::MappedSparseMatrix<Scalar, Flags, StorageIndex>;
+#endif
+
+// Matches Eigen::Map, Eigen::Ref, blocks, etc:
+template <typename T>
+using is_eigen_dense_map = all_of<is_template_base_of<Eigen::DenseBase, T>,
+                                  std::is_base_of<Eigen::MapBase<T, Eigen::ReadOnlyAccessors>, T>>;
+template <typename T>
+using is_eigen_mutable_map = std::is_base_of<Eigen::MapBase<T, Eigen::WriteAccessors>, T>;
+template <typename T>
+using is_eigen_dense_plain
+    = all_of<negation<is_eigen_dense_map<T>>, is_template_base_of<Eigen::PlainObjectBase, T>>;
+template <typename T>
+using is_eigen_sparse = is_template_base_of<Eigen::SparseMatrixBase, T>;
+// Test for objects inheriting from EigenBase<Derived> that aren't captured by the above.  This
+// basically covers anything that can be assigned to a dense matrix but that don't have a typical
+// matrix data layout that can be copied from their .data().  For example, DiagonalMatrix and
+// SelfAdjointView fall into this category.
+template <typename T>
+using is_eigen_other
+    = all_of<is_template_base_of<Eigen::EigenBase, T>,
+             negation<any_of<is_eigen_dense_map<T>, is_eigen_dense_plain<T>, is_eigen_sparse<T>>>>;
+
+// Captures numpy/eigen conformability status (returned by EigenProps::conformable()):
+template <bool EigenRowMajor>
+struct EigenConformable {
+    bool conformable = false;
+    EigenIndex rows = 0, cols = 0;
+    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, EigenIndex rstride, EigenIndex cstride)
+        : conformable{true}, rows{r}, cols{c},
+          // TODO: when Eigen bug #747 is fixed, remove the tests for non-negativity.
+          // http://eigen.tuxfamily.org/bz/show_bug.cgi?id=747
+          stride{EigenRowMajor ? (rstride > 0 ? rstride : 0)
+                               : (cstride > 0 ? cstride : 0) /* outer stride */,
+                 EigenRowMajor ? (cstride > 0 ? cstride : 0)
+                               : (rstride > 0 ? rstride : 0) /* inner stride */},
+          negativestrides{rstride < 0 || cstride < 0} {}
+    // Vector type:
+    EigenConformable(EigenIndex r, EigenIndex c, EigenIndex stride)
+        : EigenConformable(r, c, r == 1 ? c * stride : stride, c == 1 ? r : r * stride) {}
+
+    template <typename props>
+    bool stride_compatible() const {
+        // To have compatible strides, we need (on both dimensions) one of fully dynamic strides,
+        // matching strides, or a dimension size of 1 (in which case the stride value is
+        // irrelevant). Alternatively, if any dimension size is 0, the strides are not relevant
+        // (and numpy ≥ 1.23 sets the strides to 0 in that case, so we need to check explicitly).
+        if (negativestrides) {
+            return false;
+        }
+        if (rows == 0 || cols == 0) {
+            return true;
+        }
+        return (props::inner_stride == Eigen::Dynamic || props::inner_stride == stride.inner()
+                || (EigenRowMajor ? cols : rows) == 1)
+               && (props::outer_stride == Eigen::Dynamic || props::outer_stride == stride.outer()
+                   || (EigenRowMajor ? rows : cols) == 1);
+    }
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator bool() const { return conformable; }
+};
+
+template <typename Type>
+struct eigen_extract_stride {
+    using type = Type;
+};
+template <typename PlainObjectType, int MapOptions, typename StrideType>
+struct eigen_extract_stride<Eigen::Map<PlainObjectType, MapOptions, StrideType>> {
+    using type = StrideType;
+};
+template <typename PlainObjectType, int Options, typename StrideType>
+struct eigen_extract_stride<Eigen::Ref<PlainObjectType, Options, StrideType>> {
+    using type = StrideType;
+};
+
+// Helper struct for extracting information from an Eigen type
+template <typename Type_>
+struct EigenProps {
+    using Type = Type_;
+    using Scalar = typename Type::Scalar;
+    using StrideType = typename eigen_extract_stride<Type>::type;
+    static constexpr EigenIndex rows = Type::RowsAtCompileTime, cols = Type::ColsAtCompileTime,
+                                size = Type::SizeAtCompileTime;
+    static constexpr bool row_major = Type::IsRowMajor,
+                          vector
+                          = Type::IsVectorAtCompileTime, // At least one dimension has fixed size 1
+        fixed_rows = rows != Eigen::Dynamic, fixed_cols = cols != Eigen::Dynamic,
+                          fixed = size != Eigen::Dynamic, // Fully-fixed size
+        dynamic = !fixed_rows && !fixed_cols;             // Fully-dynamic size
+
+    template <EigenIndex i, EigenIndex ifzero>
+    using if_zero = std::integral_constant<EigenIndex, i == 0 ? ifzero : i>;
+    static constexpr EigenIndex inner_stride
+        = if_zero<StrideType::InnerStrideAtCompileTime, 1>::value,
+        outer_stride = if_zero < StrideType::OuterStrideAtCompileTime,
+        vector      ? size
+        : row_major ? cols
+                    : rows > ::value;
+    static constexpr bool dynamic_stride
+        = inner_stride == Eigen::Dynamic && outer_stride == Eigen::Dynamic;
+    static constexpr bool requires_row_major
+        = !dynamic_stride && !vector && (row_major ? inner_stride : outer_stride) == 1;
+    static constexpr bool requires_col_major
+        = !dynamic_stride && !vector && (row_major ? outer_stride : inner_stride) == 1;
+
+    // Takes an input array and determines whether we can make it fit into the Eigen type.  If
+    // the array is a vector, we attempt to fit it into either an Eigen 1xN or Nx1 vector
+    // (preferring the latter if it will fit in either, i.e. for a fully dynamic matrix type).
+    static EigenConformable<row_major> conformable(const array &a) {
+        const auto dims = a.ndim();
+        if (dims < 1 || dims > 2) {
+            return false;
+        }
+
+        if (dims == 2) { // Matrix type: require exact match (or dynamic)
+
+            EigenIndex np_rows = a.shape(0), 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)) {
+                return false;
+            }
+
+            return {np_rows, np_cols, np_rstride, np_cstride};
+        }
+
+        // Otherwise we're storing an n-vector.  Only one of the strides will be used, but
+        // whichever is used, we want the (single) numpy stride value.
+        const EigenIndex n = a.shape(0),
+                         stride = a.strides(0) / static_cast<ssize_t>(sizeof(Scalar));
+
+        if (vector) { // Eigen type is a compile-time vector
+            if (fixed && size != n) {
+                return false; // Vector size mismatch
+            }
+            return {rows == 1 ? 1 : n, cols == 1 ? 1 : n, stride};
+        }
+        if (fixed) {
+            // The type has a fixed size, but is not a vector: abort
+            return false;
+        }
+        if (fixed_cols) {
+            // Since this isn't a vector, cols must be != 1.  We allow this only if it exactly
+            // equals the number of elements (rows is Dynamic, and so 1 row is allowed).
+            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;
+        }
+        return {n, 1, stride};
+    }
+
+    static constexpr bool show_writeable
+        = is_eigen_dense_map<Type>::value && is_eigen_mutable_map<Type>::value;
+    static constexpr bool show_order = is_eigen_dense_map<Type>::value;
+    static constexpr bool show_c_contiguous = show_order && requires_row_major;
+    static constexpr bool show_f_contiguous
+        = !show_c_contiguous && show_order && requires_col_major;
+
+    static constexpr auto descriptor
+        = const_name("numpy.ndarray[") + npy_format_descriptor<Scalar>::name + const_name("[")
+          + const_name<fixed_rows>(const_name<(size_t) rows>(), const_name("m")) + const_name(", ")
+          + const_name<fixed_cols>(const_name<(size_t) cols>(), const_name("n")) + const_name("]")
+          +
+          // For a reference type (e.g. Ref<MatrixXd>) we have other constraints that might need to
+          // be satisfied: writeable=True (for a mutable reference), and, depending on the map's
+          // stride options, possibly f_contiguous or c_contiguous.  We include them in the
+          // descriptor output to provide some hint as to why a TypeError is occurring (otherwise
+          // it can be confusing to see that a function accepts a 'numpy.ndarray[float64[3,2]]' and
+          // an error message that you *gave* a numpy.ndarray of the right type and dimensions.
+          const_name<show_writeable>(", flags.writeable", "")
+          + const_name<show_c_contiguous>(", flags.c_contiguous", "")
+          + const_name<show_f_contiguous>(", flags.f_contiguous", "") + const_name("]");
+};
+
+// Casts an Eigen type to numpy array.  If given a base, the numpy array references the src data,
+// otherwise it'll make a copy.  writeable lets you turn off the writeable flag for the array.
+template <typename props>
+handle
+eigen_array_cast(typename props::Type const &src, handle base = handle(), bool writeable = true) {
+    constexpr ssize_t elem_size = sizeof(typename props::Scalar);
+    array a;
+    if (props::vector) {
+        a = array({src.size()}, {elem_size * src.innerStride()}, src.data(), base);
+    } else {
+        a = array({src.rows(), src.cols()},
+                  {elem_size * src.rowStride(), elem_size * src.colStride()},
+                  src.data(),
+                  base);
+    }
+
+    if (!writeable) {
+        array_proxy(a.ptr())->flags &= ~detail::npy_api::NPY_ARRAY_WRITEABLE_;
+    }
+
+    return a.release();
+}
+
+// Takes an lvalue ref to some Eigen type and a (python) base object, creating a numpy array that
+// reference the Eigen object's data with `base` as the python-registered base class (if omitted,
+// the base will be set to None, and lifetime management is up to the caller).  The numpy array is
+// non-writeable if the given type is const.
+template <typename props, typename Type>
+handle eigen_ref_array(Type &src, handle parent = none()) {
+    // none here is to get past array's should-we-copy detection, which currently always
+    // copies when there is no base.  Setting the base to None should be harmless.
+    return eigen_array_cast<props>(src, parent, !std::is_const<Type>::value);
+}
+
+// Takes a pointer to some dense, plain Eigen type, builds a capsule around it, then returns a
+// numpy array that references the encapsulated data with a python-side reference to the capsule to
+// tie its destruction to that of any dependent python objects.  Const-ness is determined by
+// whether or not the Type of the pointer given is const.
+template <typename props, typename Type, typename = enable_if_t<is_eigen_dense_plain<Type>::value>>
+handle eigen_encapsulate(Type *src) {
+    capsule base(src, [](void *o) { delete static_cast<Type *>(o); });
+    return eigen_ref_array<props>(*src, base);
+}
+
+// Type caster for regular, dense matrix types (e.g. MatrixXd), but not maps/refs/etc. of dense
+// types.
+template <typename Type>
+struct type_caster<Type, enable_if_t<is_eigen_dense_plain<Type>::value>> {
+    using Scalar = typename Type::Scalar;
+    using props = EigenProps<Type>;
+
+    bool load(handle src, bool convert) {
+        // If we're in no-convert mode, only load if given an array of the correct type
+        if (!convert && !isinstance<array_t<Scalar>>(src)) {
+            return false;
+        }
+
+        // Coerce into an array, but don't do type conversion yet; the copy below handles it.
+        auto buf = array::ensure(src);
+
+        if (!buf) {
+            return false;
+        }
+
+        auto dims = buf.ndim();
+        if (dims < 1 || dims > 2) {
+            return false;
+        }
+
+        auto fits = props::conformable(buf);
+        if (!fits) {
+            return false;
+        }
+
+        // Allocate the new type, then build a numpy reference into it
+        value = Type(fits.rows, fits.cols);
+        auto ref = reinterpret_steal<array>(eigen_ref_array<props>(value));
+        if (dims == 1) {
+            ref = ref.squeeze();
+        } else if (ref.ndim() == 1) {
+            buf = buf.squeeze();
+        }
+
+        int result = detail::npy_api::get().PyArray_CopyInto_(ref.ptr(), buf.ptr());
+
+        if (result < 0) { // Copy failed!
+            PyErr_Clear();
+            return false;
+        }
+
+        return true;
+    }
+
+private:
+    // Cast implementation
+    template <typename CType>
+    static handle cast_impl(CType *src, return_value_policy policy, handle parent) {
+        switch (policy) {
+            case return_value_policy::take_ownership:
+            case return_value_policy::automatic:
+                return eigen_encapsulate<props>(src);
+            case return_value_policy::move:
+                return eigen_encapsulate<props>(new CType(std::move(*src)));
+            case return_value_policy::copy:
+                return eigen_array_cast<props>(*src);
+            case return_value_policy::reference:
+            case return_value_policy::automatic_reference:
+                return eigen_ref_array<props>(*src);
+            case return_value_policy::reference_internal:
+                return eigen_ref_array<props>(*src, parent);
+            default:
+                throw cast_error("unhandled return_value_policy: should not happen!");
+        };
+    }
+
+public:
+    // Normal returned non-reference, non-const value:
+    static handle cast(Type &&src, return_value_policy /* policy */, handle parent) {
+        return cast_impl(&src, return_value_policy::move, parent);
+    }
+    // If you return a non-reference const, we mark the numpy array readonly:
+    static handle cast(const Type &&src, return_value_policy /* policy */, handle parent) {
+        return cast_impl(&src, return_value_policy::move, parent);
+    }
+    // lvalue reference return; default (automatic) becomes copy
+    static handle cast(Type &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast_impl(&src, policy, parent);
+    }
+    // const lvalue reference return; default (automatic) becomes copy
+    static handle cast(const Type &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast(&src, policy, parent);
+    }
+    // non-const pointer return
+    static handle cast(Type *src, return_value_policy policy, handle parent) {
+        return cast_impl(src, policy, parent);
+    }
+    // const pointer return
+    static handle cast(const Type *src, return_value_policy policy, handle parent) {
+        return cast_impl(src, policy, parent);
+    }
+
+    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>;
+
+private:
+    Type value;
+};
+
+// Base class for casting reference/map/block/etc. objects back to python.
+template <typename MapType>
+struct eigen_map_caster {
+private:
+    using props = EigenProps<MapType>;
+
+public:
+    // Directly referencing a ref/map's data is a bit dangerous (whatever the map/ref points to has
+    // to stay around), but we'll allow it under the assumption that you know what you're doing
+    // (and have an appropriate keep_alive in place).  We return a numpy array pointing directly at
+    // the ref's data (The numpy array ends up read-only if the ref was to a const matrix type.)
+    // Note that this means you need to ensure you don't destroy the object in some other way (e.g.
+    // with an appropriate keep_alive, or with a reference to a statically allocated matrix).
+    static handle cast(const MapType &src, return_value_policy policy, handle parent) {
+        switch (policy) {
+            case return_value_policy::copy:
+                return eigen_array_cast<props>(src);
+            case return_value_policy::reference_internal:
+                return eigen_array_cast<props>(src, parent, is_eigen_mutable_map<MapType>::value);
+            case return_value_policy::reference:
+            case return_value_policy::automatic:
+            case return_value_policy::automatic_reference:
+                return eigen_array_cast<props>(src, none(), is_eigen_mutable_map<MapType>::value);
+            default:
+                // move, take_ownership don't make any sense for a ref/map:
+                pybind11_fail("Invalid return_value_policy for Eigen Map/Ref/Block type");
+        }
+    }
+
+    static constexpr auto name = props::descriptor;
+
+    // Explicitly delete these: support python -> C++ conversion on these (i.e. these can be return
+    // types but not bound arguments).  We still provide them (with an explicitly delete) so that
+    // you end up here if you try anyway.
+    bool load(handle, bool) = delete;
+    operator MapType() = delete;
+    template <typename>
+    using cast_op_type = MapType;
+};
+
+// We can return any map-like object (but can only load Refs, specialized next):
+template <typename Type>
+struct type_caster<Type, enable_if_t<is_eigen_dense_map<Type>::value>> : eigen_map_caster<Type> {};
+
+// Loader for Ref<...> arguments.  See the documentation for info on how to make this work without
+// copying (it requires some extra effort in many cases).
+template <typename PlainObjectType, typename StrideType>
+struct type_caster<
+    Eigen::Ref<PlainObjectType, 0, StrideType>,
+    enable_if_t<is_eigen_dense_map<Eigen::Ref<PlainObjectType, 0, StrideType>>::value>>
+    : public eigen_map_caster<Eigen::Ref<PlainObjectType, 0, StrideType>> {
+private:
+    using Type = Eigen::Ref<PlainObjectType, 0, StrideType>;
+    using props = EigenProps<Type>;
+    using Scalar = typename props::Scalar;
+    using MapType = Eigen::Map<PlainObjectType, 0, StrideType>;
+    using Array
+        = array_t<Scalar,
+                  array::forcecast
+                      | ((props::row_major ? props::inner_stride : props::outer_stride) == 1
+                             ? array::c_style
+                         : (props::row_major ? props::outer_stride : props::inner_stride) == 1
+                             ? array::f_style
+                             : 0)>;
+    static constexpr bool need_writeable = is_eigen_mutable_map<Type>::value;
+    // Delay construction (these have no default constructor)
+    std::unique_ptr<MapType> map;
+    std::unique_ptr<Type> ref;
+    // Our array.  When possible, this is just a numpy array pointing to the source data, but
+    // sometimes we can't avoid copying (e.g. input is not a numpy array at all, has an
+    // incompatible layout, or is an array of a type that needs to be converted).  Using a numpy
+    // temporary (rather than an Eigen temporary) saves an extra copy when we need both type
+    // conversion and storage order conversion.  (Note that we refuse to use this temporary copy
+    // when loading an argument for a Ref<M> with M non-const, i.e. a read-write reference).
+    Array copy_or_ref;
+
+public:
+    bool load(handle src, bool convert) {
+        // First check whether what we have is already an array of the right type.  If not, we
+        // can't avoid a copy (because the copy is also going to do type conversion).
+        bool need_copy = !isinstance<Array>(src);
+
+        EigenConformable<props::row_major> fits;
+        if (!need_copy) {
+            // We don't need a converting copy, but we also need to check whether the strides are
+            // compatible with the Ref's stride requirements
+            auto aref = reinterpret_borrow<Array>(src);
+
+            if (aref && (!need_writeable || aref.writeable())) {
+                fits = props::conformable(aref);
+                if (!fits) {
+                    return false; // Incompatible dimensions
+                }
+                if (!fits.template stride_compatible<props>()) {
+                    need_copy = true;
+                } else {
+                    copy_or_ref = std::move(aref);
+                }
+            } else {
+                need_copy = true;
+            }
+        }
+
+        if (need_copy) {
+            // We need to copy: If we need a mutable reference, or we're not supposed to convert
+            // (either because we're in the no-convert overload pass, or because we're explicitly
+            // instructed not to copy (via `py::arg().noconvert()`) we have to fail loading.
+            if (!convert || need_writeable) {
+                return false;
+            }
+
+            Array copy = Array::ensure(src);
+            if (!copy) {
+                return false;
+            }
+            fits = props::conformable(copy);
+            if (!fits || !fits.template stride_compatible<props>()) {
+                return false;
+            }
+            copy_or_ref = std::move(copy);
+            loader_life_support::add_patient(copy_or_ref);
+        }
+
+        ref.reset();
+        map.reset(new MapType(data(copy_or_ref),
+                              fits.rows,
+                              fits.cols,
+                              make_stride(fits.stride.outer(), fits.stride.inner())));
+        ref.reset(new Type(*map));
+
+        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>;
+
+private:
+    template <typename T = Type, enable_if_t<is_eigen_mutable_map<T>::value, int> = 0>
+    Scalar *data(Array &a) {
+        return a.mutable_data();
+    }
+
+    template <typename T = Type, enable_if_t<!is_eigen_mutable_map<T>::value, int> = 0>
+    const Scalar *data(Array &a) {
+        return a.data();
+    }
+
+    // Attempt to figure out a constructor of `Stride` that will work.
+    // If both strides are fixed, use a default constructor:
+    template <typename S>
+    using stride_ctor_default = bool_constant<S::InnerStrideAtCompileTime != Eigen::Dynamic
+                                              && S::OuterStrideAtCompileTime != Eigen::Dynamic
+                                              && std::is_default_constructible<S>::value>;
+    // Otherwise, if there is a two-index constructor, assume it is (outer,inner) like
+    // Eigen::Stride, and use it:
+    template <typename S>
+    using stride_ctor_dual
+        = bool_constant<!stride_ctor_default<S>::value
+                        && std::is_constructible<S, EigenIndex, EigenIndex>::value>;
+    // Otherwise, if there is a one-index constructor, and just one of the strides is dynamic, use
+    // it (passing whichever stride is dynamic).
+    template <typename S>
+    using stride_ctor_outer
+        = bool_constant<!any_of<stride_ctor_default<S>, stride_ctor_dual<S>>::value
+                        && S::OuterStrideAtCompileTime == Eigen::Dynamic
+                        && S::InnerStrideAtCompileTime != Eigen::Dynamic
+                        && std::is_constructible<S, EigenIndex>::value>;
+    template <typename S>
+    using stride_ctor_inner
+        = bool_constant<!any_of<stride_ctor_default<S>, stride_ctor_dual<S>>::value
+                        && S::InnerStrideAtCompileTime == Eigen::Dynamic
+                        && S::OuterStrideAtCompileTime != Eigen::Dynamic
+                        && std::is_constructible<S, EigenIndex>::value>;
+
+    template <typename S = StrideType, enable_if_t<stride_ctor_default<S>::value, int> = 0>
+    static S make_stride(EigenIndex, EigenIndex) {
+        return S();
+    }
+    template <typename S = StrideType, enable_if_t<stride_ctor_dual<S>::value, int> = 0>
+    static S make_stride(EigenIndex outer, EigenIndex inner) {
+        return S(outer, inner);
+    }
+    template <typename S = StrideType, enable_if_t<stride_ctor_outer<S>::value, int> = 0>
+    static S make_stride(EigenIndex outer, EigenIndex) {
+        return S(outer);
+    }
+    template <typename S = StrideType, enable_if_t<stride_ctor_inner<S>::value, int> = 0>
+    static S make_stride(EigenIndex, EigenIndex inner) {
+        return S(inner);
+    }
+};
+
+// type_caster for special matrix types (e.g. DiagonalMatrix), which are EigenBase, but not
+// EigenDense (i.e. they don't have a data(), at least not with the usual matrix layout).
+// load() is not supported, but we can cast them into the python domain by first copying to a
+// regular Eigen::Matrix, then casting that.
+template <typename Type>
+struct type_caster<Type, enable_if_t<is_eigen_other<Type>::value>> {
+protected:
+    using Matrix
+        = Eigen::Matrix<typename Type::Scalar, Type::RowsAtCompileTime, Type::ColsAtCompileTime>;
+    using props = EigenProps<Matrix>;
+
+public:
+    static handle cast(const Type &src, return_value_policy /* policy */, handle /* parent */) {
+        handle h = eigen_encapsulate<props>(new Matrix(src));
+        return h;
+    }
+    static handle cast(const Type *src, return_value_policy policy, handle parent) {
+        return cast(*src, policy, parent);
+    }
+
+    static constexpr auto name = props::descriptor;
+
+    // Explicitly delete these: support python -> C++ conversion on these (i.e. these can be return
+    // types but not bound arguments).  We still provide them (with an explicitly delete) so that
+    // you end up here if you try anyway.
+    bool load(handle, bool) = delete;
+    operator Type() = delete;
+    template <typename>
+    using cast_op_type = Type;
+};
+
+template <typename Type>
+struct type_caster<Type, enable_if_t<is_eigen_sparse<Type>::value>> {
+    using Scalar = typename Type::Scalar;
+    using StorageIndex = remove_reference_t<decltype(*std::declval<Type>().outerIndexPtr())>;
+    using Index = typename Type::Index;
+    static constexpr bool rowMajor = Type::IsRowMajor;
+
+    bool load(handle src, bool) {
+        if (!src) {
+            return false;
+        }
+
+        auto obj = reinterpret_borrow<object>(src);
+        object sparse_module = module_::import("scipy.sparse");
+        object matrix_type = sparse_module.attr(rowMajor ? "csr_matrix" : "csc_matrix");
+
+        if (!type::handle_of(obj).is(matrix_type)) {
+            try {
+                obj = matrix_type(obj);
+            } catch (const error_already_set &) {
+                return false;
+            }
+        }
+
+        auto values = array_t<Scalar>((object) obj.attr("data"));
+        auto innerIndices = array_t<StorageIndex>((object) obj.attr("indices"));
+        auto outerIndices = array_t<StorageIndex>((object) obj.attr("indptr"));
+        auto shape = pybind11::tuple((pybind11::object) obj.attr("shape"));
+        auto nnz = obj.attr("nnz").cast<Index>();
+
+        if (!values || !innerIndices || !outerIndices) {
+            return false;
+        }
+
+        value = EigenMapSparseMatrix<Scalar,
+                                     Type::Flags &(Eigen::RowMajor | Eigen::ColMajor),
+                                     StorageIndex>(shape[0].cast<Index>(),
+                                                   shape[1].cast<Index>(),
+                                                   std::move(nnz),
+                                                   outerIndices.mutable_data(),
+                                                   innerIndices.mutable_data(),
+                                                   values.mutable_data());
+
+        return true;
+    }
+
+    static handle cast(const Type &src, return_value_policy /* policy */, handle /* parent */) {
+        const_cast<Type &>(src).makeCompressed();
+
+        object matrix_type
+            = module_::import("scipy.sparse").attr(rowMajor ? "csr_matrix" : "csc_matrix");
+
+        array data(src.nonZeros(), src.valuePtr());
+        array outerIndices((rowMajor ? src.rows() : src.cols()) + 1, src.outerIndexPtr());
+        array innerIndices(src.nonZeros(), src.innerIndexPtr());
+
+        return matrix_type(pybind11::make_tuple(
+                               std::move(data), std::move(innerIndices), std::move(outerIndices)),
+                           pybind11::make_tuple(src.rows(), src.cols()))
+            .release();
+    }
+
+    PYBIND11_TYPE_CASTER(Type,
+                         const_name<(Type::IsRowMajor) != 0>("scipy.sparse.csr_matrix[",
+                                                             "scipy.sparse.csc_matrix[")
+                             + npy_format_descriptor<Scalar>::name + const_name("]"));
+};
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

include/pybind11/eigen/tensor.h

@@ -0,0 +1,509 @@
+/*
+    pybind11/eigen/tensor.h: Transparent conversion for Eigen tensors
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#pragma once
+
+#include "../numpy.h"
+
+#if defined(__GNUC__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
+static_assert(__GNUC__ > 5, "Eigen Tensor support in pybind11 requires GCC > 5.0");
+#endif
+
+// Disable warnings for Eigen
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_MSVC(4554)
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+PYBIND11_WARNING_DISABLE_GCC("-Wmaybe-uninitialized")
+
+#include <unsupported/Eigen/CXX11/Tensor>
+
+PYBIND11_WARNING_POP
+
+static_assert(EIGEN_VERSION_AT_LEAST(3, 3, 0),
+              "Eigen Tensor support in pybind11 requires Eigen >= 3.3.0");
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+inline bool is_tensor_aligned(const void *data) {
+    return (reinterpret_cast<std::size_t>(data) % EIGEN_DEFAULT_ALIGN_BYTES) == 0;
+}
+
+template <typename T>
+constexpr int compute_array_flag_from_tensor() {
+    static_assert((static_cast<int>(T::Layout) == static_cast<int>(Eigen::RowMajor))
+                      || (static_cast<int>(T::Layout) == static_cast<int>(Eigen::ColMajor)),
+                  "Layout must be row or column major");
+    return (static_cast<int>(T::Layout) == static_cast<int>(Eigen::RowMajor)) ? array::c_style
+                                                                              : array::f_style;
+}
+
+template <typename T>
+struct eigen_tensor_helper {};
+
+template <typename Scalar_, int NumIndices_, int Options_, typename IndexType>
+struct eigen_tensor_helper<Eigen::Tensor<Scalar_, NumIndices_, Options_, IndexType>> {
+    using Type = Eigen::Tensor<Scalar_, NumIndices_, Options_, IndexType>;
+    using ValidType = void;
+
+    static Eigen::DSizes<typename Type::Index, Type::NumIndices> get_shape(const Type &f) {
+        return f.dimensions();
+    }
+
+    static constexpr bool
+    is_correct_shape(const Eigen::DSizes<typename Type::Index, Type::NumIndices> & /*shape*/) {
+        return true;
+    }
+
+    template <typename T>
+    struct helper {};
+
+    template <size_t... Is>
+    struct helper<index_sequence<Is...>> {
+        static constexpr auto value = concat(const_name(((void) Is, "?"))...);
+    };
+
+    static constexpr auto dimensions_descriptor
+        = helper<decltype(make_index_sequence<Type::NumIndices>())>::value;
+
+    template <typename... Args>
+    static Type *alloc(Args &&...args) {
+        return new Type(std::forward<Args>(args)...);
+    }
+
+    static void free(Type *tensor) { delete tensor; }
+};
+
+template <typename Scalar_, typename std::ptrdiff_t... Indices, int Options_, typename IndexType>
+struct eigen_tensor_helper<
+    Eigen::TensorFixedSize<Scalar_, Eigen::Sizes<Indices...>, Options_, IndexType>> {
+    using Type = Eigen::TensorFixedSize<Scalar_, Eigen::Sizes<Indices...>, Options_, IndexType>;
+    using ValidType = void;
+
+    static constexpr Eigen::DSizes<typename Type::Index, Type::NumIndices>
+    get_shape(const Type & /*f*/) {
+        return get_shape();
+    }
+
+    static constexpr Eigen::DSizes<typename Type::Index, Type::NumIndices> get_shape() {
+        return Eigen::DSizes<typename Type::Index, Type::NumIndices>(Indices...);
+    }
+
+    static bool
+    is_correct_shape(const Eigen::DSizes<typename Type::Index, Type::NumIndices> &shape) {
+        return get_shape() == shape;
+    }
+
+    static constexpr auto dimensions_descriptor = concat(const_name<Indices>()...);
+
+    template <typename... Args>
+    static Type *alloc(Args &&...args) {
+        Eigen::aligned_allocator<Type> allocator;
+        return ::new (allocator.allocate(1)) Type(std::forward<Args>(args)...);
+    }
+
+    static void free(Type *tensor) {
+        Eigen::aligned_allocator<Type> allocator;
+        tensor->~Type();
+        allocator.deallocate(tensor, 1);
+    }
+};
+
+template <typename Type, bool ShowDetails, bool NeedsWriteable = false>
+struct get_tensor_descriptor {
+    static constexpr auto details
+        = const_name<NeedsWriteable>(", flags.writeable", "")
+          + const_name<static_cast<int>(Type::Layout) == static_cast<int>(Eigen::RowMajor)>(
+              ", flags.c_contiguous", ", flags.f_contiguous");
+    static constexpr auto value
+        = const_name("numpy.ndarray[") + npy_format_descriptor<typename Type::Scalar>::name
+          + const_name("[") + eigen_tensor_helper<remove_cv_t<Type>>::dimensions_descriptor
+          + const_name("]") + const_name<ShowDetails>(details, const_name("")) + const_name("]");
+};
+
+// When EIGEN_AVOID_STL_ARRAY is defined, Eigen::DSizes<T, 0> does not have the begin() member
+// function. Falling back to a simple loop works around this issue.
+//
+// We need to disable the type-limits warning for the inner loop when size = 0.
+
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_GCC("-Wtype-limits")
+
+template <typename T, int size>
+std::vector<T> convert_dsizes_to_vector(const Eigen::DSizes<T, size> &arr) {
+    std::vector<T> result(size);
+
+    for (size_t i = 0; i < size; i++) {
+        result[i] = arr[i];
+    }
+
+    return result;
+}
+
+template <typename T, int size>
+Eigen::DSizes<T, size> get_shape_for_array(const array &arr) {
+    Eigen::DSizes<T, size> result;
+    const T *shape = arr.shape();
+    for (size_t i = 0; i < size; i++) {
+        result[i] = shape[i];
+    }
+
+    return result;
+}
+
+PYBIND11_WARNING_POP
+
+template <typename Type>
+struct type_caster<Type, typename eigen_tensor_helper<Type>::ValidType> {
+    using Helper = eigen_tensor_helper<Type>;
+    static constexpr auto temp_name = get_tensor_descriptor<Type, false>::value;
+    PYBIND11_TYPE_CASTER(Type, temp_name);
+
+    bool load(handle src, bool convert) {
+        if (!convert) {
+            if (!isinstance<array>(src)) {
+                return false;
+            }
+            array temp = array::ensure(src);
+            if (!temp) {
+                return false;
+            }
+
+            if (!convert && !temp.dtype().is(dtype::of<typename Type::Scalar>())) {
+                return false;
+            }
+        }
+
+        array_t<typename Type::Scalar, compute_array_flag_from_tensor<Type>()> arr(
+            reinterpret_borrow<object>(src));
+
+        if (arr.ndim() != Type::NumIndices) {
+            return false;
+        }
+        auto shape = get_shape_for_array<typename Type::Index, Type::NumIndices>(arr);
+
+        if (!Helper::is_correct_shape(shape)) {
+            return false;
+        }
+
+#if EIGEN_VERSION_AT_LEAST(3, 4, 0)
+        auto data_pointer = arr.data();
+#else
+        // Handle Eigen bug
+        auto data_pointer = const_cast<typename Type::Scalar *>(arr.data());
+#endif
+
+        if (is_tensor_aligned(arr.data())) {
+            value = Eigen::TensorMap<const Type, Eigen::Aligned>(data_pointer, shape);
+        } else {
+            value = Eigen::TensorMap<const Type>(data_pointer, shape);
+        }
+
+        return true;
+    }
+
+    static handle cast(Type &&src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::reference
+            || policy == return_value_policy::reference_internal) {
+            pybind11_fail("Cannot use a reference return value policy for an rvalue");
+        }
+        return cast_impl(&src, return_value_policy::move, parent);
+    }
+
+    static handle cast(const Type &&src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::reference
+            || policy == return_value_policy::reference_internal) {
+            pybind11_fail("Cannot use a reference return value policy for an rvalue");
+        }
+        return cast_impl(&src, return_value_policy::move, parent);
+    }
+
+    static handle cast(Type &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast_impl(&src, policy, parent);
+    }
+
+    static handle cast(const Type &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast(&src, policy, parent);
+    }
+
+    static handle cast(Type *src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic) {
+            policy = return_value_policy::take_ownership;
+        } else if (policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::reference;
+        }
+        return cast_impl(src, policy, parent);
+    }
+
+    static handle cast(const Type *src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic) {
+            policy = return_value_policy::take_ownership;
+        } else if (policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::reference;
+        }
+        return cast_impl(src, policy, parent);
+    }
+
+    template <typename C>
+    static handle cast_impl(C *src, return_value_policy policy, handle parent) {
+        object parent_object;
+        bool writeable = false;
+        switch (policy) {
+            case return_value_policy::move:
+                if (std::is_const<C>::value) {
+                    pybind11_fail("Cannot move from a constant reference");
+                }
+
+                src = Helper::alloc(std::move(*src));
+
+                parent_object
+                    = capsule(src, [](void *ptr) { Helper::free(reinterpret_cast<Type *>(ptr)); });
+                writeable = true;
+                break;
+
+            case return_value_policy::take_ownership:
+                if (std::is_const<C>::value) {
+                    // This cast is ugly, and might be UB in some cases, but we don't have an
+                    // alternative here as we must free that memory
+                    Helper::free(const_cast<Type *>(src));
+                    pybind11_fail("Cannot take ownership of a const reference");
+                }
+
+                parent_object
+                    = capsule(src, [](void *ptr) { Helper::free(reinterpret_cast<Type *>(ptr)); });
+                writeable = true;
+                break;
+
+            case return_value_policy::copy:
+                writeable = true;
+                break;
+
+            case return_value_policy::reference:
+                parent_object = none();
+                writeable = !std::is_const<C>::value;
+                break;
+
+            case return_value_policy::reference_internal:
+                // Default should do the right thing
+                if (!parent) {
+                    pybind11_fail("Cannot use reference internal when there is no parent");
+                }
+                parent_object = reinterpret_borrow<object>(parent);
+                writeable = !std::is_const<C>::value;
+                break;
+
+            default:
+                pybind11_fail("pybind11 bug in eigen.h, please file a bug report");
+        }
+
+        auto result = array_t<typename Type::Scalar, compute_array_flag_from_tensor<Type>()>(
+            convert_dsizes_to_vector(Helper::get_shape(*src)), src->data(), parent_object);
+
+        if (!writeable) {
+            array_proxy(result.ptr())->flags &= ~detail::npy_api::NPY_ARRAY_WRITEABLE_;
+        }
+
+        return result.release();
+    }
+};
+
+template <typename StoragePointerType,
+          bool needs_writeable,
+          enable_if_t<!needs_writeable, bool> = true>
+StoragePointerType get_array_data_for_type(array &arr) {
+#if EIGEN_VERSION_AT_LEAST(3, 4, 0)
+    return reinterpret_cast<StoragePointerType>(arr.data());
+#else
+    // Handle Eigen bug
+    return reinterpret_cast<StoragePointerType>(const_cast<void *>(arr.data()));
+#endif
+}
+
+template <typename StoragePointerType,
+          bool needs_writeable,
+          enable_if_t<needs_writeable, bool> = true>
+StoragePointerType get_array_data_for_type(array &arr) {
+    return reinterpret_cast<StoragePointerType>(arr.mutable_data());
+}
+
+template <typename T, typename = void>
+struct get_storage_pointer_type;
+
+template <typename MapType>
+struct get_storage_pointer_type<MapType, void_t<typename MapType::StoragePointerType>> {
+    using SPT = typename MapType::StoragePointerType;
+};
+
+template <typename MapType>
+struct get_storage_pointer_type<MapType, void_t<typename MapType::PointerArgType>> {
+    using SPT = typename MapType::PointerArgType;
+};
+
+template <typename Type, int Options>
+struct type_caster<Eigen::TensorMap<Type, Options>,
+                   typename eigen_tensor_helper<remove_cv_t<Type>>::ValidType> {
+    using MapType = Eigen::TensorMap<Type, Options>;
+    using Helper = eigen_tensor_helper<remove_cv_t<Type>>;
+
+    bool load(handle src, bool /*convert*/) {
+        // Note that we have a lot more checks here as we want to make sure to avoid copies
+        if (!isinstance<array>(src)) {
+            return false;
+        }
+        auto arr = reinterpret_borrow<array>(src);
+        if ((arr.flags() & compute_array_flag_from_tensor<Type>()) == 0) {
+            return false;
+        }
+
+        if (!arr.dtype().is(dtype::of<typename Type::Scalar>())) {
+            return false;
+        }
+
+        if (arr.ndim() != Type::NumIndices) {
+            return false;
+        }
+
+        constexpr bool is_aligned = (Options & Eigen::Aligned) != 0;
+
+        if (is_aligned && !is_tensor_aligned(arr.data())) {
+            return false;
+        }
+
+        auto shape = get_shape_for_array<typename Type::Index, Type::NumIndices>(arr);
+
+        if (!Helper::is_correct_shape(shape)) {
+            return false;
+        }
+
+        if (needs_writeable && !arr.writeable()) {
+            return false;
+        }
+
+        auto result = get_array_data_for_type<typename get_storage_pointer_type<MapType>::SPT,
+                                              needs_writeable>(arr);
+
+        value.reset(new MapType(std::move(result), std::move(shape)));
+
+        return true;
+    }
+
+    static handle cast(MapType &&src, return_value_policy policy, handle parent) {
+        return cast_impl(&src, policy, parent);
+    }
+
+    static handle cast(const MapType &&src, return_value_policy policy, handle parent) {
+        return cast_impl(&src, policy, parent);
+    }
+
+    static handle cast(MapType &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast_impl(&src, policy, parent);
+    }
+
+    static handle cast(const MapType &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic
+            || policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::copy;
+        }
+        return cast(&src, policy, parent);
+    }
+
+    static handle cast(MapType *src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic) {
+            policy = return_value_policy::take_ownership;
+        } else if (policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::reference;
+        }
+        return cast_impl(src, policy, parent);
+    }
+
+    static handle cast(const MapType *src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::automatic) {
+            policy = return_value_policy::take_ownership;
+        } else if (policy == return_value_policy::automatic_reference) {
+            policy = return_value_policy::reference;
+        }
+        return cast_impl(src, policy, parent);
+    }
+
+    template <typename C>
+    static handle cast_impl(C *src, return_value_policy policy, handle parent) {
+        object parent_object;
+        constexpr bool writeable = !std::is_const<C>::value;
+        switch (policy) {
+            case return_value_policy::reference:
+                parent_object = none();
+                break;
+
+            case return_value_policy::reference_internal:
+                // Default should do the right thing
+                if (!parent) {
+                    pybind11_fail("Cannot use reference internal when there is no parent");
+                }
+                parent_object = reinterpret_borrow<object>(parent);
+                break;
+
+            case return_value_policy::take_ownership:
+                delete src;
+                // fallthrough
+            default:
+                // move, take_ownership don't make any sense for a ref/map:
+                pybind11_fail("Invalid return_value_policy for Eigen Map type, must be either "
+                              "reference or reference_internal");
+        }
+
+        auto result = array_t<typename Type::Scalar, compute_array_flag_from_tensor<Type>()>(
+            convert_dsizes_to_vector(Helper::get_shape(*src)),
+            src->data(),
+            std::move(parent_object));
+
+        if (!writeable) {
+            array_proxy(result.ptr())->flags &= ~detail::npy_api::NPY_ARRAY_WRITEABLE_;
+        }
+
+        return result.release();
+    }
+
+#if EIGEN_VERSION_AT_LEAST(3, 4, 0)
+
+    static constexpr bool needs_writeable = !std::is_const<typename std::remove_pointer<
+        typename get_storage_pointer_type<MapType>::SPT>::type>::value;
+#else
+    // Handle Eigen bug
+    static constexpr bool needs_writeable = !std::is_const<Type>::value;
+#endif
+
+protected:
+    // TODO: Move to std::optional once std::optional has more support
+    std::unique_ptr<MapType> value;
+
+public:
+    static constexpr auto name = get_tensor_descriptor<Type, true, needs_writeable>::value;
+    explicit operator MapType *() { return value.get(); }
+    explicit operator MapType &() { return *value; }
+    explicit operator MapType &&() && { return std::move(*value); }
+
+    template <typename T_>
+    using cast_op_type = ::pybind11::detail::movable_cast_op_type<T_>;
+};
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

include/pybind11/embed.h

@@ -86,38 +86,26 @@ inline wchar_t *widen_chars(const char *safe_arg) {
     return widened_arg;
 }
 
-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 `init_signal_handlers` parameter can be used to skip the registration of
-    signal handlers (see the `Python documentation`_ for details). Calling this function
-    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,
-                                   int argc = 0,
-                                   const char *const *argv = nullptr,
-                                   bool add_program_dir_to_path = true) {
+inline void precheck_interpreter() {
     if (Py_IsInitialized() != 0) {
         pybind11_fail("The interpreter is already running");
     }
+}
 
-#if PY_VERSION_HEX < 0x030B0000
+#if !defined(PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX)
+#    define PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX (0x03080000)
+#endif
 
+#if PY_VERSION_HEX < PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+inline void initialize_interpreter_pre_pyconfig(bool init_signal_handlers,
+                                                int argc,
+                                                const char *const *argv,
+                                                bool add_program_dir_to_path) {
+    detail::precheck_interpreter();
     Py_InitializeEx(init_signal_handlers ? 1 : 0);
+#    if defined(WITH_THREAD) && PY_VERSION_HEX < 0x03070000
+    PyEval_InitThreads();
+#    endif
 
     // 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.
@@ -147,26 +135,30 @@ inline void initialize_interpreter(bool init_signal_handlers = true,
     auto *pysys_argv = widened_argv.get();
 
     PySys_SetArgvEx(argc, pysys_argv, static_cast<int>(add_program_dir_to_path));
-#else
-    PyConfig config;
-    PyConfig_InitIsolatedConfig(&config);
-    config.isolated = 0;
-    config.use_environment = 1;
-    config.install_signal_handlers = init_signal_handlers ? 1 : 0;
+}
+#endif
 
-    PyStatus status = PyConfig_SetBytesArgv(&config, argc, const_cast<char *const *>(argv));
-    if (PyStatus_Exception(status)) {
+PYBIND11_NAMESPACE_END(detail)
+
+#if PY_VERSION_HEX >= PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+inline void initialize_interpreter(PyConfig *config,
+                                   int argc = 0,
+                                   const char *const *argv = nullptr,
+                                   bool add_program_dir_to_path = true) {
+    detail::precheck_interpreter();
+    PyStatus status = PyConfig_SetBytesArgv(config, argc, const_cast<char *const *>(argv));
+    if (PyStatus_Exception(status) != 0) {
         // A failure here indicates a character-encoding failure or the python
         // interpreter out of memory. Give up.
-        PyConfig_Clear(&config);
-        throw std::runtime_error(PyStatus_IsError(status) ? status.err_msg
-                                                          : "Failed to prepare CPython");
+        PyConfig_Clear(config);
+        throw std::runtime_error(PyStatus_IsError(status) != 0 ? status.err_msg
+                                                               : "Failed to prepare CPython");
     }
-    status = Py_InitializeFromConfig(&config);
-    PyConfig_Clear(&config);
-    if (PyStatus_Exception(status)) {
-        throw std::runtime_error(PyStatus_IsError(status) ? status.err_msg
-                                                          : "Failed to init CPython");
+    status = Py_InitializeFromConfig(config);
+    if (PyStatus_Exception(status) != 0) {
+        PyConfig_Clear(config);
+        throw std::runtime_error(PyStatus_IsError(status) != 0 ? status.err_msg
+                                                               : "Failed to init CPython");
     }
     if (add_program_dir_to_path) {
         PyRun_SimpleString("import sys, os.path; "
@@ -174,6 +166,43 @@ inline void initialize_interpreter(bool init_signal_handlers = true,
                            "os.path.abspath(os.path.dirname(sys.argv[0])) "
                            "if sys.argv and os.path.exists(sys.argv[0]) else '')");
     }
+    PyConfig_Clear(config);
+}
+#endif
+
+/** \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 `init_signal_handlers` parameter can be used to skip the registration of
+    signal handlers (see the `Python documentation`_ for details). Calling this function
+    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,
+                                   int argc = 0,
+                                   const char *const *argv = nullptr,
+                                   bool add_program_dir_to_path = true) {
+#if PY_VERSION_HEX < PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+    detail::initialize_interpreter_pre_pyconfig(
+        init_signal_handlers, argc, argv, add_program_dir_to_path);
+#else
+    PyConfig config;
+    PyConfig_InitIsolatedConfig(&config);
+    config.isolated = 0;
+    config.use_environment = 1;
+    config.install_signal_handlers = init_signal_handlers ? 1 : 0;
+    initialize_interpreter(&config, argc, argv, add_program_dir_to_path);
 #endif
 }
 
@@ -261,6 +290,15 @@ public:
         initialize_interpreter(init_signal_handlers, argc, argv, add_program_dir_to_path);
     }
 
+#if PY_VERSION_HEX >= PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+    explicit scoped_interpreter(PyConfig *config,
+                                int argc = 0,
+                                const char *const *argv = nullptr,
+                                bool add_program_dir_to_path = true) {
+        initialize_interpreter(config, argc, argv, add_program_dir_to_path);
+    }
+#endif
+
     scoped_interpreter(const scoped_interpreter &) = delete;
     scoped_interpreter(scoped_interpreter &&other) noexcept { other.is_valid = false; }
     scoped_interpreter &operator=(const scoped_interpreter &) = delete;

include/pybind11/functional.h

@@ -48,9 +48,16 @@ public:
          */
         if (auto cfunc = func.cpp_function()) {
             auto *cfunc_self = PyCFunction_GET_SELF(cfunc.ptr());
-            if (isinstance<capsule>(cfunc_self)) {
+            if (cfunc_self == nullptr) {
+                PyErr_Clear();
+            } else if (isinstance<capsule>(cfunc_self)) {
                 auto c = reinterpret_borrow<capsule>(cfunc_self);
-                auto *rec = (function_record *) c;
+
+                function_record *rec = nullptr;
+                // Check that we can safely reinterpret the capsule into a function_record
+                if (detail::is_function_record_capsule(c)) {
+                    rec = c.get_pointer<function_record>();
+                }
 
                 while (rec != nullptr) {
                     if (rec->is_stateless

include/pybind11/numpy.h

@@ -36,6 +36,8 @@ static_assert(std::is_signed<Py_intptr_t>::value, "Py_intptr_t must be signed");
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
 class array; // Forward declaration
 
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -875,7 +877,7 @@ public:
      */
     template <typename T, ssize_t Dims = -1>
     detail::unchecked_mutable_reference<T, Dims> mutable_unchecked() & {
-        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims) {
+        if (Dims >= 0 && ndim() != Dims) {
             throw std::domain_error("array has incorrect number of dimensions: "
                                     + std::to_string(ndim()) + "; expected "
                                     + std::to_string(Dims));
@@ -893,7 +895,7 @@ public:
      */
     template <typename T, ssize_t Dims = -1>
     detail::unchecked_reference<T, Dims> unchecked() const & {
-        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims) {
+        if (Dims >= 0 && ndim() != Dims) {
             throw std::domain_error("array has incorrect number of dimensions: "
                                     + std::to_string(ndim()) + "; expected "
                                     + std::to_string(Dims));
@@ -1469,7 +1471,7 @@ private:
         }
 
 // Extract name, offset and format descriptor for a struct field
-#    define PYBIND11_FIELD_DESCRIPTOR(T, Field) PYBIND11_FIELD_DESCRIPTOR_EX(T, Field, #    Field)
+#    define PYBIND11_FIELD_DESCRIPTOR(T, Field) PYBIND11_FIELD_DESCRIPTOR_EX(T, Field, #Field)
 
 // The main idea of this macro is borrowed from https://github.com/swansontec/map-macro
 // (C) William Swanson, Paul Fultz
@@ -1865,9 +1867,10 @@ private:
         }
 
         auto result = returned_array::create(trivial, shape);
+
+        PYBIND11_WARNING_PUSH
 #ifdef PYBIND11_DETECTED_CLANG_WITH_MISLEADING_CALL_STD_MOVE_EXPLICITLY_WARNING
-#    pragma clang diagnostic push
-#    pragma clang diagnostic ignored "-Wreturn-std-move"
+        PYBIND11_WARNING_DISABLE_CLANG("-Wreturn-std-move")
 #endif
 
         if (size == 0) {
@@ -1883,9 +1886,7 @@ private:
         }
 
         return result;
-#ifdef PYBIND11_DETECTED_CLANG_WITH_MISLEADING_CALL_STD_MOVE_EXPLICITLY_WARNING
-#    pragma clang diagnostic pop
-#endif
+        PYBIND11_WARNING_POP
     }
 
     template <size_t... Index, size_t... VIndex, size_t... BIndex>

include/pybind11/options.h

@@ -47,6 +47,16 @@ public:
         return *this;
     }
 
+    options &disable_enum_members_docstring() & {
+        global_state().show_enum_members_docstring = false;
+        return *this;
+    }
+
+    options &enable_enum_members_docstring() & {
+        global_state().show_enum_members_docstring = true;
+        return *this;
+    }
+
     // Getter methods (return the global state):
 
     static bool show_user_defined_docstrings() {
@@ -55,6 +65,10 @@ public:
 
     static bool show_function_signatures() { return global_state().show_function_signatures; }
 
+    static bool show_enum_members_docstring() {
+        return global_state().show_enum_members_docstring;
+    }
+
     // This type is not meant to be allocated on the heap.
     void *operator new(size_t) = delete;
 
@@ -63,6 +77,8 @@ private:
         bool show_user_defined_docstrings = true; //< Include user-supplied texts in docstrings.
         bool show_function_signatures = true;     //< Include auto-generated function signatures
                                                   //  in docstrings.
+        bool show_enum_members_docstring = true;  //< Include auto-generated member list in enum
+                                                  //  docstrings.
     };
 
     static state &global_state() {

include/pybind11/pybind11.h

@@ -35,6 +35,8 @@
 #    include <cxxabi.h>
 #endif
 
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+
 /* https://stackoverflow.com/questions/46798456/handling-gccs-noexcept-type-warning
    This warning is about ABI compatibility, not code health.
    It is only actually needed in a couple places, but apparently GCC 7 "generates this warning if
@@ -43,11 +45,10 @@
    No other GCC version generates this warning.
  */
 #if defined(__GNUC__) && __GNUC__ == 7
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wnoexcept-type"
+PYBIND11_WARNING_DISABLE_GCC("-Wnoexcept-type")
 #endif
 
-PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_WARNING_DISABLE_MSVC(4127)
 
 PYBIND11_NAMESPACE_BEGIN(detail)
 
@@ -177,22 +178,22 @@ protected:
         auto *rec = unique_rec.get();
 
         /* Store the capture object directly in the function record if there is enough space */
-        if (PYBIND11_SILENCE_MSVC_C4127(sizeof(capture) <= sizeof(rec->data))) {
+        if (sizeof(capture) <= sizeof(rec->data)) {
             /* Without these pragmas, GCC warns that there might not be
                enough space to use the placement new operator. However, the
                'if' statement above ensures that this is the case. */
-#if defined(__GNUG__) && __GNUC__ >= 6 && !defined(__clang__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wplacement-new"
+            PYBIND11_WARNING_PUSH
+
+#if defined(__GNUG__) && __GNUC__ >= 6
+            PYBIND11_WARNING_DISABLE_GCC("-Wplacement-new")
 #endif
+
             new ((capture *) &rec->data) capture{std::forward<Func>(f)};
-#if defined(__GNUG__) && __GNUC__ >= 6 && !defined(__clang__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif
-#if defined(__GNUG__) && !PYBIND11_HAS_STD_LAUNDER && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wstrict-aliasing"
+
+#if !PYBIND11_HAS_STD_LAUNDER
+            PYBIND11_WARNING_DISABLE_GCC("-Wstrict-aliasing")
 #endif
+
             // UB without std::launder, but without breaking ABI and/or
             // a significant refactoring it's "impossible" to solve.
             if (!std::is_trivially_destructible<capture>::value) {
@@ -202,9 +203,7 @@ protected:
                     data->~capture();
                 };
             }
-#if defined(__GNUG__) && !PYBIND11_HAS_STD_LAUNDER && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif
+            PYBIND11_WARNING_POP
         } else {
             rec->data[0] = new capture{std::forward<Func>(f)};
             rec->free_data = [](function_record *r) { delete ((capture *) r->data[0]); };
@@ -468,13 +467,20 @@ protected:
         if (rec->sibling) {
             if (PyCFunction_Check(rec->sibling.ptr())) {
                 auto *self = PyCFunction_GET_SELF(rec->sibling.ptr());
-                capsule rec_capsule = isinstance<capsule>(self) ? reinterpret_borrow<capsule>(self)
-                                                                : capsule(self);
-                chain = (detail::function_record *) rec_capsule;
-                /* Never append a method to an overload chain of a parent class;
-                   instead, hide the parent's overloads in this case */
-                if (!chain->scope.is(rec->scope)) {
+                if (!isinstance<capsule>(self)) {
                     chain = nullptr;
+                } else {
+                    auto rec_capsule = reinterpret_borrow<capsule>(self);
+                    if (detail::is_function_record_capsule(rec_capsule)) {
+                        chain = rec_capsule.get_pointer<detail::function_record>();
+                        /* Never append a method to an overload chain of a parent class;
+                           instead, hide the parent's overloads in this case */
+                        if (!chain->scope.is(rec->scope)) {
+                            chain = nullptr;
+                        }
+                    } else {
+                        chain = nullptr;
+                    }
                 }
             }
             // Don't trigger for things like the default __init__, which are wrapper_descriptors
@@ -496,6 +502,7 @@ protected:
 
             capsule rec_capsule(unique_rec.release(),
                                 [](void *ptr) { destruct((detail::function_record *) ptr); });
+            rec_capsule.set_name(detail::get_function_record_capsule_name());
             guarded_strdup.release();
 
             object scope_module;
@@ -661,10 +668,13 @@ protected:
     /// Main dispatch logic for calls to functions bound using pybind11
     static PyObject *dispatcher(PyObject *self, PyObject *args_in, PyObject *kwargs_in) {
         using namespace detail;
+        assert(isinstance<capsule>(self));
 
         /* Iterator over the list of potentially admissible overloads */
-        const function_record *overloads = (function_record *) PyCapsule_GetPointer(self, nullptr),
+        const function_record *overloads = reinterpret_cast<function_record *>(
+                                  PyCapsule_GetPointer(self, get_function_record_capsule_name())),
                               *it = overloads;
+        assert(overloads != nullptr);
 
         /* Need to know how many arguments + keyword arguments there are to pick the right
            overload */
@@ -1416,9 +1426,9 @@ template <typename T, enable_if_t<has_operator_delete<T>::value, int> = 0>
 void call_operator_delete(T *p, size_t, size_t) {
     T::operator delete(p);
 }
-template <
-    typename T,
-    enable_if_t<!has_operator_delete<T>::value && has_operator_delete_size<T>::value, int> = 0>
+template <typename T,
+          enable_if_t<!has_operator_delete<T>::value && has_operator_delete_size<T>::value, int>
+          = 0>
 void call_operator_delete(T *p, size_t s, size_t) {
     T::operator delete(p, s);
 }
@@ -1830,8 +1840,7 @@ private:
         if (holder_ptr) {
             init_holder_from_existing(v_h, holder_ptr, std::is_copy_constructible<holder_type>());
             v_h.set_holder_constructed();
-        } else if (PYBIND11_SILENCE_MSVC_C4127(detail::always_construct_holder<holder_type>::value)
-                   || inst->owned) {
+        } else if (detail::always_construct_holder<holder_type>::value || inst->owned) {
             new (std::addressof(v_h.holder<holder_type>())) holder_type(v_h.value_ptr<type>());
             v_h.set_holder_constructed();
         }
@@ -1871,9 +1880,22 @@ private:
 
     static detail::function_record *get_function_record(handle h) {
         h = detail::get_function(h);
-        return h ? (detail::function_record *) reinterpret_borrow<capsule>(
-                   PyCFunction_GET_SELF(h.ptr()))
-                 : nullptr;
+        if (!h) {
+            return nullptr;
+        }
+
+        handle func_self = PyCFunction_GET_SELF(h.ptr());
+        if (!func_self) {
+            throw error_already_set();
+        }
+        if (!isinstance<capsule>(func_self)) {
+            return nullptr;
+        }
+        auto cap = reinterpret_borrow<capsule>(func_self);
+        if (!detail::is_function_record_capsule(cap)) {
+            return nullptr;
+        }
+        return cap.get_pointer<detail::function_record>();
     }
 };
 
@@ -1950,29 +1972,35 @@ struct enum_base {
             name("name"),
             is_method(m_base));
 
-        m_base.attr("__doc__") = static_property(
-            cpp_function(
-                [](handle arg) -> std::string {
-                    std::string docstring;
-                    dict entries = arg.attr("__entries");
-                    if (((PyTypeObject *) arg.ptr())->tp_doc) {
-                        docstring += std::string(((PyTypeObject *) arg.ptr())->tp_doc) + "\n\n";
-                    }
-                    docstring += "Members:";
-                    for (auto kv : entries) {
-                        auto key = std::string(pybind11::str(kv.first));
-                        auto comment = kv.second[int_(1)];
-                        docstring += "\n\n  " + key;
-                        if (!comment.is_none()) {
-                            docstring += " : " + (std::string) pybind11::str(comment);
+        if (options::show_enum_members_docstring()) {
+            m_base.attr("__doc__") = static_property(
+                cpp_function(
+                    [](handle arg) -> std::string {
+                        std::string docstring;
+                        dict entries = arg.attr("__entries");
+                        if (((PyTypeObject *) arg.ptr())->tp_doc) {
+                            docstring += std::string(
+                                reinterpret_cast<PyTypeObject *>(arg.ptr())->tp_doc);
+                            docstring += "\n\n";
                         }
-                    }
-                    return docstring;
-                },
-                name("__doc__")),
-            none(),
-            none(),
-            "");
+                        docstring += "Members:";
+                        for (auto kv : entries) {
+                            auto key = std::string(pybind11::str(kv.first));
+                            auto comment = kv.second[int_(1)];
+                            docstring += "\n\n  ";
+                            docstring += key;
+                            if (!comment.is_none()) {
+                                docstring += " : ";
+                                docstring += pybind11::str(comment).cast<std::string>();
+                            }
+                        }
+                        return docstring;
+                    },
+                    name("__doc__")),
+                none(),
+                none(),
+                "");
+        }
 
         m_base.attr("__members__") = static_property(cpp_function(
                                                          [](handle arg) -> dict {
@@ -2852,7 +2880,3 @@ inline function get_overload(const T *this_ptr, const char *name) {
     PYBIND11_OVERRIDE_PURE(PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), fn, __VA_ARGS__);
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#if defined(__GNUC__) && __GNUC__ == 7
-#    pragma GCC diagnostic pop // -Wnoexcept-type
-#endif

include/pybind11/pytypes.h

@@ -33,6 +33,8 @@
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
 /* A few forward declarations */
 class handle;
 class object;
@@ -230,7 +232,8 @@ public:
         detail::enable_if_t<detail::all_of<detail::none_of<std::is_base_of<handle, T>,
                                                            detail::is_pyobj_ptr_or_nullptr_t<T>>,
                                            std::is_convertible<T, PyObject *>>::value,
-                            int> = 0>
+                            int>
+        = 0>
     // NOLINTNEXTLINE(google-explicit-constructor)
     handle(T &obj) : m_ptr(obj) {}
 
@@ -246,6 +249,11 @@ public:
     const handle &inc_ref() const & {
 #ifdef PYBIND11_HANDLE_REF_DEBUG
         inc_ref_counter(1);
+#endif
+#if defined(PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF)
+        if (m_ptr != nullptr && !PyGILState_Check()) {
+            throw std::runtime_error("pybind11::handle::inc_ref() PyGILState_Check() failure.");
+        }
 #endif
         Py_XINCREF(m_ptr);
         return *this;
@@ -257,6 +265,11 @@ public:
         this function automatically. Returns a reference to itself.
     \endrst */
     const handle &dec_ref() const & {
+#if defined(PYBIND11_ASSERT_GIL_HELD_INCREF_DECREF)
+        if (m_ptr != nullptr && !PyGILState_Check()) {
+            throw std::runtime_error("pybind11::handle::dec_ref() PyGILState_Check() failure.");
+        }
+#endif
         Py_XDECREF(m_ptr);
         return *this;
     }
@@ -623,12 +636,6 @@ inline std::string error_string() {
 
 PYBIND11_NAMESPACE_END(detail)
 
-#if defined(_MSC_VER)
-#    pragma warning(push)
-#    pragma warning(disable : 4275 4251)
-//     warning C4275: An exported class was derived from a class that wasn't exported.
-//     Can be ignored when derived from a STL class.
-#endif
 /// Fetch and hold an error which was already set in Python.  An instance of this is typically
 /// thrown to propagate python-side errors back through C++ which can either be caught manually or
 /// else falls back to the function dispatcher (which then raises the captured error back to
@@ -688,9 +695,6 @@ private:
     ///          crashes (undefined behavior) if the Python interpreter is finalizing.
     static void m_fetched_error_deleter(detail::error_fetch_and_normalize *raw_ptr);
 };
-#if defined(_MSC_VER)
-#    pragma warning(pop)
-#endif
 
 /// Replaces the current Python error indicator with the chosen error, performing a
 /// 'raise from' to indicate that the chosen error was caused by the original error.
@@ -893,10 +897,8 @@ object object_or_cast(T &&o);
 // Match a PyObject*, which we want to convert directly to handle via its converting constructor
 inline handle object_or_cast(PyObject *ptr) { return ptr; }
 
-#if defined(_MSC_VER) && _MSC_VER < 1920
-#    pragma warning(push)
-#    pragma warning(disable : 4522) // warning C4522: multiple assignment operators specified
-#endif
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_MSVC(4522) // warning C4522: multiple assignment operators specified
 template <typename Policy>
 class accessor : public object_api<accessor<Policy>> {
     using key_type = typename Policy::key_type;
@@ -960,9 +962,7 @@ private:
     key_type key;
     mutable object cache;
 };
-#if defined(_MSC_VER) && _MSC_VER < 1920
-#    pragma warning(pop)
-#endif
+PYBIND11_WARNING_POP
 
 PYBIND11_NAMESPACE_BEGIN(accessor_policies)
 struct obj_attr {
@@ -1702,7 +1702,7 @@ PYBIND11_NAMESPACE_BEGIN(detail)
 // unsigned type: (A)-1 != (B)-1 when A and B are unsigned types of different sizes).
 template <typename Unsigned>
 Unsigned as_unsigned(PyObject *o) {
-    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(Unsigned) <= sizeof(unsigned long))) {
+    if (sizeof(Unsigned) <= sizeof(unsigned long)) {
         unsigned long v = PyLong_AsUnsignedLong(o);
         return v == (unsigned long) -1 && PyErr_Occurred() ? (Unsigned) -1 : (Unsigned) v;
     }
@@ -1719,7 +1719,7 @@ public:
     template <typename T, detail::enable_if_t<std::is_integral<T>::value, int> = 0>
     // NOLINTNEXTLINE(google-explicit-constructor)
     int_(T value) {
-        if (PYBIND11_SILENCE_MSVC_C4127(sizeof(T) <= sizeof(long))) {
+        if (sizeof(T) <= sizeof(long)) {
             if (std::is_signed<T>::value) {
                 m_ptr = PyLong_FromLong((long) value);
             } else {

include/pybind11/stl_bind.h

@@ -10,10 +10,13 @@
 #pragma once
 
 #include "detail/common.h"
+#include "detail/type_caster_base.h"
+#include "cast.h"
 #include "operators.h"
 
 #include <algorithm>
 #include <sstream>
+#include <type_traits>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -636,18 +639,52 @@ auto map_if_insertion_operator(Class_ &cl, std::string const &name)
         "Return the canonical string representation of this map.");
 }
 
-template <typename Map>
+template <typename KeyType>
 struct keys_view {
-    Map &map;
+    virtual size_t len() = 0;
+    virtual iterator iter() = 0;
+    virtual bool contains(const KeyType &k) = 0;
+    virtual bool contains(const object &k) = 0;
+    virtual ~keys_view() = default;
 };
 
-template <typename Map>
+template <typename MappedType>
 struct values_view {
+    virtual size_t len() = 0;
+    virtual iterator iter() = 0;
+    virtual ~values_view() = default;
+};
+
+template <typename KeyType, typename MappedType>
+struct items_view {
+    virtual size_t len() = 0;
+    virtual iterator iter() = 0;
+    virtual ~items_view() = default;
+};
+
+template <typename Map, typename KeysView>
+struct KeysViewImpl : public KeysView {
+    explicit KeysViewImpl(Map &map) : map(map) {}
+    size_t len() override { return map.size(); }
+    iterator iter() override { return make_key_iterator(map.begin(), map.end()); }
+    bool contains(const typename Map::key_type &k) override { return map.find(k) != map.end(); }
+    bool contains(const object &) override { return false; }
     Map &map;
 };
 
-template <typename Map>
-struct items_view {
+template <typename Map, typename ValuesView>
+struct ValuesViewImpl : public ValuesView {
+    explicit ValuesViewImpl(Map &map) : map(map) {}
+    size_t len() override { return map.size(); }
+    iterator iter() override { return make_value_iterator(map.begin(), map.end()); }
+    Map &map;
+};
+
+template <typename Map, typename ItemsView>
+struct ItemsViewImpl : public ItemsView {
+    explicit ItemsViewImpl(Map &map) : map(map) {}
+    size_t len() override { return map.size(); }
+    iterator iter() override { return make_iterator(map.begin(), map.end()); }
     Map &map;
 };
 
@@ -657,9 +694,11 @@ 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 StrippedKeyType = detail::remove_cvref_t<KeyType>;
+    using StrippedMappedType = detail::remove_cvref_t<MappedType>;
+    using KeysView = detail::keys_view<StrippedKeyType>;
+    using ValuesView = detail::values_view<StrippedMappedType>;
+    using ItemsView = detail::items_view<StrippedKeyType, StrippedMappedType>;
     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;
@@ -673,12 +712,57 @@ 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));
+    static constexpr auto key_type_descr = detail::make_caster<KeyType>::name;
+    static constexpr auto mapped_type_descr = detail::make_caster<MappedType>::name;
+    std::string key_type_name(key_type_descr.text), mapped_type_name(mapped_type_descr.text);
+
+    // If key type isn't properly wrapped, fall back to C++ names
+    if (key_type_name == "%") {
+        key_type_name = detail::type_info_description(typeid(KeyType));
+    }
+    // Similarly for value type:
+    if (mapped_type_name == "%") {
+        mapped_type_name = detail::type_info_description(typeid(MappedType));
+    }
+
+    // Wrap KeysView[KeyType] if it wasn't already wrapped
+    if (!detail::get_type_info(typeid(KeysView))) {
+        class_<KeysView> keys_view(
+            scope, ("KeysView[" + key_type_name + "]").c_str(), pybind11::module_local(local));
+        keys_view.def("__len__", &KeysView::len);
+        keys_view.def("__iter__",
+                      &KeysView::iter,
+                      keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+        );
+        keys_view.def("__contains__",
+                      static_cast<bool (KeysView::*)(const KeyType &)>(&KeysView::contains));
+        // Fallback for when the object is not of the key type
+        keys_view.def("__contains__",
+                      static_cast<bool (KeysView::*)(const object &)>(&KeysView::contains));
+    }
+    // Similarly for ValuesView:
+    if (!detail::get_type_info(typeid(ValuesView))) {
+        class_<ValuesView> values_view(scope,
+                                       ("ValuesView[" + mapped_type_name + "]").c_str(),
+                                       pybind11::module_local(local));
+        values_view.def("__len__", &ValuesView::len);
+        values_view.def("__iter__",
+                        &ValuesView::iter,
+                        keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+        );
+    }
+    // Similarly for ItemsView:
+    if (!detail::get_type_info(typeid(ItemsView))) {
+        class_<ItemsView> items_view(
+            scope,
+            ("ItemsView[" + key_type_name + ", ").append(mapped_type_name + "]").c_str(),
+            pybind11::module_local(local));
+        items_view.def("__len__", &ItemsView::len);
+        items_view.def("__iter__",
+                       &ItemsView::iter,
+                       keep_alive<0, 1>() /* Essential: keep view alive while iterator exists */
+        );
+    }
 
     cl.def(init<>());
 
@@ -698,19 +782,25 @@ class_<Map, holder_type> bind_map(handle scope, const std::string &name, Args &&
 
     cl.def(
         "keys",
-        [](Map &m) { return KeysView{m}; },
+        [](Map &m) {
+            return std::unique_ptr<KeysView>(new detail::KeysViewImpl<Map, KeysView>(m));
+        },
         keep_alive<0, 1>() /* Essential: keep map alive while view exists */
     );
 
     cl.def(
         "values",
-        [](Map &m) { return ValuesView{m}; },
+        [](Map &m) {
+            return std::unique_ptr<ValuesView>(new detail::ValuesViewImpl<Map, ValuesView>(m));
+        },
         keep_alive<0, 1>() /* Essential: keep map alive while view exists */
     );
 
     cl.def(
         "items",
-        [](Map &m) { return ItemsView{m}; },
+        [](Map &m) {
+            return std::unique_ptr<ItemsView>(new detail::ItemsViewImpl<Map, ItemsView>(m));
+        },
         keep_alive<0, 1>() /* Essential: keep map alive while view exists */
     );
 
@@ -749,36 +839,6 @@ 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;
 }
 

pybind11/_version.py

@@ -8,5 +8,5 @@ def _to_int(s: str) -> Union[int, str]:
         return s
 
 
-__version__ = "2.10.1"
+__version__ = "2.10.2"
 version_info = tuple(_to_int(s) for s in __version__.split("."))

setup.cfg

@@ -46,5 +46,5 @@ zip_safe = False
 max-line-length = 120
 show_source = True
 exclude = .git, __pycache__, build, dist, docs, tools, venv
-extend-ignore = E203, E722, B903, B950
-extend-select = B9
+extend-ignore = E203, E722
+extend-select = B902, B904

tests/CMakeLists.txt

@@ -128,7 +128,8 @@ set(PYBIND11_TEST_FILES
     test_custom_type_casters
     test_custom_type_setup
     test_docstring_options
-    test_eigen
+    test_eigen_matrix
+    test_eigen_tensor
     test_enum
     test_eval
     test_exceptions
@@ -233,7 +234,10 @@ list(GET PYBIND11_EIGEN_VERSION_AND_HASH 1 PYBIND11_EIGEN_VERSION_HASH)
 # 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).
-list(FIND PYBIND11_TEST_FILES test_eigen.cpp PYBIND11_TEST_FILES_EIGEN_I)
+list(FIND PYBIND11_TEST_FILES test_eigen_matrix.cpp PYBIND11_TEST_FILES_EIGEN_I)
+if(PYBIND11_TEST_FILES_EIGEN_I EQUAL -1)
+  list(FIND PYBIND11_TEST_FILES test_eigen_tensor.cpp PYBIND11_TEST_FILES_EIGEN_I)
+endif()
 if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
   # Try loading via newer Eigen's Eigen3Config first (bypassing tools/FindEigen3.cmake).
   # Eigen 3.3.1+ exports a cmake 3.0+ target for handling dependency requirements, but also
@@ -288,13 +292,34 @@ if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
       set(EIGEN3_VERSION ${EIGEN3_VERSION_STRING})
     endif()
     message(STATUS "Building tests with Eigen v${EIGEN3_VERSION}")
+
+    if(NOT (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0))
+      tests_extra_targets("test_eigen_tensor.py" "eigen_tensor_avoid_stl_array")
+    endif()
+
   else()
-    list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
+    list(FIND PYBIND11_TEST_FILES test_eigen_matrix.cpp PYBIND11_TEST_FILES_EIGEN_I)
+    if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
+      list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
+    endif()
+
+    list(FIND PYBIND11_TEST_FILES test_eigen_tensor.cpp PYBIND11_TEST_FILES_EIGEN_I)
+    if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
+      list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
+    endif()
     message(
       STATUS "Building tests WITHOUT Eigen, use -DDOWNLOAD_EIGEN=ON on CMake 3.11+ to download")
   endif()
 endif()
 
+# Some code doesn't support gcc 4
+if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
+  list(FIND PYBIND11_TEST_FILES test_eigen_tensor.cpp PYBIND11_TEST_FILES_EIGEN_I)
+  if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
+    list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_EIGEN_I})
+  endif()
+endif()
+
 # Optional dependency for some tests (boost::variant is only supported with version >= 1.56)
 find_package(Boost 1.56)
 

tests/conftest.py

@@ -7,6 +7,8 @@ Adds docstring and exceptions message sanitizers.
 import contextlib
 import difflib
 import gc
+import multiprocessing
+import os
 import re
 import textwrap
 
@@ -15,6 +17,22 @@ import pytest
 # Early diagnostic for failed imports
 import pybind11_tests
 
+
+@pytest.fixture(scope="session", autouse=True)
+def always_forkserver_on_unix():
+    if os.name == "nt":
+        return
+
+    # Full background: https://github.com/pybind/pybind11/issues/4105#issuecomment-1301004592
+    # In a nutshell: fork() after starting threads == flakiness in the form of deadlocks.
+    # It is actually a well-known pitfall, unfortunately without guard rails.
+    # "forkserver" is more performant than "spawn" (~9s vs ~13s for tests/test_gil_scoped.py,
+    # visit the issuecomment link above for details).
+    # Windows does not have fork() and the associated pitfall, therefore it is best left
+    # running with defaults.
+    multiprocessing.set_start_method("forkserver")
+
+
 _long_marker = re.compile(r"([0-9])L")
 _hexadecimal = re.compile(r"0x[0-9a-fA-F]+")
 

tests/eigen_tensor_avoid_stl_array.cpp

@@ -0,0 +1,14 @@
+/*
+    tests/eigen_tensor.cpp -- automatic conversion of Eigen Tensor
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#ifndef EIGEN_AVOID_STL_ARRAY
+#    define EIGEN_AVOID_STL_ARRAY
+#endif
+
+#include "test_eigen_tensor.inl"
+
+PYBIND11_MODULE(eigen_tensor_avoid_stl_array, m) { eigen_tensor_test::test_module(m); }

tests/extra_python_package/test_files.py

@@ -55,6 +55,11 @@ detail_headers = {
     "include/pybind11/detail/typeid.h",
 }
 
+eigen_headers = {
+    "include/pybind11/eigen/matrix.h",
+    "include/pybind11/eigen/tensor.h",
+}
+
 stl_headers = {
     "include/pybind11/stl/filesystem.h",
 }
@@ -82,7 +87,7 @@ py_files = {
     "setup_helpers.py",
 }
 
-headers = main_headers | detail_headers | stl_headers
+headers = main_headers | detail_headers | eigen_headers | stl_headers
 src_files = headers | cmake_files | pkgconfig_files
 all_files = src_files | py_files
 
@@ -92,6 +97,7 @@ sdist_files = {
     "pybind11/include",
     "pybind11/include/pybind11",
     "pybind11/include/pybind11/detail",
+    "pybind11/include/pybind11/eigen",
     "pybind11/include/pybind11/stl",
     "pybind11/share",
     "pybind11/share/cmake",

tests/test_builtin_casters.cpp

@@ -73,6 +73,9 @@ PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(pybind11)
 
 TEST_SUBMODULE(builtin_casters, m) {
+    PYBIND11_WARNING_PUSH
+    PYBIND11_WARNING_DISABLE_MSVC(4127)
+
     // test_simple_string
     m.def("string_roundtrip", [](const char *s) { return s; });
 
@@ -86,7 +89,7 @@ TEST_SUBMODULE(builtin_casters, m) {
     std::wstring wstr;
     wstr.push_back(0x61);   // a
     wstr.push_back(0x2e18); // ⸘
-    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(wchar_t) == 2)) {
+    if (sizeof(wchar_t) == 2) {
         wstr.push_back(mathbfA16_1);
         wstr.push_back(mathbfA16_2);
     } // 𝐀, utf16
@@ -113,7 +116,7 @@ TEST_SUBMODULE(builtin_casters, m) {
     // Under Python 2.7, invalid unicode UTF-32 characters didn't appear to trigger
     // UnicodeDecodeError
     m.def("bad_utf32_string", [=]() { return std::u32string({a32, char32_t(0xd800), z32}); });
-    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(wchar_t) == 2)) {
+    if (sizeof(wchar_t) == 2) {
         m.def("bad_wchar_string", [=]() {
             return std::wstring({wchar_t(0x61), wchar_t(0xd800)});
         });
@@ -384,4 +387,6 @@ TEST_SUBMODULE(builtin_casters, m) {
     m.def("takes_const_ref", [](const ConstRefCasted &x) { return x.tag; });
     m.def("takes_const_ref_wrap",
           [](std::reference_wrapper<const ConstRefCasted> x) { return x.get().tag; });
+
+    PYBIND11_WARNING_POP
 }

tests/test_callbacks.cpp

@@ -240,4 +240,41 @@ TEST_SUBMODULE(callbacks, m) {
             f();
         }
     });
+
+    auto *custom_def = []() {
+        static PyMethodDef def;
+        def.ml_name = "example_name";
+        def.ml_doc = "Example doc";
+        def.ml_meth = [](PyObject *, PyObject *args) -> PyObject * {
+            if (PyTuple_Size(args) != 1) {
+                throw std::runtime_error("Invalid number of arguments for example_name");
+            }
+            PyObject *first = PyTuple_GetItem(args, 0);
+            if (!PyLong_Check(first)) {
+                throw std::runtime_error("Invalid argument to example_name");
+            }
+            auto result = py::cast(PyLong_AsLong(first) * 9);
+            return result.release().ptr();
+        };
+        def.ml_flags = METH_VARARGS;
+        return &def;
+    }();
+
+    // rec_capsule with name that has the same value (but not pointer) as our internal one
+    // This capsule should be detected by our code as foreign and not inspected as the pointers
+    // shouldn't match
+    constexpr const char *rec_capsule_name
+        = pybind11::detail::internals_function_record_capsule_name;
+    py::capsule rec_capsule(std::malloc(1), [](void *data) { std::free(data); });
+    rec_capsule.set_name(rec_capsule_name);
+    m.add_object("custom_function", PyCFunction_New(custom_def, rec_capsule.ptr()));
+
+    // This test requires a new ABI version to pass
+#if PYBIND11_INTERNALS_VERSION > 4
+    // rec_capsule with nullptr name
+    py::capsule rec_capsule2(std::malloc(1), [](void *data) { std::free(data); });
+    m.add_object("custom_function2", PyCFunction_New(custom_def, rec_capsule2.ptr()));
+#else
+    m.add_object("custom_function2", py::none());
+#endif
 }

tests/test_callbacks.py

@@ -193,3 +193,16 @@ def test_callback_num_times():
     if len(rates) > 1:
         print("Min    Mean   Max")
         print(f"{min(rates):6.3f} {sum(rates) / len(rates):6.3f} {max(rates):6.3f}")
+
+
+def test_custom_func():
+    assert m.custom_function(4) == 36
+    assert m.roundtrip(m.custom_function)(4) == 36
+
+
+@pytest.mark.skipif(
+    m.custom_function2 is None, reason="Current PYBIND11_INTERNALS_VERSION too low"
+)
+def test_custom_func2():
+    assert m.custom_function2(3) == 27
+    assert m.roundtrip(m.custom_function2)(3) == 27

tests/test_class.cpp

@@ -22,10 +22,8 @@
 
 #include <utility>
 
-#if defined(_MSC_VER)
-#    pragma warning(disable : 4324)
+PYBIND11_WARNING_DISABLE_MSVC(4324)
 //     warning C4324: structure was padded due to alignment specifier
-#endif
 
 // test_brace_initialization
 struct NoBraceInitialization {

tests/test_constants_and_functions.cpp

@@ -52,15 +52,12 @@ int f1(int x) noexcept { return x + 1; }
 #endif
 int f2(int x) noexcept(true) { return x + 2; }
 int f3(int x) noexcept(false) { return x + 3; }
-#if defined(__GNUG__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wdeprecated"
-#endif
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_GCC("-Wdeprecated")
+PYBIND11_WARNING_DISABLE_CLANG("-Wdeprecated")
 // NOLINTNEXTLINE(modernize-use-noexcept)
 int f4(int x) throw() { return x + 4; } // Deprecated equivalent to noexcept(true)
-#if defined(__GNUG__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif
+PYBIND11_WARNING_POP
 struct C {
     int m1(int x) noexcept { return x - 1; }
     int m2(int x) const noexcept { return x - 2; }
@@ -68,17 +65,14 @@ struct C {
     int m4(int x) const noexcept(true) { return x - 4; }
     int m5(int x) noexcept(false) { return x - 5; }
     int m6(int x) const noexcept(false) { return x - 6; }
-#if defined(__GNUG__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wdeprecated"
-#endif
+    PYBIND11_WARNING_PUSH
+    PYBIND11_WARNING_DISABLE_GCC("-Wdeprecated")
+    PYBIND11_WARNING_DISABLE_CLANG("-Wdeprecated")
     // NOLINTNEXTLINE(modernize-use-noexcept)
     int m7(int x) throw() { return x - 7; }
     // NOLINTNEXTLINE(modernize-use-noexcept)
     int m8(int x) const throw() { return x - 8; }
-#if defined(__GNUG__) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif
+    PYBIND11_WARNING_POP
 };
 } // namespace test_exc_sp
 
@@ -126,14 +120,12 @@ TEST_SUBMODULE(constants_and_functions, m) {
         .def("m8", &C::m8);
     m.def("f1", f1);
     m.def("f2", f2);
-#if defined(__INTEL_COMPILER)
-#    pragma warning push
-#    pragma warning disable 878 // incompatible exception specifications
-#endif
+
+    PYBIND11_WARNING_PUSH
+    PYBIND11_WARNING_DISABLE_INTEL(878) // incompatible exception specifications
     m.def("f3", f3);
-#if defined(__INTEL_COMPILER)
-#    pragma warning pop
-#endif
+    PYBIND11_WARNING_POP
+
     m.def("f4", f4);
 
     // test_function_record_leaks

tests/test_docstring_options.cpp

@@ -85,4 +85,57 @@ TEST_SUBMODULE(docstring_options, m) {
                           &DocstringTestFoo::setValue,
                           "This is a property docstring");
     }
+
+    {
+        enum class DocstringTestEnum1 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum1>(m, "DocstringTestEnum1", "Enum docstring")
+            .value("Member1", DocstringTestEnum1::Member1)
+            .value("Member2", DocstringTestEnum1::Member2);
+    }
+
+    {
+        py::options options;
+        options.enable_enum_members_docstring();
+
+        enum class DocstringTestEnum2 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum2>(m, "DocstringTestEnum2", "Enum docstring")
+            .value("Member1", DocstringTestEnum2::Member1)
+            .value("Member2", DocstringTestEnum2::Member2);
+    }
+
+    {
+        py::options options;
+        options.disable_enum_members_docstring();
+
+        enum class DocstringTestEnum3 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum3>(m, "DocstringTestEnum3", "Enum docstring")
+            .value("Member1", DocstringTestEnum3::Member1)
+            .value("Member2", DocstringTestEnum3::Member2);
+    }
+
+    {
+        py::options options;
+        options.disable_user_defined_docstrings();
+
+        enum class DocstringTestEnum4 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum4>(m, "DocstringTestEnum4", "Enum docstring")
+            .value("Member1", DocstringTestEnum4::Member1)
+            .value("Member2", DocstringTestEnum4::Member2);
+    }
+
+    {
+        py::options options;
+        options.disable_user_defined_docstrings();
+        options.disable_enum_members_docstring();
+
+        enum class DocstringTestEnum5 { Member1, Member2 };
+
+        py::enum_<DocstringTestEnum5>(m, "DocstringTestEnum5", "Enum docstring")
+            .value("Member1", DocstringTestEnum5::Member1)
+            .value("Member2", DocstringTestEnum5::Member2);
+    }
 }

tests/test_docstring_options.py

@@ -39,3 +39,26 @@ def test_docstring_options():
     # Suppression of user-defined docstrings for non-function objects
     assert not m.DocstringTestFoo.__doc__
     assert not m.DocstringTestFoo.value_prop.__doc__
+
+    # Check existig behaviour of enum docstings
+    assert (
+        m.DocstringTestEnum1.__doc__
+        == "Enum docstring\n\nMembers:\n\n  Member1\n\n  Member2"
+    )
+
+    # options.enable_enum_members_docstring()
+    assert (
+        m.DocstringTestEnum2.__doc__
+        == "Enum docstring\n\nMembers:\n\n  Member1\n\n  Member2"
+    )
+
+    # options.disable_enum_members_docstring()
+    assert m.DocstringTestEnum3.__doc__ == "Enum docstring"
+
+    # options.disable_user_defined_docstrings()
+    assert m.DocstringTestEnum4.__doc__ == "Members:\n\n  Member1\n\n  Member2"
+
+    # options.disable_user_defined_docstrings()
+    # options.disable_enum_members_docstring()
+    # When all options are disabled, no docstring (instead of an empty one) should be generated
+    assert m.DocstringTestEnum5.__doc__ is None

tests/test_eigen_matrix.cpp

@@ -7,15 +7,13 @@
     BSD-style license that can be found in the LICENSE file.
 */
 
-#include <pybind11/eigen.h>
+#include <pybind11/eigen/matrix.h>
 #include <pybind11/stl.h>
 
 #include "constructor_stats.h"
 #include "pybind11_tests.h"
 
-#if defined(_MSC_VER)
-#    pragma warning(disable : 4996) // C4996: std::unary_negation is deprecated
-#endif
+PYBIND11_WARNING_DISABLE_MSVC(4996)
 
 #include <Eigen/Cholesky>
 
@@ -81,7 +79,7 @@ struct CustomOperatorNew {
     EIGEN_MAKE_ALIGNED_OPERATOR_NEW;
 };
 
-TEST_SUBMODULE(eigen, m) {
+TEST_SUBMODULE(eigen_matrix, m) {
     using FixedMatrixR = Eigen::Matrix<float, 5, 6, Eigen::RowMajor>;
     using FixedMatrixC = Eigen::Matrix<float, 5, 6>;
     using DenseMatrixR = Eigen::Matrix<float, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>;

tests/test_eigen_matrix.py

@@ -3,7 +3,7 @@ import pytest
 from pybind11_tests import ConstructorStats
 
 np = pytest.importorskip("numpy")
-m = pytest.importorskip("pybind11_tests.eigen")
+m = pytest.importorskip("pybind11_tests.eigen_matrix")
 
 
 ref = np.array(

tests/test_eigen_tensor.cpp

@@ -0,0 +1,18 @@
+/*
+    tests/eigen_tensor.cpp -- automatic conversion of Eigen Tensor
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#define PYBIND11_TEST_EIGEN_TENSOR_NAMESPACE eigen_tensor
+
+#ifdef EIGEN_AVOID_STL_ARRAY
+#    undef EIGEN_AVOID_STL_ARRAY
+#endif
+
+#include "test_eigen_tensor.inl"
+
+#include "pybind11_tests.h"
+
+test_initializer egien_tensor("eigen_tensor", eigen_tensor_test::test_module);

tests/test_eigen_tensor.inl

@@ -0,0 +1,333 @@
+/*
+    tests/eigen_tensor.cpp -- automatic conversion of Eigen Tensor
+
+    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/eigen/tensor.h>
+
+PYBIND11_NAMESPACE_BEGIN(eigen_tensor_test)
+
+namespace py = pybind11;
+
+PYBIND11_WARNING_DISABLE_MSVC(4127)
+
+template <typename M>
+void reset_tensor(M &x) {
+    for (int i = 0; i < x.dimension(0); i++) {
+        for (int j = 0; j < x.dimension(1); j++) {
+            for (int k = 0; k < x.dimension(2); k++) {
+                x(i, j, k) = i * (5 * 2) + j * 2 + k;
+            }
+        }
+    }
+}
+
+template <typename M>
+bool check_tensor(M &x) {
+    for (int i = 0; i < x.dimension(0); i++) {
+        for (int j = 0; j < x.dimension(1); j++) {
+            for (int k = 0; k < x.dimension(2); k++) {
+                if (x(i, j, k) != (i * (5 * 2) + j * 2 + k)) {
+                    return false;
+                }
+            }
+        }
+    }
+    return true;
+}
+
+template <int Options>
+Eigen::Tensor<double, 3, Options> &get_tensor() {
+    static Eigen::Tensor<double, 3, Options> *x;
+
+    if (!x) {
+        x = new Eigen::Tensor<double, 3, Options>(3, 5, 2);
+        reset_tensor(*x);
+    }
+
+    return *x;
+}
+
+template <int Options>
+Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> &get_tensor_map() {
+    static Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> *x;
+
+    if (!x) {
+        x = new Eigen::TensorMap<Eigen::Tensor<double, 3, Options>>(get_tensor<Options>());
+    }
+
+    return *x;
+}
+
+template <int Options>
+Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options> &get_fixed_tensor() {
+    static Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options> *x;
+
+    if (!x) {
+        Eigen::aligned_allocator<Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>>
+            allocator;
+        x = new (allocator.allocate(1))
+            Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>();
+        reset_tensor(*x);
+    }
+
+    return *x;
+}
+
+template <int Options>
+const Eigen::Tensor<double, 3, Options> &get_const_tensor() {
+    return get_tensor<Options>();
+}
+
+template <int Options>
+struct CustomExample {
+    CustomExample() : member(get_tensor<Options>()), view_member(member) {}
+
+    Eigen::Tensor<double, 3, Options> member;
+    Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> view_member;
+};
+
+template <int Options>
+void init_tensor_module(pybind11::module &m) {
+    const char *needed_options = "";
+    if (Options == Eigen::ColMajor) {
+        needed_options = "F";
+    } else {
+        needed_options = "C";
+    }
+    m.attr("needed_options") = needed_options;
+
+    m.def("setup", []() {
+        reset_tensor(get_tensor<Options>());
+        reset_tensor(get_fixed_tensor<Options>());
+    });
+
+    m.def("is_ok", []() {
+        return check_tensor(get_tensor<Options>()) && check_tensor(get_fixed_tensor<Options>());
+    });
+
+    py::class_<CustomExample<Options>>(m, "CustomExample", py::module_local())
+        .def(py::init<>())
+        .def_readonly(
+            "member", &CustomExample<Options>::member, py::return_value_policy::reference_internal)
+        .def_readonly("member_view",
+                      &CustomExample<Options>::view_member,
+                      py::return_value_policy::reference_internal);
+
+    m.def(
+        "copy_fixed_tensor",
+        []() { return &get_fixed_tensor<Options>(); },
+        py::return_value_policy::copy);
+
+    m.def(
+        "copy_tensor", []() { return &get_tensor<Options>(); }, py::return_value_policy::copy);
+
+    m.def(
+        "copy_const_tensor",
+        []() { return &get_const_tensor<Options>(); },
+        py::return_value_policy::copy);
+
+    m.def(
+        "move_fixed_tensor_copy",
+        []() -> Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options> {
+            return get_fixed_tensor<Options>();
+        },
+        py::return_value_policy::move);
+
+    m.def(
+        "move_tensor_copy",
+        []() -> Eigen::Tensor<double, 3, Options> { return get_tensor<Options>(); },
+        py::return_value_policy::move);
+
+    m.def(
+        "move_const_tensor",
+        []() -> const Eigen::Tensor<double, 3, Options> & { return get_const_tensor<Options>(); },
+        py::return_value_policy::move);
+
+    m.def(
+        "take_fixed_tensor",
+
+        []() {
+            Eigen::aligned_allocator<
+                Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>>
+                allocator;
+            return new (allocator.allocate(1))
+                Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>(
+                    get_fixed_tensor<Options>());
+        },
+        py::return_value_policy::take_ownership);
+
+    m.def(
+        "take_tensor",
+        []() { return new Eigen::Tensor<double, 3, Options>(get_tensor<Options>()); },
+        py::return_value_policy::take_ownership);
+
+    m.def(
+        "take_const_tensor",
+        []() -> const Eigen::Tensor<double, 3, Options> * {
+            return new Eigen::Tensor<double, 3, Options>(get_tensor<Options>());
+        },
+        py::return_value_policy::take_ownership);
+
+    m.def(
+        "take_view_tensor",
+        []() -> const Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> * {
+            return new Eigen::TensorMap<Eigen::Tensor<double, 3, Options>>(get_tensor<Options>());
+        },
+        py::return_value_policy::take_ownership);
+
+    m.def(
+        "reference_tensor",
+        []() { return &get_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_tensor_v2",
+        []() -> Eigen::Tensor<double, 3, Options> & { return get_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_tensor_internal",
+        []() { return &get_tensor<Options>(); },
+        py::return_value_policy::reference_internal);
+
+    m.def(
+        "reference_fixed_tensor",
+        []() { return &get_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_const_tensor",
+        []() { return &get_const_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_const_tensor_v2",
+        []() -> const Eigen::Tensor<double, 3, Options> & { return get_const_tensor<Options>(); },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor",
+        []() -> Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> {
+            return get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v2",
+        // NOLINTNEXTLINE(readability-const-return-type)
+        []() -> const Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> {
+            return get_tensor_map<Options>(); // NOLINT(readability-const-return-type)
+        },                                    // NOLINT(readability-const-return-type)
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v3",
+        []() -> Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> * {
+            return &get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v4",
+        []() -> const Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> * {
+            return &get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v5",
+        []() -> Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> & {
+            return get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_tensor_v6",
+        []() -> const Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> & {
+            return get_tensor_map<Options>();
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "reference_view_of_fixed_tensor",
+        []() {
+            return Eigen::TensorMap<
+                Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>>(
+                get_fixed_tensor<Options>());
+        },
+        py::return_value_policy::reference);
+
+    m.def("round_trip_tensor",
+          [](const Eigen::Tensor<double, 3, Options> &tensor) { return tensor; });
+
+    m.def(
+        "round_trip_tensor_noconvert",
+        [](const Eigen::Tensor<double, 3, Options> &tensor) { return tensor; },
+        py::arg("tensor").noconvert());
+
+    m.def("round_trip_tensor2",
+          [](const Eigen::Tensor<int32_t, 3, Options> &tensor) { return tensor; });
+
+    m.def("round_trip_fixed_tensor",
+          [](const Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options> &tensor) {
+              return tensor;
+          });
+
+    m.def(
+        "round_trip_view_tensor",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> view) { return view; },
+        py::return_value_policy::reference);
+
+    m.def(
+        "round_trip_view_tensor_ref",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> &view) { return view; },
+        py::return_value_policy::reference);
+
+    m.def(
+        "round_trip_view_tensor_ptr",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> *view) { return view; },
+        py::return_value_policy::reference);
+
+    m.def(
+        "round_trip_aligned_view_tensor",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 3, Options>, Eigen::Aligned> view) {
+            return view;
+        },
+        py::return_value_policy::reference);
+
+    m.def(
+        "round_trip_const_view_tensor",
+        [](Eigen::TensorMap<const Eigen::Tensor<double, 3, Options>> view) {
+            return Eigen::Tensor<double, 3, Options>(view);
+        },
+        py::return_value_policy::move);
+
+    m.def(
+        "round_trip_rank_0",
+        [](const Eigen::Tensor<double, 0, Options> &tensor) { return tensor; },
+        py::return_value_policy::move);
+
+    m.def(
+        "round_trip_rank_0_noconvert",
+        [](const Eigen::Tensor<double, 0, Options> &tensor) { return tensor; },
+        py::arg("tensor").noconvert(),
+        py::return_value_policy::move);
+
+    m.def(
+        "round_trip_rank_0_view",
+        [](Eigen::TensorMap<Eigen::Tensor<double, 0, Options>> &tensor) { return tensor; },
+        py::return_value_policy::reference);
+}
+
+void test_module(py::module_ &m) {
+    auto f_style = m.def_submodule("f_style");
+    auto c_style = m.def_submodule("c_style");
+
+    init_tensor_module<Eigen::ColMajor>(f_style);
+    init_tensor_module<Eigen::RowMajor>(c_style);
+}
+
+PYBIND11_NAMESPACE_END(eigen_tensor_test)

tests/test_eigen_tensor.py

@@ -0,0 +1,296 @@
+import sys
+
+import pytest
+
+np = pytest.importorskip("numpy")
+eigen_tensor = pytest.importorskip("pybind11_tests.eigen_tensor")
+submodules = [eigen_tensor.c_style, eigen_tensor.f_style]
+try:
+    import eigen_tensor_avoid_stl_array as avoid
+
+    submodules += [avoid.c_style, avoid.f_style]
+except ImportError as e:
+    # Ensure config, build, toolchain, etc. issues are not masked here:
+    raise RuntimeError(
+        "import eigen_tensor_avoid_stl_array FAILED, while "
+        "import pybind11_tests.eigen_tensor succeeded. "
+        "Please ensure that "
+        "test_eigen_tensor.cpp & "
+        "eigen_tensor_avoid_stl_array.cpp "
+        "are built together (or both are not built if Eigen is not available)."
+    ) from e
+
+tensor_ref = np.empty((3, 5, 2), dtype=np.int64)
+
+for i in range(tensor_ref.shape[0]):
+    for j in range(tensor_ref.shape[1]):
+        for k in range(tensor_ref.shape[2]):
+            tensor_ref[i, j, k] = i * (5 * 2) + j * 2 + k
+
+indices = (2, 3, 1)
+
+
+@pytest.fixture(autouse=True)
+def cleanup():
+    for module in submodules:
+        module.setup()
+
+    yield
+
+    for module in submodules:
+        assert module.is_ok()
+
+
+def test_import_avoid_stl_array():
+    pytest.importorskip("eigen_tensor_avoid_stl_array")
+    assert len(submodules) == 4
+
+
+def assert_equal_tensor_ref(mat, writeable=True, modified=None):
+    assert mat.flags.writeable == writeable
+
+    copy = np.array(tensor_ref)
+    if modified is not None:
+        copy[indices] = modified
+
+    np.testing.assert_array_equal(mat, copy)
+
+
+@pytest.mark.parametrize("m", submodules)
+@pytest.mark.parametrize("member_name", ["member", "member_view"])
+def test_reference_internal(m, member_name):
+
+    if not hasattr(sys, "getrefcount"):
+        pytest.skip("No reference counting")
+    foo = m.CustomExample()
+    counts = sys.getrefcount(foo)
+    mem = getattr(foo, member_name)
+    assert_equal_tensor_ref(mem, writeable=False)
+    new_counts = sys.getrefcount(foo)
+    assert new_counts == counts + 1
+    assert_equal_tensor_ref(mem, writeable=False)
+    del mem
+    assert sys.getrefcount(foo) == counts
+
+
+assert_equal_funcs = [
+    "copy_tensor",
+    "copy_fixed_tensor",
+    "copy_const_tensor",
+    "move_tensor_copy",
+    "move_fixed_tensor_copy",
+    "take_tensor",
+    "take_fixed_tensor",
+    "reference_tensor",
+    "reference_tensor_v2",
+    "reference_fixed_tensor",
+    "reference_view_of_tensor",
+    "reference_view_of_tensor_v3",
+    "reference_view_of_tensor_v5",
+    "reference_view_of_fixed_tensor",
+]
+
+assert_equal_const_funcs = [
+    "reference_view_of_tensor_v2",
+    "reference_view_of_tensor_v4",
+    "reference_view_of_tensor_v6",
+    "reference_const_tensor",
+    "reference_const_tensor_v2",
+]
+
+
+@pytest.mark.parametrize("m", submodules)
+@pytest.mark.parametrize("func_name", assert_equal_funcs + assert_equal_const_funcs)
+def test_convert_tensor_to_py(m, func_name):
+    writeable = func_name in assert_equal_funcs
+    assert_equal_tensor_ref(getattr(m, func_name)(), writeable=writeable)
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_bad_cpp_to_python_casts(m):
+
+    with pytest.raises(
+        RuntimeError, match="Cannot use reference internal when there is no parent"
+    ):
+        m.reference_tensor_internal()
+
+    with pytest.raises(RuntimeError, match="Cannot move from a constant reference"):
+        m.move_const_tensor()
+
+    with pytest.raises(
+        RuntimeError, match="Cannot take ownership of a const reference"
+    ):
+        m.take_const_tensor()
+
+    with pytest.raises(
+        RuntimeError,
+        match="Invalid return_value_policy for Eigen Map type, must be either reference or reference_internal",
+    ):
+        m.take_view_tensor()
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_bad_python_to_cpp_casts(m):
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_tensor(np.zeros((2, 3)))
+
+    with pytest.raises(TypeError, match=r"^Cannot cast array data from dtype"):
+        m.round_trip_tensor(np.zeros(dtype=np.str_, shape=(2, 3, 1)))
+
+    with pytest.raises(
+        TypeError,
+        match=r"^round_trip_tensor_noconvert\(\): incompatible function arguments",
+    ):
+        m.round_trip_tensor_noconvert(tensor_ref)
+
+    assert_equal_tensor_ref(
+        m.round_trip_tensor_noconvert(tensor_ref.astype(np.float64))
+    )
+
+    if m.needed_options == "F":
+        bad_options = "C"
+    else:
+        bad_options = "F"
+    # Shape, dtype and the order need to be correct for a TensorMap cast
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_view_tensor(
+            np.zeros((3, 5, 2), dtype=np.float64, order=bad_options)
+        )
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_view_tensor(
+            np.zeros((3, 5, 2), dtype=np.float32, order=m.needed_options)
+        )
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        m.round_trip_view_tensor(
+            np.zeros((3, 5), dtype=np.float64, order=m.needed_options)
+        )
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        temp = np.zeros((3, 5, 2), dtype=np.float64, order=m.needed_options)
+        m.round_trip_view_tensor(
+            temp[:, ::-1, :],
+        )
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_view_tensor\(\): incompatible function arguments"
+    ):
+        temp = np.zeros((3, 5, 2), dtype=np.float64, order=m.needed_options)
+        temp.setflags(write=False)
+        m.round_trip_view_tensor(temp)
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_references_actually_refer(m):
+
+    a = m.reference_tensor()
+    temp = a[indices]
+    a[indices] = 100
+    assert_equal_tensor_ref(m.copy_const_tensor(), modified=100)
+    a[indices] = temp
+    assert_equal_tensor_ref(m.copy_const_tensor())
+
+    a = m.reference_view_of_tensor()
+    a[indices] = 100
+    assert_equal_tensor_ref(m.copy_const_tensor(), modified=100)
+    a[indices] = temp
+    assert_equal_tensor_ref(m.copy_const_tensor())
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_round_trip(m):
+
+    assert_equal_tensor_ref(m.round_trip_tensor(tensor_ref))
+
+    with pytest.raises(TypeError, match="^Cannot cast array data from"):
+        assert_equal_tensor_ref(m.round_trip_tensor2(tensor_ref))
+
+    assert_equal_tensor_ref(m.round_trip_tensor2(np.array(tensor_ref, dtype=np.int32)))
+    assert_equal_tensor_ref(m.round_trip_fixed_tensor(tensor_ref))
+    assert_equal_tensor_ref(m.round_trip_aligned_view_tensor(m.reference_tensor()))
+
+    copy = np.array(tensor_ref, dtype=np.float64, order=m.needed_options)
+    assert_equal_tensor_ref(m.round_trip_view_tensor(copy))
+    assert_equal_tensor_ref(m.round_trip_view_tensor_ref(copy))
+    assert_equal_tensor_ref(m.round_trip_view_tensor_ptr(copy))
+    copy.setflags(write=False)
+    assert_equal_tensor_ref(m.round_trip_const_view_tensor(copy))
+
+    np.testing.assert_array_equal(
+        tensor_ref[:, ::-1, :], m.round_trip_tensor(tensor_ref[:, ::-1, :])
+    )
+
+    assert m.round_trip_rank_0(np.float64(3.5)) == 3.5
+    assert m.round_trip_rank_0(3.5) == 3.5
+
+    with pytest.raises(
+        TypeError,
+        match=r"^round_trip_rank_0_noconvert\(\): incompatible function arguments",
+    ):
+        m.round_trip_rank_0_noconvert(np.float64(3.5))
+
+    with pytest.raises(
+        TypeError,
+        match=r"^round_trip_rank_0_noconvert\(\): incompatible function arguments",
+    ):
+        m.round_trip_rank_0_noconvert(3.5)
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_rank_0_view\(\): incompatible function arguments"
+    ):
+        m.round_trip_rank_0_view(np.float64(3.5))
+
+    with pytest.raises(
+        TypeError, match=r"^round_trip_rank_0_view\(\): incompatible function arguments"
+    ):
+        m.round_trip_rank_0_view(3.5)
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_round_trip_references_actually_refer(m):
+
+    # Need to create a copy that matches the type on the C side
+    copy = np.array(tensor_ref, dtype=np.float64, order=m.needed_options)
+    a = m.round_trip_view_tensor(copy)
+    temp = a[indices]
+    a[indices] = 100
+    assert_equal_tensor_ref(copy, modified=100)
+    a[indices] = temp
+    assert_equal_tensor_ref(copy)
+
+
+@pytest.mark.parametrize("m", submodules)
+def test_doc_string(m, doc):
+    assert (
+        doc(m.copy_tensor) == "copy_tensor() -> numpy.ndarray[numpy.float64[?, ?, ?]]"
+    )
+    assert (
+        doc(m.copy_fixed_tensor)
+        == "copy_fixed_tensor() -> numpy.ndarray[numpy.float64[3, 5, 2]]"
+    )
+    assert (
+        doc(m.reference_const_tensor)
+        == "reference_const_tensor() -> numpy.ndarray[numpy.float64[?, ?, ?]]"
+    )
+
+    order_flag = f"flags.{m.needed_options.lower()}_contiguous"
+    assert doc(m.round_trip_view_tensor) == (
+        f"round_trip_view_tensor(arg0: numpy.ndarray[numpy.float64[?, ?, ?], flags.writeable, {order_flag}])"
+        + f" -> numpy.ndarray[numpy.float64[?, ?, ?], flags.writeable, {order_flag}]"
+    )
+    assert doc(m.round_trip_const_view_tensor) == (
+        f"round_trip_const_view_tensor(arg0: numpy.ndarray[numpy.float64[?, ?, ?], {order_flag}])"
+        + " -> numpy.ndarray[numpy.float64[?, ?, ?]]"
+    )

tests/test_embed/catch.cpp

@@ -3,11 +3,9 @@
 
 #include <pybind11/embed.h>
 
-#ifdef _MSC_VER
 // Silence MSVC C++17 deprecation warning from Catch regarding std::uncaught_exceptions (up to
 // catch 2.0.1; this should be fixed in the next catch release after 2.0.1).
-#    pragma warning(disable : 4996)
-#endif
+PYBIND11_WARNING_DISABLE_MSVC(4996)
 
 // Catch uses _ internally, which breaks gettext style defines
 #ifdef _

tests/test_embed/test_interpreter.cpp

@@ -1,10 +1,8 @@
 #include <pybind11/embed.h>
 
-#ifdef _MSC_VER
 // Silence MSVC C++17 deprecation warning from Catch regarding std::uncaught_exceptions (up to
 // catch 2.0.1; this should be fixed in the next catch release after 2.0.1).
-#    pragma warning(disable : 4996)
-#endif
+PYBIND11_WARNING_DISABLE_MSVC(4996)
 
 #include <catch.hpp>
 #include <cstdlib>
@@ -16,6 +14,11 @@
 namespace py = pybind11;
 using namespace py::literals;
 
+size_t get_sys_path_size() {
+    auto sys_path = py::module::import("sys").attr("path");
+    return py::len(sys_path);
+}
+
 class Widget {
 public:
     explicit Widget(std::string message) : message(std::move(message)) {}
@@ -168,6 +171,70 @@ TEST_CASE("There can be only one interpreter") {
     py::initialize_interpreter();
 }
 
+#if PY_VERSION_HEX >= PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+TEST_CASE("Custom PyConfig") {
+    py::finalize_interpreter();
+    PyConfig config;
+    PyConfig_InitPythonConfig(&config);
+    REQUIRE_NOTHROW(py::scoped_interpreter{&config});
+    {
+        py::scoped_interpreter p{&config};
+        REQUIRE(py::module_::import("widget_module").attr("add")(1, 41).cast<int>() == 42);
+    }
+    py::initialize_interpreter();
+}
+
+TEST_CASE("Custom PyConfig with argv") {
+    py::finalize_interpreter();
+    {
+        PyConfig config;
+        PyConfig_InitIsolatedConfig(&config);
+        char *argv[] = {strdup("a.out")};
+        py::scoped_interpreter argv_scope{&config, 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();
+}
+#endif
+
+TEST_CASE("Add program dir to path pre-PyConfig") {
+    py::finalize_interpreter();
+    size_t path_size_add_program_dir_to_path_false = 0;
+    {
+        py::scoped_interpreter scoped_interp{true, 0, nullptr, false};
+        path_size_add_program_dir_to_path_false = get_sys_path_size();
+    }
+    {
+        py::scoped_interpreter scoped_interp{};
+        REQUIRE(get_sys_path_size() == path_size_add_program_dir_to_path_false + 1);
+    }
+    py::initialize_interpreter();
+}
+
+#if PY_VERSION_HEX >= PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX
+TEST_CASE("Add program dir to path using PyConfig") {
+    py::finalize_interpreter();
+    size_t path_size_add_program_dir_to_path_false = 0;
+    {
+        PyConfig config;
+        PyConfig_InitPythonConfig(&config);
+        py::scoped_interpreter scoped_interp{&config, 0, nullptr, false};
+        path_size_add_program_dir_to_path_false = get_sys_path_size();
+    }
+    {
+        PyConfig config;
+        PyConfig_InitPythonConfig(&config);
+        py::scoped_interpreter scoped_interp{&config};
+        REQUIRE(get_sys_path_size() == path_size_add_program_dir_to_path_false + 1);
+    }
+    py::initialize_interpreter();
+}
+#endif
+
 bool has_pybind11_internals_builtin() {
     auto builtins = py::handle(PyEval_GetBuiltins());
     return builtins.contains(PYBIND11_INTERNALS_ID);

tests/test_exceptions.py

@@ -4,6 +4,7 @@ import pytest
 
 import env
 import pybind11_cross_module_tests as cm
+import pybind11_tests  # noqa: F401
 from pybind11_tests import exceptions as m
 
 
@@ -72,9 +73,9 @@ def test_cross_module_exceptions(msg):
 
 # TODO: FIXME
 @pytest.mark.xfail(
-    "env.PYPY and env.MACOS",
+    "env.MACOS and (env.PYPY or pybind11_tests.compiler_info.startswith('Homebrew Clang'))",
     raises=RuntimeError,
-    reason="Expected failure with PyPy and libc++ (Issue #2847 & PR #2999)",
+    reason="See Issue #2847, PR #2999, PR #4324",
 )
 def test_cross_module_exception_translator():
     with pytest.raises(KeyError):

tests/test_gil_scoped.py

@@ -5,6 +5,7 @@ import time
 
 import pytest
 
+import env
 from pybind11_tests import gil_scoped as m
 
 
@@ -144,7 +145,6 @@ def _intentional_deadlock():
 
 
 ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK = ALL_BASIC_TESTS + (_intentional_deadlock,)
-SKIP_IF_DEADLOCK = True  # See PR #4216
 
 
 def _run_in_process(target, *args, **kwargs):
@@ -181,7 +181,7 @@ def _run_in_process(target, *args, **kwargs):
         elif process.exitcode is None:
             assert t_delta > 0.9 * timeout
             msg = "DEADLOCK, most likely, exactly what this test is meant to detect."
-            if SKIP_IF_DEADLOCK:
+            if env.PYPY and env.WIN:
                 pytest.skip(msg)
             raise RuntimeError(msg)
         return process.exitcode

tests/test_kwargs_and_defaults.cpp

@@ -44,14 +44,13 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
 
     // test_args_and_kwargs
     m.def("args_function", [](py::args args) -> py::tuple {
+        PYBIND11_WARNING_PUSH
+
 #ifdef PYBIND11_DETECTED_CLANG_WITH_MISLEADING_CALL_STD_MOVE_EXPLICITLY_WARNING
-#    pragma clang diagnostic push
-#    pragma clang diagnostic ignored "-Wreturn-std-move"
+        PYBIND11_WARNING_DISABLE_CLANG("-Wreturn-std-move")
 #endif
         return args;
-#ifdef PYBIND11_DETECTED_CLANG_WITH_MISLEADING_CALL_STD_MOVE_EXPLICITLY_WARNING
-#    pragma clang diagnostic pop
-#endif
+        PYBIND11_WARNING_POP
     });
     m.def("args_kwargs_function", [](const py::args &args, const py::kwargs &kwargs) {
         return py::make_tuple(args, kwargs);

tests/test_numpy_array.cpp

@@ -521,4 +521,6 @@ TEST_SUBMODULE(numpy_array, sm) {
     sm.def("test_fmt_desc_double", [](const py::array_t<double> &) {});
     sm.def("test_fmt_desc_const_float", [](const py::array_t<const float> &) {});
     sm.def("test_fmt_desc_const_double", [](const py::array_t<const double> &) {});
+
+    sm.def("round_trip_float", [](double d) { return d; });
 }

tests/test_numpy_array.py

@@ -585,3 +585,9 @@ def test_dtype_refcount_leak():
     m.ndim(a)
     after = getrefcount(dtype)
     assert after == before
+
+
+def test_round_trip_float():
+    arr = np.zeros((), np.float64)
+    arr[()] = 37.2
+    assert m.round_trip_float(arr) == 37.2

tests/test_operator_overloading.cpp

@@ -132,22 +132,18 @@ struct hash<HashMe> {
 // Not a good abs function, but easy to test.
 std::string abs(const Vector2 &) { return "abs(Vector2)"; }
 
-// MSVC & Intel warns about unknown pragmas, and warnings are errors.
-#if !defined(_MSC_VER) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic push
 // clang 7.0.0 and Apple LLVM 10.0.1 introduce `-Wself-assign-overloaded` to
 // `-Wall`, which is used here for overloading (e.g. `py::self += py::self `).
-// Here, we suppress the warning using `#pragma diagnostic`.
+// Here, we suppress the warning
 // Taken from: https://github.com/RobotLocomotion/drake/commit/aaf84b46
 // TODO(eric): This could be resolved using a function / functor (e.g. `py::self()`).
-#    if defined(__APPLE__) && defined(__clang__)
-#        if (__clang_major__ >= 10)
-#            pragma GCC diagnostic ignored "-Wself-assign-overloaded"
-#        endif
-#    elif defined(__clang__)
-#        if (__clang_major__ >= 7)
-#            pragma GCC diagnostic ignored "-Wself-assign-overloaded"
-#        endif
+#if defined(__APPLE__) && defined(__clang__)
+#    if (__clang_major__ >= 10)
+PYBIND11_WARNING_DISABLE_CLANG("-Wself-assign-overloaded")
+#    endif
+#elif defined(__clang__)
+#    if (__clang_major__ >= 7)
+PYBIND11_WARNING_DISABLE_CLANG("-Wself-assign-overloaded")
 #    endif
 #endif
 
@@ -283,6 +279,3 @@ TEST_SUBMODULE(operators, m) {
 
     m.def("get_unhashable_HashMe_set", []() { return std::unordered_set<HashMe>{{"one"}}; });
 }
-#if !defined(_MSC_VER) && !defined(__INTEL_COMPILER)
-#    pragma GCC diagnostic pop
-#endif

tests/test_stl_binders.py

@@ -309,3 +309,29 @@ def test_map_delitem():
     del um["ua"]
     assert sorted(list(um)) == ["ub"]
     assert sorted(list(um.items())) == [("ub", 2.6)]
+
+
+def test_map_view_types():
+    map_string_double = m.MapStringDouble()
+    unordered_map_string_double = m.UnorderedMapStringDouble()
+    map_string_double_const = m.MapStringDoubleConst()
+    unordered_map_string_double_const = m.UnorderedMapStringDoubleConst()
+
+    assert map_string_double.keys().__class__.__name__ == "KeysView[str]"
+    assert map_string_double.values().__class__.__name__ == "ValuesView[float]"
+    assert map_string_double.items().__class__.__name__ == "ItemsView[str, float]"
+
+    keys_type = type(map_string_double.keys())
+    assert type(unordered_map_string_double.keys()) is keys_type
+    assert type(map_string_double_const.keys()) is keys_type
+    assert type(unordered_map_string_double_const.keys()) is keys_type
+
+    values_type = type(map_string_double.values())
+    assert type(unordered_map_string_double.values()) is values_type
+    assert type(map_string_double_const.values()) is values_type
+    assert type(unordered_map_string_double_const.values()) is values_type
+
+    items_type = type(map_string_double.items())
+    assert type(unordered_map_string_double.items()) is items_type
+    assert type(map_string_double_const.items()) is items_type
+    assert type(unordered_map_string_double_const.items()) is items_type

tests/test_virtual_functions.cpp

@@ -173,7 +173,8 @@ struct AdderBase {
     using DataVisitor = std::function<void(const Data &)>;
 
     virtual void
-    operator()(const Data &first, const Data &second, const DataVisitor &visitor) const = 0;
+    operator()(const Data &first, const Data &second, const DataVisitor &visitor) const
+        = 0;
     virtual ~AdderBase() = default;
     AdderBase() = default;
     AdderBase(const AdderBase &) = delete;

tools/FindPythonLibsNew.cmake

@@ -208,7 +208,9 @@ string(REGEX REPLACE "\\\\" "/" PYTHON_PREFIX "${PYTHON_PREFIX}")
 string(REGEX REPLACE "\\\\" "/" PYTHON_INCLUDE_DIR "${PYTHON_INCLUDE_DIR}")
 string(REGEX REPLACE "\\\\" "/" PYTHON_SITE_PACKAGES "${PYTHON_SITE_PACKAGES}")
 
-if(CMAKE_HOST_WIN32)
+if(DEFINED PYTHON_LIBRARY)
+  # Don't write to PYTHON_LIBRARY if it's already set
+elseif(CMAKE_HOST_WIN32)
   set(PYTHON_LIBRARY "${PYTHON_PREFIX}/libs/python${PYTHON_LIBRARY_SUFFIX}.lib")
 
   # when run in a venv, PYTHON_PREFIX points to it. But the libraries remain in the
@@ -274,7 +276,7 @@ if(NOT PYTHON_DEBUG_LIBRARY)
 endif()
 set(PYTHON_DEBUG_LIBRARIES "${PYTHON_DEBUG_LIBRARY}")
 
-find_package_message(PYTHON "Found PythonLibs: ${PYTHON_LIBRARY}"
+find_package_message(PYTHON "Found PythonLibs: ${PYTHON_LIBRARIES}"
                      "${PYTHON_EXECUTABLE}${PYTHON_VERSION_STRING}")
 
 set(PYTHONLIBS_FOUND TRUE)

tools/pybind11Common.cmake

@@ -311,6 +311,16 @@ function(_pybind11_generate_lto target prefer_thin_lto)
         HAS_FLTO "-flto${cxx_append}" "-flto${linker_append}" PYBIND11_LTO_CXX_FLAGS
         PYBIND11_LTO_LINKER_FLAGS)
     endif()
+  elseif(CMAKE_CXX_COMPILER_ID MATCHES "IntelLLVM")
+    # IntelLLVM equivalent to LTO is called IPO; also IntelLLVM is WIN32/UNIX
+    # WARNING/HELP WANTED: This block of code is currently not covered by pybind11 GitHub Actions!
+    if(WIN32)
+      _pybind11_return_if_cxx_and_linker_flags_work(
+        HAS_INTEL_IPO "-Qipo" "-Qipo" PYBIND11_LTO_CXX_FLAGS PYBIND11_LTO_LINKER_FLAGS)
+    else()
+      _pybind11_return_if_cxx_and_linker_flags_work(
+        HAS_INTEL_IPO "-ipo" "-ipo" PYBIND11_LTO_CXX_FLAGS PYBIND11_LTO_LINKER_FLAGS)
+    endif()
   elseif(CMAKE_CXX_COMPILER_ID MATCHES "Intel")
     # Intel equivalent to LTO is called IPO
     _pybind11_return_if_cxx_and_linker_flags_work(HAS_INTEL_IPO "-ipo" "-ipo"

tools/pybind11NewTools.cmake

@@ -9,7 +9,7 @@ if(CMAKE_VERSION VERSION_LESS 3.12)
   message(FATAL_ERROR "You cannot use the new FindPython module with CMake < 3.12")
 endif()
 
-include_guard(GLOBAL)
+include_guard(DIRECTORY)
 
 get_property(
   is_config
@@ -235,7 +235,7 @@ function(pybind11_add_module target_name)
 
   # Use case-insensitive comparison to match the result of $<CONFIG:cfgs>
   string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
-  if(NOT MSVC AND NOT ${uppercase_CMAKE_BUILD_TYPE} MATCHES DEBUG|RELWITHDEBINFO)
+  if(NOT MSVC AND NOT "${uppercase_CMAKE_BUILD_TYPE}" MATCHES DEBUG|RELWITHDEBINFO)
     # Strip unnecessary sections of the binary on Linux/macOS
     pybind11_strip(${target_name})
   endif()

tools/pybind11Tools.cmake

@@ -214,7 +214,7 @@ function(pybind11_add_module target_name)
 
   # Use case-insensitive comparison to match the result of $<CONFIG:cfgs>
   string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
-  if(NOT MSVC AND NOT ${uppercase_CMAKE_BUILD_TYPE} MATCHES DEBUG|RELWITHDEBINFO)
+  if(NOT MSVC AND NOT "${uppercase_CMAKE_BUILD_TYPE}" MATCHES DEBUG|RELWITHDEBINFO)
     pybind11_strip(${target_name})
   endif()
 

tools/setup_global.py.in

@@ -27,10 +27,11 @@ class InstallHeadersNested(install_headers):
 
 main_headers = glob.glob("pybind11/include/pybind11/*.h")
 detail_headers = glob.glob("pybind11/include/pybind11/detail/*.h")
+eigen_headers = glob.glob("pybind11/include/pybind11/eigen/*.h")
 stl_headers = glob.glob("pybind11/include/pybind11/stl/*.h")
 cmake_files = glob.glob("pybind11/share/cmake/pybind11/*.cmake")
 pkgconfig_files = glob.glob("pybind11/share/pkgconfig/*.pc")
-headers = main_headers + detail_headers + stl_headers
+headers = main_headers + detail_headers + stl_headers + eigen_headers
 
 cmdclass = {"install_headers": InstallHeadersNested}
 $extra_cmd
@@ -55,6 +56,7 @@ setup(
         (base + "share/pkgconfig", pkgconfig_files),
         (base + "include/pybind11", main_headers),
         (base + "include/pybind11/detail", detail_headers),
+        (base + "include/pybind11/eigen", eigen_headers),
         (base + "include/pybind11/stl", stl_headers),
     ],
     cmdclass=cmdclass,

tools/setup_main.py.in

@@ -15,6 +15,7 @@ setup(
         "pybind11",
         "pybind11.include.pybind11",
         "pybind11.include.pybind11.detail",
+        "pybind11.include.pybind11.eigen",
         "pybind11.include.pybind11.stl",
         "pybind11.share.cmake.pybind11",
         "pybind11.share.pkgconfig",
@@ -23,6 +24,7 @@ setup(
         "pybind11": ["py.typed"],
         "pybind11.include.pybind11": ["*.h"],
         "pybind11.include.pybind11.detail": ["*.h"],
+        "pybind11.include.pybind11.eigen": ["*.h"],
         "pybind11.include.pybind11.stl": ["*.h"],
         "pybind11.share.cmake.pybind11": ["*.cmake"],
         "pybind11.share.pkgconfig": ["*.pc"],