Merge 6cb1d65e77 into 1f8b4a7f1a

There was one trouble maker (all other jobs worked):

Visual Studio 15 2017:

```
cl : Command line warning D9025: overriding '/EHc' with '/EHc-' [C:\projects\pybind11\tests\exo_planet_c_api.vcxproj]
...
C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\include\xlocale(319): error C2220: warning treated as error - no 'object' file generated [C:\projects\pybind11\tests\exo_planet_c_api.vcxproj]
C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\include\xlocale(319): warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc
```

CMakeLists.txt

@@ -142,6 +142,9 @@ set(PYBIND11_HEADERS
     include/pybind11/cast.h
     include/pybind11/chrono.h
     include/pybind11/common.h
+    include/pybind11/compat/pybind11_conduit_v1.h
+    include/pybind11/compat/pybind11_platform_abi_id.h
+    include/pybind11/compat/wrap_include_python_h.h
     include/pybind11/complex.h
     include/pybind11/options.h
     include/pybind11/eigen.h

include/pybind11/compat/README.txt

@@ -0,0 +1,15 @@
+NOTE
+----
+
+The C++ code here
+
+** only depends on <Python.h> **
+
+and nothing else.
+
+DO NOT ADD CODE WITH OTHER EXTERNAL DEPENDENCIES TO THIS DIRECTORY.
+
+Read on:
+
+pybind11_conduit_v1.h — Type-safe interoperability between different
+                        independent Python/C++ bindings systems.

include/pybind11/compat/pybind11_conduit_v1.h

@@ -0,0 +1,111 @@
+// Copyright (c) 2024 The pybind Community.
+
+/* The pybind11_conduit_v1 feature enables type-safe interoperability between
+
+* different independent Python/C++ bindings systems,
+
+* including pybind11 versions with different PYBIND11_INTERNALS_VERSION's.
+
+The naming of the feature is a bit misleading:
+
+* The feature is in no way tied to pybind11 internals.
+
+* It just happens to originate from pybind11 and currently still lives there.
+
+* The only external dependency is <Python.h>.
+
+The implementation is a VERY light-weight dependency. It is designed to be
+compatible with any ISO C++11 (or higher) compiler, and does NOT require
+C++ Exception Handling to be enabled.
+
+Please see https://github.com/pybind/pybind11/pull/5296 for more background.
+
+The implementation involves a
+
+def _pybind11_conduit_v1_(
+    self,
+    pybind11_platform_abi_id: bytes,
+    cpp_type_info_capsule: capsule,
+    pointer_kind: bytes) -> capsule
+
+method that is meant to be added to Python objects wrapping C++ objects
+(e.g. pybind11::class_-wrapped types).
+
+The design of the _pybind11_conduit_v1_ feature provides two layers of
+protection against C++ ABI mismatches:
+
+* The first and most important layer is that the pybind11_platform_abi_id's
+  must match between extensions. — This will never be perfect, but is the same
+  pragmatic approach used in pybind11 since 2017
+  (https://github.com/pybind/pybind11/commit/96997a4b9d4ec3d389a570604394af5d5eee2557,
+  PYBIND11_INTERNALS_ID).
+
+* The second layer is that the typeid(std::type_info).name()'s must match
+  between extensions.
+
+The implementation below (which is shorter than this comment!), serves as a
+battle-tested specification. The main API is this one function:
+
+auto *cpp_pointer = pybind11_conduit_v1::get_type_pointer_ephemeral<YourType>(py_obj);
+
+It is meant to be a minimalistic reference implementation, intentionally
+without comprehensive error reporting. It is expected that major bindings
+systems will roll their own, compatible implementations, potentially with
+system-specific error reporting. The essential specifications all bindings
+systems need to agree on are merely:
+
+* PYBIND11_PLATFORM_ABI_ID (const char* literal).
+
+* The cpp_type_info capsule (see below: a void *ptr and a const char *name).
+
+* The cpp_conduit capsule (see below: a void *ptr and a const char *name).
+
+* "raw_pointer_ephemeral" means: the lifetime of the pointer is the lifetime
+  of the py_obj.
+
+*/
+
+// THIS MUST STAY AT THE TOP!
+#include "pybind11_platform_abi_id.h"
+
+#include <Python.h>
+#include <typeinfo>
+
+namespace pybind11_conduit_v1 {
+
+inline void *get_raw_pointer_ephemeral(PyObject *py_obj, const std::type_info *cpp_type_info) {
+    PyObject *cpp_type_info_capsule
+        = PyCapsule_New(const_cast<void *>(static_cast<const void *>(cpp_type_info)),
+                        typeid(std::type_info).name(),
+                        nullptr);
+    if (cpp_type_info_capsule == nullptr) {
+        return nullptr;
+    }
+    PyObject *cpp_conduit = PyObject_CallMethod(py_obj,
+                                                "_pybind11_conduit_v1_",
+                                                "yOy",
+                                                PYBIND11_PLATFORM_ABI_ID,
+                                                cpp_type_info_capsule,
+                                                "raw_pointer_ephemeral");
+    Py_DECREF(cpp_type_info_capsule);
+    if (cpp_conduit == nullptr) {
+        return nullptr;
+    }
+    void *raw_ptr = PyCapsule_GetPointer(cpp_conduit, cpp_type_info->name());
+    Py_DECREF(cpp_conduit);
+    if (PyErr_Occurred()) {
+        return nullptr;
+    }
+    return raw_ptr;
+}
+
+template <typename T>
+T *get_type_pointer_ephemeral(PyObject *py_obj) {
+    void *raw_ptr = get_raw_pointer_ephemeral(py_obj, &typeid(T));
+    if (raw_ptr == nullptr) {
+        return nullptr;
+    }
+    return static_cast<T *>(raw_ptr);
+}
+
+} // namespace pybind11_conduit_v1

include/pybind11/compat/pybind11_platform_abi_id.h

@@ -0,0 +1,74 @@
+#pragma once
+
+// Copyright (c) 2024 The pybind Community.
+
+// To maximize reusability:
+// DO NOT ADD CODE THAT REQUIRES C++ EXCEPTION HANDLING.
+
+#include "wrap_include_python_h.h"
+
+// Implementation details. DO NOT USE ELSEWHERE. (Unfortunately we cannot #undef them.)
+// This is duplicated here to maximize portability.
+#define PYBIND11_PLATFORM_ABI_ID_STRINGIFY(x) #x
+#define PYBIND11_PLATFORM_ABI_ID_TOSTRING(x) PYBIND11_PLATFORM_ABI_ID_STRINGIFY(x)
+
+// On MSVC, debug and release builds are not ABI-compatible!
+#if defined(_MSC_VER) && defined(_DEBUG)
+#    define PYBIND11_BUILD_TYPE "_debug"
+#else
+#    define PYBIND11_BUILD_TYPE ""
+#endif
+
+// Let's assume that different compilers are ABI-incompatible.
+// A user can manually set this string if they know their
+// compiler is compatible.
+#ifndef PYBIND11_COMPILER_TYPE
+#    if defined(_MSC_VER)
+#        define PYBIND11_COMPILER_TYPE "_msvc"
+#    elif defined(__INTEL_COMPILER)
+#        define PYBIND11_COMPILER_TYPE "_icc"
+#    elif defined(__clang__)
+#        define PYBIND11_COMPILER_TYPE "_clang"
+#    elif defined(__PGI)
+#        define PYBIND11_COMPILER_TYPE "_pgi"
+#    elif defined(__MINGW32__)
+#        define PYBIND11_COMPILER_TYPE "_mingw"
+#    elif defined(__CYGWIN__)
+#        define PYBIND11_COMPILER_TYPE "_gcc_cygwin"
+#    elif defined(__GNUC__)
+#        define PYBIND11_COMPILER_TYPE "_gcc"
+#    else
+#        define PYBIND11_COMPILER_TYPE "_unknown"
+#    endif
+#endif
+
+// Also standard libs
+#ifndef PYBIND11_STDLIB
+#    if defined(_LIBCPP_VERSION)
+#        define PYBIND11_STDLIB "_libcpp"
+#    elif defined(__GLIBCXX__) || defined(__GLIBCPP__)
+#        define PYBIND11_STDLIB "_libstdcpp"
+#    else
+#        define PYBIND11_STDLIB ""
+#    endif
+#endif
+
+// On Linux/OSX, changes in __GXX_ABI_VERSION__ indicate ABI incompatibility.
+// On MSVC, changes in _MSC_VER may indicate ABI incompatibility (#2898).
+#ifndef PYBIND11_BUILD_ABI
+#    if defined(__GXX_ABI_VERSION)
+#        define PYBIND11_BUILD_ABI "_cxxabi" PYBIND11_PLATFORM_ABI_ID_TOSTRING(__GXX_ABI_VERSION)
+#    elif defined(_MSC_VER)
+#        define PYBIND11_BUILD_ABI "_mscver" PYBIND11_PLATFORM_ABI_ID_TOSTRING(_MSC_VER)
+#    else
+#        define PYBIND11_BUILD_ABI ""
+#    endif
+#endif
+
+#ifndef PYBIND11_INTERNALS_KIND
+#    define PYBIND11_INTERNALS_KIND ""
+#endif
+
+#define PYBIND11_PLATFORM_ABI_ID                                                                  \
+    PYBIND11_INTERNALS_KIND PYBIND11_COMPILER_TYPE PYBIND11_STDLIB PYBIND11_BUILD_ABI             \
+        PYBIND11_BUILD_TYPE

include/pybind11/compat/wrap_include_python_h.h

@@ -0,0 +1,72 @@
+#pragma once
+
+// Copyright (c) 2024 The pybind Community.
+
+// STRONG REQUIREMENT:
+//   This header is a wrapper around `#include <Python.h>`, therefore it
+//   MUST BE INCLUDED BEFORE ANY STANDARD HEADERS are included.
+// See also:
+//   https://docs.python.org/3/c-api/intro.html#include-files
+// Quoting from there:
+//   Note: Since Python may define some pre-processor definitions which affect
+//   the standard headers on some systems, you must include Python.h before
+//   any standard headers are included.
+
+// To maximize reusability:
+// DO NOT ADD CODE THAT REQUIRES C++ EXCEPTION HANDLING.
+
+// Disable linking to pythonX_d.lib on Windows in debug mode.
+#if defined(_MSC_VER) && defined(_DEBUG) && !defined(Py_DEBUG)
+// Workaround for a VS 2022 issue.
+// See https://github.com/pybind/pybind11/pull/3497 for full context.
+// NOTE: This workaround knowingly violates the Python.h include order
+//       requirement (see above).
+#    include <yvals.h>
+#    if _MSVC_STL_VERSION >= 143
+#        include <crtdefs.h>
+#    endif
+#    define PYBIND11_DEBUG_MARKER
+#    undef _DEBUG
+#endif
+
+// Don't let Python.h #define (v)snprintf as macro because they are implemented
+// properly in Visual Studio since 2015.
+#if defined(_MSC_VER)
+#    define HAVE_SNPRINTF 1
+#endif
+
+#if defined(_MSC_VER)
+#    pragma warning(push)
+#    pragma warning(disable : 4505)
+// C4505: 'PySlice_GetIndicesEx': unreferenced local function has been removed
+#endif
+
+#include <Python.h>
+#include <frameobject.h>
+#include <pythread.h>
+
+#if defined(_MSC_VER)
+#    pragma warning(pop)
+#endif
+
+#if defined(PYBIND11_DEBUG_MARKER)
+#    define _DEBUG
+#    undef PYBIND11_DEBUG_MARKER
+#endif
+
+// Python #defines overrides on all sorts of core functions, which
+// tends to wreak havok in C++ codebases that expect these to work
+// like regular functions (potentially with several overloads).
+#if defined(isalnum)
+#    undef isalnum
+#    undef isalpha
+#    undef islower
+#    undef isspace
+#    undef isupper
+#    undef tolower
+#    undef toupper
+#endif
+
+#if defined(copysign)
+#    undef copysign
+#endif

include/pybind11/detail/common.h

@@ -9,6 +9,11 @@
 
 #pragma once
 
+#include <pybind11/compat/wrap_include_python_h.h>
+#if PY_VERSION_HEX < 0x03080000
+#    error "PYTHON < 3.8 IS UNSUPPORTED. pybind11 v2.13 was the last to support Python 3.7."
+#endif
+
 #define PYBIND11_VERSION_MAJOR 2
 #define PYBIND11_VERSION_MINOR 14
 #define PYBIND11_VERSION_PATCH 0.dev1
@@ -212,31 +217,6 @@
 #    define PYBIND11_MAYBE_UNUSED __attribute__((__unused__))
 #endif
 
-/* Don't let Python.h #define (v)snprintf as macro because they are implemented
-   properly in Visual Studio since 2015. */
-#if defined(_MSC_VER)
-#    define HAVE_SNPRINTF 1
-#endif
-
-/// Include Python header, disable linking to pythonX_d.lib on Windows in debug mode
-#if defined(_MSC_VER)
-PYBIND11_WARNING_PUSH
-PYBIND11_WARNING_DISABLE_MSVC(4505)
-// C4505: 'PySlice_GetIndicesEx': unreferenced local function has been removed (PyPy only)
-#    if defined(_DEBUG) && !defined(Py_DEBUG)
-// Workaround for a VS 2022 issue.
-// NOTE: This workaround knowingly violates the Python.h include order requirement:
-// https://docs.python.org/3/c-api/intro.html#include-files
-// See https://github.com/pybind/pybind11/pull/3497 for full context.
-#        include <yvals.h>
-#        if _MSVC_STL_VERSION >= 143
-#            include <crtdefs.h>
-#        endif
-#        define PYBIND11_DEBUG_MARKER
-#        undef _DEBUG
-#    endif
-#endif
-
 // https://en.cppreference.com/w/c/chrono/localtime
 #if defined(__STDC_LIB_EXT1__) && !defined(__STDC_WANT_LIB_EXT1__)
 #    define __STDC_WANT_LIB_EXT1__
@@ -271,30 +251,6 @@ PYBIND11_WARNING_DISABLE_MSVC(4505)
 #    endif
 #endif
 
-#include <Python.h>
-#if PY_VERSION_HEX < 0x03080000
-#    error "PYTHON < 3.8 IS UNSUPPORTED. pybind11 v2.13 was the last to support Python 3.7."
-#endif
-#include <frameobject.h>
-#include <pythread.h>
-
-/* Python #defines overrides on all sorts of core functions, which
-   tends to weak havok in C++ codebases that expect these to work
-   like regular functions (potentially with several overloads) */
-#if defined(isalnum)
-#    undef isalnum
-#    undef isalpha
-#    undef islower
-#    undef isspace
-#    undef isupper
-#    undef tolower
-#    undef toupper
-#endif
-
-#if defined(copysign)
-#    undef copysign
-#endif
-
 #if defined(PYBIND11_NUMPY_1_ONLY)
 #    define PYBIND11_INTERNAL_NUMPY_1_ONLY_DETECTED
 #endif
@@ -303,14 +259,6 @@ PYBIND11_WARNING_DISABLE_MSVC(4505)
 #    define PYBIND11_SIMPLE_GIL_MANAGEMENT
 #endif
 
-#if defined(_MSC_VER)
-#    if defined(PYBIND11_DEBUG_MARKER)
-#        define _DEBUG
-#        undef PYBIND11_DEBUG_MARKER
-#    endif
-PYBIND11_WARNING_POP
-#endif
-
 #include <cstddef>
 #include <cstring>
 #include <exception>

include/pybind11/detail/internals.h

@@ -15,6 +15,7 @@
 #    include <pybind11/gil.h>
 #endif
 
+#include <pybind11/compat/pybind11_platform_abi_id.h>
 #include <pybind11/pytypes.h>
 
 #include <exception>
@@ -269,67 +270,6 @@ struct type_info {
     bool module_local : 1;
 };
 
-/// On MSVC, debug and release builds are not ABI-compatible!
-#if defined(_MSC_VER) && defined(_DEBUG)
-#    define PYBIND11_BUILD_TYPE "_debug"
-#else
-#    define PYBIND11_BUILD_TYPE ""
-#endif
-
-/// Let's assume that different compilers are ABI-incompatible.
-/// A user can manually set this string if they know their
-/// compiler is compatible.
-#ifndef PYBIND11_COMPILER_TYPE
-#    if defined(_MSC_VER)
-#        define PYBIND11_COMPILER_TYPE "_msvc"
-#    elif defined(__INTEL_COMPILER)
-#        define PYBIND11_COMPILER_TYPE "_icc"
-#    elif defined(__clang__)
-#        define PYBIND11_COMPILER_TYPE "_clang"
-#    elif defined(__PGI)
-#        define PYBIND11_COMPILER_TYPE "_pgi"
-#    elif defined(__MINGW32__)
-#        define PYBIND11_COMPILER_TYPE "_mingw"
-#    elif defined(__CYGWIN__)
-#        define PYBIND11_COMPILER_TYPE "_gcc_cygwin"
-#    elif defined(__GNUC__)
-#        define PYBIND11_COMPILER_TYPE "_gcc"
-#    else
-#        define PYBIND11_COMPILER_TYPE "_unknown"
-#    endif
-#endif
-
-/// Also standard libs
-#ifndef PYBIND11_STDLIB
-#    if defined(_LIBCPP_VERSION)
-#        define PYBIND11_STDLIB "_libcpp"
-#    elif defined(__GLIBCXX__) || defined(__GLIBCPP__)
-#        define PYBIND11_STDLIB "_libstdcpp"
-#    else
-#        define PYBIND11_STDLIB ""
-#    endif
-#endif
-
-/// On Linux/OSX, changes in __GXX_ABI_VERSION__ indicate ABI incompatibility.
-/// On MSVC, changes in _MSC_VER may indicate ABI incompatibility (#2898).
-#ifndef PYBIND11_BUILD_ABI
-#    if defined(__GXX_ABI_VERSION)
-#        define PYBIND11_BUILD_ABI "_cxxabi" PYBIND11_TOSTRING(__GXX_ABI_VERSION)
-#    elif defined(_MSC_VER)
-#        define PYBIND11_BUILD_ABI "_mscver" PYBIND11_TOSTRING(_MSC_VER)
-#    else
-#        define PYBIND11_BUILD_ABI ""
-#    endif
-#endif
-
-#ifndef PYBIND11_INTERNALS_KIND
-#    define PYBIND11_INTERNALS_KIND ""
-#endif
-
-#define PYBIND11_PLATFORM_ABI_ID                                                                  \
-    PYBIND11_INTERNALS_KIND PYBIND11_COMPILER_TYPE PYBIND11_STDLIB PYBIND11_BUILD_ABI             \
-        PYBIND11_BUILD_TYPE
-
 #define PYBIND11_INTERNALS_ID                                                                     \
     "__pybind11_internals_v" PYBIND11_TOSTRING(PYBIND11_INTERNALS_VERSION)                        \
         PYBIND11_PLATFORM_ABI_ID "__"

tests/CMakeLists.txt

@@ -491,6 +491,12 @@ foreach(target ${test_targets})
   if(SKBUILD)
     install(TARGETS ${target} LIBRARY DESTINATION .)
   endif()
+
+  if("${target}" STREQUAL "exo_planet_c_api")
+    if(CMAKE_CXX_COMPILER_ID MATCHES "(GNU|Intel|Clang|NVHPC)")
+      target_compile_options(${target} PRIVATE -fno-exceptions)
+    endif()
+  endif()
 endforeach()
 
 # Provide nice organisation in IDEs

tests/exo_planet_c_api.cpp

@@ -1,59 +1,33 @@
 // Copyright (c) 2024 The pybind Community.
 
+// In production situations it is totally fine to build with
+// C++ Exception Handling enabled. However, here we want to ensure that
+// C++ Exception Handling is not required.
+#if defined(_MSC_VER) || defined(__EMSCRIPTEN__)
+// Too much trouble making the required cmake changes (see PR #5375).
+#else
+#    ifdef __cpp_exceptions
+// https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations#__cpp_exceptions
+#    error This test is meant to be built with C++ Exception Handling disabled, but __cpp_exceptions is defined.
+#    endif
+#    ifdef __EXCEPTIONS
+// https://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html
+#    error This test is meant to be built with C++ Exception Handling disabled, but __EXCEPTIONS is defined.
+#    endif
+#endif
+
 // THIS MUST STAY AT THE TOP!
-#include <pybind11/pybind11.h> // EXCLUSIVELY for PYBIND11_PLATFORM_ABI_ID
-// Potential future direction to maximize reusability:
-// (e.g. for use from SWIG, Cython, PyCLIF, nanobind):
-//     #include <pybind11/compat/platform_abi_id.h>
-// This would only depend on:
-//     1. A C++ compiler, WITHOUT requiring -fexceptions.
-//     2. Python.h
+#include <pybind11/compat/pybind11_conduit_v1.h> // VERY light-weight dependency.
 
 #include "test_cpp_conduit_traveler_types.h"
 
 #include <Python.h>
-#include <typeinfo>
 
 namespace {
 
-void *get_cpp_conduit_void_ptr(PyObject *py_obj, const std::type_info *cpp_type_info) {
-    PyObject *cpp_type_info_capsule
-        = PyCapsule_New(const_cast<void *>(static_cast<const void *>(cpp_type_info)),
-                        typeid(std::type_info).name(),
-                        nullptr);
-    if (cpp_type_info_capsule == nullptr) {
-        return nullptr;
-    }
-    PyObject *cpp_conduit = PyObject_CallMethod(py_obj,
-                                                "_pybind11_conduit_v1_",
-                                                "yOy",
-                                                PYBIND11_PLATFORM_ABI_ID,
-                                                cpp_type_info_capsule,
-                                                "raw_pointer_ephemeral");
-    Py_DECREF(cpp_type_info_capsule);
-    if (cpp_conduit == nullptr) {
-        return nullptr;
-    }
-    void *void_ptr = PyCapsule_GetPointer(cpp_conduit, cpp_type_info->name());
-    Py_DECREF(cpp_conduit);
-    if (PyErr_Occurred()) {
-        return nullptr;
-    }
-    return void_ptr;
-}
-
-template <typename T>
-T *get_cpp_conduit_type_ptr(PyObject *py_obj) {
-    void *void_ptr = get_cpp_conduit_void_ptr(py_obj, &typeid(T));
-    if (void_ptr == nullptr) {
-        return nullptr;
-    }
-    return static_cast<T *>(void_ptr);
-}
-
 extern "C" PyObject *wrapGetLuggage(PyObject * /*self*/, PyObject *traveler) {
-    const auto *cpp_traveler
-        = get_cpp_conduit_type_ptr<pybind11_tests::test_cpp_conduit::Traveler>(traveler);
+    const auto *cpp_traveler = pybind11_conduit_v1::get_type_pointer_ephemeral<
+        pybind11_tests::test_cpp_conduit::Traveler>(traveler);
     if (cpp_traveler == nullptr) {
         return nullptr;
     }
@@ -61,9 +35,8 @@ extern "C" PyObject *wrapGetLuggage(PyObject * /*self*/, PyObject *traveler) {
 }
 
 extern "C" PyObject *wrapGetPoints(PyObject * /*self*/, PyObject *premium_traveler) {
-    const auto *cpp_premium_traveler
-        = get_cpp_conduit_type_ptr<pybind11_tests::test_cpp_conduit::PremiumTraveler>(
-            premium_traveler);
+    const auto *cpp_premium_traveler = pybind11_conduit_v1::get_type_pointer_ephemeral<
+        pybind11_tests::test_cpp_conduit::PremiumTraveler>(premium_traveler);
     if (cpp_premium_traveler == nullptr) {
         return nullptr;
     }

tests/extra_python_package/test_files.py

@@ -50,6 +50,13 @@ main_headers = {
     "include/pybind11/warnings.h",
 }
 
+compat_headers = {
+    "include/pybind11/compat/README.txt",
+    "include/pybind11/compat/pybind11_conduit_v1.h",
+    "include/pybind11/compat/pybind11_platform_abi_id.h",
+    "include/pybind11/compat/wrap_include_python_h.h",
+}
+
 detail_headers = {
     "include/pybind11/detail/class.h",
     "include/pybind11/detail/common.h",
@@ -97,7 +104,7 @@ py_files = {
     "setup_helpers.py",
 }
 
-headers = main_headers | detail_headers | eigen_headers | stl_headers
+headers = main_headers | compat_headers | detail_headers | eigen_headers | stl_headers
 src_files = headers | cmake_files | pkgconfig_files
 all_files = src_files | py_files
 
@@ -106,6 +113,7 @@ sdist_files = {
     "pybind11",
     "pybind11/include",
     "pybind11/include/pybind11",
+    "pybind11/include/pybind11/compat",
     "pybind11/include/pybind11/detail",
     "pybind11/include/pybind11/eigen",
     "pybind11/include/pybind11/stl",

tools/pybind11NewTools.cmake

@@ -274,10 +274,6 @@ function(pybind11_add_module target_name)
     target_link_libraries(${target_name} PRIVATE pybind11::embed)
   endif()
 
-  if(MSVC)
-    target_link_libraries(${target_name} PRIVATE pybind11::windows_extras)
-  endif()
-
   # -fvisibility=hidden is required to allow multiple modules compiled against
   # different pybind versions to work properly, and for some features (e.g.
   # py::module_local).  We force it on everything inside the `pybind11`

tools/setup_global.py.in

@@ -26,12 +26,14 @@ class InstallHeadersNested(install_headers):
 
 
 main_headers = glob.glob("pybind11/include/pybind11/*.h")
+compat_headers = sum([glob.glob(f"pybind11/include/pybind11/compat/*.{ext}")
+                      for ext in ("h", "txt")], [])
 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 + eigen_headers
+headers = main_headers + compat_headers + detail_headers + eigen_headers + stl_headers
 
 cmdclass = {"install_headers": InstallHeadersNested}
 $extra_cmd
@@ -55,6 +57,7 @@ setup(
         (base + "share/cmake/pybind11", cmake_files),
         (base + "share/pkgconfig", pkgconfig_files),
         (base + "include/pybind11", main_headers),
+        (base + "include/pybind11/compat", compat_headers),
         (base + "include/pybind11/detail", detail_headers),
         (base + "include/pybind11/eigen", eigen_headers),
         (base + "include/pybind11/stl", stl_headers),

tools/setup_main.py.in

@@ -14,6 +14,7 @@ setup(
     packages=[
         "pybind11",
         "pybind11.include.pybind11",
+        "pybind11.include.pybind11.compat",
         "pybind11.include.pybind11.detail",
         "pybind11.include.pybind11.eigen",
         "pybind11.include.pybind11.stl",
@@ -23,6 +24,7 @@ setup(
     package_data={
         "pybind11": ["py.typed"],
         "pybind11.include.pybind11": ["*.h"],
+        "pybind11.include.pybind11.compat": ["*.h", "*.txt"],
         "pybind11.include.pybind11.detail": ["*.h"],
         "pybind11.include.pybind11.eigen": ["*.h"],
         "pybind11.include.pybind11.stl": ["*.h"],