Merge branch 'master' into annotated_any

.github/workflows/ci.yml

@@ -114,6 +114,7 @@ jobs:
       run: >
         cmake -S . -B .
         -DPYBIND11_WERROR=ON
+        -DPYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION=ON
         -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON
         -DPYBIND11_NUMPY_1_ONLY=ON
         -DDOWNLOAD_CATCH=ON

CMakeLists.txt

@@ -107,6 +107,8 @@ endif()
 option(PYBIND11_INSTALL "Install pybind11 header files?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_TEST "Build pybind11 test suite?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_NOPYTHON "Disable search for Python" OFF)
+option(PYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION
+       "To enforce that a handle_type_name<> specialization exists" OFF)
 option(PYBIND11_SIMPLE_GIL_MANAGEMENT
        "Use simpler GIL management logic that does not support disassociation" OFF)
 option(PYBIND11_NUMPY_1_ONLY
@@ -115,6 +117,9 @@ set(PYBIND11_INTERNALS_VERSION
     ""
     CACHE STRING "Override the ABI version, may be used to enable the unstable ABI.")
 
+if(PYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION)
+  add_compile_definitions(PYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION)
+endif()
 if(PYBIND11_SIMPLE_GIL_MANAGEMENT)
   add_compile_definitions(PYBIND11_SIMPLE_GIL_MANAGEMENT)
 endif()

include/pybind11/cast.h

@@ -881,9 +881,21 @@ struct is_holder_type
 template <typename base, typename deleter>
 struct is_holder_type<base, std::unique_ptr<base, deleter>> : std::true_type {};
 
+#ifdef PYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION // See PR #4888
+
+// This leads to compilation errors if a specialization is missing.
 template <typename T>
 struct handle_type_name;
 
+#else
+
+template <typename T>
+struct handle_type_name {
+    static constexpr auto name = const_name<T>();
+};
+
+#endif
+
 template <>
 struct handle_type_name<object> {
     static constexpr auto name = const_name("object");