gh-94731: Use C-style casts for _Py_CAST, even in C++

Author: encukou

Include/pyport.h

@@ -14,62 +14,14 @@
 #endif
 
 
-// Macro to use C++ static_cast<>, reinterpret_cast<> and const_cast<>
-// in the Python C API.
-//
-// In C++, _Py_CAST(type, expr) converts a constant expression to a
-// non constant type using const_cast<type>. For example,
-// _Py_CAST(PyObject*, op) can convert a "const PyObject*" to
-// "PyObject*".
-//
-// The type argument must not be a constant type.
+// Macro to use C++ static_cast<> in the Python C API.
 #ifdef __cplusplus
-#include <cstddef>
 #  define _Py_STATIC_CAST(type, expr) static_cast<type>(expr)
-extern "C++" {
-    namespace {
-        template <typename type>
-        inline type _Py_CAST_impl(long int ptr) {
-            return reinterpret_cast<type>(ptr);
-        }
-        template <typename type>
-        inline type _Py_CAST_impl(int ptr) {
-            return reinterpret_cast<type>(ptr);
-        }
-#if __cplusplus >= 201103
-        template <typename type>
-        inline type _Py_CAST_impl(std::nullptr_t) {
-            return static_cast<type>(nullptr);
-        }
-#endif
-
-        template <typename type, typename expr_type>
-            inline type _Py_CAST_impl(expr_type *expr) {
-                return reinterpret_cast<type>(expr);
-            }
-
-        template <typename type, typename expr_type>
-            inline type _Py_CAST_impl(expr_type const *expr) {
-                return reinterpret_cast<type>(const_cast<expr_type *>(expr));
-            }
-
-        template <typename type, typename expr_type>
-            inline type _Py_CAST_impl(expr_type &expr) {
-                return static_cast<type>(expr);
-            }
-
-        template <typename type, typename expr_type>
-            inline type _Py_CAST_impl(expr_type const &expr) {
-                return static_cast<type>(const_cast<expr_type &>(expr));
-            }
-    }
-}
-#  define _Py_CAST(type, expr) _Py_CAST_impl<type>(expr)
-
 #else
 #  define _Py_STATIC_CAST(type, expr) ((type)(expr))
-#  define _Py_CAST(type, expr) ((type)(expr))
 #endif
+// Macro to use the more powerful/dangerous C-style cast even in C++.
+#define _Py_CAST(type, expr) ((type)(expr))
 
 // Static inline functions should use _Py_NULL rather than using directly NULL
 // to prevent C++ compiler warnings. On C++11 and newer, _Py_NULL is defined as

Lib/test/setup_testcppext.py

@@ -17,8 +17,6 @@
         # a C++ extension using the Python C API does not emit C++ compiler
         # warnings
         '-Werror',
-        # Warn on old-style cast (C cast) like: (PyObject*)op
-        '-Wold-style-cast',
     ]
 else:
     # Don't pass any compiler flag to MSVC