gh-132097: use a macro for semantically casting function pointers (#132406)

1 files changed, 12 insertions, 3 deletions

diff --git a/Include/methodobject.h b/Include/methodobject.h
index cfff05f8033..e6ec6421d1e 100644
--- a/Include/methodobject.h
+++ b/Include/methodobject.h
@@ -33,7 +33,7 @@ typedef PyObject *(*PyCMethod)(PyObject *, PyTypeObject *, PyObject *const *,
 typedef PyCFunctionFast _PyCFunctionFast;
 typedef PyCFunctionFastWithKeywords _PyCFunctionFastWithKeywords;
 
-// Cast an function to the PyCFunction type to use it with PyMethodDef.
+// Cast a function to the PyCFunction type to use it with PyMethodDef.
 //
 // This macro can be used to prevent compiler warnings if the first parameter
 // uses a different pointer type than PyObject* (ex: METH_VARARGS and METH_O
@@ -49,8 +49,17 @@ typedef PyCFunctionFastWithKeywords _PyCFunctionFastWithKeywords;
 // used to prevent a compiler warning. If the function has a single parameter,
 // it triggers an undefined behavior when Python calls it with 2 parameters
 // (bpo-33012).
-#define _PyCFunction_CAST(func) \
-    _Py_CAST(PyCFunction, _Py_CAST(void(*)(void), (func)))
+#define _PyCFunction_CAST(func)                         \
+    _Py_FUNC_CAST(PyCFunction, func)
+// The macros below are given for semantic convenience, allowing users
+// to see whether a cast to suppress an undefined behavior is necessary.
+// Note: At runtime, the original function signature must be respected.
+#define _PyCFunctionFast_CAST(func)                     \
+    _Py_FUNC_CAST(PyCFunctionFast, func)
+#define _PyCFunctionWithKeywords_CAST(func)             \
+    _Py_FUNC_CAST(PyCFunctionWithKeywords, func)
+#define _PyCFunctionFastWithKeywords_CAST(func)         \
+    _Py_FUNC_CAST(PyCFunctionFastWithKeywords, func)
 
 PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
 PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);