gh-91320: Add _Py_reinterpret_cast() macro (#91959)

Fix C++ compiler warnings about "old-style cast"
(g++ -Wold-style-cast) in the Python C API.  Use C++
reinterpret_cast<> and static_cast<> casts when the Python C API is
used in C++.

Example of fixed warning:

    Include/object.h:107:43: error: use of old-style cast to
    ‘PyObject*’ {aka ‘struct _object*’} [-Werror=old-style-cast]
    #define _PyObject_CAST(op) ((PyObject*)(op))

Add _Py_reinterpret_cast() and _Py_static_cast() macros.

5 files changed, 16 insertions, 8 deletions

diff --git a/Include/cpython/abstract.h b/Include/cpython/abstract.h
index bdc0c49..42f766d 100644
--- a/Include/cpython/abstract.h
+++ b/Include/cpython/abstract.h
@@ -50,7 +50,8 @@ PyAPI_FUNC(PyObject *) _PyObject_MakeTpCall(
     PyObject *const *args, Py_ssize_t nargs,
     PyObject *keywords);
 
-#define PY_VECTORCALL_ARGUMENTS_OFFSET ((size_t)1 << (8 * sizeof(size_t) - 1))
+#define PY_VECTORCALL_ARGUMENTS_OFFSET \
+    (_Py_static_cast(size_t, 1) << (8 * sizeof(size_t) - 1))
 
 static inline Py_ssize_t
 PyVectorcall_NARGS(size_t n)
diff --git a/Include/cpython/listobject.h b/Include/cpython/listobject.h
index 0cd6921..298bfcb 100644
--- a/Include/cpython/listobject.h
+++ b/Include/cpython/listobject.h
@@ -25,7 +25,8 @@ PyAPI_FUNC(PyObject *) _PyList_Extend(PyListObject *, PyObject *);
 PyAPI_FUNC(void) _PyList_DebugMallocStats(FILE *out);
 
 /* Cast argument to PyListObject* type. */
-#define _PyList_CAST(op) (assert(PyList_Check(op)), (PyListObject *)(op))
+#define _PyList_CAST(op) \
+    (assert(PyList_Check(op)), _Py_reinterpret_cast(PyListObject*, (op)))
 
 // Macros and static inline functions, trading safety for speed
 
diff --git a/Include/cpython/methodobject.h b/Include/cpython/methodobject.h
index 46d1777..68cecfe 100644
--- a/Include/cpython/methodobject.h
+++ b/Include/cpython/methodobject.h
@@ -8,9 +8,11 @@ PyAPI_DATA(PyTypeObject) PyCMethod_Type;
 #define PyCMethod_Check(op) PyObject_TypeCheck(op, &PyCMethod_Type)
 
 #define _PyCFunctionObject_CAST(func) \
-    (assert(PyCFunction_Check(func)), (PyCFunctionObject *)(func))
+    (assert(PyCFunction_Check(func)), \
+     _Py_reinterpret_cast(PyCFunctionObject*, (func)))
 #define _PyCMethodObject_CAST(func) \
-    (assert(PyCMethod_Check(func)), (PyCMethodObject *)(func))
+    (assert(PyCMethod_Check(func)), \
+     _Py_reinterpret_cast(PyCMethodObject*, (func)))
 
 /* Macros for direct access to these values. Type checks are *not*
    done, so use with care. */
diff --git a/Include/cpython/tupleobject.h b/Include/cpython/tupleobject.h
index fd15ecd..8089e24 100644
--- a/Include/cpython/tupleobject.h
+++ b/Include/cpython/tupleobject.h
@@ -14,7 +14,8 @@ PyAPI_FUNC(int) _PyTuple_Resize(PyObject **, Py_ssize_t);
 PyAPI_FUNC(void) _PyTuple_MaybeUntrack(PyObject *);
 
 /* Cast argument to PyTupleObject* type. */
-#define _PyTuple_CAST(op) (assert(PyTuple_Check(op)), (PyTupleObject *)(op))
+#define _PyTuple_CAST(op) \
+    (assert(PyTuple_Check(op)), _Py_reinterpret_cast(PyTupleObject*, (op)))
 
 // Macros and static inline functions, trading safety for speed
 
diff --git a/Include/cpython/unicodeobject.h b/Include/cpython/unicodeobject.h
index 2712c58..0397f12 100644
--- a/Include/cpython/unicodeobject.h
+++ b/Include/cpython/unicodeobject.h
@@ -236,11 +236,14 @@ PyAPI_FUNC(int) _PyUnicode_CheckConsistency(
 
 
 #define _PyASCIIObject_CAST(op) \
-    (assert(PyUnicode_Check(op)), (PyASCIIObject*)(op))
+    (assert(PyUnicode_Check(op)), \
+     _Py_reinterpret_cast(PyASCIIObject*, (op)))
 #define _PyCompactUnicodeObject_CAST(op) \
-    (assert(PyUnicode_Check(op)), (PyCompactUnicodeObject*)(op))
+    (assert(PyUnicode_Check(op)), \
+     _Py_reinterpret_cast(PyCompactUnicodeObject*, (op)))
 #define _PyUnicodeObject_CAST(op) \
-    (assert(PyUnicode_Check(op)), (PyUnicodeObject*)(op))
+    (assert(PyUnicode_Check(op)), \
+     _Py_reinterpret_cast(PyUnicodeObject*, (op)))
 
 
 /* --- Flexible String Representation Helper Macros (PEP 393) -------------- */