bpo-47164: Add _PyCFunction_CAST() macro (GH-32192)

Use the macro in C files of the Python/ directory.

Author: vstinner

Doc/c-api/structures.rst

@@ -342,6 +342,9 @@ There are these calling conventions:
    hold a reference to the module or object instance.  In all cases the second
    parameter will be ``NULL``.
 
+   The function must have 2 parameters. Since the second parameter is unused,
+   :c:macro:`Py_UNUSED` can be used to prevent a compiler warning.
+
 
 .. data:: METH_O
 

Include/methodobject.h

@@ -26,6 +26,24 @@ typedef PyObject *(*_PyCFunctionFastWithKeywords) (PyObject *,
 typedef PyObject *(*PyCMethod)(PyObject *, PyTypeObject *, PyObject *const *,
                                size_t, PyObject *);
 
+// Cast an 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
+// calling conventions).
+//
+// The macro can also be used for METH_FASTCALL and METH_VARARGS|METH_KEYWORDS
+// calling conventions to avoid compiler warnings because the function has more
+// than 2 parameters. The macro first casts the function to the
+// "void func(void)" type to prevent compiler warnings.
+//
+// If a function is declared with the METH_NOARGS calling convention, it must
+// have 2 parameters. Since the second parameter is unused, Py_UNUSED() can be
+// 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) ((PyCFunction)(void(*)(void))(func))
+
 PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
 PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);
 PyAPI_FUNC(int) PyCFunction_GetFlags(PyObject *);

Python/_warnings.c

@@ -1078,7 +1078,7 @@ warnings_warn_explicit(PyObject *self, PyObject *args, PyObject *kwds)
 }
 
 static PyObject *
-warnings_filters_mutated(PyObject *self, PyObject *args)
+warnings_filters_mutated(PyObject *self, PyObject *Py_UNUSED(args))
 {
     PyInterpreterState *interp = get_current_interp();
     if (interp == NULL) {
@@ -1353,9 +1353,9 @@ PyDoc_STRVAR(warn_explicit_doc,
 
 static PyMethodDef warnings_functions[] = {
     WARNINGS_WARN_METHODDEF
-    {"warn_explicit", (PyCFunction)(void(*)(void))warnings_warn_explicit,
+    {"warn_explicit", _PyCFunction_CAST(warnings_warn_explicit),
         METH_VARARGS | METH_KEYWORDS, warn_explicit_doc},
-    {"_filters_mutated", (PyCFunction)warnings_filters_mutated, METH_NOARGS,
+    {"_filters_mutated", _PyCFunction_CAST(warnings_filters_mutated), METH_NOARGS,
         NULL},
     /* XXX(brett.cannon): add showwarning? */
     /* XXX(brett.cannon): Reasonable to add formatwarning? */

Python/bltinmodule.c

@@ -613,7 +613,7 @@ filter_reduce(filterobject *lz, PyObject *Py_UNUSED(ignored))
 PyDoc_STRVAR(reduce_doc, "Return state information for pickling.");
 
 static PyMethodDef filter_methods[] = {
-    {"__reduce__",   (PyCFunction)filter_reduce,   METH_NOARGS, reduce_doc},
+    {"__reduce__", _PyCFunction_CAST(filter_reduce), METH_NOARGS, reduce_doc},
     {NULL,           NULL}           /* sentinel */
 };
 
@@ -1354,7 +1354,7 @@ map_reduce(mapobject *lz, PyObject *Py_UNUSED(ignored))
 }
 
 static PyMethodDef map_methods[] = {
-    {"__reduce__",   (PyCFunction)map_reduce,   METH_NOARGS, reduce_doc},
+    {"__reduce__", _PyCFunction_CAST(map_reduce), METH_NOARGS, reduce_doc},
     {NULL,           NULL}           /* sentinel */
 };
 
@@ -2321,7 +2321,7 @@ PyDoc_STRVAR(builtin_sorted__doc__,
 "reverse flag can be set to request the result in descending order.");
 
 #define BUILTIN_SORTED_METHODDEF    \
-    {"sorted", (PyCFunction)(void(*)(void))builtin_sorted, METH_FASTCALL | METH_KEYWORDS, builtin_sorted__doc__},
+    {"sorted", _PyCFunction_CAST(builtin_sorted), METH_FASTCALL | METH_KEYWORDS, builtin_sorted__doc__},
 
 static PyObject *
 builtin_sorted(PyObject *self, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
@@ -2839,8 +2839,8 @@ zip_setstate(zipobject *lz, PyObject *state)
 }
 
 static PyMethodDef zip_methods[] = {
-    {"__reduce__",   (PyCFunction)zip_reduce,   METH_NOARGS, reduce_doc},
-    {"__setstate__", (PyCFunction)zip_setstate, METH_O,      setstate_doc},
+    {"__reduce__", _PyCFunction_CAST(zip_reduce), METH_NOARGS, reduce_doc},
+    {"__setstate__", _PyCFunction_CAST(zip_setstate), METH_O, setstate_doc},
     {NULL}  /* sentinel */
 };
 
@@ -2904,25 +2904,25 @@ PyTypeObject PyZip_Type = {
 
 
 static PyMethodDef builtin_methods[] = {
-    {"__build_class__", (PyCFunction)(void(*)(void))builtin___build_class__,
+    {"__build_class__", _PyCFunction_CAST(builtin___build_class__),
      METH_FASTCALL | METH_KEYWORDS, build_class_doc},
     BUILTIN___IMPORT___METHODDEF
     BUILTIN_ABS_METHODDEF
     BUILTIN_ALL_METHODDEF
     BUILTIN_ANY_METHODDEF
     BUILTIN_ASCII_METHODDEF
     BUILTIN_BIN_METHODDEF
-    {"breakpoint",      (PyCFunction)(void(*)(void))builtin_breakpoint, METH_FASTCALL | METH_KEYWORDS, breakpoint_doc},
+    {"breakpoint", _PyCFunction_CAST(builtin_breakpoint), METH_FASTCALL | METH_KEYWORDS, breakpoint_doc},
     BUILTIN_CALLABLE_METHODDEF
     BUILTIN_CHR_METHODDEF
     BUILTIN_COMPILE_METHODDEF
     BUILTIN_DELATTR_METHODDEF
-    {"dir",             builtin_dir,        METH_VARARGS, dir_doc},
+    {"dir", builtin_dir, METH_VARARGS, dir_doc},
     BUILTIN_DIVMOD_METHODDEF
     BUILTIN_EVAL_METHODDEF
     BUILTIN_EXEC_METHODDEF
     BUILTIN_FORMAT_METHODDEF
-    {"getattr",         (PyCFunction)(void(*)(void))builtin_getattr, METH_FASTCALL, getattr_doc},
+    {"getattr", _PyCFunction_CAST(builtin_getattr), METH_FASTCALL, getattr_doc},
     BUILTIN_GLOBALS_METHODDEF
     BUILTIN_HASATTR_METHODDEF
     BUILTIN_HASH_METHODDEF
@@ -2931,13 +2931,13 @@ static PyMethodDef builtin_methods[] = {
     BUILTIN_INPUT_METHODDEF
     BUILTIN_ISINSTANCE_METHODDEF
     BUILTIN_ISSUBCLASS_METHODDEF
-    {"iter",            (PyCFunction)(void(*)(void))builtin_iter,       METH_FASTCALL, iter_doc},
+    {"iter", _PyCFunction_CAST(builtin_iter), METH_FASTCALL, iter_doc},
     BUILTIN_AITER_METHODDEF
     BUILTIN_LEN_METHODDEF
     BUILTIN_LOCALS_METHODDEF
-    {"max",             (PyCFunction)(void(*)(void))builtin_max,        METH_VARARGS | METH_KEYWORDS, max_doc},
-    {"min",             (PyCFunction)(void(*)(void))builtin_min,        METH_VARARGS | METH_KEYWORDS, min_doc},
-    {"next",            (PyCFunction)(void(*)(void))builtin_next,       METH_FASTCALL, next_doc},
+    {"max", _PyCFunction_CAST(builtin_max), METH_VARARGS | METH_KEYWORDS, max_doc},
+    {"min", _PyCFunction_CAST(builtin_min), METH_VARARGS | METH_KEYWORDS, min_doc},
+    {"next", _PyCFunction_CAST(builtin_next), METH_FASTCALL, next_doc},
     BUILTIN_ANEXT_METHODDEF
     BUILTIN_OCT_METHODDEF
     BUILTIN_ORD_METHODDEF

Python/context.c

@@ -685,7 +685,7 @@ static PyMethodDef PyContext_methods[] = {
     _CONTEXTVARS_CONTEXT_KEYS_METHODDEF
     _CONTEXTVARS_CONTEXT_VALUES_METHODDEF
     _CONTEXTVARS_CONTEXT_COPY_METHODDEF
-    {"run", (PyCFunction)(void(*)(void))context_run, METH_FASTCALL | METH_KEYWORDS, NULL},
+    {"run", _PyCFunction_CAST(context_run), METH_FASTCALL | METH_KEYWORDS, NULL},
     {NULL, NULL}
 };
 

Python/hamt.c

@@ -2845,29 +2845,29 @@ hamt_py_values(PyHamtObject *self, PyObject *args)
 }
 
 static PyObject *
-hamt_py_keys(PyHamtObject *self, PyObject *args)
+hamt_py_keys(PyHamtObject *self, PyObject *Py_UNUSED(args))
 {
     return _PyHamt_NewIterKeys(self);
 }
 
 #ifdef Py_DEBUG
 static PyObject *
-hamt_py_dump(PyHamtObject *self, PyObject *args)
+hamt_py_dump(PyHamtObject *self, PyObject *Py_UNUSED(args))
 {
     return hamt_dump(self);
 }
 #endif
 
 
 static PyMethodDef PyHamt_methods[] = {
-    {"set", (PyCFunction)hamt_py_set, METH_VARARGS, NULL},
-    {"get", (PyCFunction)hamt_py_get, METH_VARARGS, NULL},
-    {"delete", (PyCFunction)hamt_py_delete, METH_O, NULL},
-    {"items", (PyCFunction)hamt_py_items, METH_NOARGS, NULL},
-    {"keys", (PyCFunction)hamt_py_keys, METH_NOARGS, NULL},
-    {"values", (PyCFunction)hamt_py_values, METH_NOARGS, NULL},
+    {"set", _PyCFunction_CAST(hamt_py_set), METH_VARARGS, NULL},
+    {"get", _PyCFunction_CAST(hamt_py_get), METH_VARARGS, NULL},
+    {"delete", _PyCFunction_CAST(hamt_py_delete), METH_O, NULL},
+    {"items", _PyCFunction_CAST(hamt_py_items), METH_NOARGS, NULL},
+    {"keys", _PyCFunction_CAST(hamt_py_keys), METH_NOARGS, NULL},
+    {"values", _PyCFunction_CAST(hamt_py_values), METH_NOARGS, NULL},
 #ifdef Py_DEBUG
-    {"__dump__", (PyCFunction)hamt_py_dump, METH_NOARGS, NULL},
+    {"__dump__", _PyCFunction_CAST(hamt_py_dump), METH_NOARGS, NULL},
 #endif
     {NULL, NULL}
 };

Python/sysmodule.c

@@ -1929,8 +1929,8 @@ sys_getandroidapilevel_impl(PyObject *module)
 static PyMethodDef sys_methods[] = {
     /* Might as well keep this in alphabetic order */
     SYS_ADDAUDITHOOK_METHODDEF
-    {"audit",           (PyCFunction)(void(*)(void))sys_audit, METH_FASTCALL, audit_doc },
-    {"breakpointhook",  (PyCFunction)(void(*)(void))sys_breakpointhook,
+    {"audit", _PyCFunction_CAST(sys_audit), METH_FASTCALL, audit_doc },
+    {"breakpointhook", _PyCFunction_CAST(sys_breakpointhook),
      METH_FASTCALL | METH_KEYWORDS, breakpointhook_doc},
     SYS__CLEAR_TYPE_CACHE_METHODDEF
     SYS__CURRENT_FRAMES_METHODDEF
@@ -1944,18 +1944,18 @@ static PyMethodDef sys_methods[] = {
     SYS_GETDLOPENFLAGS_METHODDEF
     SYS_GETALLOCATEDBLOCKS_METHODDEF
 #ifdef Py_STATS
-    {"getdxp",          _Py_GetDXProfile, METH_VARARGS},
+    {"getdxp", _Py_GetDXProfile, METH_VARARGS},
 #endif
     SYS_GETFILESYSTEMENCODING_METHODDEF
     SYS_GETFILESYSTEMENCODEERRORS_METHODDEF
     SYS__GETQUICKENEDCOUNT_METHODDEF
 #ifdef Py_TRACE_REFS
-    {"getobjects",      _Py_GetObjects, METH_VARARGS},
+    {"getobjects", _Py_GetObjects, METH_VARARGS},
 #endif
     SYS_GETTOTALREFCOUNT_METHODDEF
     SYS_GETREFCOUNT_METHODDEF
     SYS_GETRECURSIONLIMIT_METHODDEF
-    {"getsizeof",   (PyCFunction)(void(*)(void))sys_getsizeof,
+    {"getsizeof", _PyCFunction_CAST(sys_getsizeof),
      METH_VARARGS | METH_KEYWORDS, getsizeof_doc},
     SYS__GETFRAME_METHODDEF
     SYS_GETWINDOWSVERSION_METHODDEF
@@ -1966,21 +1966,21 @@ static PyMethodDef sys_methods[] = {
     SYS_SETSWITCHINTERVAL_METHODDEF
     SYS_GETSWITCHINTERVAL_METHODDEF
     SYS_SETDLOPENFLAGS_METHODDEF
-    {"setprofile",      sys_setprofile, METH_O, setprofile_doc},
+    {"setprofile", sys_setprofile, METH_O, setprofile_doc},
     SYS_GETPROFILE_METHODDEF
     SYS_SETRECURSIONLIMIT_METHODDEF
-    {"settrace",        sys_settrace, METH_O, settrace_doc},
+    {"settrace", sys_settrace, METH_O, settrace_doc},
     SYS_GETTRACE_METHODDEF
     SYS_CALL_TRACING_METHODDEF
     SYS__DEBUGMALLOCSTATS_METHODDEF
     SYS_SET_COROUTINE_ORIGIN_TRACKING_DEPTH_METHODDEF
     SYS_GET_COROUTINE_ORIGIN_TRACKING_DEPTH_METHODDEF
-    {"set_asyncgen_hooks", (PyCFunction)(void(*)(void))sys_set_asyncgen_hooks,
+    {"set_asyncgen_hooks", _PyCFunction_CAST(sys_set_asyncgen_hooks),
      METH_VARARGS | METH_KEYWORDS, set_asyncgen_hooks_doc},
     SYS_GET_ASYNCGEN_HOOKS_METHODDEF
     SYS_GETANDROIDAPILEVEL_METHODDEF
     SYS_UNRAISABLEHOOK_METHODDEF
-    {NULL,              NULL}           /* sentinel */
+    {NULL, NULL}  // sentinel
 };
 
 

Python/traceback.c

@@ -149,7 +149,7 @@ tb_next_set(PyTracebackObject *self, PyObject *new_next, void *Py_UNUSED(_))
 
 
 static PyMethodDef tb_methods[] = {
-   {"__dir__", (PyCFunction)tb_dir, METH_NOARGS},
+   {"__dir__", _PyCFunction_CAST(tb_dir), METH_NOARGS},
    {NULL, NULL, 0, NULL},
 };