Don't make METH_METHOD functions a separate Python type

Instead, PyCFunction_Type is made variable, so it can hold PyCMethodObject
(or any future extensions) directly.
(This is similar to how PyType_Type handles the need for extra storage.)

Author: encukou

Include/cpython/methodobject.h

@@ -2,8 +2,6 @@
 #  error "this header file must not be included directly"
 #endif
 
-PyAPI_DATA(PyTypeObject) PyCMethod_Type;
-
 /* Macros for direct access to these values. Type checks are *not*
    done, so use with care. */
 #define PyCFunction_GET_FUNCTION(func) \
@@ -18,7 +16,7 @@ PyAPI_DATA(PyTypeObject) PyCMethod_Type;
          ((PyCMethodObject *)func) -> mm_class : NULL)
 
 typedef struct {
-    PyObject_HEAD
+    PyObject_VAR_HEAD
     PyMethodDef *m_ml; /* Description of the C function to call */
     PyObject    *m_self; /* Passed as 'self' arg to the C func, can be NULL */
     PyObject    *m_module; /* The __module__ attribute, can be anything */

Include/methodobject.h

@@ -13,7 +13,7 @@ extern "C" {
 
 PyAPI_DATA(PyTypeObject) PyCFunction_Type;
 
-#define PyCFunction_Check(op) (Py_IS_TYPE(op, &PyCFunction_Type) || (PyType_IsSubtype(Py_TYPE(op), &PyCFunction_Type)))
+#define PyCFunction_Check(op) Py_IS_TYPE(op, &PyCFunction_Type)
 
 typedef PyObject *(*PyCFunction)(PyObject *, PyObject *);
 typedef PyObject *(*_PyCFunctionFast) (PyObject *, PyObject *const *, Py_ssize_t);

Lib/test/test_sys.py

@@ -1117,7 +1117,7 @@ def test_objecttypes(self):
         # buffer
         # XXX
         # builtin_function_or_method
-        check(len, size('5P'))
+        check(len, vsize('5P'))
         # bytearray
         samples = [b'', b'u'*100000]
         for sample in samples:

Objects/methodobject.c

@@ -84,7 +84,10 @@ PyCMethod_New(PyMethodDef *ml, PyObject *self, PyObject *module, PyTypeObject *c
                             "flag but no class");
             return NULL;
         }
-        PyCMethodObject *om = PyObject_GC_New(PyCMethodObject, &PyCMethod_Type);
+        PyCMethodObject *om = PyObject_GC_NewVar(
+            PyCMethodObject,
+            &PyCFunction_Type,
+            sizeof(PyCMethodObject) - sizeof(PyCFunctionObject));
         if (om == NULL) {
             return NULL;
         }
@@ -99,7 +102,7 @@ PyCMethod_New(PyMethodDef *ml, PyObject *self, PyObject *module, PyTypeObject *c
             return NULL;
         }
         else {
-            op = PyObject_GC_New(PyCFunctionObject, &PyCFunction_Type);
+            op = PyObject_GC_NewVar(PyCFunctionObject, &PyCFunction_Type, 0);
             if (op == NULL)
                 return NULL;
         }
@@ -334,7 +337,7 @@ PyTypeObject PyCFunction_Type = {
     PyVarObject_HEAD_INIT(&PyType_Type, 0)
     "builtin_function_or_method",
     sizeof(PyCFunctionObject),
-    0,
+    1,
     (destructor)meth_dealloc,                   /* tp_dealloc */
     offsetof(PyCFunctionObject, vectorcall),    /* tp_vectorcall_offset */
     0,                                          /* tp_getattr */
@@ -366,26 +369,6 @@ PyTypeObject PyCFunction_Type = {
     0,                                          /* tp_dict */
 };
 
-PyTypeObject PyCMethod_Type = {
-    PyVarObject_HEAD_INIT(&PyType_Type, 0)
-    .tp_name = "builtin_c_method",
-    .tp_basicsize = sizeof(PyCMethodObject),
-    .tp_dealloc = (destructor)meth_dealloc,
-    .tp_repr = (reprfunc)meth_repr,
-    .tp_hash = (hashfunc)meth_hash,
-    .tp_call = cfunction_call,
-    .tp_getattro = PyObject_GenericGetAttr,
-    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,
-    .tp_traverse = (traverseproc)meth_traverse,
-    .tp_richcompare = meth_richcompare,
-    .tp_weaklistoffset = offsetof(PyCFunctionObject, m_weakreflist),
-    .tp_methods = meth_methods,
-    .tp_members = meth_members,
-    .tp_getset = meth_getsets,
-    .tp_base = &PyCFunction_Type,
-    .tp_vectorcall_offset = offsetof(PyCFunctionObject, vectorcall),
-};
-
 /* Vectorcall functions for each of the PyCFunction calling conventions,
  * except for METH_VARARGS (possibly combined with METH_KEYWORDS) which
  * doesn't use vectorcall.