bpo-38787: C API for module state access from extension methods (PEP 573) (GH-19936)

Module C state is now accessible from C-defined heap type methods (PEP 573).
Patch by Marcel Plch and Petr Viktorin.

Co-authored-by: Marcel Plch <mplch@redhat.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

Include/methodobject.h

@@ -13,7 +13,7 @@ extern "C" {
 
 PyAPI_DATA(PyTypeObject) PyCFunction_Type;
 
-#define PyCFunction_Check(op) Py_IS_TYPE(op, &PyCFunction_Type)
+#define PyCFunction_Check(op) (Py_IS_TYPE(op, &PyCFunction_Type) || (PyType_IsSubtype(Py_TYPE(op), &PyCFunction_Type)))
 
 typedef PyObject *(*PyCFunction)(PyObject *, PyObject *);
 typedef PyObject *(*_PyCFunctionFast) (PyObject *, PyObject *const *, Py_ssize_t);
@@ -22,21 +22,13 @@ typedef PyObject *(*PyCFunctionWithKeywords)(PyObject *, PyObject *,
 typedef PyObject *(*_PyCFunctionFastWithKeywords) (PyObject *,
                                                    PyObject *const *, Py_ssize_t,
                                                    PyObject *);
+typedef PyObject *(*PyCMethod)(PyObject *, PyTypeObject *, PyObject *const *,
+                               size_t, PyObject *);
+
 PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
 PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);
 PyAPI_FUNC(int) PyCFunction_GetFlags(PyObject *);
 
-/* Macros for direct access to these values. Type checks are *not*
-   done, so use with care. */
-#ifndef Py_LIMITED_API
-#define PyCFunction_GET_FUNCTION(func) \
-        (((PyCFunctionObject *)func) -> m_ml -> ml_meth)
-#define PyCFunction_GET_SELF(func) \
-        (((PyCFunctionObject *)func) -> m_ml -> ml_flags & METH_STATIC ? \
-         NULL : ((PyCFunctionObject *)func) -> m_self)
-#define PyCFunction_GET_FLAGS(func) \
-        (((PyCFunctionObject *)func) -> m_ml -> ml_flags)
-#endif
 Py_DEPRECATED(3.9) PyAPI_FUNC(PyObject *) PyCFunction_Call(PyObject *, PyObject *, PyObject *);
 
 struct PyMethodDef {
@@ -52,6 +44,13 @@ typedef struct PyMethodDef PyMethodDef;
 PyAPI_FUNC(PyObject *) PyCFunction_NewEx(PyMethodDef *, PyObject *,
                                          PyObject *);
 
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03090000
+#define PyCFunction_NewEx(ML, SELF, MOD) PyCMethod_New((ML), (SELF), (MOD), NULL)
+PyAPI_FUNC(PyObject *) PyCMethod_New(PyMethodDef *, PyObject *,
+                                     PyObject *, PyTypeObject *);
+#endif
+
+
 /* Flag passed to newmethodobject */
 /* #define METH_OLDARGS  0x0000   -- unsupported now */
 #define METH_VARARGS  0x0001
@@ -84,15 +83,24 @@ PyAPI_FUNC(PyObject *) PyCFunction_NewEx(PyMethodDef *, PyObject *,
 #define METH_STACKLESS 0x0000
 #endif
 
+/* METH_METHOD means the function stores an
+ * additional reference to the class that defines it;
+ * both self and class are passed to it.
+ * It uses PyCMethodObject instead of PyCFunctionObject.
+ * May not be combined with METH_NOARGS, METH_O, METH_CLASS or METH_STATIC.
+ */
+
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03090000
+#define METH_METHOD 0x0200
+#endif
+
+
 #ifndef Py_LIMITED_API
-typedef struct {
-    PyObject_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 */
-    PyObject    *m_weakreflist; /* List of weak references */
-    vectorcallfunc vectorcall;
-} PyCFunctionObject;
+
+#define Py_CPYTHON_METHODOBJECT_H
+#include  "cpython/methodobject.h"
+#undef Py_CPYTHON_METHODOBJECT_H
+
 #endif
 
 #ifdef __cplusplus