bpo-33738: Fix macros which contradict PEP 384 (GH-7477)

During development of the limited API support for PySide,
we saw an error in a macro that accessed a type field.

This patch fixes the 7 errors in the Python headers.
Macros which were not written as capitals were implemented
as function.

To do the necessary analysis again, a script was included that
parses all headers and looks for "->tp_" in serctions which can
be reached with active limited API.

It is easily possible to call this script as a test.

Error listing:

../../Include/objimpl.h:243
#define PyObject_IS_GC(o) (PyType_IS_GC(Py_TYPE(o)) && \
    (Py_TYPE(o)->tp_is_gc == NULL || Py_TYPE(o)->tp_is_gc(o)))
Action: commented only

../../Include/objimpl.h:362
#define PyType_SUPPORTS_WEAKREFS(t) ((t)->tp_weaklistoffset > 0)
Action: commented only

../../Include/objimpl.h:364
#define PyObject_GET_WEAKREFS_LISTPTR(o) \
    ((PyObject **) (((char *) (o)) + Py_TYPE(o)->tp_weaklistoffset))
Action: commented only

../../Include/pyerrors.h:143
#define PyExceptionClass_Name(x) \
     ((char *)(((PyTypeObject*)(x))->tp_name))
Action: implemented function

../../Include/abstract.h:593
#define PyIter_Check(obj) \
    ((obj)->ob_type->tp_iternext != NULL && \
     (obj)->ob_type->tp_iternext != &_PyObject_NextNotImplemented)
Action: implemented function

../../Include/abstract.h:713
#define PyIndex_Check(obj)                              \
    ((obj)->ob_type->tp_as_number != NULL &&            \
     (obj)->ob_type->tp_as_number->nb_index != NULL)
Action: implemented function

../../Include/abstract.h:924
#define PySequence_ITEM(o, i)\
    ( Py_TYPE(o)->tp_as_sequence->sq_item(o, i) )
Action: commented only

3 files changed, 23 insertions, 0 deletions

diff --git a/Include/abstract.h b/Include/abstract.h
index 4088f75..e7bc2d2 100644
--- a/Include/abstract.h
+++ b/Include/abstract.h
@@ -590,9 +590,16 @@ PyAPI_FUNC(PyObject *) PyObject_Format(PyObject *obj,
    returns itself. */
 PyAPI_FUNC(PyObject *) PyObject_GetIter(PyObject *);
 
+/* Returns 1 if the object 'obj' provides iterator protocols, and 0 otherwise.
+
+   This function always succeeds. */
+#ifndef Py_LIMITED_API
 #define PyIter_Check(obj) \
     ((obj)->ob_type->tp_iternext != NULL && \
      (obj)->ob_type->tp_iternext != &_PyObject_NextNotImplemented)
+#else
+PyAPI_FUNC(int) PyIter_Check(PyObject*);
+#endif
 
 /* Takes an iterator object and calls its tp_iternext slot,
    returning the next value.
@@ -710,9 +717,15 @@ PyAPI_FUNC(PyObject *) PyNumber_Xor(PyObject *o1, PyObject *o2);
    This is the equivalent of the Python expression: o1 | o2. */
 PyAPI_FUNC(PyObject *) PyNumber_Or(PyObject *o1, PyObject *o2);
 
+/* Returns 1 if obj is an index integer (has the nb_index slot of the
+   tp_as_number structure filled in), and 0 otherwise. */
+#ifndef Py_LIMITED_API
 #define PyIndex_Check(obj)                              \
     ((obj)->ob_type->tp_as_number != NULL &&            \
      (obj)->ob_type->tp_as_number->nb_index != NULL)
+#else
+PyAPI_FUNC(int) PyIndex_Check(PyObject *);
+#endif
 
 /* Returns the object 'o' converted to a Python int, or NULL with an exception
    raised on failure. */
@@ -921,8 +934,10 @@ PyAPI_FUNC(PyObject *) PySequence_Fast(PyObject *o, const char* m);
 
 /* Assume tp_as_sequence and sq_item exist and that 'i' does not
    need to be corrected for a negative index. */
+#ifndef Py_LIMITED_API
 #define PySequence_ITEM(o, i)\
     ( Py_TYPE(o)->tp_as_sequence->sq_item(o, i) )
+#endif
 
 /* Return a pointer to the underlying item array for
    an object retured by PySequence_Fast */
diff --git a/Include/objimpl.h b/Include/objimpl.h
index 057bb50..a38906c 100644
--- a/Include/objimpl.h
+++ b/Include/objimpl.h
@@ -240,8 +240,10 @@ PyAPI_FUNC(Py_ssize_t) _PyGC_CollectIfEnabled(void);
 #define PyType_IS_GC(t) PyType_HasFeature((t), Py_TPFLAGS_HAVE_GC)
 
 /* Test if an object has a GC head */
+#ifndef Py_LIMITED_API
 #define PyObject_IS_GC(o) (PyType_IS_GC(Py_TYPE(o)) && \
     (Py_TYPE(o)->tp_is_gc == NULL || Py_TYPE(o)->tp_is_gc(o)))
+#endif
 
 PyAPI_FUNC(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, Py_ssize_t);
 #define PyObject_GC_Resize(type, op, n) \
@@ -359,10 +361,12 @@ PyAPI_FUNC(void) PyObject_GC_Del(void *);
 
 
 /* Test if a type supports weak references */
+#ifndef Py_LIMITED_API
 #define PyType_SUPPORTS_WEAKREFS(t) ((t)->tp_weaklistoffset > 0)
 
 #define PyObject_GET_WEAKREFS_LISTPTR(o) \
     ((PyObject **) (((char *) (o)) + Py_TYPE(o)->tp_weaklistoffset))
+#endif
 
 #ifdef __cplusplus
 }
diff --git a/Include/pyerrors.h b/Include/pyerrors.h
index f289471..a9929f5 100644
--- a/Include/pyerrors.h
+++ b/Include/pyerrors.h
@@ -140,8 +140,12 @@ PyAPI_FUNC(void) _PyErr_ChainExceptions(PyObject *, PyObject *, PyObject *);
 #define PyExceptionInstance_Check(x)                    \
     PyType_FastSubclass((x)->ob_type, Py_TPFLAGS_BASE_EXC_SUBCLASS)
 
+#ifndef Py_LIMITED_API
 #define PyExceptionClass_Name(x) \
      ((char *)(((PyTypeObject*)(x))->tp_name))
+#else
+     PyAPI_FUNC(char *) PyExceptionClass_Name(PyObject*);
+#endif
 
 #define PyExceptionInstance_Class(x) ((PyObject*)((x)->ob_type))