gh-103509: PEP 697 -- Limited C API for Extending Opaque Types (GH-103511)

Co-authored-by: Oleg Iarygin <oleg@arhadthedev.net>
Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>

5 files changed, 18 insertions, 5 deletions

diff --git a/Include/cpython/object.h b/Include/cpython/object.h
index ce4d13c..d8eff69 100644
--- a/Include/cpython/object.h
+++ b/Include/cpython/object.h
@@ -553,6 +553,7 @@ Py_DEPRECATED(3.11) typedef int UsingDeprecatedTrashcanMacro;
         Py_TRASHCAN_END; \
     } while(0);
 
+PyAPI_FUNC(void *) PyObject_GetItemData(PyObject *obj);
 
 PyAPI_FUNC(int) _PyObject_VisitManagedDict(PyObject *obj, visitproc visit, void *arg);
 PyAPI_FUNC(void) _PyObject_ClearManagedDict(PyObject *obj);
diff --git a/Include/descrobject.h b/Include/descrobject.h
index 0a420b8..fd66d17 100644
--- a/Include/descrobject.h
+++ b/Include/descrobject.h
@@ -83,6 +83,7 @@ struct PyMemberDef {
 #define Py_READONLY            1
 #define Py_AUDIT_READ          2 // Added in 3.10, harmless no-op before that
 #define _Py_WRITE_RESTRICTED   4 // Deprecated, no-op. Do not reuse the value.
+#define Py_RELATIVE_OFFSET     8
 
 PyAPI_FUNC(PyObject *) PyMember_GetOne(const char *, PyMemberDef *);
 PyAPI_FUNC(int) PyMember_SetOne(char *, PyMemberDef *, PyObject *);
diff --git a/Include/internal/pycore_object.h b/Include/internal/pycore_object.h
index 91853ad..b9e700e 100644
--- a/Include/internal/pycore_object.h
+++ b/Include/internal/pycore_object.h
@@ -389,11 +389,6 @@ extern PyObject ** _PyObject_ComputedDictPointer(PyObject *);
 extern void _PyObject_FreeInstanceAttributes(PyObject *obj);
 extern int _PyObject_IsInstanceDictEmpty(PyObject *);
 
-// Access macro to the members which are floating "behind" the object
-static inline PyMemberDef* _PyHeapType_GET_MEMBERS(PyHeapTypeObject *etype) {
-    return (PyMemberDef*)((char*)etype + Py_TYPE(etype)->tp_basicsize);
-}
-
 PyAPI_FUNC(PyObject *) _PyObject_LookupSpecial(PyObject *, PyObject *);
 
 /* C function call trampolines to mitigate bad function pointer casts.
diff --git a/Include/object.h b/Include/object.h
index 66c3df0..81aeb2d 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -355,6 +355,8 @@ PyAPI_FUNC(PyObject *) PyType_GetQualName(PyTypeObject *);
 #endif
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030C0000
 PyAPI_FUNC(PyObject *) PyType_FromMetaclass(PyTypeObject*, PyObject*, PyType_Spec*, PyObject*);
+PyAPI_FUNC(void *) PyObject_GetTypeData(PyObject *obj, PyTypeObject *cls);
+PyAPI_FUNC(Py_ssize_t) PyType_GetTypeDataSize(PyTypeObject *cls);
 #endif
 
 /* Generic type check */
@@ -521,6 +523,9 @@ given type object has a specified feature.
 // subject itself (rather than a mapped attribute on it):
 #define _Py_TPFLAGS_MATCH_SELF (1UL << 22)
 
+/* Items (ob_size*tp_itemsize) are found at the end of an instance's memory */
+#define Py_TPFLAGS_ITEMS_AT_END (1UL << 23)
+
 /* These flags are used to determine if a type is a subclass. */
 #define Py_TPFLAGS_LONG_SUBCLASS        (1UL << 24)
 #define Py_TPFLAGS_LIST_SUBCLASS        (1UL << 25)
diff --git a/Include/pyport.h b/Include/pyport.h
index bd0ba6d..d7c6ae6 100644
--- a/Include/pyport.h
+++ b/Include/pyport.h
@@ -765,4 +765,15 @@ extern char * _getpty(int *, int, mode_t, int);
 #undef __bool__
 #endif
 
+// Make sure we have maximum alignment, even if the current compiler
+// does not support max_align_t. Note that:
+// - Autoconf reports alignment of unknown types to 0.
+// - 'long double' has maximum alignment on *most* platforms,
+//   looks like the best we can do for pre-C11 compilers.
+// - The value is tested, see test_alignof_max_align_t
+#if !defined(ALIGNOF_MAX_ALIGN_T) || ALIGNOF_MAX_ALIGN_T == 0
+#   undef ALIGNOF_MAX_ALIGN_T
+#   define ALIGNOF_MAX_ALIGN_T _Alignof(long double)
+#endif
+
 #endif /* Py_PYPORT_H */