bpo-45459: Add Py_buffer to limited API (GH-29991)

- [x] ``Py_buffer`` struct
- [x] ``PyBuffer_*()`` API functions
- [x] ``PyBUF_*`` constants
- [x] ``Py_bf_getbuffer`` and ``Py_bf_releasebuffer`` type slots
- [x] ``PyMemoryView_FromBuffer()`` API
- [x] tests for limited API
- [x] ``make regen-limited-abi``
- [x] documentation update
- [ ] export ``PyPickleBuffer*()`` API ???

Doc/c-api/buffer.rst

@@ -499,6 +499,13 @@ Buffer-related functions
    This function fails if *len* != *src->len*.
 
 
+.. c:function:: int PyObject_CopyData(Py_buffer *dest, Py_buffer *src)
+
+   Copy data from *src* to *dest* buffer. Can convert between C-style and
+   or Fortran-style buffers.
+
+   ``0`` is returned on success, ``-1`` on error.
+
 .. c:function:: void PyBuffer_FillContiguousStrides(int ndims, Py_ssize_t *shape, Py_ssize_t *strides, int itemsize, char order)
 
    Fill the *strides* array with byte-strides of a :term:`contiguous` (C-style if

Doc/c-api/type.rst

@@ -272,12 +272,6 @@ The following functions and structs are used to create
       * :c:member:`~PyTypeObject.tp_vectorcall_offset`
         (see :ref:`PyMemberDef <pymemberdef-offsets>`)
 
-      The following fields cannot be set using :c:type:`PyType_Spec` and
-      :c:type:`PyType_Slot` under the limited API:
-
-      * :c:member:`~PyBufferProcs.bf_getbuffer`
-      * :c:member:`~PyBufferProcs.bf_releasebuffer`
-
       Setting :c:data:`Py_tp_bases` or :c:data:`Py_tp_base` may be
       problematic on some platforms.
       To avoid issues, use the *bases* argument of
@@ -287,6 +281,11 @@ The following functions and structs are used to create
 
         Slots in :c:type:`PyBufferProcs` in may be set in the unlimited API.
 
+     .. versionchanged:: 3.11
+        :c:member:`~PyBufferProcs.bf_getbuffer` and
+        :c:member:`~PyBufferProcs.bf_releasebuffer` are now available
+        under limited API.
+
    .. c:member:: void *PyType_Slot.pfunc
 
       The desired value of the slot. In most cases, this is a pointer