Set shape on exported memoryviews

Previously we would update the exposed `len` but not the `shape`. This went unnoticed since many consuming APIs only check `len` and not `shape`. This fixes the bug and adds some tests to ensure both fields are properly set.

Author: jcrist

msgspec/_core.c

@@ -15051,6 +15051,7 @@ mpack_decode_bin(
  Py_buffer *buffer = PyMemoryView_GET_BUFFER(view);
  buffer->buf = s;
  buffer->len = size;
+ buffer->shape = &(buffer->len);
  return view;
  }
 
@@ -15910,6 +15911,7 @@ mpack_decode_ext(
  buffer = PyMemoryView_GET_BUFFER(view);
  buffer->buf = data_buf;
  buffer->len = size;
+ buffer->shape = &(buffer->len);
 
  out = PyObject_CallFunctionObjArgs(self->ext_hook, pycode, view, NULL);
 done:

tests/test_msgpack.py

@@ -683,6 +683,7 @@ def test_decode_memoryview_zerocopy(self, input_type):
  res = msgspec.msgpack.decode(msg, type=memoryview)
  assert isinstance(res, memoryview)
  assert bytes(res) == b"abcde"
+ assert len(res) == 5
  if input_type is memoryview:
  assert sys.getrefcount(ref) == 3
  del msg
@@ -1301,6 +1302,7 @@ def enc_hook(x):
  def ext_hook(code, buf):
  assert isinstance(buf, memoryview)
  assert bytes(buf) == exp_buf
+ assert len(buf) == len(exp_buf)
  assert code == 5
  return pickle.loads(buf)