[Cython] Upcoming issues with NumPy deprecated APIs and Cython's sizeof checks

[Lisandro Dalcin]

I'm testing my code with numpy-dev. They are trying to discourage use
of deprecated APIs, this includes direct access to the ndarray struct.
In order to update your code, you have to pass -DNPY_NO_DEPRECATED_API
to the C compiler (or #define it before including NumPy headers).

However, they have implemented this feature by exposing the ndarray
type with just the Python object header:
https://github.com/numpy/numpy/blob/master/numpy/core/include/numpy/ndarraytypes.h#L695

Obviously, this interact bad with Cython's sizeof check, I'm getting
this runtime warning:

build/lib.linux-x86_64-2.7/petsc4py/lib/__init__.py:64:
RuntimeWarning: numpy.ndarray size changed, may indicate binary
incompatibility

I think there is nothing Cython can do about this (other than
special-casing NumPy to disable this VERY useful warning).

 I've tried the patch below with success, but I'm not convinced...
Does any of you have a suggestion for NumPy folks about how to improve
this?


diff --git a/numpy/core/include/numpy/ndarraytypes.h
b/numpy/core/include/numpy/ndarraytypes.h
index 0288272..1fcbf52 100644
--- a/numpy/core/include/numpy/ndarraytypes.h
+++ b/numpy/core/include/numpy/ndarraytypes.h
@@ -695,6 +695,7 @@ typedef struct tagPyArrayObject_fields {
 #ifdef NPY_NO_DEPRECATED_API
 typedef struct tagPyArrayObject {
         PyObject_HEAD
+        char _npy_array_fields[sizeof(PyArrayObject_fields)-sizeof(PyObject)];
 } PyArrayObject;
 #else
 /*

-- 
Lisandro Dalcin
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