Fix memory policy warnings

Fix astropy#12324 : Fix the warnings emitted by Numpy when transferring
ownership by setting ``NPY_ARRAY_OWNDATA``:

    RuntimeWarning: Trying to dealloc data, but a memory policy is not
    set.  If you take ownership of the data, you must set a base owning
    the data (e.g. a PyCapsule).

The warning was added in [1], and is now visible only when setting the
NUMPY_WARN_IF_NO_MEM_POLICY environment variable [2]. For more details
and a fix see [3].

[1] numpy/numpy#17582
[2] numpy/numpy#20200
[3] https://github.com/numpy/numpy/blob/main/doc/source/reference/c-api/data_memory.rst#what-happens-when-deallocating-if-there-is-no-policy-set

astropy/io/fits/src/compressionmodule.c

@@ -956,6 +956,13 @@ void open_from_hdu(fitsfile** fileptr, void** buf, size_t* bufsize,
 }
 
 
+/* define a PyCapsule_Destructor, using the correct deallocator for buff */
+void free_wrap(void *capsule){
+    void * obj = PyCapsule_GetPointer(capsule, PyCapsule_GetName(capsule));
+    free(obj);
+};
+
+
 PyObject* compression_compress_hdu(PyObject* self, PyObject* args)
 {
     PyObject* hdu;
@@ -1068,8 +1075,16 @@ PyObject* compression_compress_hdu(PyObject* self, PyObject* args)
            but it seems like if it fails then the outbuf NEEDS to be freed... */
         goto fail;
     }
-    PyArray_ENABLEFLAGS(tmp, NPY_ARRAY_OWNDATA);
-    /* From this point on outbuf MUST NOT BE FREED! */
+
+    // Take responsibility for outbuf by wrapping it in a capsule and
+    // setting tmp.base to the capsule
+    PyObject *capsule = PyCapsule_New(outbuf, "wrapped_data",
+                                      (PyCapsule_Destructor)&free_wrap);
+    if (PyArray_SetBaseObject(tmp, capsule) == -1) {
+        Py_DECREF(tmp);
+        /* Py_DECREF(capsule); */
+        goto cleanup;
+    }
 
     // Leaves refcount of tmp untouched, so its refcount should remain as 1
     retval = Py_BuildValue("KN", heapsize, tmp);

setup.cfg

@@ -155,7 +155,7 @@ filterwarnings =
     # reading option for now, can be removed once the issue is fixed
     ignore:parallel reading does not currently work, so falling back to serial
     # numpy configurable allocator now wants memory policy set
-    ignore:Trying to dealloc data, but a memory policy is not set.
+    # ignore:Trying to dealloc data, but a memory policy is not set.
     # Ignore deprecation warning for asdf in astropy
     ignore:ASDF functionality for astropy is being moved.*:astropy.utils.exceptions.AstropyDeprecationWarning:astropy.io.misc.asdf.types
     ignore:ASDF functionality for astropy is being moved.*:astropy.utils.exceptions.AstropyDeprecationWarning:astropy.io.misc.asdf.tags.coordinates.frames

tox.ini

@@ -22,6 +22,7 @@ pypi_filter = https://raw.githubusercontent.com/astropy/ci-helpers/main/pip_pinn
 passenv = HOME WINDIR LC_ALL LC_CTYPE CC CI IS_CRON ARCH_ON_CI
 
 setenv =
+    NUMPY_WARN_IF_NO_MEM_POLICY = 1
     # For coverage, we need to pass extra options to the C compiler
     cov: CFLAGS = --coverage -fno-inline-functions -O0
     image: MPLFLAGS = -m "mpl_image_compare" --mpl --mpl-generate-summary=html --mpl-results-path={toxinidir}/results --mpl-hash-library={toxinidir}/astropy/tests/figures/{envname}.json --mpl-baseline-path=https://raw.githubusercontent.com/astropy/astropy-figure-tests/astropy-main/figures/{envname}/ --remote-data -W ignore::DeprecationWarning