Merge pull request numpy#20365 from seberg/issue-19696

BUG: Fix failure to create aligned, empty structured dtype

Author: charris

numpy/core/src/multiarray/descriptor.c

@@ -1326,7 +1326,7 @@ _convert_from_dict(PyObject *obj, int align)
             goto fail;
         }
         /* If align is set, make sure the alignment divides into the size */
-        if (align && itemsize % new->alignment != 0) {
+        if (align && new->alignment > 0 && itemsize % new->alignment != 0) {
             PyErr_Format(PyExc_ValueError,
                     "NumPy dtype descriptor requires alignment of %d bytes, "
                     "which is not divisible into the specified itemsize %d",

numpy/core/tests/test_dtype.py

@@ -627,6 +627,12 @@ def test_alignment(self):
         t2 = np.dtype('2i4', align=True)
         assert_equal(t1.alignment, t2.alignment)
 
+    def test_aligned_empty(self):
+        # Mainly regression test for gh-19696: construction failed completely
+        dt = np.dtype([], align=True)
+        assert dt == np.dtype([])
+        dt = np.dtype({"names": [], "formats": [], "itemsize": 0}, align=True)
+        assert dt == np.dtype([])
 
 def iter_struct_object_dtypes():
     """