From be8898ce7af649f7f3b2fa96f8fef0e0b0e0280a Mon Sep 17 00:00:00 2001
From: Gregory Lee <grlee77@gmail.com>
Date: Thu, 24 Jun 2021 08:37:01 -0400
Subject: [PATCH 1/4] BUG: protect against access an attribute of a NULL
 pointer

Have PyArray_GetCastSafety return -1 if from is NULL
---
 numpy/core/src/multiarray/convert_datatype.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/numpy/core/src/multiarray/convert_datatype.c b/numpy/core/src/multiarray/convert_datatype.c
index d197a4bea31e..716e5dd3d111 100644
--- a/numpy/core/src/multiarray/convert_datatype.c
+++ b/numpy/core/src/multiarray/convert_datatype.c
@@ -417,6 +417,9 @@ PyArray_GetCastSafety(
     if (to != NULL) {
         to_dtype = NPY_DTYPE(to);
     }
+    if (from == NULL) {
+        return -1;
+    }
     PyObject *meth = PyArray_GetCastingImpl(NPY_DTYPE(from), to_dtype);
     if (meth == NULL) {
         return -1;
@@ -3293,8 +3296,10 @@ void_to_void_resolve_descriptors(
                 casting = NPY_NO_CASTING | _NPY_CAST_IS_VIEW;
             }
         }
-        NPY_CASTING field_casting = PyArray_GetCastSafety(
-                given_descrs[0]->subarray->base, given_descrs[1]->subarray->base, NULL);
+
+        PyArray_Descr *from_base = (from_sub == NULL) ? NULL : from_sub->base;
+        PyArray_Descr *to_base = (to_sub == NULL) ? NULL : to_sub->base;
+        NPY_CASTING field_casting = PyArray_GetCastSafety(from_base, to_base, NULL);
         if (field_casting < 0) {
             return -1;
         }

From 6c4e3a9889d3703b57410ea6721deff667d1c386 Mon Sep 17 00:00:00 2001
From: Gregory Lee <grlee77@gmail.com>
Date: Thu, 24 Jun 2021 11:16:22 -0400
Subject: [PATCH 2/4] pass descriptor rather than null

---
 numpy/core/src/multiarray/convert_datatype.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/numpy/core/src/multiarray/convert_datatype.c b/numpy/core/src/multiarray/convert_datatype.c
index 716e5dd3d111..1bba276d2d16 100644
--- a/numpy/core/src/multiarray/convert_datatype.c
+++ b/numpy/core/src/multiarray/convert_datatype.c
@@ -417,9 +417,6 @@ PyArray_GetCastSafety(
     if (to != NULL) {
         to_dtype = NPY_DTYPE(to);
     }
-    if (from == NULL) {
-        return -1;
-    }
     PyObject *meth = PyArray_GetCastingImpl(NPY_DTYPE(from), to_dtype);
     if (meth == NULL) {
         return -1;
@@ -3297,8 +3294,8 @@ void_to_void_resolve_descriptors(
             }
         }
 
-        PyArray_Descr *from_base = (from_sub == NULL) ? NULL : from_sub->base;
-        PyArray_Descr *to_base = (to_sub == NULL) ? NULL : to_sub->base;
+        PyArray_Descr *from_base = (from_sub == NULL) ? given_descrs[0] : from_sub->base;
+        PyArray_Descr *to_base = (to_sub == NULL) ? given_descrs[1] : to_sub->base;
         NPY_CASTING field_casting = PyArray_GetCastSafety(from_base, to_base, NULL);
         if (field_casting < 0) {
             return -1;

From 4f56383499da051acc204a6133c9480d5d7d7a26 Mon Sep 17 00:00:00 2001
From: Gregory Lee <grlee77@gmail.com>
Date: Thu, 24 Jun 2021 11:44:37 -0400
Subject: [PATCH 3/4] TST: test can_cast when only one argument has a subarray

---
 numpy/core/tests/test_casting_unittests.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/numpy/core/tests/test_casting_unittests.py b/numpy/core/tests/test_casting_unittests.py
index 2cec1acd3490..34f316d5ddc5 100644
--- a/numpy/core/tests/test_casting_unittests.py
+++ b/numpy/core/tests/test_casting_unittests.py
@@ -646,3 +646,9 @@ def test_object_to_parametric_internal_error(self):
         with pytest.raises(TypeError,
                     match="casting from object to the parametric DType"):
             cast._resolve_descriptors((np.dtype("O"), None))
+
+    def test_void_to_structured_with_subarray(self):
+        # test case corresponding to gh-19325
+        dtype = np.dtype([("foo", "<f4", (3, 2))])
+        assert np.can_cast("V4", dtype, casting="unsafe")
+        assert not np.can_cast("V4", dtype, casting="no")

From 807020ca618ba7b7272f0c0cde3cbc7fcfbcc7e1 Mon Sep 17 00:00:00 2001
From: Gregory Lee <grlee77@gmail.com>
Date: Thu, 24 Jun 2021 13:41:03 -0400
Subject: [PATCH 4/4] TST: test both argument orders

---
 numpy/core/tests/test_casting_unittests.py | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/numpy/core/tests/test_casting_unittests.py b/numpy/core/tests/test_casting_unittests.py
index 34f316d5ddc5..d1924c1fda17 100644
--- a/numpy/core/tests/test_casting_unittests.py
+++ b/numpy/core/tests/test_casting_unittests.py
@@ -647,8 +647,10 @@ def test_object_to_parametric_internal_error(self):
                     match="casting from object to the parametric DType"):
             cast._resolve_descriptors((np.dtype("O"), None))
 
-    def test_void_to_structured_with_subarray(self):
+    @pytest.mark.parametrize("casting", ["no", "unsafe"])
+    def test_void_and_structured_with_subarray(self, casting):
         # test case corresponding to gh-19325
         dtype = np.dtype([("foo", "<f4", (3, 2))])
-        assert np.can_cast("V4", dtype, casting="unsafe")
-        assert not np.can_cast("V4", dtype, casting="no")
+        expected = casting == "unsafe"
+        assert np.can_cast("V4", dtype, casting=casting) == expected
+        assert np.can_cast(dtype, "V4", casting=casting) == expected