Improve handling of masks

lib/iris/_concatenate.py

@@ -310,7 +310,7 @@ def _hash_ndarray(a: np.ndarray) -> np.ndarray:
 
     # Hash the bytes representing the array data.
     hash.update(b"data=")
-    if isinstance(a, np.ma.MaskedArray):
+    if np.ma.is_masked(a):
         # Hash only the unmasked data
         hash.update(a.compressed().tobytes())
         # Hash the mask

lib/iris/tests/unit/concatenate/test_hashing.py

@@ -21,6 +21,8 @@
         (np.array([np.nan, 1.0]), np.array([np.nan, 1.0]), True),
         (np.ma.array([1, 2], mask=[0, 1]), np.ma.array([1, 2], mask=[0, 1]), True),
         (np.ma.array([1, 2], mask=[0, 1]), np.ma.array([1, 2], mask=[0, 0]), False),
+        (np.ma.array([1, 2], mask=[1, 1]), np.ma.array([1, 2], mask=[1, 1]), True),
+        (np.ma.array([1, 2], mask=[0, 0]), np.ma.array([1, 2], mask=[0, 0]), True),
         (da.arange(6).reshape((2, 3)), da.arange(6, chunks=1).reshape((2, 3)), True),
         (da.arange(20, chunks=1), da.arange(20, chunks=2), True),
         (
@@ -33,6 +35,21 @@
             da.ma.masked_array([1, 3], mask=[0, 1]),
             True,
         ),
+        (
+            np.arange(2),
+            da.ma.masked_array(np.arange(2), mask=[0, 0]),
+            True,
+        ),
+        (
+            np.arange(2),
+            da.ma.masked_array(np.arange(2), mask=[0, 1]),
+            False,
+        ),
+        (
+            da.ma.masked_array(np.arange(10), mask=np.zeros(10)),
+            da.ma.masked_array(np.arange(10), mask=np.ma.nomask),
+            True,
+        ),
         (
             np.ma.array([1, 2], mask=[0, 1]),
             np.ma.array([1, 3], mask=[0, 1], fill_value=10),