BUG: Fix masked array raveling when `order="A"` or `order="K"`

This transitively fixes gh-22912.  I had alooked a bit into whether
it is worthwhile to preserve the mask order, but TBH, we seem to not
do so in so many places, that I don't think it really is worthwhile.

Applying `order="K"` or `order="A"` to the data and mask separately
is an big bug though.

Closes gh-22912

2 files changed, 24 insertions, 0 deletions

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index d2bd3d47e..077aaef1a 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -4631,6 +4631,7 @@ class MaskedArray(ndarray):
             otherwise.  'K' means to read the elements in the order they occur
             in memory, except for reversing the data when strides are negative.
             By default, 'C' index order is used.
+            (Masked arrays currently use 'A' on the data when 'K' is passed.)
 
         Returns
         -------
@@ -4657,6 +4658,13 @@ class MaskedArray(ndarray):
                fill_value=999999)
 
         """
+        # The order of _data and _mask could be different (it shouldn't be
+        # normally).  Passing order `K` or `A` would be incorrect.
+        # So we ignore the mask memory order.
+        # TODO: We don't actually support K, so use A instead.  We could
+        #       try to guess this correct by sorting strides or deprecate.
+        if order in "kKaA":
+            order = "C" if self._data.flags.fnc else "F"
         r = ndarray.ravel(self._data, order=order).view(type(self))
         r._update_from(self)
         if self._mask is not nomask:
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index 5db01b74a..8fcd70c26 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -3411,6 +3411,22 @@ class TestMaskedArrayMethods:
         assert_equal(a.ravel(order='C'), [1, 2, 3, 4])
         assert_equal(a.ravel(order='F'), [1, 3, 2, 4])
 
+    @pytest.mark.parametrize("order", "AKCF")
+    @pytest.mark.parametrize("data_order", "CF")
+    def test_ravel_order(self, order, data_order):
+        # Ravelling must ravel mask and data in the same order always to avoid
+        # misaligning the two in the ravel result.
+        arr = np.ones((5, 10), order=data_order)
+        arr[0, :] = 0
+        mask = np.ones((10, 5), dtype=bool, order=data_order).T
+        mask[0, :] = False
+        x = array(arr, mask=mask)
+        assert x._data.flags.fnc != x._mask.flags.fnc
+        assert (x.filled(0) == 0).all()
+        raveled = x.ravel(order)
+        assert (raveled.filled(0) == 0).all()
+
+
     def test_reshape(self):
         # Tests reshape
         x = arange(4)