From 6756edfad754ed1b65f44e8fe84cf2c9d2f53ce9 Mon Sep 17 00:00:00 2001
From: "Marten H. van Kerkwijk" <mhvk@weasel.astro.utoronto.ca>
Date: Tue, 2 Jan 2018 14:40:56 -0500
Subject: BUG: Ensure __array_finalize__ cannot back-mangle shape

---
 numpy/ma/core.py                  |  7 ++++++-
 numpy/ma/tests/test_core.py       |  4 +++-
 numpy/ma/tests/test_old_ma.py     |  6 +++++-
 numpy/ma/tests/test_regression.py | 10 ++++++++++
 4 files changed, 24 insertions(+), 3 deletions(-)

(limited to 'numpy')

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index fb28fa8e5..ba0d58577 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -2999,12 +2999,15 @@ class MaskedArray(ndarray):
                     order = "K"
 
                 _mask = _mask.astype(_mask_dtype, order)
-
+            else:
+                # Take a view so shape changes, etc., do not propagate back.
+                _mask = _mask.view()
         else:
             _mask = nomask
 
         self._mask = _mask
         # Finalize the mask
+        # FIXME: this really doesn't belong here.
         if self._mask is not nomask:
             try:
                 self._mask.shape = self.shape
@@ -3354,6 +3357,8 @@ class MaskedArray(ndarray):
                 self._mask.shape = self.shape
             except (AttributeError, TypeError):
                 pass
+        elif attr == 'shape' and getmask(self) is not nomask:
+            self._mask.shape = self.shape
 
     def __setmask__(self, mask, copy=False):
         """
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index 63703f6cd..b0d48349d 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -352,9 +352,11 @@ class TestMaskedArray(object):
         assert_equal(y1._mask.__array_interface__, m.__array_interface__)
 
         y1a = array(y1)
+        # Default for masked array is not to copy; see gh-10318.
         assert_(y1a._data.__array_interface__ ==
                         y1._data.__array_interface__)
-        assert_(y1a.mask is y1.mask)
+        assert_(y1a._mask.__array_interface__ ==
+                        y1._mask.__array_interface__)
 
         y2 = array(x1, mask=m3)
         assert_(y2._data.__array_interface__ == x1.__array_interface__)
diff --git a/numpy/ma/tests/test_old_ma.py b/numpy/ma/tests/test_old_ma.py
index 70eab0edc..d7b1e3c18 100644
--- a/numpy/ma/tests/test_old_ma.py
+++ b/numpy/ma/tests/test_old_ma.py
@@ -273,7 +273,11 @@ class TestMa(object):
         assert_(y1.mask is m)
 
         y1a = array(y1, copy=0)
-        assert_(y1a.mask is y1.mask)
+        # For copy=False, one might expect that the array would just
+        # passed on, i.e., that it would be "is" instead of "==".
+        # See gh-4043 for discussion.
+        assert_(y1a._mask.__array_interface__ ==
+                y1._mask.__array_interface__)
 
         y2 = array(x1, mask=m3, copy=0)
         assert_(y2.mask is m3)
diff --git a/numpy/ma/tests/test_regression.py b/numpy/ma/tests/test_regression.py
index 04e10d9d1..96c418a51 100644
--- a/numpy/ma/tests/test_regression.py
+++ b/numpy/ma/tests/test_regression.py
@@ -74,3 +74,13 @@ class TestRegression(object):
             r1 = np.ma.corrcoef(x, y, ddof=1)
             # ddof should not have an effect (it gets cancelled out)
             assert_allclose(r0.data, r1.data)
+
+    def test_mask_not_backmangled(self):
+        # See gh-10314.  Test case taken from gh-3140.
+        a = np.ma.MaskedArray([1., 2.], mask=[False, False])
+        assert_(a.mask.shape == (2,))
+        b = np.tile(a, (2, 1))
+        # Check that the above no longer changes a.shape to (1, 2)
+        assert_(a.mask.shape == (2,))
+        assert_(b.shape == (2, 2))
+        assert_(b.mask.shape == (2, 2))
-- 
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