[1.x] Backport of apache#19078 (apache#19095)

* Assure NDArray.reshape does not change the array size

* Truncate wikitext-2 to match target array size on reshape

Co-authored-by: r3stl355 <ulmasov@amazon.com>

python/mxnet/gluon/contrib/data/text.py

@@ -91,8 +91,11 @@ def _get_data(self):
 
         data, label = self._read_batch(path)
 
-        self._data = nd.array(data, dtype=data.dtype).reshape((-1, self._seq_len))
-        self._label = nd.array(label, dtype=label.dtype).reshape((-1, self._seq_len))
+        # https://github.com/apache/incubator-mxnet/issues/18886 breaks this unless array size is
+        # multiple of self._seq_len. Truncating the source is consistent with pre #18886 outcome
+        seq_len_mult = len(data) // self._seq_len * self._seq_len
+        self._data = nd.array(data, dtype=data.dtype)[:seq_len_mult].reshape((-1, self._seq_len))
+        self._label = nd.array(label, dtype=label.dtype)[:seq_len_mult].reshape((-1, self._seq_len))
 
     def __getitem__(self, idx):
         return self._data[idx], self._label[idx]

python/mxnet/ndarray/ndarray.py

@@ -1517,7 +1517,12 @@ def reshape(self, *shape, **kwargs):
                                            c_array(ctypes.c_int64, shape),
                                            reverse,
                                            ctypes.byref(handle)))
-        return self.__class__(handle=handle, writable=self.writable)
+        res = self.__class__(handle=handle, writable=self.writable)
+
+        # Array size should not change
+        if np.prod(res.shape) != np.prod(self.shape):
+            raise ValueError('Cannot reshape array of size {} into shape {}'.format(np.prod(self.shape), shape))
+        return res
 
     def reshape_like(self, *args, **kwargs):
         """Convenience fluent method for :py:func:`reshape_like`.

tests/python/unittest/test_ndarray.py

@@ -237,7 +237,8 @@ def test_ndarray_reshape():
     assert same(tensor.reshape(-1, 15).reshape(0, -4, 3, -1).asnumpy(), true_res.reshape(2, 3, 5).asnumpy())
     assert same(tensor.reshape(-1, 0).asnumpy(), true_res.reshape(10, 3).asnumpy())
     assert same(tensor.reshape(-1, 0, reverse=True).asnumpy(), true_res.reshape(6, 5).asnumpy())
-
+    # https://github.com/apache/incubator-mxnet/issues/18886
+    assertRaises(ValueError, tensor.reshape, (2, 3))
 
 @with_seed()
 def test_ndarray_flatten():