FIX: Fix try_append_array when appending empty arrays

Fix a problem with appending empty arrays (found by ndarray-rand's
quickcheck thank you). The try_append_array method was returning a tad
too early in this case.

Author: bluss

src/impl_owned_array.rs

@@ -201,15 +201,21 @@ impl<A, D> Array<A, D>
         }
 
         let len_to_append = array.len();
-        if len_to_append == 0 {
-            return Ok(());
-        }
 
         let array_shape = array.raw_dim();
         let mut res_dim = self.raw_dim();
         res_dim[axis.index()] += array_shape[axis.index()];
         let new_len = dimension::size_of_shape_checked(&res_dim)?;
 
+        if len_to_append == 0 {
+            // There are no elements to append and shapes are compatible:
+            // either the dimension increment is zero, or there is an existing
+            // zero in another axis in self.
+            debug_assert_eq!(self.len(), new_len);
+            self.dim = res_dim;
+            return Ok(());
+        }
+
         let self_is_empty = self.is_empty();
 
         // array must be empty or have `axis` as the outermost (longest stride) axis

tests/append.rs

@@ -195,3 +195,22 @@ fn test_append_middle_axis() {
     a.try_append_array(Axis(1), Array::from_iter(12..24).into_shape((3, 2, 2)).unwrap().view()).unwrap();
     println!("{:?}", a);
 }
+
+#[test]
+fn test_append_zero_size() {
+    {
+        let mut a = Array::<i32, _>::zeros((0, 0));
+        a.try_append_array(Axis(0), aview2(&[[]])).unwrap();
+        a.try_append_array(Axis(0), aview2(&[[]])).unwrap();
+        assert_eq!(a.len(), 0);
+        assert_eq!(a.shape(), &[2, 0]);
+    }
+
+    {
+        let mut a = Array::<i32, _>::zeros((0, 0));
+        a.try_append_array(Axis(1), ArrayView::from(&[]).into_shape((0, 1)).unwrap()).unwrap();
+        a.try_append_array(Axis(1), ArrayView::from(&[]).into_shape((0, 1)).unwrap()).unwrap();
+        assert_eq!(a.len(), 0);
+        assert_eq!(a.shape(), &[0, 2]);
+    }
+}