ARROW-12769: [Python] Fix slicing array with "negative" length (start > stop)

python/pyarrow/array.pxi

@@ -537,7 +537,8 @@ def _normalize_slice(object arrow_obj, slice key):
         indices = np.arange(start, stop, step)
         return arrow_obj.take(indices)
     else:
-        return arrow_obj.slice(start, stop - start)
+        length = max(stop - start, 0)
+        return arrow_obj.slice(start, length)
 
 
 cdef Py_ssize_t _normalize_index(Py_ssize_t index,
@@ -1103,6 +1104,8 @@ cdef class Array(_PandasConvertible):
         if length is None:
             result = self.ap.Slice(offset)
         else:
+            if length < 0:
+                raise ValueError('Length must be non-negative')
             result = self.ap.Slice(offset, length)
 
         return pyarrow_wrap_array(result)

python/pyarrow/tests/test_array.py

@@ -413,6 +413,9 @@ def test_array_slice():
     with pytest.raises(IndexError):
         arr.slice(-1)
 
+    with pytest.raises(ValueError):
+        arr.slice(2, -1)
+
     # Test slice notation
     assert arr[2:].equals(arr.slice(2))
     assert arr[2:5].equals(arr.slice(2, 3))
@@ -421,7 +424,11 @@ def test_array_slice():
     n = len(arr)
     for start in range(-n * 2, n * 2):
         for stop in range(-n * 2, n * 2):
-            assert arr[start:stop].to_pylist() == arr.to_pylist()[start:stop]
+            res = arr[start:stop]
+            res.validate()
+            expected = arr.to_pylist()[start:stop]
+            assert res.to_pylist() == expected
+            assert res.to_numpy().tolist() == expected
 
 
 def test_array_slice_negative_step():