BUG: Index.getitem returning wrong result with negative step for arrow

doc/source/whatsnew/v2.1.3.rst

@@ -21,6 +21,7 @@ Fixed regressions
 Bug fixes
 ~~~~~~~~~
 - Bug in :meth:`DatetimeIndex.diff` raising ``TypeError`` (:issue:`55080`)
+- Bug in :meth:`Index.__getitem__` returning wrong result for Arrow dtypes and negative stepsize (:issue:`55832`)
 - Bug in :meth:`Index.isin` raising for Arrow backed string and ``None`` value (:issue:`55821`)
 - Fix :func:`read_parquet` and :func:`read_feather` for `CVE-2023-47248 <https://www.cve.org/CVERecord?id=CVE-2023-47248>`__ (:issue:`55894`)
 

pandas/core/arrays/arrow/array.py

@@ -553,6 +553,17 @@ def __getitem__(self, item: PositionalIndexer):
             )
         # We are not an array indexer, so maybe e.g. a slice or integer
         # indexer. We dispatch to pyarrow.
+        if isinstance(item, slice):
+            if item.start == item.stop:
+                pass
+            elif (
+                item.stop is not None
+                and item.stop < -len(self)
+                and item.step is not None
+                and item.step < 0
+            ):
+                item = slice(item.start, None, item.step)
+
         value = self._pa_array[item]
         if isinstance(value, pa.ChunkedArray):
             return type(self)(value)

pandas/tests/indexes/object/test_indexing.py

@@ -4,6 +4,7 @@
 import pytest
 
 from pandas._libs.missing import is_matching_na
+import pandas.util._test_decorators as td
 
 import pandas as pd
 from pandas import Index
@@ -144,6 +145,13 @@ def test_get_indexer_non_unique_np_nats(self, np_nat_fixture, np_nat_fixture2):
 
 
 class TestSliceLocs:
+    @pytest.mark.parametrize(
+        "dtype",
+        [
+            "object",
+            pytest.param("string[pyarrow_numpy]", marks=td.skip_if_no("pyarrow")),
+        ],
+    )
     @pytest.mark.parametrize(
         "in_slice,expected",
         [
@@ -167,12 +175,23 @@ class TestSliceLocs:
             (pd.IndexSlice["m":"m":-1], ""),  # type: ignore[misc]
         ],
     )
-    def test_slice_locs_negative_step(self, in_slice, expected):
-        index = Index(list("bcdxy"))
+    def test_slice_locs_negative_step(self, in_slice, expected, dtype):
+        index = Index(list("bcdxy"), dtype=dtype)
 
         s_start, s_stop = index.slice_locs(in_slice.start, in_slice.stop, in_slice.step)
         result = index[s_start : s_stop : in_slice.step]
-        expected = Index(list(expected))
+        expected = Index(list(expected), dtype=dtype)
+        tm.assert_index_equal(result, expected)
+
+    @td.skip_if_no("pyarrow")
+    def test_slice_locs_negative_step_oob(self):
+        index = Index(list("bcdxy"), dtype="string[pyarrow_numpy]")
+
+        result = index[-10:5:1]
+        tm.assert_index_equal(result, index)
+
+        result = index[4:-10:-1]
+        expected = Index(list("yxdcb"), dtype="string[pyarrow_numpy]")
         tm.assert_index_equal(result, expected)
 
     def test_slice_locs_dup(self):