From 371334a8ac575769b1246f3e9966d0850e4a9d3a Mon Sep 17 00:00:00 2001
From: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>
Date: Tue, 20 Feb 2024 16:10:16 -0800
Subject: [PATCH 1/4] PERF: Return RangeIndex from RangeIndex.join when
 possible

---
 pandas/core/indexes/range.py           | 17 +++++++++++++++++
 pandas/tests/extension/base/methods.py |  2 +-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/pandas/core/indexes/range.py b/pandas/core/indexes/range.py
index 2dd6f672eca45..a82208fb49f66 100644
--- a/pandas/core/indexes/range.py
+++ b/pandas/core/indexes/range.py
@@ -53,6 +53,7 @@
     from pandas._typing import (
         Axis,
         Dtype,
+        JoinHow,
         NaPosition,
         Self,
         npt,
@@ -1016,6 +1017,22 @@ def _concat(self, indexes: list[Index], name: Hashable) -> Index:
         # In this case return an empty range index.
         return RangeIndex(_empty_range, name=name)
 
+    def _wrap_join_result(
+        self,
+        joined,
+        other,
+        lidx: npt.NDArray[np.intp] | None,
+        ridx: npt.NDArray[np.intp] | None,
+        how: JoinHow,
+    ) -> tuple[Self, npt.NDArray[np.intp] | None, npt.NDArray[np.intp] | None]:
+        join_index, lidx, ridx = super()._wrap_join_result(
+            joined, other, lidx, ridx, how
+        )
+        maybe_ri = self._shallow_copy(join_index._values)
+        if isinstance(maybe_ri, type(self)):
+            return maybe_ri, lidx, ridx
+        return join_index, lidx, ridx
+
     def __len__(self) -> int:
         """
         return the length of the RangeIndex
diff --git a/pandas/tests/extension/base/methods.py b/pandas/tests/extension/base/methods.py
index c803a8113b4a4..20f564d8f32a2 100644
--- a/pandas/tests/extension/base/methods.py
+++ b/pandas/tests/extension/base/methods.py
@@ -397,7 +397,7 @@ def test_combine_first(self, data):
         b = pd.Series(data[2:5], index=[2, 3, 4])
         result = a.combine_first(b)
         expected = pd.Series(data[:5])
-        tm.assert_series_equal(result, expected)
+        tm.assert_series_equal(result, expected, check_index_type=True)
 
     @pytest.mark.parametrize("frame", [True, False])
     @pytest.mark.parametrize(

From f5115ac4e039c88df1ef03e45d1cf2ffaf4e3be0 Mon Sep 17 00:00:00 2001
From: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>
Date: Tue, 20 Feb 2024 16:18:23 -0800
Subject: [PATCH 2/4] Add test

---
 pandas/tests/indexes/ranges/test_join.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pandas/tests/indexes/ranges/test_join.py b/pandas/tests/indexes/ranges/test_join.py
index 682b5c8def9ff..729b4d4aaeeb6 100644
--- a/pandas/tests/indexes/ranges/test_join.py
+++ b/pandas/tests/indexes/ranges/test_join.py
@@ -175,3 +175,9 @@ def test_join_self(self, join_type):
         index = RangeIndex(start=0, stop=20, step=2)
         joined = index.join(index, how=join_type)
         assert index is joined
+
+
+def test_join_overlap_returns_rangeindex():
+    result = RangeIndex(3).join(RangeIndex(2, 5), how="outer")
+    expected = RangeIndex(5)
+    tm.assert_index_equal(result, expected, exact=True)

From 1a19260e6fd1bd9bb5e6ff9caebeeab86017d86f Mon Sep 17 00:00:00 2001
From: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>
Date: Tue, 20 Feb 2024 16:19:19 -0800
Subject: [PATCH 3/4] Add whatsnew

---
 doc/source/whatsnew/v3.0.0.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/source/whatsnew/v3.0.0.rst b/doc/source/whatsnew/v3.0.0.rst
index a77e93c4ab4be..441859a764c27 100644
--- a/doc/source/whatsnew/v3.0.0.rst
+++ b/doc/source/whatsnew/v3.0.0.rst
@@ -165,6 +165,7 @@ Removal of prior version deprecations/changes
 
 Performance improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
+- :meth:`RangeIndex.join` returns a :class:`RangeIndex` instead of a :class:`Index` when appending values that could continue the :class:`RangeIndex` (:issue:`57467`)
 - Performance improvement in :meth:`DataFrame.join` for sorted but non-unique indexes (:issue:`56941`)
 - Performance improvement in :meth:`DataFrame.join` when left and/or right are non-unique and ``how`` is ``"left"``, ``"right"``, or ``"inner"`` (:issue:`56817`)
 - Performance improvement in :meth:`DataFrame.join` with ``how="left"`` or ``how="right"`` and ``sort=True`` (:issue:`56919`)

From 3aa72f9d4e3ab9d8425712d6f03ebd12d97904a5 Mon Sep 17 00:00:00 2001
From: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>
Date: Tue, 20 Feb 2024 16:19:42 -0800
Subject: [PATCH 4/4] Change number

---
 doc/source/whatsnew/v3.0.0.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v3.0.0.rst b/doc/source/whatsnew/v3.0.0.rst
index 441859a764c27..63b0442a293ff 100644
--- a/doc/source/whatsnew/v3.0.0.rst
+++ b/doc/source/whatsnew/v3.0.0.rst
@@ -165,7 +165,7 @@ Removal of prior version deprecations/changes
 
 Performance improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
-- :meth:`RangeIndex.join` returns a :class:`RangeIndex` instead of a :class:`Index` when appending values that could continue the :class:`RangeIndex` (:issue:`57467`)
+- :meth:`RangeIndex.join` returns a :class:`RangeIndex` instead of a :class:`Index` when appending values that could continue the :class:`RangeIndex` (:issue:`57543`)
 - Performance improvement in :meth:`DataFrame.join` for sorted but non-unique indexes (:issue:`56941`)
 - Performance improvement in :meth:`DataFrame.join` when left and/or right are non-unique and ``how`` is ``"left"``, ``"right"``, or ``"inner"`` (:issue:`56817`)
 - Performance improvement in :meth:`DataFrame.join` with ``how="left"`` or ``how="right"`` and ``sort=True`` (:issue:`56919`)