Backport PR #52630 on branch 2.0.x (REGR: pivot changing index name of input object) (#52636)

Backport PR #52630: REGR: pivot changing index name of input object

Co-authored-by: Patrick Hoefler <61934744+phofl@users.noreply.github.com>

Author: meeseeksmachine

doc/source/whatsnew/v2.0.1.rst

@@ -17,6 +17,7 @@ Fixed regressions
 - Fixed regression in :meth:`Series.describe` showing ``RuntimeWarning`` for extension dtype :class:`Series` with one element (:issue:`52515`)
 - Fixed regression in :meth:`DataFrame.sort_values` not resetting index when :class:`DataFrame` is already sorted and ``ignore_index=True`` (:issue:`52553`)
 - Fixed regression in :meth:`MultiIndex.isin` raising ``TypeError`` for ``Generator`` (:issue:`52568`)
+- Fixed regression in :meth:`DataFrame.pivot` changing :class:`Index` name of input object (:issue:`52629`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_201.bug_fixes:

pandas/core/reshape/pivot.py

@@ -508,6 +508,8 @@ def pivot(
     # If columns is None we will create a MultiIndex level with None as name
     # which might cause duplicated names because None is the default for
     # level names
+    data = data.copy(deep=False)
+    data.index = data.index.copy()
     data.index.names = [
         name if name is not None else lib.NoDefault for name in data.index.names
     ]

pandas/tests/reshape/test_pivot.py

@@ -2554,3 +2554,10 @@ def test_pivot_values_is_none(self):
         result = df.pivot(columns="b", values=None)
         expected = DataFrame(1, index=[0], columns=Index([2], name="b"))
         tm.assert_frame_equal(result, expected)
+
+    def test_pivot_not_changing_index_name(self):
+        # GH#52692
+        df = DataFrame({"one": ["a"], "two": 0, "three": 1})
+        expected = df.copy(deep=True)
+        df.pivot(index="one", columns="two", values="three")
+        tm.assert_frame_equal(df, expected)