Backport PR #52982 on branch 2.0.x (BUG: Have non nano rounding noop …

…return copy) (#53004)

Backport PR #52982: BUG: Have non nano rounding noop return copy

Co-authored-by: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>

pandas/core/arrays/datetimelike.py

@@ -2010,7 +2010,7 @@ def _round(self, freq, mode, ambiguous, nonexistent):
         nanos = delta_to_nanoseconds(offset, self._creso)
         if nanos == 0:
             # GH 52761
-            return self
+            return self.copy()
         result_i8 = round_nsint64(values, mode, nanos)
         result = self._maybe_mask_results(result_i8, fill_value=iNaT)
         result = result.view(self._ndarray.dtype)

pandas/tests/series/accessors/test_dt_accessor.py

@@ -392,6 +392,8 @@ def test_dt_round_nonnano_higher_resolution_no_op(self, freq):
         result = ser.dt.round(freq)
         tm.assert_series_equal(result, expected)
 
+        assert not np.shares_memory(ser.array._ndarray, result.array._ndarray)
+
     def test_dt_namespace_accessor_categorical(self):
         # GH 19468
         dti = DatetimeIndex(["20171111", "20181212"]).repeat(2)