GH ref

Author: jbrockmendel

doc/source/whatsnew/v3.0.0.rst

@@ -737,9 +737,9 @@ Other Deprecations
 - Deprecated allowing ``fill_value`` that cannot be held in the original dtype (excepting NA values for integer and bool dtypes) in :meth:`Series.shift` and :meth:`DataFrame.shift` (:issue:`53802`)
 - Deprecated backward-compatibility behavior for :meth:`DataFrame.select_dtypes` matching "str" dtype when ``np.object_`` is specified (:issue:`61916`)
 - Deprecated option "future.no_silent_downcasting", as it is no longer used. In a future version accessing this option will raise (:issue:`59502`)
+- Deprecated silent casting of non-datetime 'other' to datetime in :meth:`Series.combine_first` (:issue:`62931`)
 - Deprecated slicing on a :class:`Series` or :class:`DataFrame` with a :class:`DatetimeIndex` using a ``datetime.date`` object, explicitly cast to :class:`Timestamp` instead (:issue:`35830`)
 - Deprecated the 'inplace' keyword from :meth:`Resampler.interpolate`, as passing ``True`` raises ``AttributeError`` (:issue:`58690`)
-- Deprecated silent casting of non-datetime 'other' to datetime in :meth:`Series.combine_first` (:issue:`??`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_300.prior_deprecations:

pandas/core/series.py

@@ -3272,6 +3272,7 @@ def combine_first(self, other) -> Series:
             # TODO: try to match resos?
             other = to_datetime(other)
             warnings.warn(
+                # GH#62931
                 "Silently casting non-datetime 'other' to datetime in "
                 "Series.combine_first is deprecated and will be removed "
                 "in a future version. Explicitly cast before calling "

pandas/tests/series/methods/test_combine_first.py

@@ -78,6 +78,7 @@ def test_combine_first_dt64(self, unit):
         tm.assert_series_equal(rs, xp)
 
     def test_combine_first_dt64_casting_deprecation(self, unit):
+        # GH#62931
         s0 = to_datetime(Series(["2010", np.nan])).dt.as_unit(unit)
         s1 = Series([np.nan, "2011"])