Avoid warning in DateOffset addition (#56029)

Author: jbrockmendel

pandas/_libs/tslibs/offsets.pyx

@@ -101,12 +101,6 @@ cdef bint is_tick_object(object obj):
     return isinstance(obj, Tick)
 
 
-cdef datetime _as_datetime(datetime obj):
-    if isinstance(obj, _Timestamp):
-        return obj.to_pydatetime()
-    return obj
-
-
 cdef bint _is_normalized(datetime dt):
     if dt.hour != 0 or dt.minute != 0 or dt.second != 0 or dt.microsecond != 0:
         # Regardless of whether dt is datetime vs Timestamp
@@ -1322,7 +1316,7 @@ cdef class RelativeDeltaOffset(BaseOffset):
         if self._use_relativedelta:
             if isinstance(other, _Timestamp):
                 other_nanos = other.nanosecond
-            other = _as_datetime(other)
+                other = other.to_pydatetime(warn=False)
 
         if len(self.kwds) > 0:
             tzinfo = getattr(other, "tzinfo", None)

pandas/core/arrays/datetimes.py

@@ -2790,13 +2790,7 @@ def _generate_range(
                 break
 
             # faster than cur + offset
-            with warnings.catch_warnings():
-                warnings.filterwarnings(
-                    "ignore",
-                    "Discarding nonzero nanoseconds in conversion",
-                    category=UserWarning,
-                )
-                next_date = offset._apply(cur)
+            next_date = offset._apply(cur)
             next_date = next_date.as_unit(unit)
             if next_date <= cur:
                 raise ValueError(f"Offset {offset} did not increment date")
@@ -2811,13 +2805,7 @@ def _generate_range(
                 break
 
             # faster than cur + offset
-            with warnings.catch_warnings():
-                warnings.filterwarnings(
-                    "ignore",
-                    "Discarding nonzero nanoseconds in conversion",
-                    category=UserWarning,
-                )
-                next_date = offset._apply(cur)
+            next_date = offset._apply(cur)
             next_date = next_date.as_unit(unit)
             if next_date >= cur:
                 raise ValueError(f"Offset {offset} did not decrement date")

pandas/tests/tseries/offsets/test_offsets.py

@@ -229,18 +229,9 @@ def _check_offsetfunc_works(self, offset, funcname, dt, expected, normalize=Fals
         assert result == expected
 
         # see gh-14101
-        exp_warning = None
         ts = Timestamp(dt) + Nano(5)
-
-        if (
-            type(offset_s).__name__ == "DateOffset"
-            and (funcname in ["apply", "_apply"] or normalize)
-            and ts.nanosecond > 0
-        ):
-            exp_warning = UserWarning
-
         # test nanosecond is preserved
-        with tm.assert_produces_warning(exp_warning):
+        with tm.assert_produces_warning(None):
             result = func(ts)
 
         assert isinstance(result, Timestamp)
@@ -274,18 +265,9 @@ def _check_offsetfunc_works(self, offset, funcname, dt, expected, normalize=Fals
             assert result == expected_localize
 
             # see gh-14101
-            exp_warning = None
             ts = Timestamp(dt, tz=tz) + Nano(5)
-
-            if (
-                type(offset_s).__name__ == "DateOffset"
-                and (funcname in ["apply", "_apply"] or normalize)
-                and ts.nanosecond > 0
-            ):
-                exp_warning = UserWarning
-
             # test nanosecond is preserved
-            with tm.assert_produces_warning(exp_warning):
+            with tm.assert_produces_warning(None):
                 result = func(ts)
             assert isinstance(result, Timestamp)
             if normalize is False:
@@ -1010,6 +992,14 @@ def test_dateoffset_add_sub_timestamp_with_nano():
     result = offset + ts
     assert result == expected
 
+    offset2 = DateOffset(minutes=2, nanoseconds=9, hour=1)
+    assert offset2._use_relativedelta
+    with tm.assert_produces_warning(None):
+        # no warning about Discarding nonzero nanoseconds
+        result2 = ts + offset2
+    expected2 = Timestamp("1970-01-01 01:02:00.000000013")
+    assert result2 == expected2
+
 
 @pytest.mark.parametrize(
     "attribute",