Fix _convert_to_desired_timezone loses hightime accuracy for DST conversions

generated/nidaqmx/_time.py

@@ -22,8 +22,23 @@ def _convert_to_desired_timezone(
     # use ZoneInfo here to account for daylight savings
     if isinstance(tzinfo, ZoneInfo):
         localized_time = expected_time_utc.replace(tzinfo=tzinfo)
-        desired_expected_time = tzinfo.fromutc(localized_time)
-        return desired_expected_time  # type: ignore[return-value]  # https://github.com/ni/nidaqmx-python/issues/860
+        std_datetime_result = tzinfo.fromutc(localized_time)
+        femtosecond = getattr(expected_time_utc, "femtosecond", 0)
+        yoctosecond = getattr(expected_time_utc, "yoctosecond", 0)
+        desired_expected_time = ht_datetime(
+            std_datetime_result.year,
+            std_datetime_result.month,
+            std_datetime_result.day,
+            std_datetime_result.hour,
+            std_datetime_result.minute,
+            std_datetime_result.second,
+            std_datetime_result.microsecond,
+            femtosecond,
+            yoctosecond,
+            tzinfo=std_datetime_result.tzinfo,
+            fold=std_datetime_result.fold,
+        )
+        return desired_expected_time
 
     # if the tzinfo passed in is a timedelta function, then we don't need to consider daylight savings  # noqa: W505 - doc line too long (102 > 100 characters) (auto-generated noqa)
     elif tzinfo.utcoffset(None) is not None:

src/handwritten/_time.py

@@ -22,8 +22,23 @@ def _convert_to_desired_timezone(
     # use ZoneInfo here to account for daylight savings
     if isinstance(tzinfo, ZoneInfo):
         localized_time = expected_time_utc.replace(tzinfo=tzinfo)
-        desired_expected_time = tzinfo.fromutc(localized_time)
-        return desired_expected_time  # type: ignore[return-value]  # https://github.com/ni/nidaqmx-python/issues/860
+        std_datetime_result = tzinfo.fromutc(localized_time)
+        femtosecond = getattr(expected_time_utc, "femtosecond", 0)
+        yoctosecond = getattr(expected_time_utc, "yoctosecond", 0)
+        desired_expected_time = ht_datetime(
+            std_datetime_result.year,
+            std_datetime_result.month,
+            std_datetime_result.day,
+            std_datetime_result.hour,
+            std_datetime_result.minute,
+            std_datetime_result.second,
+            std_datetime_result.microsecond,
+            femtosecond,
+            yoctosecond,
+            tzinfo=std_datetime_result.tzinfo,
+            fold=std_datetime_result.fold,
+        )
+        return desired_expected_time
 
     # if the tzinfo passed in is a timedelta function, then we don't need to consider daylight savings  # noqa: W505 - doc line too long (102 > 100 characters) (auto-generated noqa)
     elif tzinfo.utcoffset(None) is not None:

tests/unit/test_lib_time.py

@@ -7,6 +7,7 @@
 from hightime import datetime as ht_datetime
 
 from nidaqmx._lib_time import AbsoluteTime as LibTimestamp
+from nidaqmx._time import _convert_to_desired_timezone
 from tests.unit._time_utils import (
     JAN_01_1850_DATETIME,
     JAN_01_1850_HIGHTIME,
@@ -106,6 +107,63 @@ def test___utc_datetime___convert_to_timestamp_with_dst___is_reversible(date):
     assert astimezone_date == roundtrip_dt
 
 
+@pytest.mark.parametrize(
+    "base_dt, femtosecond, subseconds",
+    [
+        (ht_datetime(2023, 3, 12, tzinfo=timezone.utc), 0, 0),
+        (ht_datetime(2023, 3, 12, tzinfo=timezone.utc), 1, 0x480F),
+        (ht_datetime(2023, 6, 1, tzinfo=timezone.utc), 0, 0),
+        (ht_datetime(2023, 6, 1, tzinfo=timezone.utc), 1, 0x480F),
+        (ht_datetime(2023, 11, 5, tzinfo=timezone.utc), 0, 0),
+        (ht_datetime(2023, 11, 5, tzinfo=timezone.utc), 1, 0x480F),
+    ],
+)
+def test___utc_datetime_with_femtoseconds___convert_to_timestamp_with_dst___is_reversible(
+    base_dt, femtosecond, subseconds
+):
+    target_timezone = ZoneInfo("America/Los_Angeles")
+    from_dt = base_dt.replace(femtosecond=femtosecond)
+    expected_la_time = _convert_to_desired_timezone(from_dt, target_timezone)
+
+    ts = LibTimestamp.from_datetime(from_dt)
+    roundtrip_dt = ts.to_datetime(tzinfo=target_timezone)
+
+    assert ts.msb == LibTimestamp.from_datetime(expected_la_time).msb
+    assert ts.lsb == subseconds
+    assert roundtrip_dt.microsecond == expected_la_time.microsecond
+    assert roundtrip_dt.femtosecond == expected_la_time.femtosecond
+    # The yoctosecond field may contain up to 1 NI-BTF tick of rounding error.
+    assert roundtrip_dt.yoctosecond <= 54210
+
+
+@pytest.mark.parametrize(
+    "base_dt, yoctosecond, subseconds",
+    [
+        (ht_datetime(2023, 3, 12, tzinfo=timezone.utc), 0, 0),
+        (ht_datetime(2023, 3, 12, tzinfo=timezone.utc), 54210, 1),
+        (ht_datetime(2023, 6, 1, tzinfo=timezone.utc), 0, 0),
+        (ht_datetime(2023, 6, 1, tzinfo=timezone.utc), 54210, 1),
+        (ht_datetime(2023, 11, 5, tzinfo=timezone.utc), 0, 0),
+        (ht_datetime(2023, 11, 5, tzinfo=timezone.utc), 54210, 1),
+    ],
+)
+def test___utc_datetime_with_yoctoseconds___convert_to_timestamp_with_dst___is_reversible(
+    base_dt, yoctosecond, subseconds
+):
+    target_timezone = ZoneInfo("America/Los_Angeles")
+    from_dt = base_dt.replace(yoctosecond=yoctosecond)
+    expected_la_time = _convert_to_desired_timezone(from_dt, target_timezone)
+
+    ts = LibTimestamp.from_datetime(from_dt)
+    roundtrip_dt = ts.to_datetime(tzinfo=target_timezone)
+
+    assert ts.msb == LibTimestamp.from_datetime(expected_la_time).msb
+    assert ts.lsb == subseconds
+    assert roundtrip_dt.microsecond == expected_la_time.microsecond
+    assert roundtrip_dt.femtosecond == expected_la_time.femtosecond
+    assert roundtrip_dt.yoctosecond == expected_la_time.yoctosecond
+
+
 @pytest.mark.parametrize(
     "datetime_cls, tzinfo, expected_offset",
     [