Reject non-ZoneInfo tzinfo on Tz write; document read-side tzdata fallback

Author: vgvoleg

docs/types.rst

@@ -202,11 +202,12 @@ Date and time
 
    ``TzDate``, ``TzDatetime`` and ``TzTimestamp`` carry an IANA timezone name.
    On write, pass a tz-aware ``datetime.datetime`` whose ``tzinfo`` is a
-   ``zoneinfo.ZoneInfo`` — its local wall-clock and zone name are stored. On
-   read, they are returned as tz-aware ``datetime.datetime`` values (``TzDate``
-   at midnight in that zone). When the matching
-   ``with_native_*_in_result_sets`` option is disabled, the raw
-   ``"<value>,<zone>"`` string is returned instead.
+   ``zoneinfo.ZoneInfo`` — its local wall-clock and zone name are stored; any
+   other ``tzinfo`` raises ``ValueError``. On read, they are returned as
+   tz-aware ``datetime.datetime`` values (``TzDate`` at midnight in that zone),
+   or the raw ``"<value>,<zone>"`` string when the matching
+   ``with_native_*_in_result_sets`` option is disabled or the zone cannot be
+   loaded from the system timezone database (e.g. no ``tzdata`` installed).
 
 Other
 ^^^^^

tests/query/test_types.py

@@ -190,10 +190,11 @@ def test_type_str_repr(driver_sync, value, ydb_type, str_repr, result_value):
 
 
 def test_tz_conversion_fallbacks():
-    # Defensive branches a real-server round-trip never reaches: an unresolvable
-    # zone name is passed through as raw text, and a non-ZoneInfo tzinfo falls
-    # back to its str() name.
+    # Edge branches a real-server round-trip never reaches: an unresolvable zone
+    # name is passed through as raw text on read, and a non-ZoneInfo tzinfo is
+    # rejected on write.
     from ydb.types import _parse_tz, _tz_name
 
     assert _parse_tz("2019-09-16T18:24:00,Not/AZone") == "2019-09-16T18:24:00,Not/AZone"
-    assert _tz_name(datetime(2019, 9, 17, tzinfo=timezone.utc)) == "UTC"
+    with pytest.raises(ValueError):
+        _tz_name(datetime(2019, 9, 17, tzinfo=tz4h))

ydb/types.py

@@ -83,9 +83,9 @@ def _to_datetime64(pb: ydb_value_pb2.Value, value: typing.Union[datetime, int])
 
 def _tz_name(value: datetime) -> str:
     tz = value.tzinfo
-    if isinstance(tz, ZoneInfo):
-        return tz.key
-    return str(tz)
+    if not isinstance(tz, ZoneInfo):
+        raise ValueError(f"Tz types require a datetime whose tzinfo is a zoneinfo.ZoneInfo, got {tz!r}")
+    return tz.key
 
 
 def _parse_tz(value: str) -> typing.Union[datetime, str]: