Avoid string types with ClassVar

As of Python 3.9.8, this does not work with Pydantic BaseModel, and
does not work in a way that causes the whole module to fail to
import.  See pydantic/pydantic#3401.

In general, Pydantic does not work well with string types as enabled
by from __future__ import annotations, which is why making that
feature the default has been delayed.  See
https://lwn.net/Articles/858576/ for more information.

Fix this by removing from __future__ import annotations from the
files using ClassVar and explicitly quote the type arguments that
contain forward references (all of which are outside the scope of
what Pydantic cares about).

python/lsst/daf/butler/core/logging.py

@@ -19,8 +19,6 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from __future__ import annotations
-
 __all__ = ("ButlerMDC", "ButlerLogRecords", "ButlerLogRecordHandler",
            "ButlerLogRecord", "JsonLogFormatter")
 
@@ -192,7 +190,7 @@ class Config:
         allow_mutation = False
 
     @classmethod
-    def from_record(cls, record: LogRecord) -> ButlerLogRecord:
+    def from_record(cls, record: LogRecord) -> "ButlerLogRecord":
         """Create a new instance from a `~logging.LogRecord`.
 
         Parameters
@@ -274,7 +272,7 @@ class ButlerLogRecords(BaseModel):
     _log_format: Optional[str] = PrivateAttr(None)
 
     @classmethod
-    def from_records(cls, records: Iterable[ButlerLogRecord]) -> ButlerLogRecords:
+    def from_records(cls, records: Iterable[ButlerLogRecord]) -> "ButlerLogRecords":
         """Create collection from iterable.
 
         Parameters
@@ -285,7 +283,7 @@ def from_records(cls, records: Iterable[ButlerLogRecord]) -> ButlerLogRecords:
         return cls(__root__=list(records))
 
     @classmethod
-    def from_file(cls, filename: str) -> ButlerLogRecords:
+    def from_file(cls, filename: str) -> "ButlerLogRecords":
         """Read records from file.
 
         Parameters
@@ -354,7 +352,7 @@ def _detect_model(startdata: Union[str, bytes]) -> bool:
         return False
 
     @classmethod
-    def from_stream(cls, stream: IO) -> ButlerLogRecords:
+    def from_stream(cls, stream: IO) -> "ButlerLogRecords":
         """Read records from I/O stream.
 
         Parameters
@@ -391,7 +389,7 @@ def from_stream(cls, stream: IO) -> ButlerLogRecords:
         return cls.from_records(records)
 
     @classmethod
-    def from_raw(cls, serialized: Union[str, bytes]) -> ButlerLogRecords:
+    def from_raw(cls, serialized: Union[str, bytes]) -> "ButlerLogRecords":
         """Parse raw serialized form and return records.
 
         Parameters
@@ -464,7 +462,7 @@ def __iter__(self) -> Iterator[ButlerLogRecord]:  # type: ignore
     def __setitem__(self, index: int, value: Record) -> None:
         self.__root__[index] = self._validate_record(value)
 
-    def __getitem__(self, index: Union[slice, int]) -> Union[ButlerLogRecords, ButlerLogRecord]:
+    def __getitem__(self, index: Union[slice, int]) -> "Union[ButlerLogRecords, ButlerLogRecord]":
         # Handles slices and returns a new collection in that
         # case.
         item = self.__root__[index]

python/lsst/daf/butler/core/serverModels.py

@@ -19,8 +19,6 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from __future__ import annotations
-
 __all__ = (
     "QueryDatasetsModel",
     "QueryDataIdsModel",
@@ -116,7 +114,7 @@ def expression(self) -> Any:
         return expression
 
     @classmethod
-    def from_expression(cls, expression: Any) -> ExpressionQueryParameter:
+    def from_expression(cls, expression: Any) -> "ExpressionQueryParameter":
         """Convert a standard dataset type expression to wire form."""
         if expression is ...:
             return cls()