Add type specification to Marshmallow Field classes

Marshmallow 4.0 makes Field generic taking a type argument

tildes/tildes/schemas/fields.py

@@ -22,7 +22,7 @@ from tildes.lib.string import simplify_string
 DataType = Optional[Mapping[str, Any]]
 
 
-class Enum(Field):
+class Enum(Field[enum.Enum]):
     """Field for a native Python Enum (or subclasses)."""
 
     def __init__(
@@ -34,9 +34,12 @@ class Enum(Field):
         self._enum_class = enum_class
 
     def _serialize(
-        self, value: enum.Enum, attr: str | None, obj: object, **kwargs: Any
-    ) -> str:
+        self, value: enum.Enum | None, attr: str | None, obj: object, **kwargs: Any
+    ) -> str | None:
         """Serialize the enum value - lowercase version of its name."""
+        if value is None:
+            return None
+
         return value.name.lower()
 
     def _deserialize(
@@ -64,7 +67,7 @@ class ID36(String):
         super().__init__(validate=Regexp(ID36_REGEX), **kwargs)
 
 
-class ShortTimePeriod(Field):
+class ShortTimePeriod(Field[Optional[SimpleHoursPeriod]]):
     """Field for short time period strings like "4h" and "2d".
 
     Also supports the string "all" which will be converted to None.
@@ -100,7 +103,7 @@ class ShortTimePeriod(Field):
         return value.as_short_form()
 
 
-class Markdown(Field):
+class Markdown(Field[str]):
     """Field for markdown strings (comments, text topic, messages, etc.)."""
 
     DEFAULT_MAX_LENGTH = 50000
@@ -132,13 +135,13 @@ class Markdown(Field):
         return value
 
     def _serialize(
-        self, value: str, attr: str | None, obj: object, **kwargs: Any
-    ) -> str:
+        self, value: str | None, attr: str | None, obj: object, **kwargs: Any
+    ) -> str | None:
         """Serialize the value (no-op in this case)."""
         return value
 
 
-class SimpleString(Field):
+class SimpleString(Field[str]):
     """Field for "simple" strings, suitable for uses like subject, title, etc.
 
     These strings should generally not contain any special formatting (such as
@@ -169,13 +172,13 @@ class SimpleString(Field):
         return simplify_string(value)
 
     def _serialize(
-        self, value: str, attr: str | None, obj: object, **kwargs: Any
-    ) -> str:
+        self, value: str | None, attr: str | None, obj: object, **kwargs: Any
+    ) -> str | None:
         """Serialize the value (no-op in this case)."""
         return value
 
 
-class Ltree(Field):
+class Ltree(Field[sqlalchemy_utils.Ltree]):
     """Field for postgresql ltree type."""
 
     # note that this regex only checks whether all of the chars are individually valid,