Make BaseDescriptor generic wrt the owning class

src/labthings_fastapi/actions.py

@@ -159,8 +159,8 @@
         """
         try:
             blobdata_to_url_ctx.get()
         except LookupError as e:
             raise NoBlobManagerError(
                 "An invocation output has been requested from a api route that "
                 "doesn't have a BlobIOContextDep dependency. This dependency is needed "
                 " for blobs to identify their url."
@@ -247,10 +247,10 @@
         ]
         # The line below confuses MyPy because self.action **evaluates to** a Descriptor
         # object (i.e. we don't call __get__ on the descriptor).
-        return self.action.invocation_model(  # type: ignore[call-overload]
+        return self.action.invocation_model(  # type: ignore[attr-defined]
             status=self.status,
             id=self.id,
-            action=self.thing.path + self.action.name,  # type: ignore[call-overload]
+            action=self.thing.path + self.action.name,  # type: ignore[attr-defined]
             href=href,
             timeStarted=self._start_time,
             timeCompleted=self._end_time,
@@ -290,7 +290,7 @@
         """
         # self.action evaluates to an ActionDescriptor. This confuses mypy,
         # which thinks we are calling ActionDescriptor.__get__.
-        action: ActionDescriptor = self.action  # type: ignore[call-overload]
+        action: ActionDescriptor = self.action  # type: ignore[assignment]
         logger = self.thing.logger
         # The line below saves records matching our ID to ``self._log``
         add_thing_log_destination(self.id, self._log)
@@ -411,8 +411,8 @@
         :param id: the unique ID of the action to retrieve.
         :return: the `.Invocation` object.
         """
         with self._invocations_lock:
             return self._invocations[id]
 
     def list_invocations(
         self,
@@ -445,10 +445,7 @@
             i.response(request=request)
             for i in self.invocations
             if thing is None or i.thing == thing
-            if action is None or i.action == action  # type: ignore[call-overload]
-            # i.action evaluates to an ActionDescriptor, which confuses mypy - it
-            # thinks we are calling ActionDescriptor.__get__ but this isn't ever
-            # called.
+            if action is None or i.action == action
         ]
 
     def expire_invocations(self) -> None:
@@ -539,8 +536,8 @@
             with self._invocations_lock:
                 try:
                     invocation: Any = self._invocations[id]
                 except KeyError as e:
                     raise HTTPException(
                         status_code=404,
                         detail="No action invocation found with ID {id}",
                     ) from e
@@ -553,7 +550,7 @@
                     invocation.output.response
                 ):
                     # TODO: honour "accept" header
                     return invocation.output.response()
                 return invocation.output
 
         @app.delete(
@@ -578,8 +575,8 @@
             with self._invocations_lock:
                 try:
                     invocation: Any = self._invocations[id]
                 except KeyError as e:
                     raise HTTPException(
                         status_code=404,
                         detail="No action invocation found with ID {id}",
                     ) from e
@@ -626,7 +623,7 @@
 
 
 class ActionDescriptor(
-    BaseDescriptor[Callable[ActionParams, ActionReturn]],
+    BaseDescriptor[OwnerT, Callable[ActionParams, ActionReturn]],
     Generic[ActionParams, ActionReturn, OwnerT],
 ):
     """Wrap actions to enable them to be run over HTTP.
@@ -691,7 +688,7 @@
         )
         self.invocation_model.__name__ = f"{name}_invocation"
 
-    def __set_name__(self, owner: type[Thing], name: str) -> None:
+    def __set_name__(self, owner: type[OwnerT], name: str) -> None:
         """Ensure the action name matches the function name.
 
         It's assumed in a few places that the function name and the
@@ -704,12 +701,12 @@
         """
         super().__set_name__(owner, name)
         if self.name != self.func.__name__:
             raise ValueError(
                 f"Action name '{self.name}' does not match function name "
                 f"'{self.func.__name__}'",
             )
 
-    def instance_get(self, obj: Thing) -> Callable[ActionParams, ActionReturn]:
+    def instance_get(self, obj: OwnerT) -> Callable[ActionParams, ActionReturn]:
         """Return the function, bound to an object as for a normal method.
 
         This currently doesn't validate the arguments, though it may do so
@@ -721,10 +718,7 @@
             descriptor.
         :return: the action function, bound to ``obj``.
         """
-        # `obj` should be of type `OwnerT`, but `BaseDescriptor` currently
-        # isn't generic in the type of the owning Thing, so we can't express
-        # that here.
-        return partial(self.func, obj)  # type: ignore[arg-type]
+        return partial(self.func, obj)
 
     def _observers_set(self, obj: Thing) -> WeakSet:
         """Return a set used to notify changes.
@@ -853,14 +847,14 @@
         try:
             responses[200]["model"] = self.output_model
             pass
         except AttributeError:
             print(f"Failed to generate response model for action {self.name}")
         # Add an additional media type if we may return a file
         if hasattr(self.output_model, "media_type"):
             responses[200]["content"][self.output_model.media_type] = {}
         # Now we can add the endpoint to the app.
         if thing.path is None:
             raise NotConnectedToServerError(
                 "Can't add the endpoint without thing.path!"
             )
         app.post(
@@ -908,7 +902,7 @@
         """
         path = path or thing.path
         if path is None:
             raise NotConnectedToServerError("Can't generate forms without a path!")
         forms = [
             Form[ActionOp](href=path + self.name, op=[ActionOp.invokeaction]),
         ]

src/labthings_fastapi/base_descriptor.py

@@ -26,6 +26,12 @@
 Value = TypeVar("Value")
 """The value returned by the descriptor, when called on an instance."""
 
+Owner = TypeVar("Owner", bound="Thing")
+"""A Thing subclass that owns a descriptor."""
+
+Descriptor = TypeVar("Descriptor", bound="BaseDescriptor")
+"""The type of a descriptor that's referred to by a `BaseDescriptorInfo` object."""
+
 
 class DescriptorNotAddedToClassError(RuntimeError):
     """Descriptor has not yet been added to a class.
@@ -138,7 +144,7 @@ def _set_prop4(self, val):
     """
 
 
-class BaseDescriptor(Generic[Value]):
+class BaseDescriptor(Generic[Owner, Value]):
     r"""A base class for descriptors in LabThings-FastAPI.
 
     This class implements several behaviours common to descriptors in LabThings:
@@ -184,7 +190,7 @@ def __init__(self) -> None:
         self._set_name_called: bool = False
         self._owner_name: str = ""
 
-    def __set_name__(self, owner: type[Thing], name: str) -> None:
+    def __set_name__(self, owner: type[Owner], name: str) -> None:
         r"""Take note of the name to which the descriptor is assigned.
 
         This is called when the descriptor is assigned to an attribute of a class.
@@ -306,12 +312,12 @@ def description(self) -> str | None:
     # I have ignored D105 (missing docstrings) on the overloads - these should not
     # exist on @overload definitions.
     @overload
-    def __get__(self, obj: Thing, type: type | None = None) -> Value: ...
+    def __get__(self, obj: Owner, type: type | None = None) -> Value: ...
 
     @overload
     def __get__(self, obj: None, type: type) -> Self: ...
 
-    def __get__(self, obj: Thing | None, type: type | None = None) -> Value | Self:
+    def __get__(self, obj: Owner | None, type: type | None = None) -> Value | Self:
         """Return the value or the descriptor, as per `property`.
 
         If ``obj`` is ``None`` (i.e. the descriptor is accessed as a class attribute),
@@ -331,7 +337,7 @@ def __get__(self, obj: Thing | None, type: type | None = None) -> Value | Self:
             return self.instance_get(obj)
         return self
 
-    def instance_get(self, obj: Thing) -> Value:
+    def instance_get(self, obj: Owner) -> Value:
         """Return the value of the descriptor.
 
         This method is called from ``__get__`` if the descriptor is accessed as an
@@ -357,7 +363,7 @@ def instance_get(self, obj: Thing) -> Value:
         )
 
 
-class FieldTypedBaseDescriptor(Generic[Value], BaseDescriptor[Value]):
+class FieldTypedBaseDescriptor(Generic[Owner, Value], BaseDescriptor[Owner, Value]):
     """A BaseDescriptor that determines its type like a dataclass field."""
 
     def __init__(self) -> None:
@@ -379,7 +385,7 @@ def __init__(self) -> None:
         # the object on which they are defined, to provide the context for the
         # evaluation.
 
-    def __set_name__(self, owner: type[Thing], name: str) -> None:
+    def __set_name__(self, owner: type[Owner], name: str) -> None:
         r"""Take note of the name and type.
 
         This function is where we determine the type of the property. It may
@@ -431,7 +437,7 @@ class MyThing(Thing):
             # __orig_class__ is set on generic classes when they are instantiated
             # with a subscripted type. It is not available during __init__, which
             # is why we check for it here.
-            self._type = typing.get_args(self.__orig_class__)[0]
+            self._type = typing.get_args(self.__orig_class__)[1]
             if isinstance(self._type, typing.ForwardRef):
                 raise MissingTypeError(
                     f"{owner}.{name} is a subscripted descriptor, where the "