Replace some isinstance calls with TypeGuard.

These aren't as ergonomic as I'd hoped because of
https://www.python.org/dev/peps/pep-0647/#narrowing-of-implicit-self-and-cls-parameters.

I added a decorator `@self_type_guard` so we can avoid needing to import
the descendent types in the typeguard implementation (which wouldn't fix
any circular imports, just move them).

game/ato/flightstate/inflight.py

@@ -12,7 +12,6 @@ from game.ato.flightwaypoint import FlightWaypoint
 from game.ato.flightwaypointtype import FlightWaypointType
 from game.ato.starttype import StartType
 from game.utils import Distance, LBS_TO_KG, Speed, pairwise
-from gen.flights.flightplan import LoiterFlightPlan
 
 if TYPE_CHECKING:
     from game.ato.flight import Flight
@@ -44,7 +43,7 @@ class InFlight(FlightState, ABC):
             # at a loiter point but still a regular InFlight (Loiter overrides this
             # method) that means we're traveling from the loiter point but no longer
             # loitering.
-            assert isinstance(self.flight.flight_plan, LoiterFlightPlan)
+            assert self.flight.flight_plan.is_loiter(self.flight.flight_plan)
             travel_time -= self.flight.flight_plan.hold_duration
         return travel_time
 

game/ato/flightstate/loiter.py

@@ -8,7 +8,6 @@ from dcs import Point
 from game.ato.flightstate import FlightState, InFlight
 from game.ato.flightstate.navigating import Navigating
 from game.utils import Distance, Speed
-from gen.flights.flightplan import LoiterFlightPlan
 
 if TYPE_CHECKING:
     from game.ato.flight import Flight
@@ -17,7 +16,7 @@ if TYPE_CHECKING:
 
 class Loiter(InFlight):
     def __init__(self, flight: Flight, settings: Settings, waypoint_index: int) -> None:
-        assert isinstance(flight.flight_plan, LoiterFlightPlan)
+        assert flight.flight_plan.is_loiter(flight.flight_plan)
         self.hold_duration = flight.flight_plan.hold_duration
         super().__init__(flight, settings, waypoint_index)
 

game/ato/flightstate/racetrack.py

@@ -10,7 +10,6 @@ from game.ato import FlightType
 from game.ato.flightstate import InFlight
 from game.threatzones import ThreatPoly
 from game.utils import Distance, Speed, dcs_to_shapely_point
-from gen.flights.flightplan import PatrollingFlightPlan
 
 if TYPE_CHECKING:
     from game.ato.flight import Flight
@@ -19,7 +18,7 @@ if TYPE_CHECKING:
 
 class RaceTrack(InFlight):
     def __init__(self, flight: Flight, settings: Settings, waypoint_index: int) -> None:
-        assert isinstance(flight.flight_plan, PatrollingFlightPlan)
+        assert flight.flight_plan.is_patrol(flight.flight_plan)
         self.patrol_duration = flight.flight_plan.patrol_duration
         super().__init__(flight, settings, waypoint_index)
         self.commit_region = LineString(

game/typeguard.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from typing import Callable, TypeGuard, TypeVar
+
+SelfT = TypeVar("SelfT")
+BaseT = TypeVar("BaseT")
+GuardT = TypeVar("GuardT")
+
+
+def self_type_guard(
+    f: Callable[[SelfT, BaseT], TypeGuard[GuardT]]
+) -> Callable[[SelfT, BaseT], TypeGuard[GuardT]]:
+    def decorator(s: SelfT, arg: BaseT) -> TypeGuard[GuardT]:
+        if id(s) != id(arg):
+            raise ValueError(
+                "self type guards must be called with self as the argument"
+            )
+        return f(s, arg)
+
+    return decorator