Fix several cases of wrongly using broken runways.

The usual symptom here was the game breaking when a carrier is
destroyed. The carrier would no longer be operational but missions would
be assigned there that could not generate flight plans.

gen/flights/ai_flight_planner.py

@@ -162,7 +162,7 @@ class AircraftAllocator:
         self, flight: ProposedFlight, task: FlightType
     ) -> Optional[Tuple[ControlPoint, Squadron]]:
         types = aircraft_for_task(task)
-        airfields_in_range = self.closest_airfields.airfields_within(
+        airfields_in_range = self.closest_airfields.operational_airfields_within(
             flight.max_distance
         )
 
@@ -258,7 +258,9 @@ class PackageBuilder:
         self, aircraft: Type[FlyingType], arrival: ControlPoint
     ) -> Optional[ControlPoint]:
         divert_limit = nautical_miles(150)
-        for airfield in self.closest_airfields.airfields_within(divert_limit):
+        for airfield in self.closest_airfields.operational_airfields_within(
+            divert_limit
+        ):
             if airfield.captured != self.is_player:
                 continue
             if airfield == arrival:
@@ -467,8 +469,10 @@ class ObjectiveFinder:
                 # Off-map spawn locations don't need protection.
                 continue
             airfields_in_proximity = self.closest_airfields_to(cp)
-            airfields_in_threat_range = airfields_in_proximity.airfields_within(
-                self.AIRFIELD_THREAT_RANGE
+            airfields_in_threat_range = (
+                airfields_in_proximity.operational_airfields_within(
+                    self.AIRFIELD_THREAT_RANGE
+                )
             )
             for airfield in airfields_in_threat_range:
                 if not airfield.is_friendly(self.is_player):

gen/flights/closestairfields.py

@@ -27,17 +27,35 @@ class ClosestAirfields:
     def operational_airfields(self) -> Iterator[ControlPoint]:
         return (c for c in self.closest_airfields if c.runway_is_operational())
 
-    def airfields_within(self, distance: Distance) -> Iterator[ControlPoint]:
+    def _airfields_within(
+        self, distance: Distance, operational: bool
+    ) -> Iterator[ControlPoint]:
+        airfields = (
+            self.operational_airfields if operational else self.closest_airfields
+        )
+        for cp in airfields:
+            if cp.distance_to(self.target) < distance.meters:
+                yield cp
+            else:
+                break
+
+    def operational_airfields_within(
+        self, distance: Distance
+    ) -> Iterator[ControlPoint]:
         """Iterates over all airfields within the given range of the target.
 
         Note that this iterates over *all* airfields, not just friendly
         airfields.
         """
-        for cp in self.closest_airfields:
-            if cp.distance_to(self.target) < distance.meters:
-                yield cp
-            else:
-                break
+        return self._airfields_within(distance, operational=True)
+
+    def all_airfields_within(self, distance: Distance) -> Iterator[ControlPoint]:
+        """Iterates over all airfields within the given range of the target.
+
+        Note that this iterates over *all* airfields, not just friendly
+        airfields.
+        """
+        return self._airfields_within(distance, operational=False)
 
 
 class ObjectiveDistanceCache:

gen/flights/flightplan.py

@@ -1807,7 +1807,7 @@ class FlightPlanBuilder:
         # We'll always have a package, but if this is being planned via the UI
         # it could be the first flight in the package.
         if not self.package.flights:
-            raise RuntimeError(
+            raise PlanningError(
                 "Cannot determine source airfield for package with no flights"
             )
 
@@ -1819,4 +1819,4 @@ class FlightPlanBuilder:
             for flight in self.package.flights:
                 if flight.departure == airfield:
                     return airfield
-        raise RuntimeError("Could not find any airfield assigned to this package")
+        raise PlanningError("Could not find any airfield assigned to this package")