Should AStarPathPlanning.get_distance() return 0.0 when no path exists?

[ToB213]

Currently, AStarPathPlanning.get_distance() returns 0.0 when no path exists between two entities.

When the destination is unreachable, get_path() returns an empty list:

return []

However, get_distance() initializes the distance to 0.0 and sums the distances along the returned path:

path: list[EntityID] = self.get_path(from_entity_id, to_entity_id)
distance: float = 0.0
for i in range(len(path) - 1):
    distance += self.distance(path[i], path[i + 1])
return distance

As a result, get_distance() returns 0.0 when get_path() returns an empty list.

This makes an unreachable destination indistinguishable from being at the destination itself (a true zero-distance case). It can also cause issues such as selecting an unreachable target as the nearest one when selecting targets based on path distance.

Would it be better for get_distance() to return float("inf") when no path exists?

Alternatively, if returning 0.0 for unreachable destinations is intentional, should this behavior be explicitly documented?