fix: refactor of routes-serving-stop fetching

The version of this function prior to the refactor in 297c302 returned
only a list of routes, returning an empty list if an error occurred.
The moved/renamed version returns an `:ok` tuple or `:error`, consistent
with other data fetching functions, but the call sites were not updated
to reflect this, and no tests failed because the mocks for the function
still used the old return type (or, in the case of `ElevatorClosures`,
the module lacked any tests at all).

This keeps the return type of the fetching function the same, so errors
can be distinguished if needed, but changes the existing call sites to
perform the "default to empty list" logic themselves, so there should be
no change in behavior.

lib/screens/routes/route.ex

@@ -62,7 +62,7 @@ defmodule Screens.Routes.Route do
   end
 
   @doc "Fetches routes that serve the given stop."
-  @spec serving_stop(Stop.id()) :: {:ok, t()} | :error
+  @spec serving_stop(Stop.id()) :: {:ok, [t()]} | :error
   def serving_stop(
         stop_id,
         get_json_fn \\ &V3Api.get_json/2,

lib/screens/v2/candidate_generator/dup/departures.ex

@@ -638,7 +638,11 @@ defmodule Screens.V2.CandidateGenerator.Dup.Departures do
        ) do
     routes =
       stop_ids
-      |> Enum.flat_map(&fetch_routes_serving_stop_fn.(&1))
+      |> Enum.map(&fetch_routes_serving_stop_fn.(&1))
+      |> Enum.flat_map(fn
+        {:ok, routes} -> routes
+        :error -> []
+      end)
       |> Enum.uniq()
 
     if route_ids == [] do

lib/screens/v2/candidate_generator/widgets/elevator_closures.ex

@@ -52,7 +52,7 @@ defmodule Screens.V2.CandidateGenerator.Widgets.ElevatorClosures do
     |> MapSet.new()
     |> MapSet.put(home_parent_station_id)
     |> Enum.map(fn station_id ->
-      {station_id, station_id |> Route.serving_stop() |> routes_to_icons()}
+      {station_id, station_id |> routes_serving_stop() |> routes_to_icons()}
     end)
     |> Enum.into(%{})
   end
@@ -66,6 +66,13 @@ defmodule Screens.V2.CandidateGenerator.Widgets.ElevatorClosures do
     end)
   end
 
+  defp routes_serving_stop(stop_id) do
+    case Route.serving_stop(stop_id) do
+      {:ok, routes} -> routes
+      :error -> []
+    end
+  end
+
   defp routes_to_icons(routes) do
     routes
     |> Enum.map(fn

test/screens/v2/candidate_generator/dup/departures_test.exs

@@ -251,12 +251,12 @@ defmodule Screens.V2.CandidateGenerator.Dup.DeparturesTest do
     fetch_vehicles_fn = fn _, _ -> [struct(Vehicle)] end
 
     fetch_routes_serving_stop_fn = fn
-      "Boat" -> [%{id: "Ferry", type: :ferry}]
-      "place-A" -> [%{id: "Orange", type: :subway}, %{id: "Green", type: :light_rail}]
-      "bus-A" -> [%{id: "Bus A", type: :bus}]
-      "bus-B" -> [%{id: "Bus B", type: :bus}]
-      "place-overnight" -> [%{id: "Red", type: :subway}]
-      _ -> [%{id: "test", type: :test}]
+      "Boat" -> {:ok, [%{id: "Ferry", type: :ferry}]}
+      "place-A" -> {:ok, [%{id: "Orange", type: :subway}, %{id: "Green", type: :light_rail}]}
+      "bus-A" -> {:ok, [%{id: "Bus A", type: :bus}]}
+      "bus-B" -> {:ok, [%{id: "Bus B", type: :bus}]}
+      "place-overnight" -> {:ok, [%{id: "Red", type: :subway}]}
+      _ -> {:ok, [%{id: "test", type: :test}]}
     end
 
     %{