use canary mapper

lib/philomena/users/ability.ex

@@ -64,6 +64,9 @@ defimpl Canada.Can, for: [Atom, Philomena.Users.User] do
       when action in [:show, :index],
       do: true
 
+  # Vote on images they can see
+  def can?(user, :vote, image), do: can?(user, :show, image)
+
   # View non-deleted comments
   def can?(_user, :show, %Comment{hidden_from_users: false}), do: true
 

lib/philomena_web/controllers/image/fave_controller.ex

@@ -7,6 +7,7 @@ defmodule PhilomenaWeb.Image.FaveController do
   alias Ecto.Multi
 
   plug PhilomenaWeb.Plugs.FilterBannedUsers
+  plug PhilomenaWeb.Plugs.CanaryMapPlug, create: :vote, delete: :vote
   plug :load_and_authorize_resource, model: Image, id_name: "image_id", persisted: true
 
   def create(conn, _params) do

lib/philomena_web/controllers/image/hide_controller.ex

@@ -7,6 +7,7 @@ defmodule PhilomenaWeb.Image.HideController do
   alias Ecto.Multi
 
   plug PhilomenaWeb.Plugs.FilterBannedUsers
+  plug PhilomenaWeb.Plugs.CanaryMapPlug, create: :vote, delete: :vote
   plug :load_and_authorize_resource, model: Image, id_name: "image_id", persisted: true
 
   def create(conn, _params) do

lib/philomena_web/controllers/image/vote_controller.ex

@@ -7,6 +7,7 @@ defmodule PhilomenaWeb.Image.VoteController do
   alias Ecto.Multi
 
   plug PhilomenaWeb.Plugs.FilterBannedUsers
+  plug PhilomenaWeb.Plugs.CanaryMapPlug, create: :vote, delete: :vote
   plug :load_and_authorize_resource, model: Image, id_name: "image_id", persisted: true
 
   def create(conn, params) do

lib/philomena_web/plugs/canary_map_plug.ex

@@ -0,0 +1,17 @@
+defmodule PhilomenaWeb.Plugs.CanaryMapPlug do
+  import Plug.Conn
+
+  def init(opts), do: opts
+
+  def call(conn, opts) do
+    phx_action = conn.private.phoenix_action
+    canary_action =
+      case Keyword.fetch(opts, phx_action) do
+        {:ok, action} -> action
+        _             -> phx_action
+      end
+
+    conn
+    |> assign(:canary_action, canary_action)
+  end
+end