Allow use Phoenix.Tracker

lib/phoenix/tracker.ex

@@ -58,9 +58,7 @@ defmodule Phoenix.Tracker do
   behaviour callbacks. An example of a minimal tracker could include:
 
       defmodule MyTracker do
-        use GenServer
-
-        @behaviour Phoenix.Tracker
+        use Phoenix.Tracker
 
         def start_link(opts) do
           opts = Keyword.merge([name: __MODULE__], opts)
@@ -106,8 +104,6 @@ defmodule Phoenix.Tracker do
   crash the tracker server, so operations that may crash the server should be
   offloaded with a `Task.Supervisor` spawned process.
   """
-  use Supervisor
-
   alias Phoenix.Tracker.Shard
   require Logger
 
@@ -117,6 +113,30 @@ defmodule Phoenix.Tracker do
   @callback init(Keyword.t) :: {:ok, state :: term} | {:error, reason :: term}
   @callback handle_diff(%{topic => {joins :: [presence], leaves :: [presence]}}, state :: term) :: {:ok, state :: term}
 
+  defmacro __using__(_opts) do
+    quote location: :keep do
+      @behaviour Phoenix.Tracker
+
+      if Module.get_attribute(__MODULE__, :doc) == nil do
+        @doc """
+        Returns a specification to start this module under a supervisor.
+
+        See `Supervisor`.
+        """
+      end
+
+      def child_spec(init_arg) do
+        default = %{
+          id: __MODULE__,
+          start: {__MODULE__, :start_link, [init_arg]},
+          type: :supervisor
+        }
+      end
+
+      defoverridable child_spec: 1
+    end
+  end
+
   ## Client
 
   @doc """

test/phoenix/tracker/shard_test.exs

@@ -0,0 +1,16 @@
+defmodule Phoenix.Tracker.ShardTest do
+  use ExUnit.Case, async: true
+  @opts [pubsub_server: nil, name: nil]
+
+  test "validates down_period" do
+    opts = Keyword.merge(@opts, [down_period: 1])
+    assert Phoenix.Tracker.Shard.init([nil, nil, opts]) ==
+      {:error, "down_period must be at least twice as large as the broadcast_period"}
+  end
+
+  test "validates permdown_period" do
+    opts = Keyword.merge(@opts, [permdown_period: 1_200_00, down_period: 1_200_000])
+    assert Phoenix.Tracker.Shard.init([nil, nil, opts]) ==
+      {:error, "permdown_period must be at least larger than the down_period"}
+  end
+end

test/phoenix/tracker/state_test.exs

@@ -409,5 +409,4 @@ defmodule Phoenix.Tracker.StateTest do
       end)
     end)
   end
-
 end

test/phoenix/tracker_test.exs

@@ -1,16 +1,17 @@
-defmodule Phoenix.Tracker.ShardTest do
+defmodule Phoenix.TrackerTest do
   use ExUnit.Case, async: true
-  @opts [pubsub_server: nil, name: nil]
 
-  test "validates down_period" do
-    opts = Keyword.merge(@opts, [down_period: 1])
-    assert Phoenix.Tracker.Shard.init([nil, nil, opts]) ==
-      {:error, "down_period must be at least twice as large as the broadcast_period"}
+  defmodule MyTracker do
+    use Phoenix.Tracker
+    def init(state), do: {:ok, state}
+    def handle_diff(_diff, state), do: {:ok, state}
   end
 
-  test "validates permdown_period" do
-    opts = Keyword.merge(@opts, [permdown_period: 1_200_00, down_period: 1_200_000])
-    assert Phoenix.Tracker.Shard.init([nil, nil, opts]) ==
-      {:error, "permdown_period must be at least larger than the down_period"}
+  test "generates child spec" do
+    assert MyTracker.child_spec([]) == %{
+             id: Phoenix.TrackerTest.MyTracker,
+             start: {Phoenix.TrackerTest.MyTracker, :start_link, [[]]},
+             type: :supervisor
+           }
   end
 end