feat: auto starts Tower.EphemeralReporter

lib/tower/application.ex

@@ -9,6 +9,7 @@ defmodule Tower.Application do
   def start(_type, _args) do
     Supervisor.start_link(
       [
+        Tower.EphemeralReporter,
         {Task.Supervisor, name: Tower.TaskSupervisor}
       ],
       strategy: :one_for_one,

lib/tower/ephemeral_reporter.ex

@@ -6,7 +6,6 @@ defmodule Tower.EphemeralReporter do
 
   ## Example
 
-      iex> {:ok, pid} = Tower.EphemeralReporter.start_link([])
       iex> Tower.EphemeralReporter.events()
       []
       iex> Application.put_env(:tower, :reporters, [Tower.EphemeralReporter])
@@ -22,19 +21,35 @@ defmodule Tower.EphemeralReporter do
       %ArithmeticError{message: "bad argument in arithmetic expression"}
       iex> Tower.detach()
       :ok
-      iex> Tower.EphemeralReporter.stop(pid)
-      :ok
   """
   @behaviour Tower.Reporter
 
   @default_level :info
 
   use Agent
 
+  require Logger
+
   alias Tower.Event
 
+  @empty_events []
+
   def start_link(_opts) do
-    Agent.start_link(fn -> [] end, name: __MODULE__)
+    Agent.start_link(fn -> @empty_events end, name: __MODULE__)
+    |> case do
+      {:error, {:already_started, existing_pid}} ->
+        Logger.warning("""
+        An attempt to start Tower.EphemeralReporter when it is already started was ignored.
+
+        If you are manually starting Tower.EphemeralReporter, you can safely stop doing it given
+        it is automatically started by Tower.
+        """)
+
+        {:ok, existing_pid}
+
+      on_start ->
+        on_start
+    end
   end
 
   def stop(pid) do
@@ -55,4 +70,9 @@ defmodule Tower.EphemeralReporter do
   def events do
     Agent.get(__MODULE__, & &1)
   end
+
+  @spec reset() :: :ok
+  def reset do
+    Agent.update(__MODULE__, fn _events -> @empty_events end)
+  end
 end

test/tower/tower_oban_test.exs

@@ -7,8 +7,6 @@ defmodule TowerObanTest do
   import ExUnit.CaptureLog, only: [capture_log: 1]
 
   setup do
-    start_link_supervised!(Tower.EphemeralReporter)
-
     start_link_supervised!({
       TestApp.Repo,
       database: "tmp/test-#{:rand.uniform(10_000)}.db", journal_mode: :memory
@@ -26,6 +24,7 @@ defmodule TowerObanTest do
 
     on_exit(fn ->
       Tower.detach()
+      Tower.EphemeralReporter.reset()
     end)
   end
 

test/tower/tower_plug_test.exs

@@ -6,11 +6,11 @@ defmodule TowerPlugTest do
   import ExUnit.CaptureLog, only: [capture_log: 1]
 
   setup do
-    start_link_supervised!(Tower.EphemeralReporter)
     Tower.attach()
 
     on_exit(fn ->
       Tower.detach()
+      Tower.EphemeralReporter.reset()
     end)
   end
 

test/tower_test.exs

@@ -7,11 +7,11 @@ defmodule TowerTest do
   import ExUnit.CaptureLog, only: [capture_log: 1]
 
   setup do
-    start_reporter()
     Tower.attach()
 
     on_exit(fn ->
       Tower.detach()
+      Tower.EphemeralReporter.reset()
     end)
   end
 
@@ -622,10 +622,6 @@ defmodule TowerTest do
     |> Task.yield()
   end
 
-  defp start_reporter do
-    Tower.EphemeralReporter.start_link([])
-  end
-
   defp reported_events do
     Tower.EphemeralReporter.events()
   end