Use the application environment when app is not loaded, closes #6846

Author: josevalim

lib/phoenix/endpoint.ex

@@ -469,7 +469,14 @@ defmodule Phoenix.Endpoint do
       end
 
       defp pubsub_server! do
-        config(:pubsub_server) ||
+        server =
+          try do
+            config(:pubsub_server)
+          rescue
+            ArgumentError -> Application.get_env(@otp_app, __MODULE__)[:pubsub_server]
+          end
+
+        server ||
           raise ArgumentError, "no :pubsub_server configured for #{inspect(__MODULE__)}"
       end
     end

test/phoenix/endpoint/endpoint_test.exs

@@ -332,6 +332,21 @@ defmodule Phoenix.Endpoint.EndpointTest do
     refute_received %Phoenix.Socket.Broadcast{}
   end
 
+  test "pubsub uses the application environment when the endpoint is not started" do
+    defmodule PubSubEnvEndpoint do
+      use Phoenix.Endpoint, otp_app: :phoenix
+    end
+
+    Application.put_env(:phoenix, PubSubEnvEndpoint, pubsub_server: :endpoint_pub)
+    PubSubEnvEndpoint.subscribe("envtopic")
+    PubSubEnvEndpoint.broadcast("envtopic", "event1", %{key: :val})
+    assert_receive %Phoenix.Socket.Broadcast{event: "event1", topic: "envtopic"}
+  after
+    Application.delete_env(:phoenix, __MODULE__.PubSubEnvEndpoint)
+    :code.purge(__MODULE__.PubSubEnvEndpoint)
+    :code.delete(__MODULE__.PubSubEnvEndpoint)
+  end
+
   test "loads cache manifest from specified application" do
     config =
       put_in(