From 4eedbb4e4c6c3408afc9c5b704bab331b43f397f Mon Sep 17 00:00:00 2001
From: Andrea Leopardi <an.leopardi@gmail.com>
Date: Sat, 28 May 2016 15:15:08 +0200
Subject: [PATCH 1/2] Add the format_status/2 optional callback to GenServer

---
 lib/elixir/lib/gen_server.ex | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/lib/elixir/lib/gen_server.ex b/lib/elixir/lib/gen_server.ex
index 8e3eea48fb3..9b835728d2a 100644
--- a/lib/elixir/lib/gen_server.ex
+++ b/lib/elixir/lib/gen_server.ex
@@ -382,6 +382,28 @@ defmodule GenServer do
     {:ok, new_state :: term} |
     {:error, reason :: term} when old_vsn: term | {:down, term}
 
+  @doc """
+  Invoked in some cases to retrieve a formatted version of the `GenServer` status.
+
+  This callback can be useful to control the *appearance* of the status of the
+  `GenServer`. For example, it can be used to return a compact representation of
+  the `GenServers`'s state to avoid having large state terms printed.
+
+    * one of `:sys.get_status/1` or `:sys.get_status/2` is invoked to get the
+      status of the `GenServer`; in such cases, `reason` is `:normal`
+
+    * the `GenServer` terminates abnormally and logs an error; in such cases,
+      `reason` is `:terminate`
+
+  `pdict_and_state` is a two-elements list `[pdict, state]` where `pdict` is a
+  list of `{key, value}` tuples representing the current process dictionary of
+  the `GenServer` and `state` is the current state of the `GenServer`.
+  """
+  @callback format_status(reason, pdict_and_state :: list) ::
+    term when reason: :normal | :terminate
+
+  @optional_callbacks format_status: 2
+
   @typedoc "Return values of `start*` functions"
   @type on_start :: {:ok, pid} | :ignore | {:error, {:already_started, pid} | term}
 

From d0879c499f6cc2660e49a64678fe41d826465fb9 Mon Sep 17 00:00:00 2001
From: Andrea Leopardi <an.leopardi@gmail.com>
Date: Sat, 28 May 2016 15:15:15 +0200
Subject: [PATCH 2/2] Use GenServer over :gen_server as the behaviour for
 GenServers

We can do this now since we support @optional_callbacks and can thus
have the GenServer.format_status/2 optional callback.
---
 lib/elixir/lib/gen_server.ex           | 2 +-
 lib/elixir/test/elixir/module_test.exs | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/elixir/lib/gen_server.ex b/lib/elixir/lib/gen_server.ex
index 9b835728d2a..aaceeec488b 100644
--- a/lib/elixir/lib/gen_server.ex
+++ b/lib/elixir/lib/gen_server.ex
@@ -436,7 +436,7 @@ defmodule GenServer do
   @doc false
   defmacro __using__(_) do
     quote location: :keep do
-      @behaviour :gen_server
+      @behaviour GenServer
 
       @doc false
       def init(args) do
diff --git a/lib/elixir/test/elixir/module_test.exs b/lib/elixir/test/elixir/module_test.exs
index 15b69b2009b..2bd7155140c 100644
--- a/lib/elixir/test/elixir/module_test.exs
+++ b/lib/elixir/test/elixir/module_test.exs
@@ -122,7 +122,7 @@ defmodule ModuleTest do
   ## Attributes
 
   test "reserved attributes" do
-    assert List.keyfind(ExUnit.Server.__info__(:attributes), :behaviour, 0) == {:behaviour, [:gen_server]}
+    assert List.keyfind(ExUnit.Server.__info__(:attributes), :behaviour, 0) == {:behaviour, [GenServer]}
   end
 
   test "registered attributes" do