Return callback module in supervisor format_status

The previous implementation of supervisor:get_callback_module/1
used sys:get_status/1 to get the supervisor inner state and
retrieve the callback module. Such implementation forbids any
other supervisor implementation that has an internal state
different than the #state{} record in supervisor.erl.

This patch allows supervisors to return the callback module
as part of the sys:get_status/1 data, no longer coupling the
callback module implementation with the inner #state{} record.

Notice we have kept the clause matching the previous
sys:get_status/1 reply for backwards compatibility purposes.

lib/stdlib/src/supervisor.erl

@@ -30,7 +30,7 @@
 
 %% Internal exports
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
-	 terminate/2, code_change/3]).
+	 terminate/2, code_change/3, format_status/2]).
 -export([try_again_restart/2]).
 
 %% For release_handler only
@@ -264,8 +264,12 @@ cast(Supervisor, Req) ->
 get_callback_module(Pid) ->
     {status, _Pid, {module, _Mod},
      [_PDict, _SysState, _Parent, _Dbg, Misc]} = sys:get_status(Pid),
-    [_Header, _Data, {data, [{"State", State}]}] = Misc,
-    State#state.module.
+    case Misc of
+	[_Header, _Data, {data, [{"State", {Mod, _}}]}] ->
+	    Mod;
+	[_Header, _Data, {data, [{"State", State}]}] ->
+	    State#state.module
+    end.
 
 %%% ---------------------------------------------------
 %%% 
@@ -1456,3 +1460,8 @@ report_progress(Child, SupName) ->
     Progress = [{supervisor, SupName},
 		{started, extract_child(Child)}],
     error_logger:info_report(progress, Progress).
+
+format_status(terminate, [_PDict, State]) ->
+    State;
+format_status(_, [_PDict, State]) ->
+    [{data, [{"State", {State#state.module, State}}]}].

lib/stdlib/test/supervisor_SUITE.erl

@@ -67,7 +67,7 @@
 
 %% Misc tests
 -export([child_unlink/1, tree/1, count_children/1,
-	 count_restarting_children/1,
+	 count_restarting_children/1, get_callback_module/1,
 	 do_not_save_start_parameters_for_temporary_children/1,
 	 do_not_save_child_specs_for_temporary_children/1,
 	 simple_one_for_one_scale_many_temporary_children/1,
@@ -91,7 +91,7 @@ all() ->
      {group, normal_termination},
      {group, shutdown_termination},
      {group, abnormal_termination}, child_unlink, tree,
-     count_children, count_restarting_children,
+     count_children, count_restarting_children, get_callback_module,
      do_not_save_start_parameters_for_temporary_children,
      do_not_save_child_specs_for_temporary_children,
      simple_one_for_one_scale_many_temporary_children, temporary_bystander,
@@ -1508,6 +1508,14 @@ count_restarting_children(Config) when is_list(Config) ->
     ok = supervisor:terminate_child(SupPid, Ch3_2),
     [1,0,0,0] = get_child_counts(SupPid).
 
+%%-------------------------------------------------------------------------
+%% Test get_callback_module
+get_callback_module(Config) when is_list(Config) ->
+    Child = {child, {supervisor_1, start_child, []}, temporary, 1000,
+	     worker, []},
+    {ok, SupPid} = start_link({ok, {{simple_one_for_one, 2, 3600}, [Child]}}),
+    supervisor_SUITE = supervisor:get_callback_module(SupPid).
+
 %%-------------------------------------------------------------------------
 %% Temporary children shall not be restarted so they should not save
 %% start parameters, as it potentially can take up a huge amount of