Fix format_status bug for unregistered gen_event processes

Port the gen_fsm code for format_status to gen_event in order to
prevent a lists:concat([...,pid()]) crash when calling
sys:get_status/1 on an unregistered gen_event process.

Refactor format_status header code from gen_* behaviours to module gen.

Extend the format_status tests in gen_event_SUITE to cover
format_status bugs with anonymous gen_event processes.

4 files changed, 15 insertions, 19 deletions

diff --git a/lib/stdlib/src/gen.erl b/lib/stdlib/src/gen.erl
index 43df6f621d..574146b1cd 100644
--- a/lib/stdlib/src/gen.erl
+++ b/lib/stdlib/src/gen.erl
@@ -29,6 +29,8 @@
 
 -export([init_it/6, init_it/7]).
 
+-export([format_status_header/2]).
+
 -define(default_timeout, 5000).
 
 %%-----------------------------------------------------------------
@@ -315,3 +317,10 @@ debug_options(Opts) ->
 	{ok, Options} -> sys:debug_options(Options);
 	_ -> []
     end.
+
+format_status_header(TagLine, Pid) when is_pid(Pid) ->
+    lists:concat([TagLine, " ", pid_to_list(Pid)]);
+format_status_header(TagLine, RegName) when is_atom(RegName) ->
+    lists:concat([TagLine, " ", RegName]);
+format_status_header(TagLine, Name) ->
+    {TagLine, Name}.
diff --git a/lib/stdlib/src/gen_event.erl b/lib/stdlib/src/gen_event.erl
index b1e9e3a02f..b00910771f 100644
--- a/lib/stdlib/src/gen_event.erl
+++ b/lib/stdlib/src/gen_event.erl
@@ -724,7 +724,8 @@ get_modules(MSL) ->
 %%-----------------------------------------------------------------
 format_status(Opt, StatusData) ->
     [PDict, SysState, Parent, _Debug, [ServerName, MSL, _Hib]] = StatusData,
-    Header = lists:concat(["Status for event handler ", ServerName]),
+    Header = gen:format_status_header("Status for event handler",
+                                      ServerName),
     FmtMSL = [case erlang:function_exported(Mod, format_status, 2) of
 		  true ->
 		      Args = [PDict, State],
diff --git a/lib/stdlib/src/gen_fsm.erl b/lib/stdlib/src/gen_fsm.erl
index 7d9960b912..f2f1365d3d 100644
--- a/lib/stdlib/src/gen_fsm.erl
+++ b/lib/stdlib/src/gen_fsm.erl
@@ -614,15 +614,8 @@ get_msg(Msg) -> Msg.
 format_status(Opt, StatusData) ->
     [PDict, SysState, Parent, Debug, [Name, StateName, StateData, Mod, _Time]] =
 	StatusData,
-    StatusHdr = "Status for state machine",
-    Header = if
-		 is_pid(Name) ->
-		     lists:concat([StatusHdr, " ", pid_to_list(Name)]);
-		 is_atom(Name); is_list(Name) ->
-		     lists:concat([StatusHdr, " ", Name]);
-		 true ->
-		     {StatusHdr, Name}
-	     end,
+    Header = gen:format_status_header("Status for state machine",
+                                      Name),
     Log = sys:get_debug(log, Debug, []),
     DefaultStatus = [{data, [{"StateData", StateData}]}],
     Specfic =
diff --git a/lib/stdlib/src/gen_server.erl b/lib/stdlib/src/gen_server.erl
index ac81df9cab..09d94a9c40 100644
--- a/lib/stdlib/src/gen_server.erl
+++ b/lib/stdlib/src/gen_server.erl
@@ -840,15 +840,8 @@ name_to_pid(Name) ->
 %%-----------------------------------------------------------------
 format_status(Opt, StatusData) ->
     [PDict, SysState, Parent, Debug, [Name, State, Mod, _Time]] = StatusData,
-    StatusHdr = "Status for generic server",
-    Header = if
-		 is_pid(Name) ->
-		     lists:concat([StatusHdr, " ", pid_to_list(Name)]);
-		 is_atom(Name); is_list(Name) ->
-		     lists:concat([StatusHdr, " ", Name]);
-		 true ->
-		     {StatusHdr, Name}
-	     end,
+    Header = gen:format_status_header("Status for generic server",
+                                      Name),
     Log = sys:get_debug(log, Debug, []),
     DefaultStatus = [{data, [{"State", State}]}],
     Specfic =