From efda33e83f2bbc666f6ec261d54ad95c38acbc36 Mon Sep 17 00:00:00 2001
From: Raimo Niskanen <raimo@erlang.org>
Date: Fri, 26 Feb 2016 10:51:53 +0100
Subject: Allow actions without containing list

Type check atom state as early as possible
---
 lib/stdlib/src/gen_statem.erl        | 21 ++++++++++++++++-----
 lib/stdlib/test/gen_statem_SUITE.erl |  6 +++---
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/lib/stdlib/src/gen_statem.erl b/lib/stdlib/src/gen_statem.erl
index 16c296794f..83de4114a7 100644
--- a/lib/stdlib/src/gen_statem.erl
+++ b/lib/stdlib/src/gen_statem.erl
@@ -571,7 +571,9 @@ init_result(Starter, Parent, ServerRef, Module, Result, Opts) ->
     case Result of
 	{CallbackMode,State,Data} ->
 	    case callback_mode(CallbackMode) of
-		true ->
+		true
+		  when CallbackMode =:= state_functions, is_atom(State);
+		       CallbackMode =/= state_functions ->
 		    proc_lib:init_ack(Starter, {ok,self()}),
 		    enter(
 		      Module, Opts, CallbackMode, State, Data,
@@ -840,7 +842,7 @@ loop_events(
 %% Interpret all callback return value variants
 loop_event_result(
   Parent, Debug,
-  #{state := State, data := Data} = S,
+  #{callback_mode := CallbackMode, state := State, data := Data} = S,
   Events, Event, Result) ->
     case Result of
 	stop ->
@@ -866,12 +868,15 @@ loop_event_result(
 		  exit, Reason, ?STACKTRACE(), Debug, NewS, Q, Replies),
 	    %% Since we got back here Replies was bad
 	    terminate(Class, NewReason, Stacktrace, NewDebug, NewS, Q);
-	{next_state,NewState,NewData} ->
+	{next_state,NewState,NewData}
+	  when CallbackMode =:= state_functions, is_atom(NewState);
+	       CallbackMode =/= state_functions ->
 	    loop_event_actions(
 	      Parent, Debug, S, Events, Event,
 	      State, NewState, NewData, []);
 	{next_state,NewState,NewData,Actions}
-	  when is_list(Actions) ->
+	  when CallbackMode =:= state_functions, is_atom(NewState);
+	       CallbackMode =/= state_functions ->
 	    loop_event_actions(
 	      Parent, Debug, S, Events, Event,
 	      State, NewState, NewData, Actions);
@@ -900,7 +905,13 @@ loop_event_actions(
   Parent, Debug, S, Events, Event, State, NewState, NewData, Actions) ->
     loop_event_actions(
       Parent, Debug, S, Events, Event, State, NewState, NewData,
-      false, false, undefined, [], Actions).
+      false, false, undefined, [],
+      if
+	  is_list(Actions) ->
+	      Actions;
+	  true ->
+	      [Actions]
+      end).
 %%
 loop_event_actions(
   Parent, Debug, #{postponed := P0} = S, Events, Event,
diff --git a/lib/stdlib/test/gen_statem_SUITE.erl b/lib/stdlib/test/gen_statem_SUITE.erl
index 09b309c36f..0429c0e5f4 100644
--- a/lib/stdlib/test/gen_statem_SUITE.erl
+++ b/lib/stdlib/test/gen_statem_SUITE.erl
@@ -1178,7 +1178,7 @@ idle({call,From}, {delayed_answer,T}, Data) ->
     end;
 idle({call,From}, {timeout,Time}, _Data) ->
     {next_state,timeout,{From,Time},
-     [{timeout,Time,idle}]};
+     {timeout,Time,idle}};
 idle(Type, Content, Data) ->
     case handle_common_events(Type, Content, idle, Data) of
 	undefined ->
@@ -1220,7 +1220,7 @@ timeout3(_, _, Data) ->
 
 wfor_conf({call,From}, confirm, Data) ->
     {next_state,connected,Data,
-     [{reply,From,yes}]};
+     {reply,From,yes}};
 wfor_conf(cast, {ping,_,_}, _) ->
     {keep_state_and_data,[postpone]};
 wfor_conf(cast, confirm, Data) ->
@@ -1241,7 +1241,7 @@ wfor_conf(Type, Content, Data) ->
 
 connected({call,From}, {msg,Ref}, Data) ->
     {keep_state,Data,
-     [{reply,From,{ack,Ref}}]};
+     {reply,From,{ack,Ref}}};
 connected(cast, {msg,From,Ref}, Data) ->
     From ! {ack,Ref},
     {keep_state,Data};
-- 
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