Merge branch 'raimo/stdlib/gen_statem-types-and-templates/ERL-172_ERL-187/OTP-13746' into maint

* raimo/stdlib/gen_statem-types-and-templates/ERL-172_ERL-187/OTP-13746:
  Fix type and template errors from bugs.erlang.org: ERL-172 and ERL-187

2 files changed, 20 insertions, 11 deletions

diff --git a/lib/stdlib/doc/src/gen_statem.xml b/lib/stdlib/doc/src/gen_statem.xml
index c57a31fa21..ed44eef912 100644
--- a/lib/stdlib/doc/src/gen_statem.xml
+++ b/lib/stdlib/doc/src/gen_statem.xml
@@ -1262,9 +1262,9 @@ handle_event(_, _, State, Data) ->
         <v>&nbsp;&nbsp;Vsn = term()</v>
         <v>OldState = NewState = term()</v>
         <v>Extra = term()</v>
-	<v>Result = {NewCallbackMode,NewState,NewData} | Reason</v>
+	<v>Result = {CallbackMode,NewState,NewData} | Reason</v>
 	<v>
-	  NewCallbackMode =
+	  CallbackMode =
 	  <seealso marker="#type-callback_mode">callback_mode()</seealso>
 	</v>
 	<v>
@@ -1321,11 +1321,19 @@ handle_event(_, _, State, Data) ->
 	<p>
 	  If successful, the function must return the updated
 	  internal state in an
-	  <c>{NewCallbackMode,NewState,NewData}</c> tuple.
+	  <c>{CallbackMode,NewState,NewData}</c> tuple.
 	</p>
 	<p>
-	  If the function returns <c>Reason</c>, the ongoing
-	  upgrade fails and rolls back to the old release.</p>
+	  If the function returns a failure <c>Reason</c>, the ongoing
+	  upgrade fails and rolls back to the old release.
+	  Note that <c>Reason</c> can not be a 3-tuple since that
+	  will be regarded as a
+	  <c>{CallbackMode,NewState,NewData}</c> tuple,
+	  and that a tuple matching <c>{ok,_}</c>
+	  is an invalid failure <c>Reason</c>.
+	  It is recommended to use an atom as <c>Reason</c> since
+	  it will be wrapped in an <c>{error,Reason}</c> tuple.
+	</p>
 	<p>
 	  This function can use
 	  <seealso marker="erts:erlang#throw/1"><c>erlang:throw/1</c></seealso>
diff --git a/lib/stdlib/src/gen_statem.erl b/lib/stdlib/src/gen_statem.erl
index 23bddafeed..c02e6a1a19 100644
--- a/lib/stdlib/src/gen_statem.erl
+++ b/lib/stdlib/src/gen_statem.erl
@@ -219,9 +219,10 @@
 	    OldState :: state(),
 	    OldData :: data(),
 	    Extra :: term()) ->
-    {NewCallbackMode :: callback_mode(),
+    {CallbackMode :: callback_mode(),
      NewState :: state(),
-     NewData :: data()}.
+     NewData :: data()} |
+    (Reason :: term()).
 
 %% Format the callback module state in some sensible that is
 %% often condensed way.  For StatusOption =:= 'normal' the perferred
@@ -630,11 +631,11 @@ system_code_change(
 	    Result -> Result
 	end
     of
-	{NewCallbackMode,NewState,NewData} ->
-	    callback_mode(NewCallbackMode) orelse
-		error({callback_mode,NewCallbackMode}),
+	{CallbackMode,NewState,NewData} ->
+	    callback_mode(CallbackMode) orelse
+		error({callback_mode,CallbackMode}),
 	    {ok,
-	     S#{callback_mode := NewCallbackMode,
+	     S#{callback_mode := CallbackMode,
 		state := NewState,
 		data := NewData}};
 	{ok,_} = Error ->