Fix dialyzer warnings in supervisor

Dialyzer complained over a mismatch between the callback spec of
Mod:code_change in gen_server and the spec of supervisor:code_change
(which is the implementation of a gen_server Mod:code_change).

This commit changes the callback spec to allow {error,Reason} as
return value. Also, release_handler is updated to handle this return
value.

lib/sasl/src/release_handler_1.erl

@@ -505,15 +505,20 @@ resume(Pids) ->
 
 change_code(Pids, Mod, Vsn, Extra, Timeout) ->
     Fun = fun(Pid) -> 
-		  case Timeout of
-		      default ->
-			  ok = sys:change_code(Pid, Mod, Vsn, Extra);
-		      _Else ->
-			  ok = sys:change_code(Pid, Mod, Vsn, Extra, Timeout)
+		  case sys_change_code(Pid, Mod, Vsn, Extra, Timeout) of
+		      ok ->
+			  ok;
+		      {error,Reason} ->
+			  throw({code_change_failed,Pid,Mod,Vsn,Reason})
 		  end
 	  end,
     lists:foreach(Fun, Pids).
 
+sys_change_code(Pid, Mod, Vsn, Extra, default) ->
+    sys:change_code(Pid, Mod, Vsn, Extra);
+sys_change_code(Pid, Mod, Vsn, Extra, Timeout) ->
+    sys:change_code(Pid, Mod, Vsn, Extra, Timeout).
+
 stop(Mod, Procs) ->
     lists:zf(fun({undefined, _Name, _Pid, _Mods}) ->
 		     false;

lib/stdlib/doc/src/gen_server.xml

@@ -4,7 +4,7 @@
 <erlref>
   <header>
     <copyright>
-      <year>1996</year><year>2010</year>
+      <year>1996</year><year>2011</year>
       <holder>Ericsson AB. All Rights Reserved.</holder>
     </copyright>
     <legalnotice>
@@ -570,13 +570,14 @@ gen_server:abcast     -----> Module:handle_cast/2
       </desc>
     </func>
     <func>
-      <name>Module:code_change(OldVsn, State, Extra) -> {ok, NewState}</name>
+      <name>Module:code_change(OldVsn, State, Extra) -> {ok, NewState} | {error, Reason}</name>
       <fsummary>Update the internal state during upgrade/downgrade.</fsummary>
       <type>
         <v>OldVsn = Vsn | {down, Vsn}</v>
         <v>&nbsp;&nbsp;Vsn = term()</v>
         <v>State = NewState = term()</v>
         <v>Extra = term()</v>
+	<v>Reason = term()</v>
       </type>
       <desc>
         <p>This function is called by a gen_server when it should
@@ -595,7 +596,10 @@ gen_server:abcast     -----> Module:handle_cast/2
         <p><c>State</c> is the internal state of the gen_server.</p>
         <p><c>Extra</c> is passed as-is from the <c>{advanced,Extra}</c>
           part of the update instruction.</p>
-        <p>The function should return the updated internal state.</p>
+        <p>If successful, the function shall return the updated
+          internal state.</p>
+	<p>If the function returns <c>{error,Reason}</c>, the ongoing
+	  upgrade will fail and roll back to the old release.</p>
       </desc>
     </func>
     <func>

lib/stdlib/src/gen_server.erl

@@ -134,7 +134,7 @@
     term().
 -callback code_change(OldVsn :: (term() | {down, term()}), State :: term(),
                       Extra :: term()) ->
-    {ok, NewState :: term()}.
+    {ok, NewState :: term()} | {error, Reason :: term()}.
 
 %%%  -----------------------------------------------------------------
 %%% Starts a generic server.

lib/stdlib/src/supervisor.erl

@@ -37,7 +37,7 @@
 
 %%--------------------------------------------------------------------------
 
--type child()    :: pid() | 'undefined'.
+-type child()    :: 'undefined' | pid() | [pid()].
 -type child_id() :: term().
 -type mfargs()   :: {M :: module(), F :: atom(), A :: [term()] | undefined}.
 -type modules()  :: [module()] | 'dynamic'.