Introduce the attribute -optional_callbacks in the context of behaviours

29 files changed, 611 insertions, 134 deletions

diff --git a/bootstrap/lib/stdlib/ebin/gen_event.beam b/bootstrap/lib/stdlib/ebin/gen_event.beam
index d45e508d22..bf7e2184d8 100644
--- a/bootstrap/lib/stdlib/ebin/gen_event.beam
+++ b/bootstrap/lib/stdlib/ebin/gen_event.beam
diff --git a/bootstrap/lib/stdlib/ebin/gen_fsm.beam b/bootstrap/lib/stdlib/ebin/gen_fsm.beam
index bf5bbb7839..46c8a9e183 100644
--- a/bootstrap/lib/stdlib/ebin/gen_fsm.beam
+++ b/bootstrap/lib/stdlib/ebin/gen_fsm.beam
diff --git a/bootstrap/lib/stdlib/ebin/gen_server.beam b/bootstrap/lib/stdlib/ebin/gen_server.beam
index fe95ca0826..1b6c74b9a7 100644
--- a/bootstrap/lib/stdlib/ebin/gen_server.beam
+++ b/bootstrap/lib/stdlib/ebin/gen_server.beam
diff --git a/lib/compiler/src/sys_pre_expand.erl b/lib/compiler/src/sys_pre_expand.erl
index 761ae8409c..6410b73941 100644
--- a/lib/compiler/src/sys_pre_expand.erl
+++ b/lib/compiler/src/sys_pre_expand.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1996-2012. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2014. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -33,12 +33,15 @@
 
 -include("../include/erl_bits.hrl").
 
+-type fa() :: {atom(), arity()}.
+
 -record(expand, {module=[],                     %Module name
                  exports=[],                    %Exports
                  imports=[],                    %Imports
                  compile=[],                    %Compile flags
                  attributes=[],                 %Attributes
                  callbacks=[],                  %Callbacks
+                 optional_callbacks=[] :: [fa()],  %Optional callbacks
                  defined,			%Defined functions (gb_set)
                  vcount=0,                      %Variable counter
                  func=[],                       %Current function
@@ -99,7 +102,21 @@ define_functions(Forms, #expand{defined=Predef}=St) ->
 module_attrs(#expand{attributes=Attributes}=St) ->
     Attrs = [{attribute,Line,Name,Val} || {Name,Line,Val} <- Attributes],
     Callbacks = [Callback || {_,_,callback,_}=Callback <- Attrs],
-    {Attrs,St#expand{callbacks=Callbacks}}.
+    OptionalCallbacks = get_optional_callbacks(Attrs),
+    {Attrs,St#expand{callbacks=Callbacks,
+                     optional_callbacks=OptionalCallbacks}}.
+
+get_optional_callbacks(Attrs) ->
+    L = [O ||
+            {attribute, _, optional_callbacks, O} <- Attrs,
+            is_fa_list(O)],
+    lists:append(L).
+
+is_fa_list([{FuncName, Arity}|L])
+  when is_atom(FuncName), is_integer(Arity), Arity >= 0 ->
+    is_fa_list(L);
+is_fa_list([]) -> true;
+is_fa_list(_) -> false.
 
 module_predef_funcs(St) ->
     {Mpf1,St1}=module_predef_func_beh_info(St),
@@ -108,19 +125,24 @@ module_predef_funcs(St) ->
 
 module_predef_func_beh_info(#expand{callbacks=[]}=St) ->
     {[], St};
-module_predef_func_beh_info(#expand{callbacks=Callbacks,defined=Defined,
+module_predef_func_beh_info(#expand{callbacks=Callbacks,
+                                    optional_callbacks=OptionalCallbacks,
+                                    defined=Defined,
 				    exports=Exports}=St) ->
     PreDef=[{behaviour_info,1}],
     PreExp=PreDef,
-    {[gen_beh_info(Callbacks)],
+    {[gen_beh_info(Callbacks, OptionalCallbacks)],
      St#expand{defined=gb_sets:union(gb_sets:from_list(PreDef), Defined),
 	       exports=union(from_list(PreExp), Exports)}}.
 
-gen_beh_info(Callbacks) ->
+gen_beh_info(Callbacks, OptionalCallbacks) ->
     List = make_list(Callbacks),
+    OptionalList = make_optional_list(OptionalCallbacks),
     {function,0,behaviour_info,1,
      [{clause,0,[{atom,0,callbacks}],[],
-       [List]}]}.
+       [List]},
+      {clause,0,[{atom,0,optional_callbacks}],[],
+       [OptionalList]}]}.
 
 make_list([]) -> {nil,0};
 make_list([{_,_,_,[{{Name,Arity},_}]}|Rest]) ->
@@ -130,6 +152,14 @@ make_list([{_,_,_,[{{Name,Arity},_}]}|Rest]) ->
        {integer,0,Arity}]},
      make_list(Rest)}.
 
+make_optional_list([]) -> {nil,0};
+make_optional_list([{Name,Arity}|Rest]) ->
+    {cons,0,
+     {tuple,0,
+      [{atom,0,Name},
+       {integer,0,Arity}]},
+     make_optional_list(Rest)}.
+
 module_predef_funcs_mod_info(St) ->
     PreDef = [{module_info,0},{module_info,1}],
     PreExp = PreDef,
diff --git a/lib/dialyzer/src/dialyzer_behaviours.erl b/lib/dialyzer/src/dialyzer_behaviours.erl
index 1d458b49fc..bbedd3201e 100644
--- a/lib/dialyzer/src/dialyzer_behaviours.erl
+++ b/lib/dialyzer/src/dialyzer_behaviours.erl
@@ -102,14 +102,18 @@ check_all_callbacks(Module, Behaviour, [Cb|Rest],
 		    #state{plt = Plt, codeserver = Codeserver,
 			   records = Records} = State, Acc) ->
   {{Behaviour, Function, Arity},
-   {{_BehFile, _BehLine}, Callback}} = Cb,
+   {{_BehFile, _BehLine}, Callback, Xtra}} = Cb,
   CbMFA = {Module, Function, Arity},
   CbReturnType = dialyzer_contracts:get_contract_return(Callback),
   CbArgTypes = dialyzer_contracts:get_contract_args(Callback),
   Acc0 = Acc,
   Acc1 = 
     case dialyzer_plt:lookup(Plt, CbMFA) of
-      'none' -> [{callback_missing, [Behaviour, Function, Arity]}|Acc0];
+      'none' ->
+        case lists:member(optional_callback, Xtra) of
+          true -> Acc0;
+          false -> [{callback_missing, [Behaviour, Function, Arity]}|Acc0]
+        end;
       {'value', RetArgTypes} ->
 	Acc00 = Acc0,
 	{ReturnType, ArgTypes} = RetArgTypes,
@@ -137,7 +141,7 @@ check_all_callbacks(Module, Behaviour, [Cb|Rest],
   Acc2 =
     case dialyzer_codeserver:lookup_mfa_contract(CbMFA, Codeserver) of
       'error' -> Acc1;
-      {ok, {{File, Line}, Contract}} ->
+      {ok, {{File, Line}, Contract, _Xtra}} ->
 	Acc10 = Acc1,
 	SpecReturnType0 = dialyzer_contracts:get_contract_return(Contract),
 	SpecArgTypes0 = dialyzer_contracts:get_contract_args(Contract),
diff --git a/lib/dialyzer/src/dialyzer_codeserver.erl b/lib/dialyzer/src/dialyzer_codeserver.erl
index aab3d6add6..593e71f30b 100644
--- a/lib/dialyzer/src/dialyzer_codeserver.erl
+++ b/lib/dialyzer/src/dialyzer_codeserver.erl
@@ -278,10 +278,10 @@ lookup_mod_contracts(Mod, #codeserver{contracts = ContDict})
   case ets_dict_find(Mod, ContDict) of
     error -> dict:new();
     {ok, Keys} ->
-      dict:from_list([get_contract_pair(Key, ContDict)|| Key <- Keys])
+      dict:from_list([get_file_contract(Key, ContDict)|| Key <- Keys])
   end.
 
-get_contract_pair(Key, ContDict) ->
+get_file_contract(Key, ContDict) ->
   {Key, ets:lookup_element(ContDict, Key, 2)}.
 
 -spec lookup_mfa_contract(mfa(), codeserver()) ->
diff --git a/lib/dialyzer/src/dialyzer_contracts.erl b/lib/dialyzer/src/dialyzer_contracts.erl
index 283031eb9a..462275e713 100644
--- a/lib/dialyzer/src/dialyzer_contracts.erl
+++ b/lib/dialyzer/src/dialyzer_contracts.erl
@@ -45,7 +45,7 @@
 %% Types used in other parts of the system below
 %%-----------------------------------------------------------------------
 
--type file_contract() :: {file_line(), #contract{}}.
+-type file_contract() :: {file_line(), #contract{}, Extra :: [_]}.
 
 -type plt_contracts() :: [{mfa(), #contract{}}]. % actually, an orddict()
 
@@ -148,10 +148,10 @@ process_contract_remote_types(CodeServer) ->
   ExpTypes = dialyzer_codeserver:get_exported_types(CodeServer),
   RecordDict = dialyzer_codeserver:get_records(CodeServer),
   ContractFun =
-    fun({_M, _F, _A}, {File, #tmp_contract{contract_funs = CFuns, forms = Forms}}) ->
+    fun({_M, _F, _A}, {File, #tmp_contract{contract_funs = CFuns, forms = Forms}, Xtra}) ->
 	NewCs = [CFun(ExpTypes, RecordDict) || CFun <- CFuns],
 	Args = general_domain(NewCs),
-	{File, #contract{contracts = NewCs, args = Args, forms = Forms}}
+	{File, #contract{contracts = NewCs, args = Args, forms = Forms}, Xtra}
     end,
   ModuleFun =
     fun(_ModuleName, ContractDict) ->
@@ -177,7 +177,7 @@ check_contracts(Contracts, Callgraph, FunTypes, FindOpaques) ->
 	case dialyzer_callgraph:lookup_name(Label, Callgraph) of
 	  {ok, {M,F,A} = MFA} ->
 	    case orddict:find(MFA, Contracts) of
-	      {ok, {_FileLine, Contract}} ->
+	      {ok, {_FileLine, Contract, _Xtra}} ->
                 Opaques = FindOpaques(M),
 		case check_contract(Contract, Type, Opaques) of
 		  ok ->
@@ -364,7 +364,7 @@ contracts_without_fun(Contracts, AllFuns0, Callgraph) ->
   [warn_spec_missing_fun(MFA, Contracts) || MFA <- ErrorContractMFAs].
 
 warn_spec_missing_fun({M, F, A} = MFA, Contracts) ->
-  {FileLine, _Contract} = dict:fetch(MFA, Contracts),
+  {FileLine, _Contract, _Xtra} = dict:fetch(MFA, Contracts),
   {?WARN_CONTRACT_SYNTAX, FileLine, {spec_missing_fun, [M, F, A]}}.
 
 %% This treats the "when" constraints. It will be extended, we hope.
@@ -388,14 +388,16 @@ insert_constraints([], Dict) -> Dict.
 
 -type types() :: erl_types:type_table().
 
--spec store_tmp_contract(mfa(), file_line(), [_], contracts(), types()) ->
+-type spec_data() :: {TypeSpec :: [_], Xtra:: [_]}.
+
+-spec store_tmp_contract(mfa(), file_line(), spec_data(), contracts(), types()) ->
         contracts().
 
-store_tmp_contract(MFA, FileLine, TypeSpec, SpecDict, RecordsDict) ->
+store_tmp_contract(MFA, FileLine, {TypeSpec, Xtra}, SpecDict, RecordsDict) ->
   %% io:format("contract from form: ~p\n", [TypeSpec]),
   TmpContract = contract_from_form(TypeSpec, RecordsDict, FileLine),
   %% io:format("contract: ~p\n", [TmpContract]),
-  dict:store(MFA, {FileLine, TmpContract}, SpecDict).
+  dict:store(MFA, {FileLine, TmpContract, Xtra}, SpecDict).
 
 contract_from_form(Forms, RecDict, FileLine) ->
   {CFuns, Forms1} = contract_from_form(Forms, RecDict, FileLine, [], []),
@@ -599,7 +601,7 @@ get_invalid_contract_warnings_modules([Mod|Mods], CodeServer, Plt, FindOpaques,
 get_invalid_contract_warnings_modules([], _CodeServer, _Plt, _FindOpaques, Acc) ->
   Acc.
 
-get_invalid_contract_warnings_funs([{MFA, {FileLine, Contract}}|Left],
+get_invalid_contract_warnings_funs([{MFA, {FileLine, Contract, _Xtra}}|Left],
 				   Plt, RecDict, FindOpaques, Acc) ->
   case dialyzer_plt:lookup(Plt, MFA) of
     none ->
diff --git a/lib/dialyzer/src/dialyzer_plt.erl b/lib/dialyzer/src/dialyzer_plt.erl
index 63798f44b1..7c970daf41 100644
--- a/lib/dialyzer/src/dialyzer_plt.erl
+++ b/lib/dialyzer/src/dialyzer_plt.erl
@@ -158,9 +158,7 @@ lookup_contract(#mini_plt{contracts = ETSContracts},
   ets_table_lookup(ETSContracts, MFA).
 
 -spec lookup_callbacks(plt(), module()) ->
-	 'none' | {'value', [{mfa(), {{Filename::string(),
-				       Line::pos_integer()},
-				      #contract{}}}]}.
+	 'none' | {'value', [{mfa(), dialyzer_contracts:file_contract()}]}.
 
 lookup_callbacks(#mini_plt{callbacks = ETSCallbacks}, Mod) when is_atom(Mod) ->
   ets_table_lookup(ETSCallbacks, Mod).
@@ -618,9 +616,7 @@ table_insert_list(Plt, [{Key, Val}|Left]) ->
 table_insert_list(Plt, []) ->
   Plt.
 
-table_insert(Plt, Key, {_Ret, _Arg} = Obj) ->
-  dict:store(Key, Obj, Plt);
-table_insert(Plt, Key, #contract{} = C) ->
+table_insert(Plt, Key, {_File, #contract{}, _Xtra} = C) ->
   dict:store(Key, C, Plt).
 
 table_lookup(Plt, Obj) ->
diff --git a/lib/dialyzer/src/dialyzer_succ_typings.erl b/lib/dialyzer/src/dialyzer_succ_typings.erl
index ef9b00e203..fa034816a4 100644
--- a/lib/dialyzer/src/dialyzer_succ_typings.erl
+++ b/lib/dialyzer/src/dialyzer_succ_typings.erl
@@ -201,7 +201,7 @@ postprocess_dataflow_warns([{?WARN_CONTRACT_RANGE, {CallF, CallL}, Msg}|Rest],
 			   Codeserver, WAcc, Acc) ->
   {contract_range, [Contract, M, F, A, ArgStrings, CRet]} = Msg,
   case dialyzer_codeserver:lookup_mfa_contract({M,F,A}, Codeserver) of
-    {ok, {{ContrF, _ContrL} = FileLine, _C}} ->
+    {ok, {{ContrF, _ContrL} = FileLine, _C, _X}} ->
       case CallF =:= ContrF of
 	true ->
 	  NewMsg = {contract_range, [Contract, M, F, ArgStrings, CallL, CRet]},
@@ -401,7 +401,7 @@ decorate_succ_typings(Contracts, Callgraph, FunTypes, FindOpaques) ->
           case dialyzer_callgraph:lookup_name(Label, Callgraph) of
             {ok, MFA} ->
               case orddict:find(MFA, Contracts) of
-                {ok, {_FileLine, Contract}} ->
+                {ok, {_FileLine, Contract, _Xtra}} ->
                   Args = dialyzer_contracts:get_contract_args(Contract),
                   Ret = dialyzer_contracts:get_contract_return(Contract),
                   C = erl_types:t_fun(Args, Ret),
diff --git a/lib/dialyzer/src/dialyzer_utils.erl b/lib/dialyzer/src/dialyzer_utils.erl
index 21183e3459..54f8d1d673 100644
--- a/lib/dialyzer/src/dialyzer_utils.erl
+++ b/lib/dialyzer/src/dialyzer_utils.erl
@@ -322,8 +322,26 @@ merge_records(NewRecords, OldRecords) ->
         {'ok', spec_dict(), callback_dict()} | {'error', string()}.
 
 get_spec_info(ModName, AbstractCode, RecordsDict) ->
+  OptionalCallbacks0 = get_optional_callbacks(AbstractCode, ModName),
+  OptionalCallbacks = gb_sets:from_list(OptionalCallbacks0),
   get_spec_info(AbstractCode, dict:new(), dict:new(),
-		RecordsDict, ModName, "nofile").
+		RecordsDict, ModName, OptionalCallbacks, "nofile").
+
+get_optional_callbacks(Abs, ModName) ->
+  [{ModName, F, A} || {F, A} <- get_optional_callbacks(Abs)].
+
+get_optional_callbacks(Abs) ->
+    L = [O ||
+            {attribute, _, optional_callbacks, O} <- Abs,
+            is_fa_list(O)],
+    lists:append(L).
+
+is_fa_list([{FuncName, Arity}|L])
+  when is_atom(FuncName), is_integer(Arity), Arity >= 0 ->
+    is_fa_list(L);
+is_fa_list([]) -> true;
+is_fa_list(_) -> false.
+
 
 %% TypeSpec is a list of conditional contracts for a function.
 %% Each contract is of the form {[Argument], Range, [Constraint]} where
@@ -332,13 +350,14 @@ get_spec_info(ModName, AbstractCode, RecordsDict) ->
 %%    are erl_types:erl_type()
 
 get_spec_info([{attribute, Ln, Contract, {Id, TypeSpec}}|Left],
-	      SpecDict, CallbackDict, RecordsDict, ModName, File)
+	      SpecDict, CallbackDict, RecordsDict, ModName, OptCb, File)
   when ((Contract =:= 'spec') or (Contract =:= 'callback')),
        is_list(TypeSpec) ->
   MFA = case Id of
 	  {_, _, _} = T -> T;
 	  {F, A} -> {ModName, F, A}
 	end,
+  Xtra = [optional_callback || gb_sets:is_member(MFA, OptCb)],
   ActiveDict =
     case Contract of
       spec     -> SpecDict;
@@ -346,8 +365,9 @@ get_spec_info([{attribute, Ln, Contract, {Id, TypeSpec}}|Left],
     end,
   try dict:find(MFA, ActiveDict) of
     error ->
+      SpecData = {TypeSpec, Xtra},
       NewActiveDict =
-	dialyzer_contracts:store_tmp_contract(MFA, {File, Ln}, TypeSpec,
+	dialyzer_contracts:store_tmp_contract(MFA, {File, Ln}, SpecData,
 					      ActiveDict, RecordsDict),
       {NewSpecDict, NewCallbackDict} =
 	case Contract of
@@ -355,8 +375,8 @@ get_spec_info([{attribute, Ln, Contract, {Id, TypeSpec}}|Left],
 	  callback -> {SpecDict, NewActiveDict}
 	end,
       get_spec_info(Left, NewSpecDict, NewCallbackDict,
-		    RecordsDict, ModName,File);
-    {ok, {{OtherFile, L},_C}} ->
+		    RecordsDict, ModName, OptCb, File);
+    {ok, {{OtherFile, L}, _D}} ->
       {Mod, Fun, Arity} = MFA,
       Msg = flat_format("  Contract/callback for function ~w:~w/~w "
 			"already defined in ~s:~w\n",
@@ -368,13 +388,15 @@ get_spec_info([{attribute, Ln, Contract, {Id, TypeSpec}}|Left],
 			  [Ln, Error])}
   end;
 get_spec_info([{attribute, _, file, {IncludeFile, _}}|Left],
-	      SpecDict, CallbackDict, RecordsDict, ModName, _File) ->
+	      SpecDict, CallbackDict, RecordsDict, ModName, OptCb, _File) ->
   get_spec_info(Left, SpecDict, CallbackDict,
-		RecordsDict, ModName, IncludeFile);
+		RecordsDict, ModName, OptCb, IncludeFile);
 get_spec_info([_Other|Left], SpecDict, CallbackDict,
-	      RecordsDict, ModName, File) ->
-  get_spec_info(Left, SpecDict, CallbackDict, RecordsDict, ModName, File);
-get_spec_info([], SpecDict, CallbackDict, _RecordsDict, _ModName, _File) ->
+	      RecordsDict, ModName, OptCb, File) ->
+  get_spec_info(Left, SpecDict, CallbackDict,
+                RecordsDict, ModName, OptCb, File);
+get_spec_info([], SpecDict, CallbackDict,
+              _RecordsDict, _ModName, _OptCb, _File) ->
   {ok, SpecDict, CallbackDict}.
 
 %% ============================================================================
diff --git a/lib/dialyzer/test/small_SUITE_data/results/behaviour_info b/lib/dialyzer/test/small_SUITE_data/results/behaviour_info
new file mode 100644
index 0000000000..2da4d26acb
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/results/behaviour_info
@@ -0,0 +1,2 @@
+
+with_bad_format_status.erl:12: The inferred type for the 1st argument of format_status/2 ('bad_arg') is not a supertype of 'normal' | 'terminate', which is expected type for this argument in the callback of the gen_server behaviour
diff --git a/lib/dialyzer/test/small_SUITE_data/src/behaviour_info/with_bad_format_status.erl b/lib/dialyzer/test/small_SUITE_data/src/behaviour_info/with_bad_format_status.erl
new file mode 100644
index 0000000000..24591e08fa
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/src/behaviour_info/with_bad_format_status.erl
@@ -0,0 +1,12 @@
+-module(with_bad_format_status).
+
+-behaviour(gen_server).
+-export([handle_call/3,handle_cast/2,handle_info/2,
+         code_change/3, init/1, terminate/2, format_status/2]).
+handle_call(_, _, S) -> {noreply, S}.
+handle_cast(_, S) -> {noreply, S}.
+handle_info(_, S) -> {noreply, S}.
+code_change(_, _, _) -> {error, not_implemented}.
+init(_) -> {ok, state}.
+terminate(_, _) -> ok.
+format_status(bad_arg, _) -> ok. % optional callback
diff --git a/lib/dialyzer/test/small_SUITE_data/src/behaviour_info/with_format_status.erl b/lib/dialyzer/test/small_SUITE_data/src/behaviour_info/with_format_status.erl
new file mode 100644
index 0000000000..a56ff63d1d
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/src/behaviour_info/with_format_status.erl
@@ -0,0 +1,13 @@
+-module(with_format_status).
+
+-behaviour(gen_server).
+-export([handle_call/3,handle_cast/2,handle_info/2,
+         code_change/3, init/1, terminate/2, format_status/2]).
+-export([handle_call/3,handle_cast/2,handle_info/2]).
+handle_call(_, _, S) -> {noreply, S}.
+handle_cast(_, S) -> {noreply, S}.
+handle_info(_, S) -> {noreply, S}.
+code_change(_, _, _) -> {error, not_implemented}.
+init(_) -> {ok, state}.
+terminate(_, _) -> ok.
+format_status(normal, _) -> ok. % optional callback
diff --git a/lib/stdlib/src/erl_lint.erl b/lib/stdlib/src/erl_lint.erl
index 39cc03cf7a..5deddf6bd1 100644
--- a/lib/stdlib/src/erl_lint.erl
+++ b/lib/stdlib/src/erl_lint.erl
@@ -130,6 +130,8 @@ value_option(Flag, Default, On, OnVal, Off, OffVal, Opts) ->
                    :: dict:dict(mfa(), line()),
                callbacks = dict:new()           %Callback types
                    :: dict:dict(mfa(), line()),
+               optional_callbacks = dict:new()  %Optional callbacks
+                   :: dict:dict(mfa(), line()),
                types = dict:new()               %Type definitions
                    :: dict:dict(ta(), #typeinfo{}),
                exp_types=gb_sets:empty()        %Exported types
@@ -313,13 +315,20 @@ format_error({undefined_behaviour,Behaviour}) ->
     io_lib:format("behaviour ~w undefined", [Behaviour]);
 format_error({undefined_behaviour_callbacks,Behaviour}) ->
     io_lib:format("behaviour ~w callback functions are undefined",
-                  [Behaviour]);
+		  [Behaviour]);
 format_error({ill_defined_behaviour_callbacks,Behaviour}) ->
     io_lib:format("behaviour ~w callback functions erroneously defined",
 		  [Behaviour]);
+format_error({ill_defined_optional_callbacks,Behaviour}) ->
+    io_lib:format("behaviour ~w optional callback functions erroneously defined",
+		  [Behaviour]);
 format_error({behaviour_info, {_M,F,A}}) ->
     io_lib:format("cannot define callback attibute for ~w/~w when "
                   "behaviour_info is defined",[F,A]);
+format_error({redefine_optional_callback, {F, A}}) ->
+    io_lib:format("optional callback ~w/~w duplicated", [F, A]);
+format_error({undefined_callback, {_M, F, A}}) ->
+    io_lib:format("callback ~w/~w is undefined", [F, A]);
 %% --- types and specs ---
 format_error({singleton_typevar, Name}) ->
     io_lib:format("type variable ~w is only used once (is unbound)", [Name]);
@@ -727,6 +736,8 @@ attribute_state({attribute,L,spec,{Fun,Types}}, St) ->
     spec_decl(L, Fun, Types, St);
 attribute_state({attribute,L,callback,{Fun,Types}}, St) ->
     callback_decl(L, Fun, Types, St);
+attribute_state({attribute,L,optional_callbacks,Es}, St) ->
+    optional_callbacks(L, Es, St);
 attribute_state({attribute,L,on_load,Val}, St) ->
     on_load(L, Val, St);
 attribute_state({attribute,_L,_Other,_Val}, St) -> % Ignore others
@@ -834,57 +845,73 @@ check_behaviour(St0) ->
 %%  Check behaviours for existence and defined functions.
 
 behaviour_check(Bs, St0) ->
-    {AllBfs,St1} = all_behaviour_callbacks(Bs, [], St0),
-    St = behaviour_missing_callbacks(AllBfs, St1),
+    {AllBfs0, St1} = all_behaviour_callbacks(Bs, [], St0),
+    St = behaviour_missing_callbacks(AllBfs0, St1),
+    Exports = exports(St0),
+    F = fun(Bfs, OBfs) ->
+                [B || B <- Bfs,
+                      not lists:member(B, OBfs)
+                      orelse gb_sets:is_member(B, Exports)]
+        end,
+    %% After fixing missing callbacks new warnings may be emitted.
+    AllBfs = [{Item,F(Bfs0, OBfs0)} || {Item,Bfs0,OBfs0} <- AllBfs0],
     behaviour_conflicting(AllBfs, St).
 
 all_behaviour_callbacks([{Line,B}|Bs], Acc, St0) ->
-    {Bfs0,St} = behaviour_callbacks(Line, B, St0),
-    all_behaviour_callbacks(Bs, [{{Line,B},Bfs0}|Acc], St);
+    {Bfs0,OBfs0,St} = behaviour_callbacks(Line, B, St0),
+    all_behaviour_callbacks(Bs, [{{Line,B},Bfs0,OBfs0}|Acc], St);
 all_behaviour_callbacks([], Acc, St) -> {reverse(Acc),St}.
 
 behaviour_callbacks(Line, B, St0) ->
     try B:behaviour_info(callbacks) of
-        Funcs when is_list(Funcs) ->
-            All = all(fun({FuncName, Arity}) ->
-                              is_atom(FuncName) andalso is_integer(Arity);
-			 ({FuncName, Arity, Spec}) ->
-			      is_atom(FuncName) andalso is_integer(Arity)
-				  andalso is_list(Spec);
-                         (_Other) ->
-                              false
-                      end,
-                      Funcs),
-	    MaybeRemoveSpec = fun({_F,_A}=FA) -> FA;
-				 ({F,A,_S}) -> {F,A};
-				 (Other) -> Other
-			      end,
-            if
-                All =:= true ->
-                    {[MaybeRemoveSpec(F) || F <- Funcs], St0};
+        undefined ->
+            St1 = add_warning(Line, {undefined_behaviour_callbacks, B}, St0),
+            {[], [], St1};
+        Funcs ->
+            case is_fa_list(Funcs) of
                 true ->
+                    try B:behaviour_info(optional_callbacks) of
+                        undefined ->
+                            {Funcs, [], St0};
+                        OptFuncs ->
+                            %% OptFuncs should always be OK thanks to
+                            %% sys_pre_expand.
+                            case is_fa_list(OptFuncs) of
+                                true ->
+                                    {Funcs, OptFuncs, St0};
+                                false ->
+                                    W = {ill_defined_optional_callbacks, B},
+                                    St1 = add_warning(Line, W, St0),
+                                    {Funcs, [], St1}
+                            end
+                    catch
+                        _:_ ->
+                            {Funcs, [], St0}
+                    end;
+                false ->
                     St1 = add_warning(Line,
-                                      {ill_defined_behaviour_callbacks,B},
+                                      {ill_defined_behaviour_callbacks, B},
                                       St0),
-                    {[], St1}
-            end;
-        undefined ->
-            St1 = add_warning(Line, {undefined_behaviour_callbacks,B}, St0),
-            {[], St1};
-        _Other ->
-            St1 = add_warning(Line, {ill_defined_behaviour_callbacks,B}, St0),
-            {[], St1}
+                    {[], [], St1}
+            end
     catch
         _:_ ->
-            St1 = add_warning(Line, {undefined_behaviour,B}, St0),
-            {[], St1}
+            St1 = add_warning(Line, {undefined_behaviour, B}, St0),
+            {[], [], St1}
     end.
 
-behaviour_missing_callbacks([{{Line,B},Bfs}|T], St0) ->
+behaviour_missing_callbacks([{{Line,B},Bfs0,OBfs}|T], St0) ->
+    Bfs = ordsets:subtract(ordsets:from_list(Bfs0), ordsets:from_list(OBfs)),
     Exports = gb_sets:to_list(exports(St0)),
-    Missing = ordsets:subtract(ordsets:from_list(Bfs), Exports),
+    Missing = ordsets:subtract(Bfs, Exports),
     St = foldl(fun (F, S0) ->
-		       add_warning(Line, {undefined_behaviour_func,F,B}, S0)
+                       case is_fa(F) of
+                           true ->
+                               M = {undefined_behaviour_func,F,B},
+                               add_warning(Line, M, S0);
+                           false ->
+                               S0 % ill_defined_behaviour_callbacks
+                       end
 	       end, St0, Missing),
     behaviour_missing_callbacks(T, St);
 behaviour_missing_callbacks([], St) -> St.
@@ -1127,19 +1154,29 @@ check_unused_records(Forms, St0) ->
     end.
 
 check_callback_information(#lint{callbacks = Callbacks,
-				 defined = Defined} = State) ->
-    case gb_sets:is_member({behaviour_info,1}, Defined) of
-	false -> State;
+                                 optional_callbacks = OptionalCbs,
+				 defined = Defined} = St0) ->
+    OptFun = fun({MFA, Line}, St) ->
+                     case dict:is_key(MFA, Callbacks) of
+                         true ->
+                             St;
+                         false ->
+                             add_error(Line, {undefined_callback, MFA}, St)
+                     end
+             end,
+    St1 = lists:foldl(OptFun, St0, dict:to_list(OptionalCbs)),
+    case gb_sets:is_member({behaviour_info, 1}, Defined) of
+	false -> St1;
 	true ->
 	    case dict:size(Callbacks) of
-		0 -> State;
+		0 -> St1;
 		_ ->
 		    CallbacksList = dict:to_list(Callbacks),
 		    FoldL =
-			fun({Fa,Line},St) ->
+			fun({Fa, Line}, St) ->
 				add_error(Line, {behaviour_info, Fa}, St)
 			end,
-		    lists:foldl(FoldL, State, CallbacksList)
+		    lists:foldl(FoldL, St1, CallbacksList)
 	    end
     end.
 
@@ -2927,6 +2964,39 @@ callback_decl(Line, MFA0, TypeSpecs,
 	false -> check_specs(TypeSpecs, Arity, St1)
     end.
 
+%% optional_callbacks(Line, FAs, State) -> State.
+
+optional_callbacks(Line, Term, St0) ->
+    try true = is_fa_list(Term), Term of
+        FAs ->
+            optional_cbs(Line, FAs, St0)
+    catch
+        _:_ ->
+            St0 % ignore others
+    end.
+
+optional_cbs(_Line, [], St) ->
+    St;
+optional_cbs(Line, [{F,A}|FAs], St0) ->
+    #lint{optional_callbacks = OptionalCbs, module = Mod} = St0,
+    MFA = {Mod, F, A},
+    St1 = St0#lint{optional_callbacks = dict:store(MFA, Line, OptionalCbs)},
+    St2 = case dict:is_key(MFA, OptionalCbs) of
+              true ->
+                  add_error(Line, {redefine_optional_callback, {F,A}}, St1);
+              false ->
+                  St1
+          end,
+    optional_cbs(Line, FAs, St2).
+
+is_fa_list([E|L]) -> is_fa(E) andalso is_fa_list(L);
+is_fa_list([]) -> true;
+is_fa_list(_) -> false.
+
+is_fa({FuncName, Arity})
+  when is_atom(FuncName), is_integer(Arity), Arity >= 0 -> true;
+is_fa(_) -> false.
+
 check_specs([FunType|Left], Arity, St0) ->
     {FunType1, CTypes} =
 	case FunType of
diff --git a/lib/stdlib/src/erl_pp.erl b/lib/stdlib/src/erl_pp.erl
index 82bc2c1460..788dbb40b6 100644
--- a/lib/stdlib/src/erl_pp.erl
+++ b/lib/stdlib/src/erl_pp.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1996-2013. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2014. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -232,13 +232,21 @@ lattribute(import, Name, _Opts, _State) when is_list(Name) ->
     attr("import", [{var,0,pname(Name)}]);
 lattribute(import, {From,Falist}, _Opts, _State) ->
     attr("import",[{var,0,pname(From)},falist(Falist)]);
+lattribute(optional_callbacks, Falist, Opts, _State) ->
+    ArgL = try falist(Falist)
+           catch _:_ -> abstract(Falist, Opts)
+           end,
+    call({var,0,"-optional_callbacks"}, [ArgL], 0, options(none));
 lattribute(file, {Name,Line}, _Opts, State) ->
     attr("file", [{var,0,(State#pp.string_fun)(Name)},{integer,0,Line}]);
 lattribute(record, {Name,Is}, Opts, _State) ->
     Nl = leaf(format("-record(~w,", [Name])),
     [{first,Nl,record_fields(Is, Opts)},$)];
-lattribute(Name, Arg, #options{encoding = Encoding}, _State) ->
-    attr(write(Name), [erl_parse:abstract(Arg, [{encoding,Encoding}])]).
+lattribute(Name, Arg, Options, _State) ->
+    attr(write(Name), [abstract(Arg, Options)]).
+
+abstract(Arg, #options{encoding = Encoding}) ->
+    erl_parse:abstract(Arg, [{encoding,Encoding}]).
 
 typeattr(Tag, {TypeName,Type,Args}, _Opts) ->
     {first,leaf("-"++atom_to_list(Tag)++" "),
diff --git a/lib/stdlib/src/gen_event.erl b/lib/stdlib/src/gen_event.erl
index d39dd89d3a..bb0ff46268 100644
--- a/lib/stdlib/src/gen_event.erl
+++ b/lib/stdlib/src/gen_event.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1996-2013. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2014. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -101,6 +101,14 @@
 -callback code_change(OldVsn :: (term() | {down, term()}),
                       State :: term(), Extra :: term()) ->
     {ok, NewState :: term()}.
+-callback format_status(Opt, StatusData) -> Status when
+      Opt :: 'normal' | 'terminate',
+      StatusData :: [PDict | State],
+      PDict :: [{Key :: term(), Value :: term()}],
+      State :: term(),
+      Status :: term().
+
+-optional_callbacks([format_status/2]).
 
 %%---------------------------------------------------------------------------
 
diff --git a/lib/stdlib/src/gen_fsm.erl b/lib/stdlib/src/gen_fsm.erl
index e914f7d0b2..56137cde13 100644
--- a/lib/stdlib/src/gen_fsm.erl
+++ b/lib/stdlib/src/gen_fsm.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1996-2013. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2014. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -160,6 +160,14 @@
 -callback code_change(OldVsn :: term() | {down, term()}, StateName :: atom(),
 		      StateData :: term(), Extra :: term()) ->
     {ok, NextStateName :: atom(), NewStateData :: term()}.
+-callback format_status(Opt, StatusData) -> Status when
+      Opt :: 'normal' | 'terminate',
+      StatusData :: [PDict | State],
+      PDict :: [{Key :: term(), Value :: term()}],
+      State :: term(),
+      Status :: term().
+
+-optional_callbacks([format_status/2]).
 
 %%% ---------------------------------------------------
 %%% Starts a generic state machine.
diff --git a/lib/stdlib/src/gen_server.erl b/lib/stdlib/src/gen_server.erl
index 202a931fae..22acdf10b7 100644
--- a/lib/stdlib/src/gen_server.erl
+++ b/lib/stdlib/src/gen_server.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1996-2013. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2014. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -137,6 +137,15 @@
 -callback code_change(OldVsn :: (term() | {down, term()}), State :: term(),
                       Extra :: term()) ->
     {ok, NewState :: term()} | {error, Reason :: term()}.
+-callback format_status(Opt, StatusData) -> Status when
+      Opt :: 'normal' | 'terminate',
+      StatusData :: [PDict | State],
+      PDict :: [{Key :: term(), Value :: term()}],
+      State :: term(),
+      Status :: term().
+
+-optional_callbacks([format_status/2]).
+
 
 %%%  -----------------------------------------------------------------
 %%% Starts a generic server.
diff --git a/lib/stdlib/test/erl_internal_SUITE.erl b/lib/stdlib/test/erl_internal_SUITE.erl
index b6b3c004ea..197a7a33eb 100644
--- a/lib/stdlib/test/erl_internal_SUITE.erl
+++ b/lib/stdlib/test/erl_internal_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 1999-2011. All Rights Reserved.
+%% Copyright Ericsson AB 1999-2014. All Rights Reserved.
 %% 
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -51,7 +51,7 @@ end_per_group(_GroupName, Config) ->
 -define(default_timeout, ?t:minutes(2)).
 
 init_per_testcase(_Case, Config) ->
-    ?line Dog = test_server:timetrap(?default_timeout),
+    Dog = test_server:timetrap(?default_timeout),
     [{watchdog, Dog}|Config].
 
 end_per_testcase(_Case, Config) ->
@@ -63,27 +63,50 @@ behav(suite) -> [];
 behav(doc) ->
     ["Check that the behaviour callbacks are correctly defined"];
 behav(_) ->
-    ?line check_behav_list([{start,2}, {stop,1}], 
-			   application:behaviour_info(callbacks)),
-    ?line check_behav_list([{init,1}, {handle_call,3}, {handle_cast,2},
-			    {handle_info,2}, {terminate,2}, {code_change,3}],
-			   gen_server:behaviour_info(callbacks)),
-    ?line check_behav_list([{init,1}, {handle_event,3}, {handle_sync_event,4},
-			    {handle_info,3}, {terminate,3}, {code_change,4}],
-			   gen_fsm:behaviour_info(callbacks)),
-    ?line check_behav_list([{init,1}, {handle_event,2}, {handle_call,2},
-			    {handle_info,2}, {terminate,2}, {code_change,3}],
-			   gen_event:behaviour_info(callbacks)),
-    ?line check_behav_list( [{init,1}, {terminate,2}], 
-			   supervisor_bridge:behaviour_info(callbacks)),
-    ?line check_behav_list([{init,1}],
-			   supervisor:behaviour_info(callbacks)),
-    ok.
+    Modules = [application, gen_server, gen_fsm, gen_event,
+               supervisor_bridge, supervisor],
+    lists:foreach(fun check_behav/1, Modules).
+
+check_behav(Module) ->
+    Callbacks = callbacks(Module),
+    Optional = optional_callbacks(Module),
+    check_behav_list(Callbacks, Module:behaviour_info(callbacks)),
+    check_behav_list(Optional, Module:behaviour_info(optional_callbacks)).
 
 check_behav_list([], []) -> ok;
 check_behav_list([L | L1], L2) ->
-    ?line true = lists:member(L, L2),
-    ?line L3 = lists:delete(L, L2),
+    true = lists:member(L, L2),
+    L3 = lists:delete(L, L2),
     check_behav_list(L1, L3).
 
-
+callbacks(application) ->
+    [{start,2}, {stop,1}];
+callbacks(gen_server) ->
+    [{init,1}, {handle_call,3}, {handle_cast,2},
+     {handle_info,2}, {terminate,2}, {code_change,3},
+     {format_status,2}];
+callbacks(gen_fsm) ->
+    [{init,1}, {handle_event,3}, {handle_sync_event,4},
+     {handle_info,3}, {terminate,3}, {code_change,4},
+     {format_status,2}];
+callbacks(gen_event) ->
+    [{init,1}, {handle_event,2}, {handle_call,2},
+     {handle_info,2}, {terminate,2}, {code_change,3},
+     {format_status,2}];
+callbacks(supervisor_bridge) ->
+    [{init,1}, {terminate,2}];
+callbacks(supervisor) ->
+    [{init,1}].
+
+optional_callbacks(application) ->
+    [];
+optional_callbacks(gen_server) ->
+    [{format_status,2}];
+optional_callbacks(gen_fsm) ->
+    [{format_status,2}];
+optional_callbacks(gen_event) ->
+    [{format_status,2}];
+optional_callbacks(supervisor_bridge) ->
+    [];
+optional_callbacks(supervisor) ->
+    [].
diff --git a/lib/stdlib/test/erl_lint_SUITE.erl b/lib/stdlib/test/erl_lint_SUITE.erl
index ea61b2082b..5506d3d166 100644
--- a/lib/stdlib/test/erl_lint_SUITE.erl
+++ b/lib/stdlib/test/erl_lint_SUITE.erl
@@ -55,7 +55,7 @@
           otp_11772/1, otp_11771/1, otp_11872/1,
           export_all/1,
 	  bif_clash/1,
-	  behaviour_basic/1, behaviour_multiple/1,
+	  behaviour_basic/1, behaviour_multiple/1, otp_11861/1,
 	  otp_7550/1,
 	  otp_8051/1,
 	  format_warn/1,
@@ -89,7 +89,7 @@ all() ->
      otp_5362, otp_5371, otp_7227, otp_5494, otp_5644,
      otp_5878, otp_5917, otp_6585, otp_6885, otp_10436, otp_11254,
      otp_11772, otp_11771, otp_11872, export_all,
-     bif_clash, behaviour_basic, behaviour_multiple,
+     bif_clash, behaviour_basic, behaviour_multiple, otp_11861,
      otp_7550, otp_8051, format_warn, {group, on_load},
      too_many_arguments, basic_errors, bin_syntax_errors, predef,
      maps, maps_type].
@@ -3080,6 +3080,193 @@ behaviour_multiple(Config) when is_list(Config) ->
     ?line [] = run(Config, Ts),
     ok.
 
+otp_11861(doc) ->
+    "OTP-11861. behaviour_info() and -callback.";
+otp_11861(suite) -> [];
+otp_11861(Conf) when is_list(Conf) ->
+    CallbackFiles = [callback1, callback2, callback3,
+                     bad_behaviour1, bad_behaviour2],
+    lists:foreach(fun(M) ->
+                          F = filename:join(?datadir, M),
+                          Opts = [{outdir,?privdir}, return],
+                          {ok, M, []} = compile:file(F, Opts)
+                  end, CallbackFiles),
+    CodePath = code:get_path(),
+    true = code:add_path(?privdir),
+    Ts = [{otp_11861_1,
+           <<"
+              -export([b1/1]).
+              -behaviour(callback1).
+              -behaviour(callback2).
+
+              -spec b1(atom()) -> integer().
+              b1(A) when is_atom(A)->
+                  3.
+             ">>,
+           [],
+           %% b2/1 is optional in both modules
+           {warnings,[{4,erl_lint,
+                       {conflicting_behaviours,{b1,1},callback2,3,callback1}}]}},
+          {otp_11861_2,
+           <<"
+              -export([b2/1]).
+              -behaviour(callback1).
+              -behaviour(callback2).
+
+              -spec b2(integer()) -> atom().
+              b2(I) when is_integer(I)->
+                  a.
+             ">>,
+           [],
+           %% b2/1 is optional in callback2, but not in callback1
+           {warnings,[{3,erl_lint,{undefined_behaviour_func,{b1,1},callback1}},
+                      {4,erl_lint,
+                       {conflicting_behaviours,{b2,1},callback2,3,callback1}}]}},
+          {otp_11861_3,
+           <<"
+              -callback b(_) -> atom().
+              -optional_callbacks({b1,1}). % non-existing and ignored
+             ">>,
+           [],
+           []},
+          {otp_11861_4,
+           <<"
+              -callback b(_) -> atom().
+              -optional_callbacks([{b1,1}]). % non-existing
+             ">>,
+           [],
+           %% No behaviour-info(), but callback.
+           {errors,[{3,erl_lint,{undefined_callback,{lint_test,b1,1}}}],[]}},
+          {otp_11861_5,
+           <<"
+              -optional_callbacks([{b1,1}]). % non-existing
+             ">>,
+           [],
+           %% No behaviour-info() and no callback: warning anyway
+           {errors,[{2,erl_lint,{undefined_callback,{lint_test,b1,1}}}],[]}},
+          {otp_11861_6,
+           <<"
+              -optional_callbacks([b1/1]). % non-existing
+              behaviour_info(callbacks) -> [{b1,1}].
+             ">>,
+           [],
+           %% behaviour-info() and no callback: warning anyway
+           {errors,[{2,erl_lint,{undefined_callback,{lint_test,b1,1}}}],[]}},
+          {otp_11861_7,
+           <<"
+              -optional_callbacks([b1/1]). % non-existing
+              -callback b(_) -> atom().
+              behaviour_info(callbacks) -> [{b1,1}].
+             ">>,
+           [],
+           %% behaviour-info() callback: warning
+           {errors,[{2,erl_lint,{undefined_callback,{lint_test,b1,1}}},
+                    {3,erl_lint,{behaviour_info,{lint_test,b,1}}}],
+            []}},
+          {otp_11861_8,
+           <<"
+              -callback b(_) -> atom().
+              -optional_callbacks([b/1, {b, 1}]).
+             ">>,
+           [],
+           {errors,[{3,erl_lint,{redefine_optional_callback,{b,1}}}],[]}},
+          {otp_11861_9,
+           <<"
+              -behaviour(gen_server).
+              -export([handle_call/3,handle_cast/2,handle_info/2,
+                       code_change/3, init/1, terminate/2]).
+              handle_call(_, _, _) -> ok.
+              handle_cast(_, _) -> ok.
+              handle_info(_, _) -> ok.
+              code_change(_, _, _) -> ok.
+              init(_) -> ok.
+              terminate(_, _) -> ok.
+             ">>,
+           [],
+           []},
+          {otp_11861_9,
+           <<"
+              -behaviour(gen_server).
+              -export([handle_call/3,handle_cast/2,handle_info/2,
+                       code_change/3, init/1, terminate/2, format_status/2]).
+              handle_call(_, _, _) -> ok.
+              handle_cast(_, _) -> ok.
+              handle_info(_, _) -> ok.
+              code_change(_, _, _) -> ok.
+              init(_) -> ok.
+              terminate(_, _) -> ok.
+              format_status(_, _) -> ok. % optional callback
+             ">>,
+           [],
+           %% Nothing...
+           []},
+          {otp_11861_10,
+           <<"
+              -optional_callbacks([{b1,1,bad}]). % badly formed and ignored
+              behaviour_info(callbacks) -> [{b1,1}].
+             ">>,
+           [],
+           []},
+          {otp_11861_11,
+           <<"
+              -behaviour(bad_behaviour1).
+             ">>,
+           [],
+           {warnings,[{2,erl_lint,
+                       {ill_defined_behaviour_callbacks,bad_behaviour1}}]}},
+          {otp_11861_12,
+           <<"
+              -behaviour(non_existing_behaviour).
+             ">>,
+           [],
+           {warnings,[{2,erl_lint,
+                       {undefined_behaviour,non_existing_behaviour}}]}},
+          {otp_11861_13,
+           <<"
+              -behaviour(bad_behaviour_none).
+             ">>,
+           [],
+           {warnings,[{2,erl_lint,{undefined_behaviour,bad_behaviour_none}}]}},
+          {otp_11861_14,
+           <<"
+              -callback b(_) -> atom().
+             ">>,
+           [],
+           []},
+          {otp_11861_15,
+           <<"
+              -optional_callbacks([{b1,1,bad}]). % badly formed
+              -callback b(_) -> atom().
+             ">>,
+           [],
+           []},
+          {otp_11861_16,
+           <<"
+              -callback b(_) -> atom().
+              -callback b(_) -> atom().
+             ">>,
+           [],
+           {errors,[{3,erl_lint,{redefine_callback,{lint_test,b,1}}}],[]}},
+          {otp_11861_17,
+           <<"
+              -behaviour(bad_behaviour2).
+             ">>,
+           [],
+           {warnings,[{2,erl_lint,{undefined_behaviour_callbacks,
+                                   bad_behaviour2}}]}},
+          {otp_11861_18,
+           <<"
+              -export([f1/1]).
+              -behaviour(callback3).
+              f1(_) -> ok.
+             ">>,
+           [],
+           []}
+	 ],
+    ?line [] = run(Conf, Ts),
+    true = code:set_path(CodePath),
+    ok.
+
 otp_7550(doc) ->
     "Test that the new utf8/utf16/utf32 types do not allow size or unit specifiers.";
 otp_7550(Config) when is_list(Config) ->
diff --git a/lib/stdlib/test/erl_lint_SUITE_data/bad_behaviour1.erl b/lib/stdlib/test/erl_lint_SUITE_data/bad_behaviour1.erl
new file mode 100644
index 0000000000..230f4b4519
--- /dev/null
+++ b/lib/stdlib/test/erl_lint_SUITE_data/bad_behaviour1.erl
@@ -0,0 +1,6 @@
+-module(bad_behaviour1).
+
+-export([behaviour_info/1]).
+
+behaviour_info(callbacks) ->
+    [{a,1,bad}].
diff --git a/lib/stdlib/test/erl_lint_SUITE_data/bad_behaviour2.erl b/lib/stdlib/test/erl_lint_SUITE_data/bad_behaviour2.erl
new file mode 100644
index 0000000000..bb755ce18b
--- /dev/null
+++ b/lib/stdlib/test/erl_lint_SUITE_data/bad_behaviour2.erl
@@ -0,0 +1,6 @@
+-module(bad_behaviour2).
+
+-export([behaviour_info/1]).
+
+behaviour_info(callbacks) ->
+    undefined.
diff --git a/lib/stdlib/test/erl_lint_SUITE_data/callback1.erl b/lib/stdlib/test/erl_lint_SUITE_data/callback1.erl
new file mode 100644
index 0000000000..3cc5b51879
--- /dev/null
+++ b/lib/stdlib/test/erl_lint_SUITE_data/callback1.erl
@@ -0,0 +1,6 @@
+-module(callback1).
+
+-callback b1(I :: integer()) -> atom().
+-callback b2(A :: atom()) -> integer().
+
+-optional_callbacks([{b2,1}]).
diff --git a/lib/stdlib/test/erl_lint_SUITE_data/callback2.erl b/lib/stdlib/test/erl_lint_SUITE_data/callback2.erl
new file mode 100644
index 0000000000..211cf9f115
--- /dev/null
+++ b/lib/stdlib/test/erl_lint_SUITE_data/callback2.erl
@@ -0,0 +1,6 @@
+-module(callback2).
+
+-callback b1(I :: integer()) -> atom().
+-callback b2(A :: atom()) -> integer().
+
+-optional_callbacks([b1/1, b2/1]).
diff --git a/lib/stdlib/test/erl_lint_SUITE_data/callback3.erl b/lib/stdlib/test/erl_lint_SUITE_data/callback3.erl
new file mode 100644
index 0000000000..97b3ecb860
--- /dev/null
+++ b/lib/stdlib/test/erl_lint_SUITE_data/callback3.erl
@@ -0,0 +1,8 @@
+-module(callback3).
+
+-export([behaviour_info/1]).
+
+behaviour_info(callbacks) ->
+    [{f1, 1}];
+behaviour_info(_) ->
+    undefined.
diff --git a/lib/stdlib/test/erl_pp_SUITE.erl b/lib/stdlib/test/erl_pp_SUITE.erl
index babf3a49eb..d0892c6d79 100644
--- a/lib/stdlib/test/erl_pp_SUITE.erl
+++ b/lib/stdlib/test/erl_pp_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2006-2013. All Rights Reserved.
+%% Copyright Ericsson AB 2006-2014. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -50,7 +50,7 @@
 
 	  otp_6321/1, otp_6911/1, otp_6914/1, otp_8150/1, otp_8238/1,
 	  otp_8473/1, otp_8522/1, otp_8567/1, otp_8664/1, otp_9147/1,
-          otp_10302/1, otp_10820/1, otp_11100/1]).
+          otp_10302/1, otp_10820/1, otp_11100/1, otp_11861/1]).
 
 %% Internal export.
 -export([ehook/6]).
@@ -83,7 +83,7 @@ groups() ->
      {tickets, [],
       [otp_6321, otp_6911, otp_6914, otp_8150, otp_8238,
        otp_8473, otp_8522, otp_8567, otp_8664, otp_9147,
-       otp_10302, otp_10820, otp_11100]}].
+       otp_10302, otp_10820, otp_11100, otp_11861]}].
 
 init_per_suite(Config) ->
     Config.
@@ -1204,8 +1204,18 @@ otp_11100(Config) when is_list(Config) ->
              []}}),
     ok.
 
+otp_11861(doc) ->
+    "OTP-11861. behaviour_info() and -callback.";
+otp_11861(suite) -> [];
+otp_11861(Config) when is_list(Config) ->
+    "-optional_callbacks([bar/0]).\n" =
+        pf({attribute,3,optional_callbacks,[{bar,0}]}),
+    "-optional_callbacks([{bar,1,bad}]).\n" =
+        pf({attribute,4,optional_callbacks,[{bar,1,bad}]}),
+    ok.
+
 pf(Form) ->
-    lists:flatten(erl_pp:form(Form,none)).
+    lists:flatten(erl_pp:form(Form, none)).
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
diff --git a/lib/syntax_tools/src/erl_syntax.erl b/lib/syntax_tools/src/erl_syntax.erl
index c9996c954e..f7819c2662 100644
--- a/lib/syntax_tools/src/erl_syntax.erl
+++ b/lib/syntax_tools/src/erl_syntax.erl
@@ -3320,6 +3320,11 @@ attribute_arguments(Node) ->
 		    [set_pos(
 		       list(unfold_function_names(Data, Pos)),
 		       Pos)];
+		optional_callbacks ->
+                    D = try list(unfold_function_names(Data, Pos))
+                        catch _:_ -> abstract(Data)
+                        end,
+		    [set_pos(D, Pos)];
 		import ->
 		    {Module, Imports} = Data,
 		    [set_pos(atom(Module), Pos),
diff --git a/lib/typer/src/typer.erl b/lib/typer/src/typer.erl
index 572bf24ca4..cbad05081e 100644
--- a/lib/typer/src/typer.erl
+++ b/lib/typer/src/typer.erl
@@ -405,7 +405,7 @@ get_type({{M, F, A} = MFA, Range, Arg}, CodeServer, Records) ->
   case dialyzer_codeserver:lookup_mfa_contract(MFA, CodeServer) of
     error ->
       {{F, A}, {Range, Arg}};
-    {ok, {_FileLine, Contract}} ->
+    {ok, {_FileLine, Contract, _Xtra}} ->
       Sig = erl_types:t_fun(Arg, Range),
       case dialyzer_contracts:check_contract(Contract, Sig) of
 	ok -> {{F, A}, {contract, Contract}};
diff --git a/system/doc/design_principles/spec_proc.xml b/system/doc/design_principles/spec_proc.xml
index e4fb5fdca7..e849388a38 100644
--- a/system/doc/design_principles/spec_proc.xml
+++ b/system/doc/design_principles/spec_proc.xml
@@ -431,43 +431,79 @@ loop(...) ->
 
   <section>
     <title>User-Defined Behaviours</title>
-    <p><marker id="behaviours"/>To implement a user-defined behaviour, write code similar to
-      code for a special process but calling functions in a callback
-      module for handling specific tasks.</p>
-    <p>If it is desired that the compiler should warn for missing callback
-    functions, as it does for the OTP behaviours, add <c>-callback</c> attributes in the
-    behaviour module to describe the expected callbacks:</p>
+
+    <p><marker id="behaviours"/>To implement a user-defined behaviour,
+      write code similar to code for a special process but calling
+      functions in a callback module for handling specific tasks.</p>
+    <p>If it is desired that the compiler should warn for missing
+      callback functions, as it does for the OTP behaviours, add
+      <c>-callback</c> attributes in the behaviour module to describe
+      the expected callback functions:</p>
+
     <code type="none">
 -callback Name1(Arg1_1, Arg1_2, ..., Arg1_N1) -> Res1.
 -callback Name2(Arg2_1, Arg2_2, ..., Arg2_N2) -> Res2.
 ...
 -callback NameM(ArgM_1, ArgM_2, ..., ArgM_NM) -> ResM.</code>
-    <p>where <c>NameX</c> are the names of the expected callbacks and
-    <c>ArgX_Y</c>, <c>ResX</c> are types as they are described in Specifications
-    for functions in <seealso marker="../reference_manual/typespec">Types and
-    Function Specifications</seealso>. The whole syntax of <c>-spec</c> attribute is
-    supported by <c>-callback</c> attribute.</p>
-    <p>Alternatively you may directly implement and export the function:</p>
+
+    <p>where each <c>Name</c> is the name of a callback function and
+      <c>Arg</c> and <c>Res</c> are types as described in
+      Specifications for functions in <seealso
+      marker="../reference_manual/typespec">Types and Function
+      Specifications</seealso>. The whole syntax of the
+      <c>-spec</c> attribute is supported by <c>-callback</c>
+      attribute.</p>
+    <p>Callback functions that are optional for the user of the
+      behaviour to implement are specified by use of the
+      <c>-optional_callbacks</c> attribute:</p>
+
+<code type="none">
+-optional_callbacks([OptName1/OptArity1, ..., OptNameK/OptArityK]).</code>
+
+    <p>where each <c>OptName/OptArity</c> specifies the name and arity
+      of a callback function. Note that the <c>-optional_callbacks</c>
+      attribute is to be used together with the <c>-callback</c>
+      attribute; it cannot be combined with the
+      <c>behaviour_info()</c> function described below.</p>
+    <p>Tools that need to know about optional callback functions can
+      call <c>Behaviour:behaviour_info(optional_callbacks)</c> to get
+      a list of all optional callback functions.</p>
+
+    <note><p>We recommend using the <c>-callback</c> attribute rather
+      than the <c>behaviour_info()</c> function. The reason is that
+      the extra type information can be used by tools to produce
+      documentation or find discrepancies.</p></note>
+
+    <p>As an alternative to the <c>-callback</c> and
+      <c>-optional_callbacks</c> attributes you may directly implement
+      and export <c>behaviour_info()</c>:</p>
+
     <code type="none">
 behaviour_info(callbacks) ->
     [{Name1, Arity1},...,{NameN, ArityN}].</code>
-    <p>where each <c>{Name, Arity}</c> specifies the name and arity of a callback
-    function. This function is otherwise automatically generated by the compiler
-    using the <c>-callback</c> attributes.</p>
+
+    <p>where each <c>{Name, Arity}</c> specifies the name and arity of
+      a callback function. This function is otherwise automatically
+      generated by the compiler using the <c>-callback</c>
+      attributes.</p>
     <p>When the compiler encounters the module attribute
-    <c>-behaviour(Behaviour).</c> in a module <c>Mod</c>, it will call
-    <c>Behaviour:behaviour_info(callbacks)</c> and compare the result with the
-    set of functions actually exported from <c>Mod</c>, and issue a warning if
-    any callback function is missing.</p>
+      <c>-behaviour(Behaviour).</c> in a module <c>Mod</c>, it will
+      call <c>Behaviour:behaviour_info(callbacks)</c> and compare the
+      result with the set of functions actually exported from
+      <c>Mod</c>, and issue a warning if any callback function is
+      missing.</p>
     <p>Example:</p>
     <code type="none">
 %% User-defined behaviour module
 -module(simple_server).
--export([start_link/2,...]).
+-export([start_link/2, init/3, ...]).
 
 -callback init(State :: term()) -> 'ok'.
 -callback handle_req(Req :: term(), State :: term()) -> {'ok', Reply :: term()}.
 -callback terminate() -> 'ok'.
+-callback format_state(State :: term()) -> term().
+
+-optional_callbacks([format_state/1]).
 
 %% Alternatively you may define:
 %%