Automatically generate 'behaviour_info' function from '-callback' attributes

'behaviour_info(callbacks)' is a special function that is defined in a module
which describes a behaviour and returns a list of its callbacks.

This function is now automatically generated using the '-callback' specs. An
error is returned by lint if user defines both '-callback' attributes and the
behaviour_info/1 function. If no type info is needed for a callback use a
generic spec for it.

2 files changed, 56 insertions, 3 deletions

diff --git a/lib/compiler/src/sys_pre_expand.erl b/lib/compiler/src/sys_pre_expand.erl
index 249bd7a8e7..0fa1fea09f 100644
--- a/lib/compiler/src/sys_pre_expand.erl
+++ b/lib/compiler/src/sys_pre_expand.erl
@@ -43,6 +43,7 @@
                  mod_imports,                   %Module Imports
                  compile=[],                    %Compile flags
                  attributes=[],                 %Attributes
+                 callbacks=[],                  %Callbacks
                  defined=[],                    %Defined functions
                  vcount=0,                      %Variable counter
                  func=[],                       %Current function
@@ -172,10 +173,41 @@ define_functions(Forms, #expand{defined=Predef}=St) ->
                end, Predef, Forms),
     St#expand{defined=ordsets:from_list(Fs)}.
 
-module_attrs(St) ->
-    {[{attribute,Line,Name,Val} || {Name,Line,Val} <- St#expand.attributes],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}}.
 
 module_predef_funcs(St) ->
+    {Mpf1,St1}=module_predef_func_beh_info(St),
+    {Mpf2,St2}=module_predef_funcs_mod_info(St1),
+    {Mpf1++Mpf2,St2}.
+
+module_predef_func_beh_info(#expand{callbacks=[]}=St) ->
+    {[], St};
+module_predef_func_beh_info(#expand{callbacks=Callbacks,defined=Defined,
+				    exports=Exports}=St) ->
+    PreDef=[{behaviour_info,1}],
+    PreExp=PreDef,
+    {[gen_beh_info(Callbacks)],
+     St#expand{defined=union(from_list(PreDef), Defined),
+	       exports=union(from_list(PreExp), Exports)}}.
+
+gen_beh_info(Callbacks) ->
+    List = make_list(Callbacks),
+    {function,0,behaviour_info,1,
+     [{clause,0,[{atom,0,callbacks}],[],
+       [List]}]}.
+
+make_list([]) -> {nil,0};
+make_list([{_,_,_,[{{Name,Arity},_}]}|Rest]) ->
+    {cons,0,
+     {tuple,0,
+      [{atom,0,Name},
+       {integer,0,Arity}]},
+     make_list(Rest)}.
+
+module_predef_funcs_mod_info(St) ->
     PreDef = [{module_info,0},{module_info,1}],
     PreExp = PreDef,
     {[{function,0,module_info,0,
diff --git a/lib/stdlib/src/erl_lint.erl b/lib/stdlib/src/erl_lint.erl
index 0d8773ff0d..78b996d94b 100644
--- a/lib/stdlib/src/erl_lint.erl
+++ b/lib/stdlib/src/erl_lint.erl
@@ -319,6 +319,9 @@ format_error({undefined_behaviour_callbacks,Behaviour}) ->
 format_error({ill_defined_behaviour_callbacks,Behaviour}) ->
     io_lib:format("behaviour ~w 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]);
 %% --- types and specs ---
 format_error({singleton_typevar, Name}) ->
     io_lib:format("type variable ~w is only used once (is unbound)", [Name]);
@@ -845,7 +848,8 @@ post_traversal_check(Forms, St0) ->
     StB = check_unused_types(Forms, StA),
     StC = check_untyped_records(Forms, StB),
     StD = check_on_load(StC),
-    check_unused_records(Forms, StD).
+    StE = check_unused_records(Forms, StD),
+    check_callback_information(StE).
 
 %% check_behaviour(State0) -> State
 %% Check that the behaviour attribute is valid.
@@ -1144,6 +1148,23 @@ check_unused_records(Forms, St0) ->
             St0
     end.
 
+check_callback_information(#lint{callbacks = Callbacks,
+				 defined = Defined} = State) ->
+    case gb_sets:is_member({behaviour_info,1}, Defined) of
+	false -> State;
+	true ->
+	    case dict:size(Callbacks) of
+		0 -> State;
+		_ ->
+		    CallbacksList = dict:to_list(Callbacks),
+		    FoldL =
+			fun({Fa,Line},St) ->
+				add_error(Line, {behaviour_info, Fa}, St)
+			end,
+		    lists:foldl(FoldL, State, CallbacksList)
+	    end
+    end.
+
 %% For storing the import list we use the orddict module.
 %% We know an empty set is [].