dialyzer: Suppress warns on generated case stmts

Warnings about clauses that cannot match and are also compiler generated
are suppressed unless none of the clauses return.

This feature is useful for non-Erlang BEAM languages (such as Elixir)
that compile to Erlang and expand certain language constructs into case
statements. In that case, as long as the language construct can succeed,
these warnings are undesired and appear spurious to users that do not
check the Erlang code that their program expands into.

Thanks to José Valim for the test (slightly modified).

1 files changed, 36 insertions, 26 deletions

diff --git a/lib/dialyzer/src/dialyzer_dataflow.erl b/lib/dialyzer/src/dialyzer_dataflow.erl
index 9399789464..963c953447 100644
--- a/lib/dialyzer/src/dialyzer_dataflow.erl
+++ b/lib/dialyzer/src/dialyzer_dataflow.erl
@@ -978,12 +978,21 @@ handle_case(Tree, Map, State) ->
           false -> State1
         end,
       Map2 = join_maps_begin(Map1),
-      {MapList, State3, Type} =
+      {MapList, State3, Type, Warns} =
 	handle_clauses(Clauses, Arg, ArgType, ArgType, State2,
-		       [], Map2, [], []),
+		       [], Map2, [], [], []),
+      %% Non-Erlang BEAM languages, such as Elixir, expand language constructs
+      %% into case statements. In that case, we do not want to warn on
+      %% individual clauses not matching unless none of them can.
+      SupressForced = is_compiler_generated(cerl:get_ann(Tree))
+	andalso not (t_is_none(Type)),
+      State4 = lists:foldl(fun({T,R,M,F}, S) ->
+			       state__add_warning(
+				 S,T,R,M,F andalso (not SupressForced))
+			   end, State3, Warns),
       Map3 = join_maps_end(MapList, Map2),
       debug_pp_map(Map3),
-      {State3, Map3, Type}
+      {State4, Map3, Type}
   end.
 
 %%----------------------------------------
@@ -1082,22 +1091,24 @@ handle_receive(Tree, Map, State) ->
                                RaceListSize + 1, State);
       false -> State
     end,
-  {MapList, State2, ReceiveType} =
+  {MapList, State2, ReceiveType, Warns} =
     handle_clauses(Clauses, ?no_arg, t_any(), t_any(), State1, [], Map,
-                   [], []),
+		   [], [], []),
+  State3 = lists:foldl(fun({T,R,M,F}, S) -> state__add_warning(S,T,R,M,F) end,
+		       State2, Warns),
   Map1 = join_maps(MapList, Map),
-  {State3, Map2, TimeoutType} = traverse(Timeout, Map1, State2),
-  Opaques = State3#state.opaques,
+  {State4, Map2, TimeoutType} = traverse(Timeout, Map1, State3),
+  Opaques = State4#state.opaques,
   case (t_is_atom(TimeoutType, Opaques) andalso
 	(t_atom_vals(TimeoutType, Opaques) =:= ['infinity'])) of
     true ->
-      {State3, Map2, ReceiveType};
+      {State4, Map2, ReceiveType};
     false ->
       Action = cerl:receive_action(Tree),
-      {State4, Map3, ActionType} = traverse(Action, Map, State3),
+      {State5, Map3, ActionType} = traverse(Action, Map, State4),
       Map4 = join_maps([Map3, Map1], Map),
       Type = t_sup(ReceiveType, ActionType),
-      {State4, Map4, Type}
+      {State5, Map4, Type}
   end.
 
 %%----------------------------------------
@@ -1245,7 +1256,7 @@ handle_tuple(Tree, Map, State) ->
 %% Clauses
 %%
 handle_clauses([C|Left], Arg, ArgType, OrigArgType, State, CaseTypes, MapIn,
-	       Acc, ClauseAcc) ->
+	       Acc, ClauseAcc, WarnAcc0) ->
   IsRaceAnalysisEnabled = is_race_analysis_enabled(State),
   State1 =
     case IsRaceAnalysisEnabled of
@@ -1258,8 +1269,8 @@ handle_clauses([C|Left], Arg, ArgType, OrigArgType, State, CaseTypes, MapIn,
           State);
       false -> State
     end,
-  {State2, ClauseMap, BodyType, NewArgType} =
-    do_clause(C, Arg, ArgType, OrigArgType, MapIn, State1),
+  {State2, ClauseMap, BodyType, NewArgType, WarnAcc} =
+    do_clause(C, Arg, ArgType, OrigArgType, MapIn, State1, WarnAcc0),
   {NewClauseAcc, State3} =
     case IsRaceAnalysisEnabled of
       true ->
@@ -1277,9 +1288,9 @@ handle_clauses([C|Left], Arg, ArgType, OrigArgType, State, CaseTypes, MapIn,
       false -> {[BodyType|CaseTypes], [ClauseMap|Acc]}
     end,
   handle_clauses(Left, Arg, NewArgType, OrigArgType, State3,
-                 NewCaseTypes, MapIn, NewAcc, NewClauseAcc);
+		 NewCaseTypes, MapIn, NewAcc, NewClauseAcc, WarnAcc);
 handle_clauses([], _Arg, _ArgType, _OrigArgType, State, CaseTypes, _MapIn, Acc,
-	       ClauseAcc) ->
+	       ClauseAcc, WarnAcc) ->
   State1 =
     case is_race_analysis_enabled(State) of
       true ->
@@ -1289,9 +1300,9 @@ handle_clauses([], _Arg, _ArgType, _OrigArgType, State, CaseTypes, _MapIn, Acc,
 	  RaceListSize + 1, State);
       false -> State
     end,
-  {lists:reverse(Acc), State1, t_sup(CaseTypes)}.
+  {lists:reverse(Acc), State1, t_sup(CaseTypes), WarnAcc}.
 
-do_clause(C, Arg, ArgType0, OrigArgType, Map, State) ->
+do_clause(C, Arg, ArgType0, OrigArgType, Map, State, Warns) ->
   Pats = cerl:clause_pats(C),
   Guard = cerl:clause_guard(C),
   Body = cerl:clause_body(C),
@@ -1323,7 +1334,7 @@ do_clause(C, Arg, ArgType0, OrigArgType, Map, State) ->
 	     [cerl_prettypr:format(C), format_type(ArgType0, State1)]),
       case state__warning_mode(State1) of
         false ->
-          {State1, Map, t_none(), ArgType0};
+	  {State1, Map, t_none(), ArgType0, Warns};
 	true ->
 	  {Msg, Force} =
 	    case t_is_none(ArgType0) of
@@ -1403,8 +1414,7 @@ do_clause(C, Arg, ArgType0, OrigArgType, Map, State) ->
 		       {record_match, _} -> ?WARN_MATCHING;
 		       {pattern_match_cov, _} -> ?WARN_MATCHING
 		     end,
-          {state__add_warning(State1, WarnType, C, Msg, Force),
-           Map, t_none(), ArgType0}
+	  {State1, Map, t_none(), ArgType0, [{WarnType, C, Msg, Force}|Warns]}
       end;
     {Map2, PatTypes} ->
       Map3 =
@@ -1437,9 +1447,9 @@ do_clause(C, Arg, ArgType0, OrigArgType, Map, State) ->
 	      false ->
 		{guard_fail_pat, [PatString, format_type(ArgType0, State1)]}
 	    end,
-	  State2 =
+	  Warn =
 	    case Reason of
-	      none -> state__add_warning(State1, ?WARN_MATCHING, C, DefaultMsg);
+	      none -> {?WARN_MATCHING, C, DefaultMsg, false};
 	      {FailGuard, Msg} ->
 		case is_compiler_generated(cerl:get_ann(FailGuard)) of
 		  false ->
@@ -1448,15 +1458,15 @@ do_clause(C, Arg, ArgType0, OrigArgType, Map, State) ->
 				 {neg_guard_fail, _} -> ?WARN_MATCHING;
 				 {opaque_guard, _} -> ?WARN_OPAQUE
 			       end,
-		    state__add_warning(State1, WarnType, FailGuard, Msg);
+		    {WarnType, FailGuard, Msg, false};
 		  true ->
-		    state__add_warning(State1, ?WARN_MATCHING, C, Msg)
+		    {?WARN_MATCHING, C, Msg, false}
 		end
 	    end,
-          {State2, Map, t_none(), NewArgType};
+	  {State1, Map, t_none(), NewArgType, [Warn|Warns]};
         Map4 ->
           {RetState, RetMap, BodyType} = traverse(Body, Map4, State1),
-          {RetState, RetMap, BodyType, NewArgType}
+          {RetState, RetMap, BodyType, NewArgType, Warns}
       end
   end.