dialyzer: Do not emit warnings for unreachable funs

Warnings are not generated for funs residing in dead code.

In particular, warnings like "The created fun has no local return" are
no longer generated for funs declared in clauses or functions that
cannot be run.

1 files changed, 34 insertions, 10 deletions

diff --git a/lib/dialyzer/src/dialyzer_dataflow.erl b/lib/dialyzer/src/dialyzer_dataflow.erl
index c5f93a3392..45b4abb253 100644
--- a/lib/dialyzer/src/dialyzer_dataflow.erl
+++ b/lib/dialyzer/src/dialyzer_dataflow.erl
@@ -102,6 +102,8 @@
                                       | 'undefined', % race
                 fun_homes            :: dict:dict(label(), mfa())
                                       | 'undefined', % race
+                reachable_funs       :: sets:set(label())
+                                      | 'undefined', % race
 		plt		     :: dialyzer_plt:plt()
                                       | 'undefined', % race
 		opaques              :: [type()]
@@ -269,9 +271,11 @@ traverse(Tree, Map, State) ->
       case state__warning_mode(State) of
         true -> {State, Map, Type};
         false ->
-          State2 = state__add_work(get_label(Tree), State),
+          FunLbl = get_label(Tree),
+          State2 = state__add_work(FunLbl, State),
           State3 = state__update_fun_env(Tree, Map, State2),
-          {State3, Map, Type}
+          State4 = state__add_reachable(FunLbl, State3),
+          {State4, Map, Type}
       end;
     'let' ->
       handle_let(Tree, Map, State);
@@ -3039,25 +3043,35 @@ state__new(Callgraph, Codeserver, Tree, Plt, Module, Records) ->
   {TreeMap, FunHomes} = build_tree_map(Tree, Callgraph),
   Funs = dict:fetch_keys(TreeMap),
   FunTab = init_fun_tab(Funs, dict:new(), TreeMap, Callgraph, Plt),
-  ExportedFuns =
-    [Fun || Fun <- Funs--[top], dialyzer_callgraph:is_escaping(Fun, Callgraph)],
-  Work = init_work(ExportedFuns),
+  ExportedFunctions =
+    [Fun ||
+      Fun <- Funs--[top],
+      dialyzer_callgraph:is_escaping(Fun, Callgraph),
+      dialyzer_callgraph:lookup_name(Fun, Callgraph) =/= error
+    ],
+  Work = init_work(ExportedFunctions),
   Env = lists:foldl(fun(Fun, Env) -> dict:store(Fun, map__new(), Env) end,
 		    dict:new(), Funs),
   #state{callgraph = Callgraph, codeserver = Codeserver,
          envs = Env, fun_tab = FunTab, fun_homes = FunHomes, opaques = Opaques,
 	 plt = Plt, races = dialyzer_races:new(), records = Records,
 	 warning_mode = false, warnings = [], work = Work, tree_map = TreeMap,
-	 module = Module}.
+	 module = Module, reachable_funs = sets:new()}.
 
 state__warning_mode(#state{warning_mode = WM}) ->
   WM.
 
 state__set_warning_mode(#state{tree_map = TreeMap, fun_tab = FunTab,
-                               races = Races} = State) ->
+                               races = Races, callgraph = Callgraph,
+                               reachable_funs = ReachableFuns} = State) ->
   ?debug("==========\nStarting warning pass\n==========\n", []),
   Funs = dict:fetch_keys(TreeMap),
-  State#state{work = init_work([top|Funs--[top]]),
+  Work =
+    [Fun ||
+      Fun <- Funs--[top],
+      dialyzer_callgraph:lookup_name(Fun, Callgraph) =/= error orelse
+        sets:is_element(Fun, ReachableFuns)],
+  State#state{work = init_work(Work),
 	      fun_tab = FunTab, warning_mode = true,
               races = dialyzer_races:put_race_analysis(true, Races)}.
 
@@ -3149,7 +3163,8 @@ state__get_race_warnings(#state{races = Races} = State) ->
   State1#state{races = Races1}.
 
 state__get_warnings(#state{tree_map = TreeMap, fun_tab = FunTab,
-			   callgraph = Callgraph, plt = Plt} = State) ->
+			   callgraph = Callgraph, plt = Plt,
+                           reachable_funs = ReachableFuns} = State) ->
   FoldFun =
     fun({top, _}, AccState) -> AccState;
        ({FunLbl, Fun}, AccState) ->
@@ -3184,7 +3199,12 @@ state__get_warnings(#state{tree_map = TreeMap, fun_tab = FunTab,
 		      GenRet = dialyzer_contracts:get_contract_return(C),
 		      not t_is_unit(GenRet)
 		  end,
-		case Warn of
+                %% Do not output warnings for unreachable funs.
+		case
+                  Warn andalso
+                  (dialyzer_callgraph:lookup_name(FunLbl, Callgraph) =/= error
+                   orelse sets:is_element(FunLbl, ReachableFuns))
+                of
 		  true ->
 		    case classify_returns(Fun) of
 		      no_match ->
@@ -3255,6 +3275,10 @@ state__get_args_and_status(Tree, #state{fun_tab = FunTab}) ->
     {ok, {ArgTypes, _}} -> {ArgTypes, true}
   end.
 
+state__add_reachable(FunLbl, #state{reachable_funs = ReachableFuns}=State) ->
+  NewReachableFuns = sets:add_element(FunLbl, ReachableFuns),
+  State#state{reachable_funs = NewReachableFuns}.
+
 build_tree_map(Tree, Callgraph) ->
   Fun =
     fun(T, {Dict, Homes, FunLbls} = Acc) ->