Dialyzer now plays nicely with funs that come as "external" arguments

Two steps are needed to make this work:

1) Avoid generating the additional "apply_constraint" in dialyzer_typesig by
   reporting every function argument as a potential external function (patch on
   dialyzer_dep).

   This will produce correct success typings for all functions in the test case,
   but dataflow would miss the key warnings that help identify the bugs.

2) Patch dialyzer_dataflow so that it uses the "handle just external" path as a
   fallback whenever there are any external calls. As a result, if we have info
   about some paths, then:

   a) use the old "handle known apply" code to mark these functions as used and
   b) ignore the generalized result and use the one found by typesig for the
      return value of the apply itself.

4 files changed, 123 insertions, 24 deletions

diff --git a/lib/dialyzer/src/dialyzer_dataflow.erl b/lib/dialyzer/src/dialyzer_dataflow.erl
index 692684cd99..e0873b17f8 100644
--- a/lib/dialyzer/src/dialyzer_dataflow.erl
+++ b/lib/dialyzer/src/dialyzer_dataflow.erl
@@ -363,20 +363,24 @@ traverse_list([], Map, State, Acc) ->
 handle_apply(Tree, Map, State) ->
   Args = cerl:apply_args(Tree),
   Op = cerl:apply_op(Tree),
-  {State1, Map1, ArgTypes} = traverse_list(Args, Map, State),
-  {State2, Map2, OpType} = traverse(Op, Map1, State1),
+  {State0, Map1, ArgTypes} = traverse_list(Args, Map, State),
+  {State1, Map2, OpType} = traverse(Op, Map1, State0),
   case any_none(ArgTypes) of
     true ->
-      {State2, Map2, t_none()};
+      {State1, Map2, t_none()};
     false ->
-      {CallSitesKnown, FunList} =
-	case state__lookup_call_site(Tree, State2) of
-	  error -> {false, []};
-	  {ok, [external]} -> {false, []};
-	  {ok, List} -> {true, List}
+      FunList =
+	case state__lookup_call_site(Tree, State) of
+	  error -> [external]; %% so that we go directly in the fallback
+	  {ok, List} -> List
 	end,
-      case CallSitesKnown of
-	false ->
+      FunInfoList = [{local, state__fun_info(Fun, State)} || Fun <- FunList],
+      case
+        handle_apply_or_call(FunInfoList, Args, ArgTypes, Map2, Tree, State1)
+      of
+	{had_external, State2} ->
+	  %% Fallback: use whatever info we collected from traversing the op
+	  %% instead of the result that has been generalized to t_any().
 	  Arity = length(Args),
 	  OpType1 = t_inf(OpType, t_fun(Arity, t_any())),
 	  case t_is_none(OpType1) of
@@ -408,25 +412,23 @@ handle_apply(Tree, Map, State) ->
 		  {State2, enter_type(Op, OpType1, Map3), Range}
 	      end
 	  end;
-	true ->
-	  FunInfoList = [{local, state__fun_info(Fun, State)}
-			 || Fun <- FunList],
-	  handle_apply_or_call(FunInfoList, Args, ArgTypes, Map2, Tree, State1)
+	Normal -> Normal
       end
   end.
 
 handle_apply_or_call(FunInfoList, Args, ArgTypes, Map, Tree, State) ->
   None = t_none(),
   handle_apply_or_call(FunInfoList, Args, ArgTypes, Map, Tree, State,
-		       [None || _ <- ArgTypes], None).
+		       [None || _ <- ArgTypes], None, false).
 
 handle_apply_or_call([{local, external}|Left], Args, ArgTypes, Map, Tree, State,
-		     _AccArgTypes, _AccRet) ->
+		     _AccArgTypes, _AccRet, _HadExternal) ->
   handle_apply_or_call(Left, Args, ArgTypes, Map, Tree, State,
-		       ArgTypes, t_any());
+		       ArgTypes, t_any(), true);
 handle_apply_or_call([{TypeOfApply, {Fun, Sig, Contr, LocalRet}}|Left],
 		     Args, ArgTypes, Map, Tree,
-                     #state{opaques = Opaques} = State, AccArgTypes, AccRet) ->
+                     #state{opaques = Opaques} = State,
+                     AccArgTypes, AccRet, HadExternal) ->
   Any = t_any(),
   AnyArgs = [Any || _ <- Args],
   GenSig = {AnyArgs, fun(_) -> t_any() end},
@@ -573,11 +575,16 @@ handle_apply_or_call([{TypeOfApply, {Fun, Sig, Contr, LocalRet}}|Left],
   NewAccRet = t_sup(AccRet, TotalRet),
   ?debug("NewAccRet: ~s\n", [t_to_string(NewAccRet)]),
   handle_apply_or_call(Left, Args, ArgTypes, Map, Tree,
-		       State3, NewAccArgTypes, NewAccRet);
+		       State3, NewAccArgTypes, NewAccRet, HadExternal);
 handle_apply_or_call([], Args, _ArgTypes, Map, _Tree, State,
-		     AccArgTypes, AccRet) ->
-  NewMap = enter_type_lists(Args, AccArgTypes, Map),
-  {State, NewMap, AccRet}.
+		     AccArgTypes, AccRet, HadExternal) ->
+  case HadExternal of
+    false ->
+      NewMap = enter_type_lists(Args, AccArgTypes, Map),
+      {State, NewMap, AccRet};
+    true ->
+      {had_external, State}
+  end.
 
 apply_fail_reason(FailedSig, FailedBif, FailedContract) ->
   if
diff --git a/lib/dialyzer/src/dialyzer_dep.erl b/lib/dialyzer/src/dialyzer_dep.erl
index e3ece144c9..572e60278d 100644
--- a/lib/dialyzer/src/dialyzer_dep.erl
+++ b/lib/dialyzer/src/dialyzer_dep.erl
@@ -124,8 +124,10 @@ traverse(Tree, Out, State, CurrentFun) ->
 	    TmpState = state__add_deps(Label, O1, State),
 	    state__add_deps(CurrentFun, O2,TmpState)
 	end,
-      {BodyFuns, State2} = traverse(Body, Out, State1, 
-				    cerl_trees:get_label(Tree)),
+      Vars = cerl:fun_vars(Tree),
+      Out1 = bind_single(Vars, output(set__singleton(external)), Out),
+      {BodyFuns, State2} =
+        traverse(Body, Out1, State1, cerl_trees:get_label(Tree)),
       {output(set__singleton(Label)), state__add_esc(BodyFuns, State2)};
     'let' ->
       Vars = cerl:let_vars(Tree),
diff --git a/lib/dialyzer/test/small_SUITE_data/results/funs_from_outside b/lib/dialyzer/test/small_SUITE_data/results/funs_from_outside
new file mode 100644
index 0000000000..3e597ef1bc
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/results/funs_from_outside
@@ -0,0 +1,7 @@
+
+funs_from_outside.erl:18: The pattern 'error' can never match the type {'ok','nothing' | 'something'}
+funs_from_outside.erl:32: Function run2/2 has no local return
+funs_from_outside.erl:35: Function testb/3 has no local return
+funs_from_outside.erl:41: The pattern 'error' can never match the type {'ok','nothing' | 'something'}
+funs_from_outside.erl:78: Function test2/1 has no local return
+funs_from_outside.erl:83: The pattern 'error' can never match the type 'ok'
diff --git a/lib/dialyzer/test/small_SUITE_data/src/funs_from_outside.erl b/lib/dialyzer/test/small_SUITE_data/src/funs_from_outside.erl
new file mode 100644
index 0000000000..f4cbf31160
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/src/funs_from_outside.erl
@@ -0,0 +1,83 @@
+-module(funs_from_outside).

+

+-export([run1/2, run2/2, run3/2]).

+-export([test1/1, test2/1]).

+

+%%------------------------------------------------------------------------------

+

+run1(X, Y) ->

+    testa(fun do_something/1, X, Y).

+

+testa(Fun, X, Y) ->

+    F = case even(X) of

+	    true -> Fun;

+	    false -> fun do_nothing/1

+	end,

+    case F(Y) of

+	{ok, _} -> ok;

+	error -> error

+    end.

+

+do_nothing(_) -> {ok, nothing}.

+

+do_something(_) -> {ok, something}.

+

+even(X) ->

+    X rem 2 =:= 0.

+

+%%------------------------------------------------------------------------------

+

+%% Duplicating code since we are monovariant...

+

+run2(X, Y) ->

+    testb(fun do_something/1, X, Y).

+

+testb(Fun, X, Y) ->

+    F = case even(X) of

+	    true -> Fun;

+	    false -> fun do_nothing/1

+	end,

+    case F(Y) of

+	error -> error

+    end.

+

+%%------------------------------------------------------------------------------

+

+%% Duplicating code since we are monovariant...

+

+run3(X, Y) ->

+    testc(fun do_something_2/1, X, Y).

+

+testc(Fun, X, Y) ->

+    F = case even(X) of

+	    true -> Fun;

+	    false -> fun do_nothing/1

+	end,

+    case F(Y) of

+	{ok, _} -> ok;

+        %% This pattern can match. 

+	error -> error

+    end.

+

+do_something_2(foo) -> {ok, something};

+do_something_2(_) -> error.

+

+%%------------------------------------------------------------------------------

+

+test1(Fun) ->

+    F = case get(test1) of

+            test1_t -> Fun;

+            test1_f -> fun fok/0

+        end,

+    error = F().

+

+fok() -> ok.

+

+%%------------------------------------------------------------------------------

+

+test2(Fun) ->

+    F = case get(test1) of

+            test1_t -> fun fok/0;

+            test1_f -> fun fok/0

+        end,

+    error = F().