Do not emit blatantly illformed Core Erlang apply expressions

(fun f/1)() should be compiled to let X = 'f'/1 in apply X () to let the compiler
properly generate code that will fail with badarity at runtime.

Reported-by: Ulf Norell

lib/compiler/src/v3_core.erl

@@ -623,7 +623,7 @@ expr({call,Lc,{atom,Lf,F},As0}, St0) ->
     Op = #c_var{anno=lineno_anno(Lf, St1),name={F,length(As1)}},
     {#iapply{anno=#a{anno=lineno_anno(Lc, St1)},op=Op,args=As1},Aps,St1};
 expr({call,L,FunExp,As0}, St0) ->
-    {Fun,Fps,St1} = safe(FunExp, St0),
+    {Fun,Fps,St1} = safe_fun(length(As0), FunExp, St0),
     {As1,Aps,St2} = safe_list(As0, St1),
     Lanno = lineno_anno(L, St2),
     {#iapply{anno=#a{anno=Lanno},op=Fun,args=As1},Fps ++ Aps,St2};
@@ -1408,6 +1408,15 @@ safe(E0, St0) ->
     {Se,Sps,St2} = force_safe(E1, St1),
     {Se,Eps ++ Sps,St2}.
 
+safe_fun(A0, E0, St0) ->
+    case safe(E0, St0) of
+        {#c_var{name={_,A1}}=E1,Eps,St1} when A1 =/= A0 ->
+            {V,St2} = new_var(St1),
+            {V,Eps ++ [#iset{var=V,arg=E1}],St2};
+        Result ->
+            Result
+    end.
+
 safe_list(Es, St) ->
     foldr(fun (E, {Ces,Esp,St0}) ->
 		  {Ce,Ep,St1} = safe(E, St0),

lib/compiler/test/fun_SUITE.erl

@@ -21,7 +21,7 @@
 -export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1, 
 	 init_per_group/2,end_per_group/2,
 	 test1/1,overwritten_fun/1,otp_7202/1,bif_fun/1,
-	 external/1,eep37/1]).
+	 external/1,eep37/1,badarity/1]).
 
 %% Internal export.
 -export([call_me/1]).
@@ -32,7 +32,7 @@ suite() -> [{ct_hooks,[ts_install_cth]}].
 
 all() -> 
     test_lib:recompile(?MODULE),
-    [test1,overwritten_fun,otp_7202,bif_fun,external,eep37].
+    [test1,overwritten_fun,otp_7202,bif_fun,external,eep37,badarity].
 
 groups() -> 
     [].
@@ -206,5 +206,9 @@ eep37(Config) when is_list(Config) ->
     50 = UnusedName(8),
     ok.
 
+badarity(Config) when is_list(Config) ->
+    {'EXIT',{{badarity,{_,[]}},_}} = (catch (fun badarity/1)()),
+    ok.
+
 id(I) ->
     I.