BIFs should be considered exported

All BIFs now have stub functions and are exported. For example
in the erlang module:

-export([..., is_list/1, ...]).
.
.
.
is_list(_Term) ->
    erlang:nif_error(undefined).

But erlang:function_exported(erlang, is_list, 1) returns false,
which is weird.

Change erlang:function_exported/3 to return true for BIFs.

2 files changed, 12 insertions, 8 deletions

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index 0f4dfc0f98..03d184f4d2 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -1252,10 +1252,11 @@ true
       <fsummary>Check if a function is exported and loaded</fsummary>
       <desc>
         <p>Returns <c>true</c> if the module <c><anno>Module</anno></c> is loaded
-          and contains an exported function <c><anno>Function</anno>/<anno>Arity</anno></c>;
-          otherwise <c>false</c>.</p>
-        <p>Returns <c>false</c> for any BIF (functions implemented in C
-          rather than in Erlang).</p>
+          and contains an exported function <c><anno>Function</anno>/<anno>Arity</anno></c>,
+	  or if there is a BIF (a built-in function implemented in C)
+	  with the given name; otherwise returns <c>false</c>.</p>
+	  <note><p>This function used to return false for built-in
+	  functions before the 18.0 release.</p></note>
       </desc>
     </func>
     <func>
diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index 06a1230ca0..787a3da1f4 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -3984,16 +3984,19 @@ BIF_RETTYPE halt_2(BIF_ALIST_2)
 
 BIF_RETTYPE function_exported_3(BIF_ALIST_3)
 {
+    int arity;
     if (is_not_atom(BIF_ARG_1) ||
 	is_not_atom(BIF_ARG_2) || 
 	is_not_small(BIF_ARG_3)) {
 	BIF_ERROR(BIF_P, BADARG);
     }
-    if (erts_find_function(BIF_ARG_1, BIF_ARG_2, signed_val(BIF_ARG_3),
-			   erts_active_code_ix()) == NULL) {
-	BIF_RET(am_false);
+    arity = signed_val(BIF_ARG_3);
+    if (erts_find_function(BIF_ARG_1, BIF_ARG_2, arity,
+			   erts_active_code_ix()) != NULL ||
+	erts_is_builtin(BIF_ARG_1, BIF_ARG_2, arity)) {
+	BIF_RET(am_true);
     }
-    BIF_RET(am_true);
+    BIF_RET(am_false);
 }
 
 /**********************************************************************/