5 files changed, 62 insertions, 2 deletions
diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index 276bef2bbb..33738dc20b 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -696,3 +696,4 @@ bif ets:whereis/1
 bif erts_internal:gather_alloc_histograms/1
 bif erts_internal:gather_carrier_info/1
 ubif erlang:map_get/2
+ubif erlang:is_map_key/2
diff --git a/erts/emulator/beam/erl_db_util.c b/erts/emulator/beam/erl_db_util.c
index 6354abfd1f..ef22cda1f0 100644
--- a/erts/emulator/beam/erl_db_util.c
+++ b/erts/emulator/beam/erl_db_util.c
@@ -644,6 +644,12 @@ static DMCGuardBif guard_tab[] =
         DBIF_ALL
     },
     {
+        am_is_map_key,
+        &is_map_key_2,
+        2,
+        DBIF_ALL
+    },
+    {
 	am_bit_size,
 	&bit_size_1,
 	1,
diff --git a/erts/emulator/beam/erl_map.c b/erts/emulator/beam/erl_map.c
index f577b017c3..3d565b1bb8 100644
--- a/erts/emulator/beam/erl_map.c
+++ b/erts/emulator/beam/erl_map.c
@@ -43,6 +43,7 @@
  *
  * DONE:
  * - erlang:is_map/1
+ * - erlang:is_map_key/2
  * - erlang:map_size/1
  * - erlang:map_get/2
  *
@@ -919,7 +920,7 @@ static int hxnodecmp(hxnode_t *a, hxnode_t *b) {
 	return -1;
 }
 
-/* maps:is_key/2 */
+/* maps:is_key/2 and erlang:is_map_key/2 */
 
 BIF_RETTYPE maps_is_key_2(BIF_ALIST_2) {
     if (is_map(BIF_ARG_2)) {
@@ -929,6 +930,10 @@ BIF_RETTYPE maps_is_key_2(BIF_ALIST_2) {
     BIF_ERROR(BIF_P, BADMAP);
 }
 
+BIF_RETTYPE is_map_key_2(BIF_ALIST_2) {
+    BIF_RET(maps_is_key_2(BIF_CALL_ARGS));
+}
+
 /* maps:keys/1 */
 
 BIF_RETTYPE maps_keys_1(BIF_ALIST_1) {
diff --git a/erts/emulator/test/map_SUITE.erl b/erts/emulator/test/map_SUITE.erl
index 43807b4388..f93c637650 100644
--- a/erts/emulator/test/map_SUITE.erl
+++ b/erts/emulator/test/map_SUITE.erl
@@ -38,6 +38,7 @@
          t_map_size/1,
          t_map_get/1,
          t_is_map/1,
+         t_is_map_key/1,
 
          %% Specific Map BIFs
          t_bif_map_get/1,
@@ -718,7 +719,47 @@ t_map_get(Config) when is_list(Config) ->
     true = if map_get(a, M2) =:= 1 -> true; true -> false end,
     false = if map_get(x, M2) =:= 1 -> true; true -> false end,
     do_badmap(fun
-        (T) when map_get(T, x) =:= 1 -> ok;
+        (T) when map_get(x, T) =:= 1 -> ok;
+        (T) -> false = is_map(T)
+    end),
+    ok.
+
+t_is_map_key(Config) when is_list(Config) ->
+    %% small map
+    true = is_map_key(a, id(#{a=>1})),
+    true = is_map_key(b, id(#{a=>1, b=>2})),
+    true = is_map_key("hello", id(#{a=>1, "hello"=>"hi"})),
+    true = is_map_key({1,1.0}, id(#{a=>a, {1,1.0}=>"tuple hi"})),
+
+    M0   = id(#{ k1=>"v1", <<"k2">> => <<"v3">> }),
+    true = is_map_key(<<"k2">>, M0#{<<"k2">> => "v4"}),
+
+    %% large map
+    M1   = maps:from_list([{I,I}||I<-lists:seq(1,100)] ++
+			  [{a,1},{b,2},{"hello","hi"},{{1,1.0},"tuple hi"},
+			   {k1,"v1"},{<<"k2">>,"v3"}]),
+    true = is_map_key(a, M1),
+    true = is_map_key(b, M1),
+    true = is_map_key("hello", M1),
+    true = is_map_key({1,1.0}, M1),
+    true = is_map_key(<<"k2">>, M1),
+
+    %% error cases
+    do_badmap(fun(T) ->
+		      {'EXIT',{{badmap,T},[{erlang,is_map_key,_,_}|_]}} =
+			  (catch is_map_key(a, T))
+	      end),
+
+    false = is_map_key({1,1}, id(#{{1,1.0}=>"tuple"})),
+    false = is_map_key(a, id(#{})),
+    false = is_map_key(a, id(#{b=>1, c=>2})),
+
+    %% in guards
+    M2 = id(#{a=>1}),
+    true = if is_map_key(a, M2) -> true; true -> false end,
+    false = if is_map_key(x, M2) -> true; true -> false end,
+    do_badmap(fun
+        (T) when is_map_key(T, x) =:= 1 -> ok;
         (T) -> false = is_map(T)
     end),
     ok.
diff --git a/erts/emulator/test/match_spec_SUITE.erl b/erts/emulator/test/match_spec_SUITE.erl
index c1bc01f01e..4415d8d1b9 100644
--- a/erts/emulator/test/match_spec_SUITE.erl
+++ b/erts/emulator/test/match_spec_SUITE.erl
@@ -898,6 +898,13 @@ maps(Config) when is_list(Config) ->
     {ok,false,[],[]} = erlang:match_spec_test(not_a_map, [{'$1',[{map_get,b,'$1'}],['$_']}], table),
     {ok,true,[],[]} = erlang:match_spec_test(#{a => true}, [{'$1',[{map_get,a,'$1'}],[true]}], table),
 
+    {ok,true,[],[]} = erlang:match_spec_test(#{a => 1}, [{'$1',[],[{is_map_key,a,'$1'}]}], table),
+    {ok,false,[],[]} = erlang:match_spec_test(#{a => 1}, [{'$1',[],[{is_map_key,b,'$1'}]}], table),
+    {ok,'EXIT',[],[]} = erlang:match_spec_test(not_a_map, [{'$1',[],[{is_map_key,a,'$1'}]}], table),
+    {ok,false,[],[]} = erlang:match_spec_test(#{a => 1}, [{'$1',[{is_map_key,b,'$1'}],['$_']}], table),
+    {ok,false,[],[]} = erlang:match_spec_test(not_a_map, [{'$1',[{is_map_key,b,'$1'}],['$_']}], table),
+    {ok,true,[],[]} = erlang:match_spec_test(#{a => true}, [{'$1',[{is_map_key,a,'$1'}],[true]}], table),
+
     %% large maps
 
     Ls0 = [{I,<<I:32>>}||I <- lists:seq(1,415)],