Fix issue with filtering duplicates in auth_mnesia:get_users()

Previous version was only correct when data to process
was sorted, which was not always the case.

This add common implementation of lists:uniq in misc that works
also on <R25, and switches get_users to use it.

src/ejabberd_auth_mnesia.erl

@@ -151,13 +151,7 @@ get_users(Server, []) ->
     Users = mnesia:dirty_select(passwd,
 			[{#passwd{us = '$1', _ = '_'},
 			  [{'==', {element, 2, '$1'}, Server}], ['$1']}]),
-    {_, Res} = lists:foldl(
-	fun({U, S, _}, {{U2, S2}, _} = Acc) when U == U2 andalso S == S2 ->
-	    Acc;
-	   ({U, S, _}, {_, Res}) ->
-	       {{U, S}, [{U, S} | Res]}
-	end, {{none, none}, []}, Users),
-    Res;
+    misc:lists_uniq([{U, S} || {U, S, _} <- Users]);
 get_users(Server, [{from, Start}, {to, End}])
   when is_integer(Start) and is_integer(End) ->
     get_users(Server, [{limit, End - Start + 1}, {offset, Start}]);

src/ejabberd_config.erl

@@ -631,22 +631,7 @@ callback_modules(external) ->
 	      end
       end, beams(external));
 callback_modules(all) ->
-    lists_uniq(callback_modules(local) ++ callback_modules(external)).
-
--ifdef(OTP_BELOW_25).
-lists_uniq(List) ->
-    {Res, _} = lists:foldr(
-	fun(El, {Result, Existing} = Acc) ->
-	    case maps:is_key(El, Existing) of
-		true -> Acc;
-		_ -> {[El | Result], Existing#{El => true}}
-	    end
-	end, {[], #{}}, List),
-    Res.
--else.
-lists_uniq(List) ->
-    lists:uniq(List).
--endif.
+    misc:lists_uniq(callback_modules(local) ++ callback_modules(external)).
 
 -spec validators(module(), [atom()], [any()]) -> econf:validators().
 validators(Mod, Disallowed, DK) ->

src/misc.erl

@@ -46,7 +46,8 @@
          json_encode/1, json_decode/1,
 	 set_proc_label/1,
 	 match_ip_mask/3, format_hosts_list/1, format_cycle/1, delete_dir/1,
-	 semver_to_xxyy/1, logical_processors/0, get_mucsub_event_type/1]).
+	 semver_to_xxyy/1, logical_processors/0, get_mucsub_event_type/1,
+         lists_uniq/1]).
 
 %% Deprecated functions
 -export([decode_base64/1, encode_base64/1]).
@@ -819,3 +820,21 @@ set_proc_label(_Label) ->
 set_proc_label(Label) ->
     proc_lib:set_label(Label).
 -endif.
+
+-ifdef(OTP_BELOW_25).
+-spec lists_uniq([term()]) -> [term()].
+lists_uniq(List) ->
+    lists_uniq_int(List, #{}).
+
+lists_uniq_int([El | Rest], Existing) ->
+    case maps:is_key(El, Existing) of
+        true -> lists_uniq_int(Rest, Existing);
+        _ -> [El | lists_uniq_int(Rest, Existing#{El => true})]
+    end;
+lists_uniq_int([], _) ->
+    [].
+-else.
+-spec lists_uniq([term()]) -> [term()].
+lists_uniq(List) ->
+    lists:uniq(List).
+-endif.