Changes suggested by Kostis, Dialyzer -Wunmatched_returns and Tidier

Makefile

@@ -39,7 +39,7 @@ dialyzer: compile
 	@echo Use "'make build_plt'" to build PLT prior to using this target.
 	@echo
 	@sleep 1
-	dialyzer -Wno_return --plt $(COMBO_PLT) ebin | \
+	dialyzer -Wno_return -Wunmatched_returns --plt $(COMBO_PLT) ebin | \
 	    fgrep -v -f ./dialyzer.ignore-warnings
 
 cleanplt:

src/error_logger_lager_h.erl

@@ -35,14 +35,16 @@
 -define(LOG(Level, Pid, Msg),
     case ?SHOULD_LOG(Level) of
         true ->
-            lager:log(Level, Pid, Msg);
+            _ =lager:log(Level, Pid, Msg),
+            ok;
         _ -> ok
     end).
 
 -define(LOG(Level, Pid, Fmt, Args),
     case ?SHOULD_LOG(Level) of
         true ->
-            lager:log(Level, Pid, Fmt, Args);
+            _ = lager:log(Level, Pid, Fmt, Args),
+            ok;
         _ -> ok
     end).
 

src/lager.erl

@@ -125,7 +125,7 @@ trace_file(File, Filter, Level) ->
         {ok, Trace} ->
             Handlers = gen_event:which_handlers(lager_event),
             %% check if this file backend is already installed
-            case lists:member({lager_file_backend, File}, Handlers) of
+            Res = case lists:member({lager_file_backend, File}, Handlers) of
                 false ->
                     %% install the handler
                     supervisor:start_child(lager_handler_watcher_sup,
@@ -133,14 +133,20 @@ trace_file(File, Filter, Level) ->
                 _ ->
                     ok
             end,
-            %% install the trace.
-            {MinLevel, Traces} = lager_mochiglobal:get(loglevel),
-            case lists:member(Trace, Traces) of
-                false ->
+            case Res of
+              {ok, _} ->
+                %% install the trace.
+                {MinLevel, Traces} = lager_mochiglobal:get(loglevel),
+                case lists:member(Trace, Traces) of
+                  false ->
                     lager_mochiglobal:put(loglevel, {MinLevel, [Trace|Traces]});
-                _ -> ok
-            end,
-            {ok, Trace};
+                  _ ->
+                    ok
+                end,
+                {ok, Trace};
+              {error, _} = E ->
+                E
+            end;
         Error ->
             Error
     end.
@@ -184,15 +190,14 @@ stop_trace({_Filter, _Level, Target} = Trace) ->
 clear_all_traces() ->
     {MinLevel, _Traces} = lager_mochiglobal:get(loglevel),
     lager_mochiglobal:put(loglevel, {MinLevel, []}),
-    [begin
-                case get_loglevel(Handler) of
-                    none ->
-                        gen_event:delete_handler(lager_event, Handler, []);
-                    _ ->
-                        ok
-                end
-        end || Handler <- gen_event:which_handlers(lager_event)],
-    ok.
+    lists:foreach(fun(Handler) ->
+          case get_loglevel(Handler) of
+            none ->
+              gen_event:delete_handler(lager_event, Handler, []);
+            _ ->
+              ok
+          end
+      end, gen_event:which_handlers(lager_event)).
 
 status() ->
     Handlers = gen_event:which_handlers(lager_event),
@@ -283,8 +288,7 @@ safe_format(Fmt, Args, Limit) ->
     safe_format(Fmt, Args, Limit, []).
 
 safe_format(Fmt, Args, Limit, Options) ->
-    try lager_trunc_io:format(Fmt, Args, Limit, Options) of
-        Result -> Result
+    try lager_trunc_io:format(Fmt, Args, Limit, Options)
     catch
         _:_ -> lager_trunc_io:format("FORMAT ERROR: ~p ~p", [Fmt, Args], Limit)
     end.

src/lager_app.erl

@@ -43,7 +43,8 @@ start(_StartType, _StartArgs) ->
             Val
     end,
 
-    [supervisor:start_child(lager_handler_watcher_sup, [lager_event, Module, Config]) ||
+    %% handlers failing to start are handled in the handler_watcher
+    _ = [supervisor:start_child(lager_handler_watcher_sup, [lager_event, Module, Config]) ||
         {Module, Config} <- expand_handlers(Handlers)],
 
     %% mask the messages we have no use for
@@ -55,18 +56,23 @@ start(_StartType, _StartArgs) ->
         {ok, false} ->
             [];
         _ ->
-            supervisor:start_child(lager_handler_watcher_sup, [error_logger, error_logger_lager_h, []]),
-            %% Should we allow user to whitelist handlers to not be removed?
-            [begin error_logger:delete_report_handler(X), X end ||
-                X <- gen_event:which_handlers(error_logger) -- [error_logger_lager_h]]
+            case supervisor:start_child(lager_handler_watcher_sup, [error_logger, error_logger_lager_h, []]) of
+              {ok, _} ->
+                %% Should we allow user to whitelist handlers to not be removed?
+                [begin error_logger:delete_report_handler(X), X end ||
+                  X <- gen_event:which_handlers(error_logger) -- [error_logger_lager_h]];
+              {error, _} ->
+                []
+            end
     end,
 
     {ok, Pid, SavedHandlers}.
 
 
 stop(Handlers) ->
-    [error_logger:add_report_handler(Handler) || Handler <- Handlers],
-    ok.
+    lists:foreach(fun(Handler) ->
+          error_logger:add_report_handler(Handler)
+      end, Handlers).
 
 expand_handlers([]) ->
     [];

src/lager_crash_log.erl

@@ -110,9 +110,10 @@ code_change(_OldVsn, State, _Extra) ->
     {ok, State}.
 
 schedule_rotation(undefined) ->
-    undefined;
+    ok;
 schedule_rotation(Date) ->
-    erlang:send_after(lager_util:calculate_next_rotation(Date) * 1000, self(), rotate).
+    erlang:send_after(lager_util:calculate_next_rotation(Date) * 1000, self(), rotate),
+    ok.
 
 %% ===== Begin code lifted from riak_err =====
 

src/lager_file_backend.erl

@@ -108,8 +108,8 @@ handle_info(_Info, State) ->
 %% @private
 terminate(_Reason, #state{fd=FD}) ->
     %% flush and close any file handles
-    file:datasync(FD),
-    file:close(FD),
+    _ = file:datasync(FD),
+    _ = file:close(FD),
     ok.
 
 %% @private
@@ -123,7 +123,8 @@ write(#state{name=Name, fd=FD, inode=Inode, flap=Flap, size=RotSize,
             lager_util:rotate_logfile(Name, Count),
             write(State, Level, Msg);
         {ok, {NewFD, NewInode, _}} ->
-            file:write(NewFD, Msg),
+            %% delayed_write doesn't report errors
+            _ = file:write(NewFD, Msg),
             case Level of
                 _ when Level =< ?ERROR ->
                     %% force a sync on any message at error severity or above
@@ -196,9 +197,10 @@ validate_logfile(H) ->
     false.
 
 schedule_rotation(_, undefined) ->
-    undefined;
+    ok;
 schedule_rotation(Name, Date) ->
-    erlang:send_after(lager_util:calculate_next_rotation(Date) * 1000, self(), {rotate, Name}).
+    erlang:send_after(lager_util:calculate_next_rotation(Date) * 1000, self(), {rotate, Name}),
+    ok.
 
 -ifdef(TEST).
 

src/lager_handler_watcher.erl

@@ -61,9 +61,14 @@ handle_info({gen_event_EXIT, Module, shutdown}, #state{module=Module} = State) -
     {stop, normal, State};
 handle_info({gen_event_EXIT, Module, Reason}, #state{module=Module,
         config=Config, event=Event} = State) ->
-    lager:log(error, self(), "Lager event handler ~p exited with reason ~s",
-        [Module, error_logger_lager_h:format_reason(Reason)]),
-    install_handler(Event, Module, Config),
+    case lager:log(error, self(), "Lager event handler ~p exited with reason ~s",
+        [Module, error_logger_lager_h:format_reason(Reason)]) of
+      ok ->
+        install_handler(Event, Module, Config);
+      {error, _} ->
+        %% lager is not working, so installing a handler won't work
+        ok
+    end,
     {noreply, State};
 handle_info(reinstall_handler, #state{module=Module, config=Config, event=Event} = State) ->
     install_handler(Event, Module, Config),
@@ -82,13 +87,14 @@ code_change(_OldVsn, State, _Extra) ->
 install_handler(Event, Module, Config) ->
     case gen_event:add_sup_handler(Event, Module, Config) of
         ok ->
-            lager:log(debug, self(), "Lager installed handler ~p into ~p", [Module, Event]),
+            _ = lager:log(debug, self(), "Lager installed handler ~p into ~p", [Module, Event]),
             ok;
         Error ->
             %% try to reinstall it later
-            lager:log(error, self(), "Lager failed to install handler ~p into"
+            _ = lager:log(error, self(), "Lager failed to install handler ~p into"
                " ~p, retrying later : ~p", [Module, Event, Error]),
-            erlang:send_after(5000, self(), reinstall_handler)
+            erlang:send_after(5000, self(), reinstall_handler),
+            ok
     end.
 
 -ifdef(TEST).

src/lager_trunc_io.erl

@@ -60,8 +60,7 @@ format(Fmt, Args, Max) ->
     format(Fmt, Args, Max, []).
 
 format(Fmt, Args, Max, Options) ->
-    try lager_format:format(Fmt, Args, Max, Options) of
-        Result -> Result
+    try lager_format:format(Fmt, Args, Max, Options)
     catch
         _:_ ->
             erlang:error(badarg, [Fmt, Args])

src/lager_util.erl

@@ -79,8 +79,8 @@ ensure_logfile(Name, FD, Inode, Buffer) ->
                     {ok, {FD, Inode, FInfo#file_info.size}};
                 false ->
                     %% delayed write can cause file:close not to do a close
-                    file:close(FD),
-                    file:close(FD),
+                    _ = file:close(FD),
+                    _ = file:close(FD),
                     case open_logfile(Name, Buffer) of
                         {ok, {FD2, Inode3, Size}} ->
                             %% inode changed, file was probably moved and
@@ -92,8 +92,8 @@ ensure_logfile(Name, FD, Inode, Buffer) ->
             end;
         _ ->
             %% delayed write can cause file:close not to do a close
-            file:close(FD),
-            file:close(FD),
+            _ = file:close(FD),
+            _ = file:close(FD),
             case open_logfile(Name, Buffer) of
                 {ok, {FD2, Inode3, Size}} ->
                     %% file was removed
@@ -117,13 +117,15 @@ maybe_utc({Date, {H, M, S, Ms}}) ->
             {Date1, {H1, M1, S1, Ms}}
     end.
 
+%% renames and deletes failing are OK
 rotate_logfile(File, 0) ->
-    file:delete(File);
+    _ = file:delete(File),
+    ok;
 rotate_logfile(File, 1) ->
-    file:rename(File, File++".0"),
+    _ = file:rename(File, File++".0"),
     rotate_logfile(File, 0);
 rotate_logfile(File, Count) ->
-    file:rename(File ++ "." ++ integer_to_list(Count - 2), File ++ "." ++
+    _ =file:rename(File ++ "." ++ integer_to_list(Count - 2), File ++ "." ++
         integer_to_list(Count - 1)),
     rotate_logfile(File, Count - 1).