refactor: statsd supervisor API no need to return error

Also to make dialyzer happy

apps/emqx_management/src/emqx_mgmt_api_trace.erl

@@ -308,7 +308,7 @@ download_trace_log(get, #{bindings := #{name := Name}}) ->
             %% TODO use file replace file_binary.(delete file after send is not ready now).
             {ok, Binary} = file:read_file(ZipFile),
             ZipName = filename:basename(ZipFile),
-            file:delete(ZipFile),
+            _ = file:delete(ZipFile),
             Headers = #{
                 <<"content-type">> => <<"application/x-zip">>,
                 <<"content-disposition">> => iolist_to_binary("attachment; filename=" ++ ZipName)

apps/emqx_statsd/src/emqx_statsd_api.erl

@@ -61,10 +61,10 @@ statsd(put, #{body := Body}) ->
         {ok, #{raw_config := NewConfig, config := Config}} ->
             case maps:get(<<"enable">>, Body) of
                 true ->
-                    _ = emqx_statsd_sup:stop_child(?APP),
+                    ok = emqx_statsd_sup:ensure_child_stopped(?APP),
-                    _ = emqx_statsd_sup:start_child(?APP, maps:get(config, Config));
+                    ok = emqx_statsd_sup:ensure_child_started(?APP, maps:get(config, Config));
                 false ->
-                    _ = emqx_statsd_sup:stop_child(?APP)
+                    ok = emqx_statsd_sup:ensure_child_stopped(?APP)
             end,
             {200, NewConfig};
         {error, Reason} ->

apps/emqx_statsd/src/emqx_statsd_app.erl

@@ -34,7 +34,7 @@ stop(_) ->
 maybe_enable_statsd() ->
     case emqx_conf:get([statsd, enable], false) of
         true ->
-            emqx_statsd_sup:start_child(?APP, emqx_conf:get([statsd], #{}));
+            emqx_statsd_sup:ensure_child_started(?APP, emqx_conf:get([statsd], #{}));
         false ->
             ok
     end.

apps/emqx_statsd/src/emqx_statsd_sup.erl

@@ -8,9 +8,9 @@
 -behaviour(supervisor).
 
 -export([ start_link/0
-        , start_child/1
+        , ensure_child_started/1
-        , start_child/2
+        , ensure_child_started/2
-        , stop_child/1
+        , ensure_child_stopped/1
         ]).
 
 -export([init/1]).
@@ -26,19 +26,24 @@
 start_link() ->
     supervisor:start_link({local, ?MODULE}, ?MODULE, []).
 
--spec start_child(supervisor:child_spec()) -> ok.
+-spec ensure_child_started(supervisor:child_spec()) -> ok.
-start_child(ChildSpec) when is_map(ChildSpec) ->
+ensure_child_started(ChildSpec) when is_map(ChildSpec) ->
     assert_started(supervisor:start_child(?MODULE, ChildSpec)).
 
--spec start_child(atom(), map()) -> ok.
+-spec ensure_child_started(atom(), map()) -> ok.
-start_child(Mod, Opts) when is_atom(Mod) andalso is_map(Opts) ->
+ensure_child_started(Mod, Opts) when is_atom(Mod) andalso is_map(Opts) ->
     assert_started(supervisor:start_child(?MODULE, ?CHILD(Mod, Opts))).
 
--spec(stop_child(any()) -> ok | {error, term()}).
+%% @doc Stop the child worker process.
-stop_child(ChildId) ->
+-spec ensure_child_stopped(any()) -> ok.
+ensure_child_stopped(ChildId) ->
     case supervisor:terminate_child(?MODULE, ChildId) of
-        ok -> supervisor:delete_child(?MODULE, ChildId);
+        ok ->
-        Error -> Error
+            %% with terminate_child/2 returned 'ok', it's not possible
+            %% for supervisor:delete_child/2 to return {error, Reason}
+            ok = supervisor:delete_child(?MODULE, ChildId);
+        {error, not_found} ->
+            ok
     end.
 
 init([]) ->