refactor(emqx_app): start quic listener condition

when the app is present, and when listners are configured

apps/emqx/src/emqx_app.erl

@@ -96,14 +96,23 @@ maybe_start_listeners() ->
     end.
 
 maybe_start_quicer() ->
-    case os:getenv("EMQX_NO_QUIC") of
-        X when X =:= "1" orelse X =:= "true" ->
-            ok;
-        _ ->
-            {ok, _} = application:ensure_all_started(quicer),
-            ok
+    case is_quicer_app_present() andalso is_quic_listener_configured() of
+        true -> {ok, _} = application:ensure_all_started(quicer), ok;
+        false -> ok
     end.
 
+is_quicer_app_present() ->
+    case application:load(quicer) of
+        ok -> true;
+        {error, {already_loaded, _}} -> true;
+        _ ->
+            ?SLOG(info, #{msg => "quicer_app_not_found"}),
+            false
+    end.
+
+is_quic_listener_configured() ->
+    emqx_listeners:has_enabled_listener_conf_by_type(quic).
+
 get_description() ->
     {ok, Descr0} = application:get_key(?APP, description),
     case os:getenv("EMQX_DESCRIPTION") of

apps/emqx/src/emqx_listeners.erl

@@ -34,7 +34,7 @@
         , stop_listener/3
         , restart_listener/1
         , restart_listener/3
-        , has_listener_conf_by_type/1
+        , has_enabled_listener_conf_by_type/1
         ]).
 
 %% @doc List configured listeners.
@@ -296,10 +296,11 @@ foreach_listeners(Do) ->
                 Do(ZoneName, LName, LConf)
         end, do_list()).
 
-has_listener_conf_by_type(Type) ->
+has_enabled_listener_conf_by_type(Type) ->
     lists:any(
         fun({_Zone, _LName, LConf}) when is_map(LConf) ->
-                Type =:= maps:get(type, LConf)
+                Type =:= maps:get(type, LConf) andalso
+                maps:get(enabled, LConf, true)
         end, do_list()).
 
 %% merge the configs in zone and listeners in a manner that

apps/emqx_machine/src/emqx_machine_app.erl

@@ -127,15 +127,11 @@ start_one_app(App) ->
 %% 1. due to static static config change
 %% 2. after join a cluster
 reboot_apps() ->
-    [gproc, esockd, ranch, cowboy, ekka, quicer, emqx | ?EMQX_DEP_APPS].
-
-%% quicer can not be added to emqx's .app because it might be opted out at build time
-implicit_deps() ->
-    [{emqx, [quicer]}].
+    [gproc, esockd, ranch, cowboy, ekka, emqx | ?EMQX_DEP_APPS].
 
 sorted_reboot_apps() ->
     Apps = [{App, app_deps(App)} || App <- reboot_apps()],
-    sorted_reboot_apps(Apps ++ implicit_deps()).
+    sorted_reboot_apps(Apps).
 
 app_deps(App) ->
     case application:get_key(App, applications) of