fix(plugins): do not stop Elixir protected apps

On one hand, Elixir plugins might include Elixir itself, when targetting a non-Elixir EMQX
release.  If, on the other hand, the EMQX release already includes Elixir, we shouldn't
stop Elixir nor IEx, or the running IEx shell will break.

apps/emqx_plugins/src/emqx_plugins.erl

@@ -986,14 +986,7 @@ start_app(App) ->
 %% but not the ones shared with others.
 ensure_apps_stopped(#{<<"rel_apps">> := Apps}) ->
     %% load plugin apps and beam code
-    AppsToStop =
+    AppsToStop = lists:filtermap(fun parse_name_vsn_for_stopping/1, Apps),
-        lists:map(
-            fun(NameVsn) ->
-                {ok, AppName, _AppVsn} = parse_name_vsn(NameVsn),
-                AppName
-            end,
-            Apps
-        ),
     case tryit("stop_apps", fun() -> stop_apps(AppsToStop) end) of
         {ok, []} ->
             %% all apps stopped
@@ -1009,6 +1002,30 @@ ensure_apps_stopped(#{<<"rel_apps">> := Apps}) ->
             {error, Reason}
     end.
 
+%% On one hand, Elixir plugins might include Elixir itself, when targetting a non-Elixir
+%% EMQX release.  If, on the other hand, the EMQX release already includes Elixir, we
+%% shouldn't stop Elixir nor IEx.
+-ifdef(EMQX_ELIXIR).
+is_protected_app(elixir) -> true;
+is_protected_app(iex) -> true;
+is_protected_app(_) -> false.
+
+parse_name_vsn_for_stopping(NameVsn) ->
+    {ok, AppName, _AppVsn} = parse_name_vsn(NameVsn),
+    case is_protected_app(AppName) of
+        true ->
+            false;
+        false ->
+            {true, AppName}
+    end.
+%% ELSE ifdef(EMQX_ELIXIR)
+-else.
+parse_name_vsn_for_stopping(NameVsn) ->
+    {ok, AppName, _AppVsn} = parse_name_vsn(NameVsn),
+    {true, AppName}.
+%% END ifdef(EMQX_ELIXIR)
+-endif.
+
 stop_apps(Apps) ->
     RunningApps = running_apps(),
     case do_stop_apps(Apps, [], RunningApps) of
@@ -1045,8 +1062,10 @@ stop_app(App) ->
 
 unload_moudle_and_app(App) ->
     case application:get_key(App, modules) of
-        {ok, Modules} -> lists:foreach(fun code:soft_purge/1, Modules);
+        {ok, Modules} ->
-        _ -> ok
+            lists:foreach(fun code:soft_purge/1, Modules);
+        _ ->
+            ok
     end,
     _ = application:unload(App),
     ok.

mix.exs

@@ -270,6 +270,7 @@ defmodule EMQXUmbrella.MixProject do
       :debug_info,
       {:compile_info, [{:emqx_vsn, String.to_charlist(version)}]},
       {:d, :EMQX_RELEASE_EDITION, erlang_edition(edition_type)},
+      {:d, :EMQX_ELIXIR},
       {:d, :snk_kind, :msg}
     ]
   end