rabbit: Change start_apps/2 to call application:ensure_all_started/2

.. instead of reinventing about the same logic.

start_apps/2 is not called to start the `rabbit` application anymore (it
is started as a normal Erlang application now). It means it's only used
to start plugins which are also supposed to be regular Erlang
applications.

It runs boot steps unconditionally as well (because this function never
starts `rabbit).

One difference with the previous code is that the previous code started
all loaded applications. This seemed unnecessary and even caused issues
with testsuites where some applications were loaded like `rabbitmqctl`
but were not meant to be started.

Another difference is that before, all boot steps were executed at once,
then all plugins were started. Now, to improve consistency and make sure
that a dependency is fully ready before a plugin which depends on it
starts, for each application we execute the boot steps then start it,
before moving to the next.

[#170870798]

1 files changed, 14 insertions, 8 deletions

diff --git a/src/rabbit.erl b/src/rabbit.erl
index 292272738d..35ffc6ea16 100644
--- a/src/rabbit.erl
+++ b/src/rabbit.erl
@@ -599,21 +599,27 @@ start_apps(Apps) ->
 -spec start_apps([app_name()],
                  #{app_name() => restart_type()}) -> 'ok'.
 
+%% TODO: start_apps/2 and start_loaded_apps/2 are now specific to
+%% plugins. Those function should be moved over `rabbit_plugins`, along
+%% with top_apps/1, once the latter stops using app_utils as well.
+
 start_apps(Apps, RestartTypes) ->
     app_utils:load_applications(Apps),
     ok = rabbit_feature_flags:refresh_feature_flags_after_app_load(Apps),
     start_loaded_apps(Apps, RestartTypes).
 
 start_loaded_apps(Apps, RestartTypes) ->
+    false = lists:member(rabbit, Apps), %% Assertion.
     rabbit_prelaunch_conf:decrypt_config(Apps),
-    OrderedApps = app_utils:app_dependency_order(Apps, false),
-    case lists:member(rabbit, Apps) of
-        false -> rabbit_boot_steps:run_boot_steps(Apps); %% plugin activation
-        true  -> ok                    %% will run during start of rabbit app
-    end,
-    ok = app_utils:start_applications(OrderedApps,
-                                      handle_app_error(could_not_start),
-                                      RestartTypes).
+    lists:foreach(
+      fun(App) ->
+              RestartType = maps:get(App, RestartTypes, temporary),
+              ok = rabbit_boot_steps:run_boot_steps([App]),
+              case application:ensure_all_started(App, RestartType) of
+                  {ok, _}         -> ok;
+                  {error, Reason} -> throw({could_not_start, App, Reason})
+              end
+      end, Apps).
 
 -spec stop_apps([app_name()]) -> 'ok'.