Fix rake gitlab:incoming_email:check and make it

report error properly, so that we know what's really wrong.

changelogs/unreleased/38197-fix-ImapAuthenticationCheck.yml

+---
+title: Fix `rake gitlab:incoming_email:check` and make it report the actual error
+merge_request: 14423
+author:
+type: fixed

lib/system_check/incoming_email/imap_authentication_check.rb

@@ -4,22 +4,17 @@ module SystemCheck
       set_name 'IMAP server credentials are correct?'
 
       def check?
-        if mailbox_config
-          begin
-            imap = Net::IMAP.new(config[:host], port: config[:port], ssl: config[:ssl])
-            imap.starttls if config[:start_tls]
-            imap.login(config[:email], config[:password])
-            connected = true
-          rescue
-            connected = false
+        if config
+          try_connect_imap
+        else
+          @error = "#{mail_room_config_path} does not have mailboxes setup"
+          false
         end
       end
 
-        connected
-      end
-
       def show_error
         try_fixing_it(
+          "An error occurred: #{@error.class}: #{@error.message}",
           'Check that the information in config/gitlab.yml is correct'
         )
         for_more_information(
@@ -30,15 +25,31 @@ module SystemCheck
 
       private
 
-      def mailbox_config
-        return @config if @config
+      def try_connect_imap
+        imap = Net::IMAP.new(config[:host], port: config[:port], ssl: config[:ssl])
+        imap.starttls if config[:start_tls]
+        imap.login(config[:email], config[:password])
+        true
+      rescue => error
+        @error = error
+        false
+      end
+
+      def config
+        @config ||= load_config
+      end
+
+      def mail_room_config_path
+        @mail_room_config_path ||=
+          Rails.root.join('config', 'mail_room.yml').to_s
+      end
 
-        config_path = Rails.root.join('config', 'mail_room.yml').to_s
-        erb = ERB.new(File.read(config_path))
-        erb.filename = config_path
+      def load_config
+        erb = ERB.new(File.read(mail_room_config_path))
+        erb.filename = mail_room_config_path
         config_file = YAML.load(erb.result)
 
-        @config = config_file[:mailboxes]&.first
+        config_file.dig(:mailboxes, 0)
       end
     end
   end