Fully unload add-ons under a mutex when shutting down (#2970)

lib/ruby_lsp/addon.rb

@@ -97,6 +97,15 @@ def load_addons(global_state, outgoing_queue, include_project_addons: true)
         errors
       end
 
+      # Unloads all add-ons. Only intended to be invoked once when shutting down the Ruby LSP server
+      sig { void }
+      def unload_addons
+        @addons.each(&:deactivate)
+        @addons.clear
+        @addon_classes.clear
+        @file_watcher_addons.clear
+      end
+
       # Get a reference to another add-on object by name and version. If an add-on exports an API that can be used by
       # other add-ons, this is the way to get access to that API.
       #

lib/ruby_lsp/base_server.rb

@@ -95,11 +95,9 @@ def start
              "$/cancelRequest"
           process_message(message)
         when "shutdown"
-          send_log_message("Shutting down Ruby LSP...")
-
-          shutdown
-
           @mutex.synchronize do
+            send_log_message("Shutting down Ruby LSP...")
+            shutdown
             run_shutdown
             @writer.write(Result.new(id: message[:id], response: nil).to_hash)
           end

lib/ruby_lsp/server.rb

@@ -1123,7 +1123,7 @@ def workspace_dependencies(message)
 
     sig { override.void }
     def shutdown
-      Addon.addons.each(&:deactivate)
+      Addon.unload_addons
     end
 
     sig { void }