Cleanup plugin mixin registry (#4790)

* collect mixins dynamically

* remove unfinsihed option to reorder mixins

* clean up settings

* fix text

* fix mixin lookup

* stupid error

* fix assertations

* use regustered function instead of private dict

* switch to dict for reg

* fix test

* makke sure mixins also works with class

* cleanup

* fix reqs

* fix test assertations

InvenTree/plugin/registry.py

@@ -42,7 +42,7 @@ class PluginsRegistry:
 
     DEFAULT_MIXIN_ORDER = [SettingsMixin, ScheduleMixin, AppMixin, UrlsMixin]
 
-    def __init__(self, mixin_order: list = None) -> None:
+    def __init__(self) -> None:
         """Initialize registry.
 
         Set up all needed references for internal and external states.
@@ -53,6 +53,7 @@ class PluginsRegistry:
         self.plugins_full: Dict[str, InvenTreePlugin] = {}      # List of all plugin instances
 
         self.plugin_modules: List(InvenTreePlugin) = []         # Holds all discovered plugins
+        self.mixin_modules: Dict[str, any] = {}                 # Holds all discovered mixins
 
         self.errors = {}                                        # Holds discovering errors
 
@@ -63,10 +64,6 @@ class PluginsRegistry:
 
         self.installed_apps = []                                # Holds all added plugin_paths
 
-        # mixins
-        self.mixins_settings = {}
-        self.mixin_order = mixin_order or self.DEFAULT_MIXIN_ORDER
-
     def get_plugin(self, slug):
         """Lookup plugin by slug (unique key)."""
         if slug not in self.plugins:
@@ -322,6 +319,15 @@ class PluginsRegistry:
 
         return collected_plugins
 
+    def discover_mixins(self):
+        """Discover all mixins from plugins and register them."""
+        collected_mixins = {}
+
+        for plg in self.plugins.values():
+            collected_mixins.update(plg.get_registered_mixins())
+
+        self.mixin_modules = collected_mixins
+
     def install_plugin_file(self):
         """Make sure all plugins are installed in the current environment."""
         if settings.PLUGIN_FILE_CHECKED:
@@ -468,6 +474,17 @@ class PluginsRegistry:
             else:  # pragma: no cover
                 safe_reference(plugin=plg, key=plg_key, active=False)
 
+    def __get_mixin_order(self):
+        """Returns a list of mixin classes, in the order that they should be activated."""
+        # Preset list of mixins
+        order = self.DEFAULT_MIXIN_ORDER
+
+        # Append mixins that are not defined in the default list
+        order += [m.get('cls') for m in self.mixin_modules.values() if m.get('cls') not in order]
+
+        # Final list of mixins
+        return order
+
     def _activate_plugins(self, force_reload=False, full_reload: bool = False):
         """Run activation functions for all plugins.
 
@@ -475,11 +492,14 @@ class PluginsRegistry:
             force_reload (bool, optional): Also reload base apps. Defaults to False.
             full_reload (bool, optional): Reload everything - including plugin mechanism. Defaults to False.
         """
-        # activate integrations
+        # Collect mixins
+        self.discover_mixins()
+
+        # Activate integrations
         plugins = self.plugins.items()
         logger.info(f'Found {len(plugins)} active plugins')
 
-        for mixin in self.mixin_order:
+        for mixin in self.__get_mixin_order():
             if hasattr(mixin, '_activate_mixin'):
                 mixin._activate_mixin(self, plugins, force_reload=force_reload, full_reload=full_reload)
 
@@ -491,7 +511,7 @@ class PluginsRegistry:
         Args:
             force_reload (bool, optional): Also reload base apps. Defaults to False.
         """
-        for mixin in self.mixin_order:
+        for mixin in reversed(self.__get_mixin_order()):
             if hasattr(mixin, '_deactivate_mixin'):
                 mixin._deactivate_mixin(self, force_reload=force_reload)