genric logic to get load method for custom model

src/diffusers/pipeline_utils.py

@@ -125,18 +125,25 @@ class DiffusionPipeline(ConfigMixin):
 
         init_kwargs = {}
 
+        # get all importable classes to get the load method name for custom models/components
+        # here we enforce that custom models/components should always subclass from base classes in tansformers and diffusers 
+        all_importable_classes = {}
+        for library in LOADABLE_CLASSES:
+            all_importable_classes.update(LOADABLE_CLASSES[library])
+
         for name, (library_name, class_name) in init_dict.items():
             
             # if the model is not in diffusers or transformers, we need to load it from the hub
             # assumes that it's a subclass of ModelMixin
             if library_name == module_candidate_name:
                 class_obj = get_class_from_dynamic_module(cached_folder, module, class_name, cached_folder)
-                load_method_name = "from_pretrained"
+                # since it's not from a library, we need to check class candidates for all importable classes
+                importable_classes = all_importable_classes
+                class_candidates = {c: class_obj for c in all_importable_classes}
             else:
-                importable_classes = LOADABLE_CLASSES[library_name]
-
                 library = importlib.import_module(library_name)
                 class_obj = getattr(library, class_name)
+                importable_classes = LOADABLE_CLASSES[library_name]
                 class_candidates = {c: getattr(library, c) for c in importable_classes.keys()}
 
             load_method_name = None