Better typing for model.config (#39132)

* Apply to all models config annotation

* Update modular to preserve order

* Apply modular

* fix define docstring

* fix dinov2 consistency (docs<->modular)

* fix InstructBlipVideoForConditionalGeneration docs<->modular consistency

* fixup

* remove duplicate code

* Delete config_class attribute from the modeling code

* Add config_class attribute in base model

* Update init sub class

* Deprecated models update

* Update new models

* Fix remote code BC issue

* fixup

* fixing more corner cases

* fix new models

* add test

* modular docs update

* fix comment a bit

* fix for py3.9

src/transformers/modeling_utils.py

@@ -33,7 +33,7 @@ from contextlib import contextmanager
 from enum import Enum
 from functools import partial, wraps
 from threading import Thread
-from typing import Any, Callable, Optional, TypeVar, Union
+from typing import Any, Callable, Optional, TypeVar, Union, get_type_hints
 from zipfile import is_zipfile
 
 import torch
@@ -2060,6 +2060,30 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin, PushToHubMixin, PeftAdapterMi
         """
         return "pt"
 
+    def __init_subclass__(cls, **kwargs):
+        super().__init_subclass__(**kwargs)
+        # For BC we keep the original `config_class` definition in case
+        # there is a `config_class` attribute (e.g. remote code models),
+        # otherwise we derive it from the annotated `config` attribute.
+
+        # defined in this particular subclass
+        child_annotation = cls.__dict__.get("__annotations__", {}).get("config", None)
+        child_attribute = cls.__dict__.get("config_class", None)
+
+        # defined in the class (this subclass or any parent class)
+        full_annotation = get_type_hints(cls).get("config", None)
+        full_attribute = cls.config_class
+
+        # priority (child class_config -> child annotation -> global class_config -> global annotation)
+        if child_attribute is not None:
+            cls.config_class = child_attribute
+        elif child_annotation is not None:
+            cls.config_class = child_annotation
+        elif full_attribute is not None:
+            cls.config_class = full_attribute
+        elif full_annotation is not None:
+            cls.config_class = full_annotation
+
     def __init__(self, config: PretrainedConfig, *inputs, **kwargs):
         super().__init__()
         if not isinstance(config, PretrainedConfig):