Include an error message hint for inherited ordering (#7124)

Co-authored-by: David Montague <35119617+dmontagu@users.noreply.github.com>

pydantic/_internal/_model_construction.py

@@ -138,15 +138,20 @@ def wrapped_model_post_init(self: BaseModel, __context: Any) -> None:
                 if parameters and parent_parameters and not all(x in parameters for x in parent_parameters):
                     combined_parameters = parent_parameters + tuple(x for x in parameters if x not in parent_parameters)
                     parameters_str = ', '.join([str(x) for x in combined_parameters])
+                    generic_type_label = f'typing.Generic[{parameters_str}]'
                     error_message = (
                         f'All parameters must be present on typing.Generic;'
-                        f' you should inherit from typing.Generic[{parameters_str}]'
+                        f' you should inherit from {generic_type_label}.'
                     )
                     if Generic not in bases:  # pragma: no cover
-                        # This branch will only be hit if I have misunderstood how `__parameters__` works.
-                        # If that is the case, and a user hits this, I could imagine it being very helpful
-                        # to have this extra detail in the reported traceback.
-                        error_message += f' (bases={bases})'
+                        # We raise an error here not because it is desirable, but because some cases are mishandled.
+                        # It would be nice to remove this error and still have things behave as expected, it's just
+                        # challenging because we are using a custom `__class_getitem__` to parametrize generic models,
+                        # and not returning a typing._GenericAlias from it.
+                        bases_str = ', '.join([x.__name__ for x in bases] + [generic_type_label])
+                        error_message += (
+                            f' Note: `typing.Generic` must go last: `class {cls.__name__}({bases_str}): ...`)'
+                        )
                     raise TypeError(error_message)
 
                 cls.__pydantic_generic_metadata__ = {

tests/test_generics.py

@@ -2022,6 +2022,27 @@ class B(A[T], Generic[S]):
             ...
 
 
+def test_generic_subclass_with_extra_type_with_hint_message():
+    E = TypeVar('E', bound=BaseModel)
+    D = TypeVar('D')
+
+    class BaseGenericClass(Generic[E, D], BaseModel):
+        uid: str
+        name: str
+
+    with pytest.raises(
+        TypeError,
+        match=re.escape(
+            'All parameters must be present on typing.Generic; you should inherit from typing.Generic[~E, ~D].'
+            ' Note: `typing.Generic` must go last:'
+            ' `class ChildGenericClass(BaseGenericClass, typing.Generic[~E, ~D]): ...`'
+        ),
+    ):
+
+        class ChildGenericClass(BaseGenericClass[E, Dict[str, Any]]):
+            ...
+
+
 def test_multi_inheritance_generic_binding():
     T = TypeVar('T')