Fix misbehavior related to copying of RootModel (#6918)

pydantic/root_model.py

@@ -3,11 +3,12 @@
 from __future__ import annotations as _annotations
 
 import typing
+from copy import copy, deepcopy
 
 from pydantic_core import PydanticUndefined
 
 from ._internal import _repr
-from .main import BaseModel
+from .main import BaseModel, _object_setattr
 
 if typing.TYPE_CHECKING:
     from typing import Any
@@ -68,6 +69,34 @@ def model_construct(cls: type[Model], root: RootModelRootType, _fields_set: set[
         """
         return super().model_construct(root=root, _fields_set=_fields_set)
 
+    def __getstate__(self) -> dict[Any, Any]:
+        return {
+            '__dict__': self.__dict__,
+            '__pydantic_fields_set__': self.__pydantic_fields_set__,
+        }
+
+    def __setstate__(self, state: dict[Any, Any]) -> None:
+        _object_setattr(self, '__pydantic_fields_set__', state['__pydantic_fields_set__'])
+        _object_setattr(self, '__dict__', state['__dict__'])
+
+    def __copy__(self: Model) -> Model:
+        """Returns a shallow copy of the model."""
+        cls = type(self)
+        m = cls.__new__(cls)
+        _object_setattr(m, '__dict__', copy(self.__dict__))
+        _object_setattr(m, '__pydantic_fields_set__', copy(self.__pydantic_fields_set__))
+        return m
+
+    def __deepcopy__(self: Model, memo: dict[int, Any] | None = None) -> Model:
+        """Returns a deep copy of the model."""
+        cls = type(self)
+        m = cls.__new__(cls)
+        _object_setattr(m, '__dict__', deepcopy(self.__dict__, memo=memo))
+        # This next line doesn't need a deepcopy because __pydantic_fields_set__ is a set[str],
+        # and attempting a deepcopy would be marginally slower.
+        _object_setattr(m, '__pydantic_fields_set__', copy(self.__pydantic_fields_set__))
+        return m
+
     if typing.TYPE_CHECKING:
 
         def model_dump(

tests/test_root_model.py

@@ -612,3 +612,13 @@ def test_help(create_module):
         )
 
     assert 'class RootModel' in module.help_result_string
+
+
+def test_copy_preserves_equality():
+    model = RootModel()
+
+    copied = model.__copy__()
+    assert model == copied
+
+    deepcopied = model.__deepcopy__()
+    assert model == deepcopied