Dataclass deepcopy 1.10 (#4963)

* add test to reproduce #4949

* fix infinitely recursive deepcopy

* add test for shallow copy of wrapped dataclass

* fix infinitely recursive copy of wrapped dataclass

---------

Co-authored-by: Martin Billinger-Finke <[email protected]>

Author: mbillingr

changes/4949-mbillingr.md

@@ -0,0 +1 @@
+Fix `RecursionError` when deep-copying dataclass types wrapped by pydantic.

pydantic/dataclasses.py

@@ -31,6 +31,7 @@ class M:
 The trick is to create a wrapper around `M` that will act as a proxy to trigger
 validation without altering default `M` behaviour.
 """
+import copy
 import sys
 from contextlib import contextmanager
 from functools import wraps
@@ -260,6 +261,12 @@ def __setattr__(self, __name: str, __value: Any) -> None:
     def __instancecheck__(self, instance: Any) -> bool:
         return isinstance(instance, self.__dataclass__)
 
+    def __copy__(self) -> 'DataclassProxy':
+        return DataclassProxy(copy.copy(self.__dataclass__))
+
+    def __deepcopy__(self, memo: Any) -> 'DataclassProxy':
+        return DataclassProxy(copy.deepcopy(self.__dataclass__, memo))
+
 
 def _add_pydantic_validation_attributes(  # noqa: C901 (ignore complexity)
     dc_cls: Type['Dataclass'],

tests/test_dataclasses.py

@@ -1,3 +1,4 @@
+import copy
 import dataclasses
 import pickle
 import re
@@ -1608,3 +1609,25 @@ def check_b(cls, v):
     assert m1.a == m2.a == 3
     assert m1.b == m2.b == 'b'
     assert m1.c == m2.c == 3.0
+
+
+def test_can_copy_wrapped_dataclass_type():
+    @pydantic.dataclasses.dataclass
+    @dataclasses.dataclass
+    class A:
+        name: int
+
+    B = copy.copy(A)
+    assert B is not A
+    assert B(1) == A(1)
+
+
+def test_can_deepcopy_wrapped_dataclass_type():
+    @pydantic.dataclasses.dataclass
+    @dataclasses.dataclass
+    class A:
+        name: int
+
+    B = copy.deepcopy(A)
+    assert B is not A
+    assert B(1) == A(1)