Fix error with empty dataclass inheritance

changes/4576-dolfinus.md

@@ -0,0 +1 @@
+Fix `@pydantic.dataclasses.dataclass()` syntax failure on inheriting dataclass without changing fields list

pydantic/dataclasses.py

@@ -197,7 +197,7 @@ def dataclass(
     def wrap(cls: Type[Any]) -> 'DataclassClassOrWrapper':
         import dataclasses
 
-        if is_builtin_dataclass(cls) and _extra_dc_args(_cls) == _extra_dc_args(_cls.__bases__[0]):  # type: ignore
+        if is_builtin_dataclass(cls) and _extra_dc_args(cls) == _extra_dc_args(cls.__bases__[0]):
             dc_cls_doc = ''
             dc_cls = DataclassProxy(cls)
             default_validate_on_init = False

tests/test_dataclasses.py

@@ -1472,3 +1472,26 @@ def __post_init__(self):
             self.a *= 3
 
     assert C().a == 6  # 1 * 3 + 3
+
+
+def test_issue_4565():
+    @dataclasses.dataclass
+    class A:
+        a: int = 1
+
+    # both @decorator and @decorator() syntax shold be okay
+    @pydantic.dataclasses.dataclass
+    class B(A):
+        b: int = 2
+
+    @pydantic.dataclasses.dataclass
+    class C(A):
+        ...
+
+    @pydantic.dataclasses.dataclass()
+    class BB(A):
+        bb: int = 2
+
+    @pydantic.dataclasses.dataclass()
+    class CC(A):
+        ...