fix: always call __post_init__ when set in dataclasses

changes/4477-PrettyWood.md

@@ -0,0 +1 @@
+fix: dataclass wrapper was not always called

pydantic/dataclasses.py

@@ -184,7 +184,9 @@ def dataclass(
     def wrap(cls: Type[Any]) -> 'DataclassClassOrWrapper':
         import dataclasses
 
-        if is_builtin_dataclass(cls):
+        if is_builtin_dataclass(cls) and not (
+            is_builtin_dataclass(cls.__bases__[0]) and not hasattr(cls.__bases__[0], '__post_init__')
+        ):
             dc_cls_doc = ''
             dc_cls = DataclassProxy(cls)
             default_validate_on_init = False

tests/test_dataclasses.py

@@ -1395,3 +1395,80 @@ class Bar:
         @pydantic.dataclasses.dataclass
         class Foo:
             a: List[Bar(a=1)]
+
+
+def test_parent_post_init():
+    @dataclasses.dataclass
+    class A:
+        a: float = 1
+
+        def __post_init__(self):
+            self.a *= 2
+
+    @pydantic.dataclasses.dataclass
+    class B(A):
+        @validator('a')
+        def validate_a(cls, value):
+            value += 3
+            return value
+
+    assert B().a == 5  # 1 * 2 + 3
+
+
+def test_subclass_post_init_post_parse():
+    @dataclasses.dataclass
+    class A:
+        a: float = 1
+
+    @pydantic.dataclasses.dataclass
+    class B(A):
+        def __post_init_post_parse__(self):
+            self.a *= 2
+
+        @validator('a')
+        def validate_a(cls, value):
+            value += 3
+            return value
+
+    assert B().a == 8  # (1 + 3) * 2
+
+
+def test_subclass_post_init():
+    @dataclasses.dataclass
+    class A:
+        a: int = 1
+
+    @pydantic.dataclasses.dataclass
+    class B(A):
+        def __post_init__(self):
+            self.a *= 2
+
+        @validator('a')
+        def validate_a(cls, value):
+            value += 3
+            return value
+
+    assert B().a == 5  # 1 * 2 + 3
+
+
+def test_subclass_post_init_inheritance():
+    @dataclasses.dataclass
+    class A:
+        a: int = 1
+
+    @pydantic.dataclasses.dataclass
+    class B(A):
+        def __post_init__(self):
+            self.a *= 2
+
+        @validator('a')
+        def validate_a(cls, value):
+            value += 3
+            return value
+
+    @pydantic.dataclasses.dataclass
+    class C(B):
+        def __post_init__(self):
+            self.a *= 3
+
+    assert C().a == 6  # 1 * 3 + 3