From c4a0de276fee815b8642ab68b7d7fcc084c23c2e Mon Sep 17 00:00:00 2001
From: Eric Jolibois <em.jolibois@gmail.com>
Date: Mon, 5 Sep 2022 15:09:31 +0200
Subject: [PATCH] fix: always call `__post_init__` when set in dataclasses

---
 changes/4477-PrettyWood.md |  1 +
 pydantic/dataclasses.py    | 20 +++++++++++---
 tests/test_dataclasses.py  | 54 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+), 3 deletions(-)
 create mode 100644 changes/4477-PrettyWood.md

diff --git a/changes/4477-PrettyWood.md b/changes/4477-PrettyWood.md
new file mode 100644
index 00000000000..7800bb091ba
--- /dev/null
+++ b/changes/4477-PrettyWood.md
@@ -0,0 +1 @@
+fix: always call __post_init__ when set in dataclasses
diff --git a/pydantic/dataclasses.py b/pydantic/dataclasses.py
index f60f04b239a..7da17d50336 100644
--- a/pydantic/dataclasses.py
+++ b/pydantic/dataclasses.py
@@ -256,7 +256,6 @@ def _add_pydantic_validation_attributes(  # noqa: C901 (ignore complexity)
     """
     init = dc_cls.__init__
 
-    @wraps(init)
     def handle_extra_init(self: 'Dataclass', *args: Any, **kwargs: Any) -> None:
         if config.extra == Extra.ignore:
             init(self, *args, **{k: v for k, v in kwargs.items() if k in self.__dataclass_fields__})
@@ -285,8 +284,23 @@ def new_post_init(self: 'Dataclass', *args: Any, **kwargs: Any) -> None:
             if config.post_init_call == 'after_validation':
                 post_init(self, *args, **kwargs)
 
-        setattr(dc_cls, '__init__', handle_extra_init)
-        setattr(dc_cls, '__post_init__', new_post_init)
+        if is_builtin_dataclass(dc_cls.__bases__[0]) and not hasattr(dc_cls.__bases__[0], '__post_init__'):
+            # `__post_init__` won't be called so we need to call it manually
+            @wraps(init)
+            def new_init(self: 'Dataclass', *args: Any, **kwargs: Any) -> None:
+                handle_extra_init(self, *args, **kwargs)
+                new_post_init(self, *args, **kwargs)
+
+            setattr(dc_cls, '__init__', new_init)
+            setattr(dc_cls, '__post_init__', new_post_init)
+        else:
+
+            @wraps(init)
+            def new_init(self: 'Dataclass', *args: Any, **kwargs: Any) -> None:
+                handle_extra_init(self, *args, **kwargs)
+
+            setattr(dc_cls, '__init__', handle_extra_init)
+            setattr(dc_cls, '__post_init__', new_post_init)
 
     else:
 
diff --git a/tests/test_dataclasses.py b/tests/test_dataclasses.py
index f29bdfc3c80..bf57fda0ab5 100644
--- a/tests/test_dataclasses.py
+++ b/tests/test_dataclasses.py
@@ -1395,3 +1395,57 @@ class Bar:
         @pydantic.dataclasses.dataclass
         class Foo:
             a: List[Bar(a=1)]
+
+
+def test_parent_post_init():
+    @dataclasses.dataclass
+    class A:
+        a: float = 1.1
+
+        def __post_init__(self):
+            self.a *= 2
+
+    @pydantic.dataclasses.dataclass
+    class B(A):
+        @validator('a')
+        def validate_a(cls, value):
+            value += 1
+            return value
+
+    assert B().a == 3.2  # 2 * 1.1 + 1
+
+
+def test_subclass_post_init_post_parse():
+    @dataclasses.dataclass
+    class A:
+        a: float = 1.1
+
+    @pydantic.dataclasses.dataclass
+    class B(A):
+        def __post_init_post_parse__(self):
+            self.a *= 2
+
+        @validator('a')
+        def validate_a(cls, value):
+            value += 1
+            return value
+
+    assert B().a == 4.2  # (1.1 + 1) * 2
+
+
+def test_subclass_post_init():
+    @dataclasses.dataclass
+    class A:
+        a: float = 1.1
+
+    @pydantic.dataclasses.dataclass
+    class B(A):
+        def __post_init__(self):
+            self.a *= 2
+
+        @validator('a')
+        def validate_a(cls, value):
+            value += 1
+            return value
+
+    assert B().a == 3.2  # 2 * 1.1 + 1