From 06f7de3a37706df5880137e4253e8373dc49ff8c Mon Sep 17 00:00:00 2001
From: detachhead <detachhead@users.noreply.github.com>
Date: Tue, 9 Aug 2022 10:37:40 +1000
Subject: [PATCH] fix "extra fields not permitted" error when dataclass with
 `Extra.forbid` is validated multiple times

---
 changes/4343-detachhead.md |  1 +
 pydantic/dataclasses.py    |  4 ++++
 tests/test_dataclasses.py  | 24 ++++++++++++++++++++++++
 3 files changed, 29 insertions(+)
 create mode 100644 changes/4343-detachhead.md

diff --git a/changes/4343-detachhead.md b/changes/4343-detachhead.md
new file mode 100644
index 0000000000..8a9f424f48
--- /dev/null
+++ b/changes/4343-detachhead.md
@@ -0,0 +1 @@
+fix "extra fields not permitted" error when dataclass with `Extra.forbid` is validated multiple times
\ No newline at end of file
diff --git a/pydantic/dataclasses.py b/pydantic/dataclasses.py
index 1a9008cc6c..36529a88fa 100644
--- a/pydantic/dataclasses.py
+++ b/pydantic/dataclasses.py
@@ -385,6 +385,10 @@ def create_pydantic_model_from_dataclass(
 
 
 def _dataclass_validate_values(self: 'Dataclass') -> None:
+    # validation errors can occur if this function is called twice on an already initialised dataclass.
+    # for example if Extra.forbid is enabled, it would consider __pydantic_initialised__ an invalid extra property
+    if getattr(self, '__pydantic_initialised__'):
+        return
     if getattr(self, '__pydantic_has_field_info_default__', False):
         # We need to remove `FieldInfo` values since they are not valid as input
         # It's ok to do that because they are obviously the default values!
diff --git a/tests/test_dataclasses.py b/tests/test_dataclasses.py
index f74b087485..ff300afa0d 100644
--- a/tests/test_dataclasses.py
+++ b/tests/test_dataclasses.py
@@ -1360,3 +1360,27 @@ class A:
         A(1, '')
 
     assert A(b='hi').b == 'hi'
+
+
+def test_extra_forbid_list_no_error():
+    @pydantic.dataclasses.dataclass(config=dict(extra=Extra.forbid))
+    class Bar:
+        ...
+
+    @pydantic.dataclasses.dataclass
+    class Foo:
+        a: List[Bar]
+
+    assert isinstance(Foo(a=[Bar()]).a[0], Bar)
+
+
+def test_extra_forbid_list_error():
+    @pydantic.dataclasses.dataclass(config=dict(extra=Extra.forbid))
+    class Bar:
+        ...
+
+    with pytest.raises(TypeError, match=re.escape("__init__() got an unexpected keyword argument 'a'")):
+
+        @pydantic.dataclasses.dataclass
+        class Foo:
+            a: List[Bar(a=1)]