fix: support pydantic.Field(kw_only=True) with inherited dataclasses

pydantic/dataclasses.py

@@ -12,7 +12,7 @@
 from ._internal import _dataclasses as _pydantic_dataclasses
 from ._migration import getattr_migration
 from .config import ConfigDict
-from .fields import Field
+from .fields import Field, FieldInfo
 
 if TYPE_CHECKING:
     from ._internal._dataclasses import PydanticDataclass
@@ -143,9 +143,29 @@ def dataclass(
 
     if sys.version_info >= (3, 10):
         kwargs = dict(kw_only=kw_only, slots=slots)
+
+        def make_pydantic_fields_compatible(cls: type[Any]) -> None:
+            """Make sure that stdlib `dataclasses` understands `Field` kwargs like `kw_only`
+            To do that, we simply change
+              `x: int = pydantic.Field(..., kw_only=True)`
+            into
+              `x: int = dataclasses.field(default=pydantic.Field(..., kw_only=True), kw_only=True)`
+            """
+            for field_name in cls.__annotations__:
+                try:
+                    field_value = getattr(cls, field_name)
+                except AttributeError:
+                    # no default value has been set for this field
+                    continue
+                if isinstance(field_value, FieldInfo) and field_value.kw_only:
+                    setattr(cls, field_name, dataclasses.field(default=field_value, kw_only=True))
+
     else:
         kwargs = {}
 
+        def make_pydantic_fields_compatible(_):
+            return None
+
     def create_dataclass(cls: type[Any]) -> type[PydanticDataclass]:
         """Create a Pydantic dataclass from a regular dataclass.
 
@@ -185,6 +205,8 @@ def create_dataclass(cls: type[Any]) -> type[PydanticDataclass]:
                 bases = bases + (generic_base,)
             cls = types.new_class(cls.__name__, bases)
 
+        make_pydantic_fields_compatible(cls)
+
         cls = dataclasses.dataclass(  # type: ignore[call-overload]
             cls,
             # the value of init here doesn't affect anything except that it makes it easier to generate a signature

tests/test_dataclasses.py

@@ -1644,6 +1644,21 @@ class A:
     assert A(b='hi').b == 'hi'
 
 
+@pytest.mark.skipif(sys.version_info < (3, 10), reason='kw_only is not available in python < 3.10')
+def test_kw_only_subclass():
+    @pydantic.dataclasses.dataclass
+    class A:
+        x: int
+        y: int = pydantic.Field(default=0, kw_only=True)
+
+    @pydantic.dataclasses.dataclass
+    class B(A):
+        z: int
+
+    assert B(1, 2) == B(x=1, y=0, z=2)
+    assert B(1, y=2, z=3) == B(x=1, y=2, z=3)
+
+
 def dataclass_decorators(include_identity: bool = False, exclude_combined: bool = False):
     decorators = [pydantic.dataclasses.dataclass, dataclasses.dataclass]
     ids = ['pydantic', 'stdlib']