Signature of inherited dataclass does not include subclass field

[shinaji]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

Hello, I found that the signature of inherited dataclass seems to have only its superclass fields. Is this expected behavior at pydantic v2? Due to this, FastAPI seems to ignore the subclass field value.

Example Code

from pydantic.dataclasses import dataclass

@dataclass
class A:
    a: int

@dataclass
class B(A):
    b: int

# In [4]: B.__signature__
# Out[4]: <Signature (a: int) -> None>  # "b: int" is missing

Python, Pydantic & OS Version

pydantic version: 2.4.2
        pydantic-core version: 2.10.1
          pydantic-core build: profile=release pgo=false
               python version: 3.9.13 (main, Sep 17 2022, 22:53:18)  [Clang 14.0.0 (clang-1400.0.29.102)]
                     platform: macOS-13.6-arm64-arm-64bit
             related packages: email-validator-2.0.0.post2 pydantic-extra-types-2.1.0 mypy-1.3.0 typing_extensions-4.8.0 fastapi-0.104.0 pydantic-settings-2.0.3

[sydney-runkle]

Hi @shinaji,

Thanks for reporting this. Looks like a bug with the pydantic dataclass signature generation. I've marked this with the good first issue tag, if anyone wants to help!

[sydney-runkle]

This should be helpful:

pydantic/pydantic/_internal/_dataclasses.py

Lines 188 to 193 in f645f19

	def generate_dataclass_signature(cls: type[StandardDataclass]) -> Signature:
	"""Generate signature for a pydantic dataclass.
	This implementation assumes we do not support custom `__init__`, which is currently true for pydantic dataclasses.
	If we change this eventually, we should make this function's logic more closely mirror that from
	`pydantic._internal._model_construction.generate_model_signature`.

[howsunjow]

@sydney-runkle I've contributed a fix in a PR. Not sure how exactly to assign a reviewer though.

[sydney-runkle]

@howsunjow awesome, thanks! I just submitted a review. Thanks for your contribution 👍 ⭐