How can I use field on dataclasses or pydantic.BaseModel?

[josephnowak]

It's my first time using mypyc, I think it's an amazing project with a lot of potential, and I want to use it to compile one of my project, but it is heavily dependent on the use of the Field of Pydantic, and I have not been able to figure out the way to use it without breaking the code. I get errors like the type is not inferred correctly. Is the Field not a completely supported functionality yet? Or am I doing something wrong? You can find attached an example that recreates the problem:

Environment

• Python: 3.13.5
• OS: Windows 11
• mypy: 1.17.1
• mypyc: 0.0.1
• pydantic: 2.11.7
• setuptools: 80.9.0

Setup

from mypyc.build import mypycify
from setuptools import setup

# Run this to compile and test: python mypyc_setup.py build_ext --inplace
setup(
    name="mypyc_output",
    ext_modules=mypycify(
        ["src/mypyc_testing/test_compilation.py"],
        opt_level="3",
        debug_level="1",
        strict_dunder_typing=True,
    ),
)

Compiled code

If I remove the Optional, it works well, if I add a type hint like int | None, it fails, if I remove the use of the Annotated, it fails at compilation time because it can not assign Field to an int attribute. I included this code on a package called mypyc_testing on a script called test_compilation.py

from pydantic.main import BaseModel
from pydantic.fields import Field
from dataclasses import dataclass, field
from typing import Annotated, Optional

class A(BaseModel):
    a: Annotated[Optional[int], Field(default=-1, description="ID")]


@dataclass
class B:
    a: Annotated[Optional[int], field(default=-1, metadata={"description": "ID"})]

Executable code

from mypyc_testing.test_compilation import A, B
from pydantic import ValidationError

try:
    A()
except ValidationError as e:
    print(e)


try:
    B()
except TypeError as e:
    print(e)

Errors

1 validation error for A
a
  Field required [type=missing, input_value={}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.11/v/missing

B.__init__() missing 1 required positional argument: 'a'