bug: Add annotation to ModelField for use in BaseModel.__signature__

[adriangb]

Currently, ModelField.outer_type_ is used for Model.__signature__.

This leads to signatures that differ from dataclasses or classes with a manual __init__ of the same types.

from dataclasses import dataclass
from inspect import signature
from typing import Optional

from pydantic import BaseModel

@dataclass
class Dataclass:
    foo: Optional[int] = None

class CustomClass:
    def __init__(self, foo: Optional[int] = None) -> None:
        ...

class PydanticModel(BaseModel):
    foo: Optional[int] = None


print(signature(Dataclass).parameters["foo"].annotation)  # Optional[int]
print(signature(CustomClass).parameters["foo"].annotation)  # Optional[int]
print(signature(PydanticModel).parameters["foo"].annotation)  # <class 'int'>

This PR fixes this by storing the annotation in ModelField.annotation and then using that for the signature instead of outer_type_.
I realize this is adding a public attribute to ModelField, and that it is not as simple as storing the type_ passed into the constructor (I tried to handle the case where the type is inferred from the default value, I think successfully), so this may not be the best solution, but it is the best I could come up with today.

[samuelcolvin]

Seems good to me, but please add a change description.

I don't think this can go in v1.9.1 as it's not a bug fix for v1.9

[samuelcolvin]

please update.

[adriangb]

Hmm. While I am adding a public attribute, and that could be considered a feature, I am only doing it to fix what I would consider a bug (incorrect results from inspect.signsture). One of my main questions here was: can you think of a way of doing this that does not add a public attribute?

[samuelcolvin]

I don't mind the public attribute, I don't see another (simply) way.

Which of my points were you questioning? The current description, out which release this goes in?

[adriangb]

I was just questioning if this is a bug fix or a feature. I think the underlying problem is a bug, but if we're adding a public attribute it's more like a feature.

I'll add the change description.

[samuelcolvin]

Otherwise lgtm

[adriangb]

@samuelcolvin I guess we didn't merge this 😅

[samuelcolvin]

@samuelcolvin I guess we didn't merge this sweat_smile

Got there in the end 😓.

Thank so much, as ever, sorry for the delay.

[JacobHayes]

@samuelcolvin looks like this one won't auto-merge because of the old "request changes" - I think it'll need an approval to override.

[samuelcolvin]

Thanks @JacobHayes, missed that.

[JacobHayes]

Yup, I missed the auto-merge announcement so excited to find it in the wild!

[samuelcolvin]

Ye, it's been a god sent for this work.