Pydantic validators raise a pydantic.Validation error instead of raising a tyro.Instantiation error

[sander76]

Pydantic has strong property validation capabilities that go beyond the capabilities of type Annotations.
Consider the following pydantic model which has a custom validator included:

class Model(BaseModel):
    a: int

    @field_validator("a")
    def below_ten(cls, v):
        if v > 10:
            raise ValueError("Must be below 10")

Tyro doesn't take them into account during model validation which is -I think- taking place somewhere here:

tyro/tyro/_calling.py

Line 99 in a47b2f8

value = arg.lowered.instantiator(value)

Pydantic does the above validation at model instantiation, which is happening here:

tyro/tyro/_calling.py

Line 217 in a47b2f8

return unwrapped_f(*positional_args, **kwargs), consumed_keywords # type: ignore

It would be great to leverage the validation rules inside tyro.

[brentyi]

Thanks for the suggestion @sander76!

This is mostly an aesthetics/user-friendliness thing, right? We get an error message either way, we just want it to be formatted as a tyro error instead of a pydantic one?

The easiest solution here would be to drop a try/except pair around the model instantiation line (return unwrapped_f(...)). We can catch pydantic.ValidationError, and then form a cleaner error message.

If there's a way to pull out the individual validator for a field we could also do it on the output of value = arg.lowered.instantiator(value), but this is more involved and I'm not sure it'd be worth it.

[sander76]

Yes it is. I like the way tyro does the output. And I see the pydantic validators as a powerful way to validate the arguments.

[brentyi]

Okay, I like it! This seems like an easy way to add a lot of argument validation flexibility to tyro, which is nice. :)

No worries if not, but if you have time to take a stab at a (even partial) PR I'd appreciate it, otherwise I can experiment with these errors as soon as I catch up on some other responsibilities.

[sander76]

I will come up with something! 👍