simplify recursive refs

[adriangb]

I'm not sure if this would be possible (I'm guessing it's not), but it would be nice to be able to recursively refer to a parent validator without having to know a-priori if it will be recursive or not.

Currently, if you are parsing something like:

class Outer:
    inner: List[Outer]

You would have to know that Outer is recursive before you parse its fields.

Would it be possible to have an optional "id" property on every validator that acts as the reference for recursive schemas instead of a special "recursive-container" validator? So:

from typing import List

from pydantic_core import SchemaValidator


class Outer:
    inner: "List[Outer]"


v = SchemaValidator(
    {
        "type": "model-class",
        # id is optional, required for this to be usable as a recursive ref
        # the value is arbitrary, the id of the type seems like a safe choice
        "id": str(id(Outer)),
        "schema": {
            "type": "model",
            "fields": {
                "inner": {
                    "type": "list",
                    "items": {
                        "type": "recursive-ref",
                        "id": str(id(Outer)),
                    }
                },
            },
        },
    }
)

[samuelcolvin]

I suspect it would be possible.

What I don't think you can remove (unfortunately) is the actual RecursiveValidator in rust. I've tried to keep the definitions and the actual data structure in rust as close as possible.

But if you can make this work cleanly, happy to accept a PR.