recursive object results in `ValueError: Recursion limit reached`

[braingram]

Thanks for working on this library. I've been following it as a possible replacement for the python jsonschema library in https://github.com/asdf-format/asdf One of the features we needed was custom keywords which I was excited to see was added to the python API in the latest release. ASDF uses jsonschemas to validate instances that can often be recursive.

Are there plans to support recursive objects? The following example:

import jsonschema_rs
a = {}
a['a'] = a
jsonschema_rs.validate({"properties": {"a": {"type": "object"}}}, a)

fails with ValueError: Recursion limit reached.

Let me know if more information is helpful of if you have suggestions for work-arounds.

[Stranger6667]

Hi!

This is theoretically possible if #239 is in place, but requires quite a lot of work on the compiler first. Right now the data model is based on serde_json::Value that does not support cycles. I am positive on supporting it, but didn't get into planning yet.

Could you share some specific use case from asdf?

[braingram]

Thanks!

Here's one example and please let me know if more information is helpful.

ASDF is used to represent data structures for the JWST and Roman space telescopes. One structure represents the sequence of coordinate transforms to convert on-detector pixel coordinates to positions on the "sky" this is commonly referred to as the "world coordinate system" or WCS object. This WCS object uses astropy models to represent these transforms.

Each transform (let's say A) can have a user-defined inverse (let's say B) that is also a transform that has an inverse (A again). Here's a toy example that creates a file with a similar structure (using asdf and the asdf-astropy package which supports the structures in astropy).

import io
import asdf
from astropy.modeling.models import Shift
a = Shift(1)
b = Shift(-1)
a.inverse = b
b.inverse = a
bio = io.BytesIO(asdf.dumps({"transform": a}))
print(asdf.util.load_yaml(bio)["transform"])

Running the above produces a print out of the serialized transform a which is a recursive dictionary

{'inputs': ['x'], 'inverse': {'inputs': ['x'], 'inverse': {...}, 'offset': -1.0, 'outputs': ['y']}, 'offset': 1.0, 'outputs': ['y']}

It's something similar to this structure that we pass through jsonschema for validation (to check that the serialized transforms in this case conform to a schema).

Hopefully I didn't go too far into unhelpful details. Please let me know if there is anything I can do to help.