bug: Panic when using a JSON schema with recursive elements

[liamg]

Short description

I'm using the Go API to apply some policies to a variety of different inputs. I'm using a JSON schema for each input type to validate rules and have come across a panic when using a schema with recursive elements. Minimal example below.

• OPA version: v0.44.0

The example below is simplified for readability but we need this feature to parse tree structures etc.

Steps To Reproduce

1. Use the following schema (schema.json):

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://github.com/open-policy-agent/opa/issues/5166",
  "type": "object",
  "properties": {
    "Something": {
      "$ref": "#/$defs/X"
    }
  },
  "$defs": {
    "X": {
      "type": "object",
      "properties": {
        "Y": {
          "$ref": "#/$defs/Y"
        }
      }
    },
    "Y": {
      "type": "object",
      "properties": {
        "X": {
          "$ref": "#/$defs/X"
        }
      }
    }
  }
}

2. Run opa check -s schema.json input.json (where input.rego is pretty much anything)
3. KABOOM

Expected behavior

The input.rego should be validated against the input schema.

Happy to have a go at fixing this if I can manage it 🤞

[boranx]

fwiw, yeah feel free to fix it :) I was debugging the issue and saw it goes into a loop as the child objects are continuously x->y->x->y then at some point the stack overflows

https://github.com/open-policy-agent/opa/blob/main/ast/compile.go#L1132-L1136

or the following might help for debugging

git diff
diff --git a/ast/compile.go b/ast/compile.go
index 6e863585..5eaa4312 100644
--- a/ast/compile.go
+++ b/ast/compile.go
@@ -1133,6 +1133,7 @@ func parseSchema(schema interface{}) (types.Type, error) {
                        if len(subSchema.PropertiesChildren) > 0 {
                                staticProps := make([]*types.StaticProperty, 0, len(subSchema.PropertiesChildren))
                                for _, pSchema := range subSchema.PropertiesChildren {
+                                       fmt.Println("pSchema:", pSchema.Ref.String())

[liamg]

@boranx Thanks, I raised a PR :)