XGtsRefValidator does not traverse oneOf/anyOf/allOf subschemas

[GeraBart]

Bug Description

XGtsRefValidator::visit_instance() only recurses into properties (for objects) and items (for arrays), but does not traverse into JSON Schema combinators (oneOf, anyOf, allOf). This means x-gts-ref constraints nested inside these combinators are silently ignored during instance validation.

Additionally, remove_x_gts_ref_fields() in store.rs strips all x-gts-ref fields before passing the schema to the jsonschema crate. Subschemas containing only x-gts-ref become empty schemas {}. When placed inside oneOf, both empty subschemas match any value, causing oneOf to always fail (it requires exactly 1 match out of N).

The combined effect: x-gts-ref inside oneOf/anyOf/allOf is broken at both validation layers.

This is the same issue as GlobalTypeSystem/gts-ts#10 in the TypeScript adapter.

Root Cause

In gts/src/x_gts_ref.rs, visit_instance() (lines ~165-220) handles:

• ✅ schema.properties — recurses into object properties
• ✅ schema.items — recurses into array items
• ❌ schema.oneOf — not traversed
• ❌ schema.anyOf — not traversed
• ❌ schema.allOf — not traversed

Note that visit_schema() does correctly handle combinators because it generically iterates over all keys. The inconsistency is only in visit_instance().

Reproduction

Schema (action.v1.json)

{
  "$id": "gts://gts.hai3.mfes.comm.action.v1~",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "type": {
      "x-gts-ref": "/$id"
    },
    "target": {
      "type": "string",
      "oneOf": [
        { "x-gts-ref": "gts.hai3.mfes.ext.domain.v1~*" },
        { "x-gts-ref": "gts.hai3.mfes.ext.extension.v1~*" }
      ]
    }
  },
  "required": ["type", "target"]
}

Instance (valid action targeting a domain)

{
  "type": "gts.hai3.mfes.comm.action.v1~hai3.mfes.ext.mount_ext.v1",
  "target": "gts.hai3.mfes.ext.domain.v1~hai3.screensets.layout.screen.v1"
}

Expected behavior

Validation passes — target matches the first x-gts-ref pattern (gts.hai3.mfes.ext.domain.v1~*).

Actual behavior

Validation fails. The jsonschema crate sees both oneOf subschemas as {} (since x-gts-ref was stripped), both match the string value, and oneOf fails because 2 subschemas matched instead of 1. Meanwhile, visit_instance() never sees the x-gts-ref constraints at all because it does not recurse into oneOf branches.

Suggested Fix

visit_instance() should recurse into combinator subschemas:

// After handling properties and items:
for combinator in &["oneOf", "anyOf", "allOf"] {
    if let Some(Value::Array(sub_schemas)) = sch_obj.get(*combinator) {
        for sub_schema in sub_schemas {
            self.visit_instance(inst, sub_schema, root_schema, path, errors);
        }
    }
}

For oneOf semantics specifically, the validator should check that the instance matches exactly one x-gts-ref pattern among the subschemas (mirroring JSON Schema oneOf semantics).

Impact

This bug blocks any schema that uses x-gts-ref inside JSON Schema combinators. The workaround is to flatten x-gts-ref to the property level (e.g., using a broader wildcard pattern), but this loses the ability to express "target must be one of these specific type families."