core[patch]: fixed circular dependency with json schema (#18657)

**Description:** Circular dependencies when parsing references leading
to `RecursionError: maximum recursion depth exceeded` issue. This PR
address the issue by handling previously seen refs as in any typical DFS
to avoid infinite depths.

**Issue:** #12163

 **Twitter handle:** https://twitter.com/theBhulawat 


- [x] **Add tests and docs**: If you're adding a new integration, please
include
1. a test for the integration, preferably unit tests that do not rely on
network access,
2. an example notebook showing its use. It lives in
`docs/docs/integrations` directory.


- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>
Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>

libs/core/langchain_core/utils/json_schema.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from copy import deepcopy
-from typing import Any, List, Optional, Sequence
+from typing import Any, Dict, List, Optional, Sequence, Set
 
 
 def _retrieve_ref(path: str, schema: dict) -> dict:
@@ -21,40 +21,66 @@ def _retrieve_ref(path: str, schema: dict) -> dict:
 
 
 def _dereference_refs_helper(
-    obj: Any, full_schema: dict, skip_keys: Sequence[str]
+    obj: Any,
+    full_schema: Dict[str, Any],
+    skip_keys: Sequence[str],
+    processed_refs: Optional[Set[str]] = None,
 ) -> Any:
+    if processed_refs is None:
+        processed_refs = set()
+
     if isinstance(obj, dict):
         obj_out = {}
         for k, v in obj.items():
             if k in skip_keys:
                 obj_out[k] = v
             elif k == "$ref":
+                if v in processed_refs:
+                    continue
+                processed_refs.add(v)
                 ref = _retrieve_ref(v, full_schema)
-                return _dereference_refs_helper(ref, full_schema, skip_keys)
+                full_ref = _dereference_refs_helper(
+                    ref, full_schema, skip_keys, processed_refs
+                )
+                processed_refs.remove(v)
+                return full_ref
             elif isinstance(v, (list, dict)):
-                obj_out[k] = _dereference_refs_helper(v, full_schema, skip_keys)
+                obj_out[k] = _dereference_refs_helper(
+                    v, full_schema, skip_keys, processed_refs
+                )
             else:
                 obj_out[k] = v
         return obj_out
     elif isinstance(obj, list):
-        return [_dereference_refs_helper(el, full_schema, skip_keys) for el in obj]
+        return [
+            _dereference_refs_helper(el, full_schema, skip_keys, processed_refs)
+            for el in obj
+        ]
     else:
         return obj
 
 
-def _infer_skip_keys(obj: Any, full_schema: dict) -> List[str]:
+def _infer_skip_keys(
+    obj: Any, full_schema: dict, processed_refs: Optional[Set[str]] = None
+) -> List[str]:
+    if processed_refs is None:
+        processed_refs = set()
+
     keys = []
     if isinstance(obj, dict):
         for k, v in obj.items():
             if k == "$ref":
+                if v in processed_refs:
+                    continue
+                processed_refs.add(v)
                 ref = _retrieve_ref(v, full_schema)
                 keys.append(v.split("/")[1])
-                keys += _infer_skip_keys(ref, full_schema)
+                keys += _infer_skip_keys(ref, full_schema, processed_refs)
             elif isinstance(v, (list, dict)):
-                keys += _infer_skip_keys(v, full_schema)
+                keys += _infer_skip_keys(v, full_schema, processed_refs)
     elif isinstance(obj, list):
         for el in obj:
-            keys += _infer_skip_keys(el, full_schema)
+            keys += _infer_skip_keys(el, full_schema, processed_refs)
     return keys
 
 

libs/core/tests/unit_tests/utils/test_json_schema.py

@@ -181,3 +181,54 @@ def test_dereference_refs_integer_ref() -> None:
     }
     actual = dereference_refs(schema)
     assert actual == expected
+
+
+def test_dereference_refs_cyclical_refs() -> None:
+    schema = {
+        "type": "object",
+        "properties": {
+            "user": {"$ref": "#/$defs/user"},
+            "customer": {"$ref": "#/$defs/user"},
+        },
+        "$defs": {
+            "user": {
+                "type": "object",
+                "properties": {
+                    "friends": {"type": "array", "items": {"$ref": "#/$defs/user"}}
+                },
+            }
+        },
+    }
+    expected = {
+        "type": "object",
+        "properties": {
+            "user": {
+                "type": "object",
+                "properties": {
+                    "friends": {
+                        "type": "array",
+                        "items": {},  # Recursion is broken here
+                    }
+                },
+            },
+            "customer": {
+                "type": "object",
+                "properties": {
+                    "friends": {
+                        "type": "array",
+                        "items": {},  # Recursion is broken here
+                    }
+                },
+            },
+        },
+        "$defs": {
+            "user": {
+                "type": "object",
+                "properties": {
+                    "friends": {"type": "array", "items": {"$ref": "#/$defs/user"}}
+                },
+            }
+        },
+    }
+    actual = dereference_refs(schema)
+    assert actual == expected