fix: allow for self-referencing pydantic schema

fastapi_mcp/openapi/utils.py

@@ -1,4 +1,4 @@
-from typing import Any, Dict
+from typing import Any, Dict, Optional, Set
 
 
 def get_single_param_type_from_schema(param_schema: Dict[str, Any]) -> str:
@@ -16,7 +16,11 @@ def get_single_param_type_from_schema(param_schema: Dict[str, Any]) -> str:
     return param_schema.get("type", "string")
 
 
-def resolve_schema_references(schema_part: Dict[str, Any], reference_schema: Dict[str, Any]) -> Dict[str, Any]:
+def resolve_schema_references(
+    schema_part: Dict[str, Any],
+    reference_schema: Dict[str, Any],
+    seen: Optional[Set[str]] = None,
+) -> Dict[str, Any]:
     """
     Resolve schema references in OpenAPI schemas.
 
@@ -27,6 +31,8 @@ def resolve_schema_references(schema_part: Dict[str, Any], reference_schema: Dic
     Returns:
         The schema with references resolved
     """
+    seen = seen or set()
+
     # Make a copy to avoid modifying the input schema
     schema_part = schema_part.copy()
 
@@ -35,6 +41,9 @@ def resolve_schema_references(schema_part: Dict[str, Any], reference_schema: Dic
         ref_path = schema_part["$ref"]
         # Standard OpenAPI references are in the format "#/components/schemas/ModelName"
         if ref_path.startswith("#/components/schemas/"):
+            if ref_path in seen:
+                return {"$ref": ref_path}
+            seen.add(ref_path)
             model_name = ref_path.split("/")[-1]
             if "components" in reference_schema and "schemas" in reference_schema["components"]:
                 if model_name in reference_schema["components"]["schemas"]:
@@ -47,11 +56,12 @@ def resolve_schema_references(schema_part: Dict[str, Any], reference_schema: Dic
     # Recursively resolve references in all dictionary values
     for key, value in schema_part.items():
         if isinstance(value, dict):
-            schema_part[key] = resolve_schema_references(value, reference_schema)
+            schema_part[key] = resolve_schema_references(value, reference_schema, seen)
         elif isinstance(value, list):
             # Only process list items that are dictionaries since only they can contain refs
             schema_part[key] = [
-                resolve_schema_references(item, reference_schema) if isinstance(item, dict) else item for item in value
+                resolve_schema_references(item, reference_schema, seen) if isinstance(item, dict) else item
+                for item in value
             ]
 
     return schema_part

tests/fixtures/types.py

@@ -1,3 +1,4 @@
+from __future__ import annotations
 from typing import Optional, List, Dict, Any
 from datetime import datetime, date
 from enum import Enum
@@ -95,6 +96,7 @@ class Product(BaseModel):
     updated_at: Optional[datetime] = None
     is_available: bool = True
     metadata: Dict[str, Any] = {}
+    related_products: Optional[List[Product]] = None
 
 
 class OrderItem(BaseModel):