From 14d1b8a94d8d56ff66c80e07cfddf41b28c35f35 Mon Sep 17 00:00:00 2001
From: "Owen W. Taylor" <otaylor@fishsoup.net>
Date: Fri, 20 Jun 2025 14:30:55 -0400
Subject: [PATCH] openapi: Rewrite recursive #/components/schemas/ references

When a schema referenced another schema as #/components/schemas/...
that wasn't properly rewritten into #/$defs/..
---
 src/fastmcp/utilities/openapi.py              |  8 ++++---
 .../openapi/test_openapi_advanced.py          | 22 +++++++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/fastmcp/utilities/openapi.py b/src/fastmcp/utilities/openapi.py
index 44c0216f6..0cae85cb2 100644
--- a/src/fastmcp/utilities/openapi.py
+++ b/src/fastmcp/utilities/openapi.py
@@ -262,16 +262,18 @@ class OpenAPIParser(
 
             if isinstance(resolved_schema, (self.schema_cls)):
                 # Convert schema to dictionary
-                return resolved_schema.model_dump(
+                result = resolved_schema.model_dump(
                     mode="json", by_alias=True, exclude_none=True
                 )
             elif isinstance(resolved_schema, dict):
-                return resolved_schema
+                result = resolved_schema
             else:
                 logger.warning(
                     f"Expected Schema after resolving, got {type(resolved_schema)}. Returning empty dict."
                 )
-                return {}
+                result = {}
+
+            return _replace_ref_with_defs(result)
         except Exception as e:
             logger.error(f"Failed to extract schema as dict: {e}", exc_info=False)
             return {}
diff --git a/tests/utilities/openapi/test_openapi_advanced.py b/tests/utilities/openapi/test_openapi_advanced.py
index 6b7ec8af3..979ca9b28 100644
--- a/tests/utilities/openapi/test_openapi_advanced.py
+++ b/tests/utilities/openapi/test_openapi_advanced.py
@@ -294,6 +294,28 @@ def test_complex_schema_route_count(parsed_complex_routes):
     assert len(parsed_complex_routes) == 3
 
 
+def test_complex_schema_ref_rewriting(parsed_complex_routes):
+    """Test that all #/components references have been rewritten."""
+
+    def no_components(value):
+        if isinstance(value, dict):
+            for k, v in value.items():
+                if k == "$ref":
+                    assert not v.startswith("#/components/"), (
+                        f"reference '{v}' was not rewritten"
+                    )
+                else:
+                    no_components(v)
+        elif isinstance(value, list):
+            for v in value:
+                no_components(v)
+
+    for route in parsed_complex_routes:
+        no_components(route.schema_definitions)
+        for param in route.parameters:
+            no_components(param.schema_)
+
+
 def test_complex_schema_list_users_query_param_limit(complex_route_map):
     """Test that a reference to a limit query parameter is correctly resolved."""
     list_users = complex_route_map["listUsers"]