fix(mcpserver): treat bare typing.Dict and typing sequence generics consistently in func_metadata

Author: chauvuusvn

src/mcp/server/mcpserver/utilities/func_metadata.py

@@ -2,6 +2,7 @@
 import inspect
 import json
 import sys
+import typing
 from collections.abc import Awaitable, Callable, Sequence
 from itertools import chain
 from typing import Annotated, Any, NotRequired, Union, cast, get_args, get_origin
@@ -446,7 +447,9 @@ def func_metadata(
     else:
         original_annotation = effective_annotation
 
-    if structured_output is None and (return_type_expr in (list, tuple) or _returns_content(return_type_expr)):
+    if structured_output is None and (
+        return_type_expr in (list, tuple, typing.List, typing.Tuple) or _returns_content(return_type_expr)
+    ):
         # Content blocks and the Image/Audio helpers are what the model reads, not data for the
         # application: a derived schema would advertise the block's own model as output_schema (and,
         # unless the tool builds its own CallToolResult, echo every block into structured_content).
@@ -520,6 +523,9 @@ def _create_output_model(original_annotation: Any, type_expr: Any, func_name: st
                 # TODO: should we use the original annotation? We are losing any potential `Annotated`
                 # metadata for Pydantic here:
                 model = type_expr
+            elif len(args) == 0:
+                # Bare typing.Dict is equivalent to bare dict -> top-level JSON object
+                model = dict[str, Any]
             else:
                 # dict with non-str keys needs wrapping
                 model = _create_wrapped_model(func_name, original_annotation)

tests/server/mcpserver/test_func_metadata.py

@@ -309,6 +309,17 @@ def func_typing_dict() -> typing.Dict[str, str]:  # noqa: UP006
     assert isinstance(result, CallToolResult)
     assert result.structured_content == {"name": "John"}
 
+    # Test bare typing.Dict (unparameterized) - should match bare dict behavior without wrapping
+    def func_bare_typing_dict() -> typing.Dict:  # noqa: UP006
+        return {"msg": "hello", "code": 200}
+
+    meta_bare = func_metadata(func_bare_typing_dict)
+    assert meta_bare.output_schema == IsPartialDict(type="object")
+    assert not meta_bare.wrap_output
+    result_bare = meta_bare.convert_result(func_bare_typing_dict())
+    assert isinstance(result_bare, CallToolResult)
+    assert result_bare.structured_content == {"msg": "hello", "code": 200}
+
     # Test dict[int, str] - should be wrapped since key is not str
     def func_dict_int_key() -> dict[int, str]:  # pragma: no cover
         return {1: "a", 2: "b"}
@@ -318,6 +329,31 @@ def func_dict_int_key() -> dict[int, str]:  # pragma: no cover
     assert "result" in meta.output_schema["properties"]
 
 
+def test_bare_typing_sequence_opts_out_of_structured_output():
+    """Test that bare typing.List and typing.Tuple opt out of structured output like bare list/tuple."""
+    def func_bare_list() -> list:
+        return ["a", "b"]
+
+    def func_bare_typing_list() -> typing.List:  # noqa: UP006
+        return ["a", "b"]
+
+    def func_bare_tuple() -> tuple:
+        return ("a", "b")
+
+    def func_bare_typing_tuple() -> typing.Tuple:  # noqa: UP006
+        return ("a", "b")
+
+    meta_list = func_metadata(func_bare_list)
+    meta_typing_list = func_metadata(func_bare_typing_list)
+    meta_tuple = func_metadata(func_bare_tuple)
+    meta_typing_tuple = func_metadata(func_bare_typing_tuple)
+
+    assert meta_list.output_schema is None
+    assert meta_typing_list.output_schema is None
+    assert meta_tuple.output_schema is None
+    assert meta_typing_tuple.output_schema is None
+
+
 @pytest.mark.anyio
 async def test_lambda_function():
     """Test lambda function schema and validation"""