chore: exempt tests from ANN, enable mypy-init-return

Align with ecosystem norms per review feedback:
- Add mypy-init-return = true to skip -> None on __init__ when args are typed
- Exempt tests/** from ANN rules (near-universal practice)
- Revert test file annotations and __init__-only changes

Shrinks diff from 149 to ~47 files, keeping the valuable src/ return
type annotations that close the pyright gap.

Author: maxisbey

README.v2.md

@@ -518,7 +518,7 @@ class UserProfile:
     age: int
     email: str | None = None
 
-    def __init__(self, name: str, age: int, email: str | None = None) -> None:
+    def __init__(self, name: str, age: int, email: str | None = None):
         self.name = name
         self.age = age
         self.email = email
@@ -532,7 +532,7 @@ def get_user(user_id: str) -> UserProfile:
 
 # Classes WITHOUT type hints cannot be used for structured output
 class UntypedConfig:
-    def __init__(self, setting1, setting2) -> None:  # type: ignore[reportMissingParameterType]  # noqa: ANN001
+    def __init__(self, setting1, setting2):  # type: ignore[reportMissingParameterType]  # noqa: ANN001, ANN204
         self.setting1 = setting1
         self.setting2 = setting2
 

examples/servers/simple-auth/mcp_simple_auth/auth_server.py

@@ -47,7 +47,7 @@ class SimpleAuthProvider(SimpleOAuthProvider):
     2. Stores token state for introspection by Resource Servers
     """
 
-    def __init__(self, auth_settings: SimpleAuthSettings, auth_callback_path: str, server_url: str) -> None:
+    def __init__(self, auth_settings: SimpleAuthSettings, auth_callback_path: str, server_url: str):
         super().__init__(auth_settings, auth_callback_path, server_url)
 
 

examples/servers/simple-auth/mcp_simple_auth/legacy_as_server.py

@@ -39,7 +39,7 @@ class ServerSettings(BaseModel):
 class LegacySimpleOAuthProvider(SimpleOAuthProvider):
     """Simple OAuth provider for legacy MCP server."""
 
-    def __init__(self, auth_settings: SimpleAuthSettings, auth_callback_path: str, server_url: str) -> None:
+    def __init__(self, auth_settings: SimpleAuthSettings, auth_callback_path: str, server_url: str):
         super().__init__(auth_settings, auth_callback_path, server_url)
 
 

examples/servers/simple-auth/mcp_simple_auth/simple_auth_provider.py

@@ -51,7 +51,7 @@ class SimpleOAuthProvider(OAuthAuthorizationServerProvider[AuthorizationCode, Re
     3. Maintaining token state for introspection
     """
 
-    def __init__(self, settings: SimpleAuthSettings, auth_callback_url: str, server_url: str) -> None:
+    def __init__(self, settings: SimpleAuthSettings, auth_callback_url: str, server_url: str):
         self.settings = settings
         self.auth_callback_url = auth_callback_url
         self.server_url = server_url

examples/servers/simple-auth/mcp_simple_auth/token_verifier.py

@@ -25,7 +25,7 @@ def __init__(
         introspection_endpoint: str,
         server_url: str,
         validate_resource: bool = False,
-    ) -> None:
+    ):
         self.introspection_endpoint = introspection_endpoint
         self.server_url = server_url
         self.validate_resource = validate_resource

examples/snippets/servers/structured_output.py

@@ -57,7 +57,7 @@ class UserProfile:
     age: int
     email: str | None = None
 
-    def __init__(self, name: str, age: int, email: str | None = None) -> None:
+    def __init__(self, name: str, age: int, email: str | None = None):
         self.name = name
         self.age = age
         self.email = email
@@ -71,7 +71,7 @@ def get_user(user_id: str) -> UserProfile:
 
 # Classes WITHOUT type hints cannot be used for structured output
 class UntypedConfig:
-    def __init__(self, setting1, setting2) -> None:  # type: ignore[reportMissingParameterType]  # noqa: ANN001
+    def __init__(self, setting1, setting2):  # type: ignore[reportMissingParameterType]  # noqa: ANN001, ANN204
         self.setting1 = setting1
         self.setting2 = setting2
 

pyproject.toml

@@ -149,6 +149,7 @@ ignore = [
 
 [tool.ruff.lint.flake8-annotations]
 allow-star-arg-any = true
+mypy-init-return = true
 
 [tool.ruff.lint.flake8-tidy-imports.banned-api]
 "pydantic.RootModel".msg = "Use `pydantic.TypeAdapter` instead."
@@ -159,9 +160,8 @@ max-complexity = 24 # Default is 10
 
 [tool.ruff.lint.per-file-ignores]
 "__init__.py" = ["F401"]
-# ANN001: these files intentionally define untyped parameters to test schema inference
-"tests/server/mcpserver/test_func_metadata.py" = ["ANN001", "E501"]
-"tests/server/mcpserver/test_server.py" = ["ANN001"]
+"tests/**" = ["ANN"]
+"tests/server/mcpserver/test_func_metadata.py" = ["E501"]
 "tests/shared/test_progress_notifications.py" = ["PLW0603"]
 
 [tool.ruff.lint.pylint]

src/mcp/client/auth/oauth2.py

@@ -232,7 +232,7 @@ def __init__(
         timeout: float = 300.0,
         client_metadata_url: str | None = None,
         validate_resource_url: Callable[[str, str | None], Awaitable[None]] | None = None,
-    ) -> None:
+    ):
         """Initialize OAuth2 authentication.
 
         Args:

src/mcp/os/win32/utilities.py

@@ -71,7 +71,7 @@ class FallbackProcess:
     so that MCP clients expecting async streams can work properly.
     """
 
-    def __init__(self, popen_obj: subprocess.Popen[bytes]) -> None:
+    def __init__(self, popen_obj: subprocess.Popen[bytes]):
         self.popen: subprocess.Popen[bytes] = popen_obj
         self.stdin_raw = popen_obj.stdin  # type: ignore[assignment]
         self.stdout_raw = popen_obj.stdout  # type: ignore[assignment]

src/mcp/server/auth/middleware/auth_context.py

@@ -29,7 +29,7 @@ class AuthContextMiddleware:
     being stored in the context.
     """
 
-    def __init__(self, app: ASGIApp) -> None:
+    def __init__(self, app: ASGIApp):
         self.app = app
 
     async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None: