context_getter typing is broken after v0.254.1

[YaraslauZhylko]

Unexpected mypy error for context_getter after v0.254.1.

Describe the Bug

I have a working configuration (slimmed down):

import strawberry
from fastapi import Depends
from strawberry.fastapi import BaseContext, GraphQLRouter


class MyContext(BaseContext):
    def __init__(self) -> None:
        self.test = "test"


@strawberry.type
class Query:
    noop: str = strawberry.field(resolver=lambda: "noop")


class MyGraphQLRouter(GraphQLRouter):
    pass  # some unrelated customizations here


def get_context(context: MyContext = Depends(MyContext)) -> MyContext:
    return context


schema = strawberry.Schema(Query)


router: GraphQLRouter = MyGraphQLRouter(schema, context_getter=get_context)  # error here

Before v0.254.1, MyPy used to correctly check this config:

Success: no issues found in 1 source file

But after v0.254.1 (PR #3732), I get a weird error like this:

test.py:27: error: Argument "context_getter" to "MyGraphQLRouter" has incompatible type "Callable[[MyContext], MyContext]"; expected "Callable[..., None] | None"  [arg-type]
Found 1 error in 1 file (checked 1 source file)

Meanwhile, context_getter is defined like this:

strawberry/strawberry/fastapi/router.py

Line 128 in 2d4234a

context_getter: Optional[Callable[..., Optional[Context]]] = None,

Seems quite compatible with what I have.

I susspect, this this behaviour might be caused by this definition:

strawberry/strawberry/http/typevars.py

Line 8 in 2d4234a

Context = TypeVar("Context", default=None)

System Information

• Operating system: Linux
• Python version: 3.12.8
• Strawberry version: 0.254.1 or higher
• FastAPI version: 0.115.6
• MyPy version: 1.14.0 and 1.14.1

[YaraslauZhylko]

cc: @patrick91