Request's class covariant is not allowed in Sanic constructor

Questions and Help
#1

Hello!

I’m using Sanic with custom generics, and this works fine:

app = Sanic[MyConfig, AppCtx](
    'test',
    ctx=AppCtx(),
    config=MyConfig(),
    request_class=Request[Sanic[Config, SimpleNamespace], SimpleNamespace]
)

However, when I try to use a custom request context that inherits from SimpleNamespace, I get a type error:

class RequestCtx(SimpleNamespace):
    pass

app = Sanic[MyConfig, AppCtx](
    'test',
    ctx=AppCtx(),
    config=MyConfig(),
    request_class=Request[Sanic[Config, SimpleNamespace], RequestCtx]
)

The error from mypy is:

Argument “request_class” to “Sanic” has incompatible type “type[Request[Sanic[Config, SimpleNamespace], RequestCtx]]”; expected “type[Request[Sanic[Config, SimpleNamespace], SimpleNamespace]] | None”

This happens because the second generic parameter ctx_type in the Request class does not accept covariant subtypes — even though RequestCtx is clearly a subtype of SimpleNamespace.

Is this behavior expected? Or is it something that could/should be relaxed in Sanic’s generic typing?

Thanks!