I'm curious why we need this as opposed to simply using asyncio.AbstractServer?

asyncio.AbstractServer is defined as follows in typeshed:

class AbstractServer:
    sockets: Optional[List[socket]]
    def close(self) -> None: ...
    if sys.version_info >= (3, 7):
        async def __aenter__(self: _T) -> _T: ...
        async def __aexit__(self, *exc: Any) -> None: ...
        def get_loop(self) -> AbstractEventLoop: ...
        def is_serving(self) -> bool: ...
        async def start_serving(self) -> None: ...
        async def serve_forever(self) -> None: ...
    async def wait_closed(self) -> None: ...

Since uvloop works on Python 3.5+ and Server defines those methods for all versions, asyncio.AbstractServer will be wrong for uvloop on Python 3.5 and 3.6.

I'll be dropping support for 3.5 and 3.6. 3.5 is no longer supported by Python core devs; 3.6 is in security fixes only mode. And with 3.9 now out, uvloop will be 3.7+ only in its next release, supporting three Python versions: 3.7, 3.8, and 3.9.

That's good to know! I'll go back over this PR with that in mind.

One thing to note: I think we'll still need _Server because AbstractServer.sockets is Optional[List[Socket]] and Server.sockets is List[Socket].

I think we should stick to AbstractServer typing here too. That makes it easy for us to fix our Server.sockets property to follow the spec.

Some of these others I added while I was navigating the source. I'll make sure I validate all of these are needed when I go over this again.

Yes, thanks. And we can always fix uvloop code that doesn't conform to asyncio APIs.

Sorry that it's taken so long to get back to this. I've updated the PR based on your feedback and rebased on master. Unfortunately, the PR checks are failing prematurely.