You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: connection_provider.rs
    path of file: ./repos/phaser/phaser/vendor/trust-dns-resolver/src/name_server
    
    the code of the file until where you have to start completion: // Copyright 2015-2019 Benjamin Fry <benjaminfry@me.com>
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

use std::marker::Unpin;
use std::pin::Pin;
use std::task::{Context, Poll};

use futures_util::future::{Future, FutureExt};
use futures_util::ready;
#[cfg(feature = "tokio-runtime")]
use tokio::net::TcpStream as TokioTcpStream;
#[cfg(all(feature = "dns-over-native-tls", not(feature = "dns-over-rustls")))]
use tokio_native_tls::TlsStream as TokioTlsStream;
#[cfg(all(
    feature = "dns-over-openssl",
    not(feature = "dns-over-rustls"),
    not(feature = "dns-over-native-tls")
))]
use tokio_openssl::SslStrea
    
    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        Poll::Ready(Ok(match &mut self.connect {
            ConnectionConnect::Udp(ref mut conn) => {
                let (conn, bg) = ready!(conn.poll_unpin(cx))?;
                self.spawner.spawn_bg(bg);
                GenericConnection(conn)
            }
            ConnectionConnect::Tcp(ref mut conn) => {
                let (conn, bg) = ready!(conn.poll_unpin(cx))?;
                self.spawner.spawn_bg(bg);
                GenericConnection(conn)
            }
            #[cfg(feature = "dns-over-tls")]
            ConnectionConnect::Tls(ref mut conn) => {
                let (conn, bg) = ready!(conn.poll_unpin(cx))?;
                self.spawner.spawn_bg(bg);
                GenericConnection(conn)
            }
            #[cfg(feature = "dns-over-https")]
            ConnectionConnect::Https(ref mut conn) => {
                let (conn, bg) = ready!(conn.poll_unpin(cx))?;
                self.spawner.spawn_bg(bg);
                GenericConnection(conn)
            }
            #[cfg(feature = "mdns")]
            ConnectionConnect::Mdns(ref mut conn) => {
                let (conn, bg) = ready!(conn.poll_unpin(cx))?;
                self.spawner.spawn_bg(bg);
                GenericConnection(conn)
            }
        }))
    }