feat(server): deprecate server conn structs

[oddgrd]

This is based on #3102 which needs to be merged before this.

I had some difficulty with deprecations inside the pin-project-lite macros, it doesn't seem to be possible to set #[cfg_attr(feature = "deprecated", allow(deprecated))]on the fields of a struct inside pin_project!. That server::conn::Connection is inside pin_project! makes it difficult to deprecate as well. 🤔 I'll need to come back to this tomorrow. For example, in hyper/server/server.rs:

pin_project! {
    /// A listening HTTP server that accepts connections in both HTTP1 and HTTP2 by default.
    ///
    /// `Server` is a `Future` mapping a bound listener with a set of service
    /// handlers. It is built using the [`Builder`](Builder), and the future
    /// completes when the server has been shutdown. It should be run by an
    /// `Executor`.
    pub struct Server<I, S, E = Exec> {
        #[pin]
        incoming: I,
        make_service: S,
        #[cfg_attr(feature = "deprecated", allow(deprecated))] // <- This doesn't work.
        protocol: Http_<E>,
    }
}

[seanmonstar]

What if you just add the allow on struct Server, instead? Seems fine, since it's only allowing when our own feature is enabled, normal CI will catch any other deprecated stuff we're using from libstd.

[oddgrd]

CI passes but it's still showing warnings with the deprecated feature enabled and the allow on the struct itself, unfortunately.

[seanmonstar]

That seems weird... (Also, does that mean we need an additional CI job to notice that?)

[seanmonstar]

I'll make a PR to add the CI job.

[seanmonstar]

Ok, added in #3162.

[oddgrd]

Yes, I am very confused about this. Here is a cargo check output:

cargo check --features deprecated,full
    Checking hyper v0.14.24 (/home/oddgrd/dev/hyper)
warning: use of deprecated struct `server::conn::Http`: This struct will be replaced with `server::conn::http1::Builder` and `server::conn::http2::Builder` in 1.0, enable the "backports" feature to use them now.
  --> src/server/server.rs:42:19
   |
42 |         protocol: Http_<E>,
   |                   ^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

warning: use of deprecated struct `server::conn::Http`: This struct will be replaced with `server::conn::http1::Builder` and `server::conn::http2::Builder` in 1.0, enable the "backports" feature to use them now.
   --> src/server/server.rs:786:19
    |
786 |         protocol: Http_<E>,
    |                   ^^^^^

warning: `hyper` (lib) generated 2 warnings
    Finished dev [unoptimized + debuginfo] target(s) in 0.73s