feat(core): deprecate upgrade::from_fn

This functionality isn't needed anywhere in `rust-libp2p` so we can deprecate and later remove it and thus reduce our API surface. Users relying on this function can vendor it.

Pull-Request: #3747.

core/CHANGELOG.md

@@ -1,3 +1,11 @@
+## 0.39.2 - unreleased
+
+- Deprecate `upgrade::from_fn` without replacement as it is not used within `rust-libp2p`.
+  If you depend on it, we suggest you vendor it.
+  See [PR 3747].
+
+[PR 3747]: https://github.com/libp2p/rust-libp2p/pull/3747
+
 ## 0.39.1
 
 - Migrate from `prost` to `quick-protobuf`. This removes `protoc` dependency. See [PR 3312].

core/Cargo.toml

@@ -3,7 +3,7 @@ name = "libp2p-core"
 edition = "2021"
 rust-version = "1.60.0"
 description = "Core traits and structs of libp2p"
-version = "0.39.1"
+version = "0.39.2"
 authors = ["Parity Technologies <admin@parity.io>"]
 license = "MIT"
 repository = "https://github.com/libp2p/rust-libp2p"

core/src/upgrade.rs

@@ -71,11 +71,12 @@ mod transfer;
 
 use futures::future::Future;
 
+#[allow(deprecated)]
+pub use self::from_fn::{from_fn, FromFnUpgrade};
 pub use self::{
     apply::{apply, apply_inbound, apply_outbound, InboundUpgradeApply, OutboundUpgradeApply},
     denied::DeniedUpgrade,
     error::UpgradeError,
-    from_fn::{from_fn, FromFnUpgrade},
     map::{MapInboundUpgrade, MapInboundUpgradeErr, MapOutboundUpgrade, MapOutboundUpgradeErr},
     optional::OptionalUpgrade,
     pending::PendingUpgrade,

core/src/upgrade/from_fn.rs

@@ -35,6 +35,7 @@ use std::iter;
 /// # use libp2p_core::{upgrade, Negotiated};
 /// # use std::io;
 /// # use futures::AsyncWriteExt;
+/// # #[allow(deprecated)]
 /// let _transport = MemoryTransport::default()
 ///     .and_then(move |out, cp| {
 ///         upgrade::apply(out, upgrade::from_fn("/foo/1", move |mut sock: Negotiated<Channel<Vec<u8>>>, endpoint| async move {
@@ -52,6 +53,10 @@ use std::iter;
 ///     });
 /// ```
 ///
+#[deprecated(
+    note = "`from_fn` upgrade will be removed without replacement as it is not used within `rust-libp2p`."
+)]
+#[allow(deprecated)]
 pub fn from_fn<P, F, C, Fut, Out, Err>(protocol_name: P, fun: F) -> FromFnUpgrade<P, F>
 where
     // Note: these bounds are there in order to help the compiler infer types
@@ -66,11 +71,15 @@ where
 ///
 /// The upgrade consists in calling the function passed when creating this struct.
 #[derive(Debug, Clone)]
+#[deprecated(
+    note = "`from_fn` upgrade will be removed without replacement as it is not used within `rust-libp2p`."
+)]
 pub struct FromFnUpgrade<P, F> {
     protocol_name: P,
     fun: F,
 }
 
+#[allow(deprecated)]
 impl<P, F> UpgradeInfo for FromFnUpgrade<P, F>
 where
     P: ProtocolName + Clone,
@@ -83,6 +92,7 @@ where
     }
 }
 
+#[allow(deprecated)]
 impl<C, P, F, Fut, Err, Out> InboundUpgrade<C> for FromFnUpgrade<P, F>
 where
     P: ProtocolName + Clone,
@@ -98,6 +108,7 @@ where
     }
 }
 
+#[allow(deprecated)]
 impl<C, P, F, Fut, Err, Out> OutboundUpgrade<C> for FromFnUpgrade<P, F>
 where
     P: ProtocolName + Clone,