feat(swarm): deprecate KeepAlive::Until

In preparation for removing this variant, we are issuing a deprecation notice. The linked issue describes why and guides users in migrating away from it. This deprecation is backwards-compatible and allows us to remove the variant in the next breaking release. We haven't migrated all internal protocols yet but that isn't strictly necessary to issue the deprecation.

Related: #3844.

Pull-Request: #4656.

swarm/src/connection.rs

@@ -347,6 +347,7 @@ where
             // Ask the handler whether it wants the connection (and the handler itself)
             // to be kept alive, which determines the planned shutdown, if any.
             let keep_alive = handler.connection_keep_alive();
+            #[allow(deprecated)]
             match (&mut *shutdown, keep_alive) {
                 (Shutdown::Later(timer, deadline), KeepAlive::Until(t)) => {
                     if *deadline != t {
@@ -1005,6 +1006,7 @@ mod tests {
         }
 
         fn connection_keep_alive(&self) -> KeepAlive {
+            #[allow(deprecated)]
             KeepAlive::Until(self.until)
         }
 

swarm/src/handler.rs

@@ -728,6 +728,9 @@ where
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub enum KeepAlive {
     /// If nothing new happens, the connection should be closed at the given `Instant`.
+    #[deprecated(
+        note = "Use `swarm::Config::with_idle_connection_timeout` instead. See <https://github.com/libp2p/rust-libp2p/issues/3844> for details."
+    )]
     Until(Instant),
     /// Keep the connection alive.
     Yes,
@@ -748,6 +751,7 @@ impl PartialOrd for KeepAlive {
     }
 }
 
+#[allow(deprecated)]
 impl Ord for KeepAlive {
     fn cmp(&self, other: &KeepAlive) -> Ordering {
         use self::KeepAlive::*;

swarm/src/handler/one_shot.rs

@@ -176,6 +176,7 @@ where
         } else {
             self.dial_queue.shrink_to_fit();
 
+            #[allow(deprecated)]
             if self.dial_negotiated == 0 && self.keep_alive.is_yes() {
                 self.keep_alive = KeepAlive::Until(Instant::now() + self.config.keep_alive_timeout);
             }
@@ -199,6 +200,7 @@ where
                 ..
             }) => {
                 // If we're shutting down the connection for inactivity, reset the timeout.
+                #[allow(deprecated)]
                 if !self.keep_alive.is_yes() {
                     self.keep_alive =
                         KeepAlive::Until(Instant::now() + self.config.keep_alive_timeout);
@@ -258,6 +260,7 @@ mod tests {
     use void::Void;
 
     #[test]
+    #[allow(deprecated)]
     fn do_not_keep_idle_connection_alive() {
         let mut handler: OneShotHandler<_, DeniedUpgrade, Void> = OneShotHandler::new(
             SubstreamProtocol::new(DeniedUpgrade {}, ()),