[main] Upgrade to latest Rust version (#6501)

This is our monthly toolchain upgrade to the latest stable version. Since iotedge/edgelet is a binary package, we want to be tracking Rust compiler releases closely in the event a stdlib vulnerability is found. We do not pin to "stable", however, since that has caused pipeline breakage when some code patterns are made illegal (like in the upgrade from 1.47 to 1.48 [^0]) or, more often, clippy lints are added.

- Use $crate metavariable in macros referencing crate
- Remove `let () = ..`
- Fix build failure in edgehub-proxy

[^0]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#compatibility-notes-11
  Namely, the point on `mem::uninitialized`.

## Azure IoT Edge PR checklist:

edge-modules/edgehub-proxy/src/logging.rs

@@ -3,7 +3,6 @@
 use std::env;
 use std::io::Write;
 
-use edgelet_utils::log_failure;
 use env_logger;
 use log::{Level, LevelFilter};
 
@@ -59,5 +58,5 @@ fn syslog_level(level: Level) -> i8 {
 }
 
 pub fn log_error(error: &Error) {
-    log_failure(Level::Error, error);
+    log::error!("{}", error);
 }

edgelet/edgelet-test-utils/src/route.rs

@@ -22,6 +22,9 @@ macro_rules! test_route_err {
     };
 }
 
+// NOTE: allowing the use of `crate::` since the macro is intended to
+// use the type `crate::Service` for the crates it is used in.
+#[allow(clippy::crate_in_macro_def)]
 #[macro_export]
 macro_rules! test_route {
     ($path:expr) => {{

mqtt/mqtt3/examples/publisher.rs

@@ -103,11 +103,11 @@ async fn main() {
         .shutdown_handle()
         .expect("couldn't get shutdown handle");
     tokio::spawn(async move {
-        let () = tokio::signal::ctrl_c()
+        tokio::signal::ctrl_c()
             .await
             .expect("couldn't get Ctrl-C notification");
         let result = shutdown_handle.shutdown().await;
-        let () = result.expect("couldn't send shutdown notification");
+        result.expect("couldn't send shutdown notification");
     });
 
     let payload: bytes::Bytes = payload.into();
@@ -135,7 +135,7 @@ async fn main() {
                         payload,
                     })
                     .await;
-                let () = result.expect("couldn't publish");
+                result.expect("couldn't publish");
                 log::info!("Published to {}", topic);
                 Ok::<_, ()>(())
             });

mqtt/mqtt3/examples/subscriber.rs

@@ -90,11 +90,11 @@ async fn main() {
         .shutdown_handle()
         .expect("couldn't get shutdown handle");
     tokio::spawn(async move {
-        let () = tokio::signal::ctrl_c()
+        tokio::signal::ctrl_c()
             .await
             .expect("couldn't get Ctrl-C notification");
         let result = shutdown_handle.shutdown().await;
-        let () = result.expect("couldn't send shutdown notification");
+        result.expect("couldn't send shutdown notification");
     });
 
     let mut update_subscription_handle = client

mqtt/mqtt3/src/client/connect.rs

@@ -73,6 +73,10 @@ where
     }
 }
 
+// NOTE: clippy is incorrectly marking this as a duplicated trait bound.
+// An upstream issue exists documenting this behavior:
+// https://github.com/rust-lang/rust-clippy/issues/9076
+#[allow(clippy::trait_duplication_in_bounds)]
 impl<IoS> Connect<IoS>
 where
     IoS: super::IoSource,

mqtt/mqtt3/tests/common/mod.rs

@@ -100,7 +100,7 @@ impl mqtt3::IoSource for IoSource {
             // If the connection broke while there were still steps remaining in the TestConnection, then the dropped sender will cause the test
             // to receive a futures_channel::oneshot::Canceled error, so the test will panic before this deadline elapses anyway.
             Box::pin(async {
-                let () = tokio::time::sleep(std::time::Duration::from_secs(5)).await;
+                tokio::time::sleep(std::time::Duration::from_secs(5)).await;
                 unreachable!();
             })
         }

rust-toolchain.toml

@@ -1,2 +1,2 @@
 [toolchain]
-channel = "1.61"
+channel = "1.62"