minor doc chores (#4219)

* fix/warn: name is unused, only in debug would be used and but nobody does

* chore: Add better docs to `expansion` and why it exists

* chore: fmt

* Revert "chore: fmt"

This reverts commit 94d39bab5d1553d082a032ab6e31f579316dfa40.

polkadot/node/metered-channel/src/oneshot.rs

@@ -78,7 +78,7 @@ pub fn channel<T>(
 	let (tx, rx) = oneshot::channel();
 
 	(
-		MeteredSender { name, inner: tx },
+		MeteredSender { inner: tx },
 		MeteredReceiver {
 			name,
 			inner: rx,
@@ -113,14 +113,13 @@ impl Measurable for Error {
 /// Oneshot sender, created by [`channel`].
 #[derive(Debug)]
 pub struct MeteredSender<T> {
-	name: &'static str,
 	inner: oneshot::Sender<(Instant, T)>,
 }
 
 impl<T> MeteredSender<T> {
 	/// Send a value.
 	pub fn send(self, t: T) -> Result<(), T> {
-		let Self { inner, name: _ } = self;
+		let Self { inner } = self;
 		inner.send((Instant::now(), t)).map_err(|(_, t)| t)
 	}
 

polkadot/node/overseer/overseer-gen/proc-macro/Cargo.toml

@@ -23,5 +23,5 @@ assert_matches = "1.5.0"
 [features]
 default = []
 # write the expanded version to a `overlord-expansion.rs`
-# in the `cwd`
+# in the `OUT_DIR` as defined by `cargo`.
 expansion = []

polkadot/node/overseer/overseer-gen/proc-macro/src/impl_channels_out.rs

@@ -56,7 +56,8 @@ pub(crate) fn impl_channels_out_struct(info: &OverseerInfo) -> Result<proc_macro
 			)*
 		}
 
-		#[allow(unreachable_code)] // when no defined messages in enum
+		#[allow(unreachable_code)]
+		// when no defined messages in enum
 		impl ChannelsOut {
 			/// Send a message via a bounded channel.
 			pub async fn send_and_log_error(

polkadot/node/overseer/overseer-gen/proc-macro/src/lib.rs

@@ -98,6 +98,8 @@ pub(crate) fn impl_overseer_gen(
 	additive.extend(impl_message_wrapper_enum(&info)?);
 	additive.extend(impl_dispatch(&info));
 
+	// Write to a file for expansion, and then use it via `include!()`
+	// in order to obtain better compiler errors when modifying `overlord`.
 	if cfg!(feature = "expansion") {
 		use std::io::Write;