Log structured channel id

Since most log messages no longer include the channel ID in their text,
this commit updates the test logger to output the structured channel ID
instead. The ID is truncated for readability.

Author: joostjager

lightning/src/util/logger.rs

@@ -107,7 +107,8 @@ pub struct Record<$($args)?> {
 	/// generated.
 	pub peer_id: Option<PublicKey>,
 	/// The channel id of the channel pertaining to the logged record. May be a temporary id before
-	/// the channel has been funded.
+	/// the channel has been funded. Since channel_id is not repeated in the message body,
+	/// include it in the log output so entries remain clear.
 	pub channel_id: Option<ChannelId>,
 	#[cfg(not(c_bindings))]
 	/// The message body.
@@ -156,8 +157,10 @@ impl<$($args)?> Record<$($args)?> {
 
 impl<$($args)?> Display for Record<$($args)?> {
 	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+		let chan_id = self.channel_id.map(|id| format!("{}", id));
+		let chan_str = chan_id.as_deref().and_then(|s| s.get(..6)).unwrap_or("");
 		let context = format!("{:<5} [{}:{}]", self.level, self.module_path, self.line);
-		write!(f, "{:<48} {}", context, self.args)
+		write!(f, "{:<48} {:<6} {}", context, chan_str, self.args)
 	}
 }
 } }
@@ -166,9 +169,11 @@ impl_record!('a, );
 #[cfg(c_bindings)]
 impl_record!(, 'a);
 
-/// A trait encapsulating the operations required of a logger.
+/// A trait encapsulating the operations required of a logger. Keep in mind that log messages might not be entirely
+/// self-explanatory and may need accompanying context fields to be fully understood.
 pub trait Logger {
-	/// Logs the [`Record`].
+	/// Logs the [`Record`]. Since the record's [`Record::channel_id`] is not embedded in the message body, log
+	/// implementations should print it alongside the message to keep entries clear.
 	fn log(&self, record: Record);
 }