Remove redundent logging code (#4059)

1. The `CustomFmtContext::ContextWithFormatFields` enum arm isn't
actually used and thus we don't need the enum anymore.

2. We don't do anything with most of the normalized metadata that's
created by calling `event.normalized_metadata();` - the `target` we can
get from `event.metadata.target()` and level we can get from
`event.metadata.level()` - let's just call them direct to simplify
things. (`event.metadata()` is just a field call under the hood)

Changelog: No functional changes, might run a tad faster with lots of
logging turned on.

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

prdoc/pr_4059.prdoc

@@ -0,0 +1,13 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Remove redundent logging code
+
+doc:
+  - audience: Node Dev
+    description: |
+      Simplified logging code, now does slightly less work while logging.
+
+crates:
+- name: sc-tracing
+  bump: minor

substrate/client/tracing/src/logging/event_format.rs

@@ -21,12 +21,9 @@ use ansi_term::Colour;
 use regex::Regex;
 use std::fmt::{self, Write};
 use tracing::{Event, Level, Subscriber};
-use tracing_log::NormalizeEvent;
 use tracing_subscriber::{
-	field::RecordFields,
 	fmt::{format, time::FormatTime, FmtContext, FormatEvent, FormatFields},
-	layer::Context,
-	registry::{LookupSpan, SpanRef},
+	registry::LookupSpan,
 };
 
 /// A pre-configured event formatter.
@@ -54,7 +51,7 @@ where
 	//       https://github.com/tokio-rs/tracing/blob/2f59b32/tracing-subscriber/src/fmt/format/mod.rs#L449
 	pub(crate) fn format_event_custom<'b, 'w, S, N>(
 		&self,
-		ctx: CustomFmtContext<'b, S, N>,
+		ctx: &FmtContext<'b, S, N>,
 		writer: format::Writer<'w>,
 		event: &Event,
 	) -> fmt::Result
@@ -63,12 +60,10 @@ where
 		N: for<'a> FormatFields<'a> + 'static,
 	{
 		let mut writer = &mut ControlCodeSanitizer::new(!self.enable_color, writer);
-		let normalized_meta = event.normalized_metadata();
-		let meta = normalized_meta.as_ref().unwrap_or_else(|| event.metadata());
 		time::write(&self.timer, &mut format::Writer::new(&mut writer), self.enable_color)?;
 
 		if self.display_level {
-			let fmt_level = { FmtLevel::new(meta.level(), self.enable_color) };
+			let fmt_level = FmtLevel::new(event.metadata().level(), self.enable_color);
 			write!(writer, "{} ", fmt_level)?;
 		}
 
@@ -86,7 +81,7 @@ where
 		}
 
 		if self.display_target {
-			write!(writer, "{}: ", meta.target())?;
+			write!(writer, "{}: ", event.metadata().target())?;
 		}
 
 		// Custom code to display node name
@@ -137,12 +132,12 @@ where
 		{
 			let mut out = String::new();
 			let buf_writer = format::Writer::new(&mut out);
-			self.format_event_custom(CustomFmtContext::FmtContext(ctx), buf_writer, event)?;
+			self.format_event_custom(ctx, buf_writer, event)?;
 			writer.write_str(&out)?;
 			print!("{}", out);
 			Ok(())
 		} else {
-			self.format_event_custom(CustomFmtContext::FmtContext(ctx), writer, event)
+			self.format_event_custom(ctx, writer, event)
 		}
 	}
 }
@@ -261,48 +256,6 @@ mod time {
 	}
 }
 
-// NOTE: `FmtContext`'s fields are private. This enum allows us to make a `format_event` function
-//       that works with `FmtContext` or `Context` with `FormatFields`
-#[allow(dead_code)]
-pub(crate) enum CustomFmtContext<'a, S, N> {
-	FmtContext(&'a FmtContext<'a, S, N>),
-	ContextWithFormatFields(&'a Context<'a, S>, &'a N),
-}
-
-impl<'a, S, N> FormatFields<'a> for CustomFmtContext<'a, S, N>
-where
-	S: Subscriber + for<'lookup> LookupSpan<'lookup>,
-	N: for<'writer> FormatFields<'writer> + 'static,
-{
-	fn format_fields<R: RecordFields>(&self, writer: format::Writer<'_>, fields: R) -> fmt::Result {
-		match self {
-			CustomFmtContext::FmtContext(fmt_ctx) => fmt_ctx.format_fields(writer, fields),
-			CustomFmtContext::ContextWithFormatFields(_ctx, fmt_fields) =>
-				fmt_fields.format_fields(writer, fields),
-		}
-	}
-}
-
-// NOTE: the following code has been duplicated from tracing-subscriber
-//
-//       https://github.com/tokio-rs/tracing/blob/2f59b32/tracing-subscriber/src/fmt/fmt_layer.rs#L788
-impl<'a, S, N> CustomFmtContext<'a, S, N>
-where
-	S: Subscriber + for<'lookup> LookupSpan<'lookup>,
-	N: for<'writer> FormatFields<'writer> + 'static,
-{
-	#[inline]
-	pub fn lookup_current(&self) -> Option<SpanRef<'_, S>>
-	where
-		S: for<'lookup> LookupSpan<'lookup>,
-	{
-		match self {
-			CustomFmtContext::FmtContext(fmt_ctx) => fmt_ctx.lookup_current(),
-			CustomFmtContext::ContextWithFormatFields(ctx, _) => ctx.lookup_current(),
-		}
-	}
-}
-
 /// A writer which (optionally) strips out terminal control codes from the logs.
 ///
 /// This is used by [`EventFormat`] to sanitize the log messages.