From d479e88dd1510e0b0da4fc98eb9e0152710c6985 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ole=20Sch=C3=B6nburg?= <ole.schoenburg@gmail.com>
Date: Tue, 2 Mar 2021 22:33:13 +0000
Subject: [PATCH 1/2] subscriber: fix extra padding in pretty format

This fixes #1212 where extra padding was written when logging with
metadata. With this change we only write padding when we actually
decide to write a value, not when skipping a metadata value.
---
 tracing-subscriber/src/fmt/format/pretty.rs | 27 ++++++++++-----------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/tracing-subscriber/src/fmt/format/pretty.rs b/tracing-subscriber/src/fmt/format/pretty.rs
index 3aa94b9b8b..5fb557eeff 100644
--- a/tracing-subscriber/src/fmt/format/pretty.rs
+++ b/tracing-subscriber/src/fmt/format/pretty.rs
@@ -241,12 +241,14 @@ impl<'a> PrettyVisitor<'a> {
         Self { style, ..self }
     }
 
-    fn maybe_pad(&mut self) {
-        if self.is_empty {
+    fn write_padded(&mut self, value: &dyn fmt::Debug) {
+        let padding = if self.is_empty {
             self.is_empty = false;
+            ""
         } else {
-            self.result = write!(self.writer, ", ");
-        }
+            ", "
+        };
+        self.result = write!(self.writer, "{}{:?}", padding, value);
     }
 }
 
@@ -287,28 +289,25 @@ impl<'a> field::Visit for PrettyVisitor<'a> {
             return;
         }
         let bold = self.style.bold();
-        self.maybe_pad();
-        self.result = match field.name() {
-            "message" => write!(self.writer, "{}{:?}", self.style.prefix(), value,),
+        match field.name() {
+            "message" => self.write_padded(&format_args!("{}{:?}", self.style.prefix(), value,)),
             // Skip fields that are actually log metadata that have already been handled
             #[cfg(feature = "tracing-log")]
-            name if name.starts_with("log.") => Ok(()),
-            name if name.starts_with("r#") => write!(
-                self.writer,
+            name if name.starts_with("log.") => self.result = Ok(()),
+            name if name.starts_with("r#") => self.write_padded(&format_args!(
                 "{}{}{}: {:?}",
                 bold.prefix(),
                 &name[2..],
                 bold.infix(self.style),
                 value
-            ),
-            name => write!(
-                self.writer,
+            )),
+            name => self.write_padded(&format_args!(
                 "{}{}{}: {:?}",
                 bold.prefix(),
                 name,
                 bold.infix(self.style),
                 value
-            ),
+            )),
         };
     }
 }

From e4f8cdbdc25df433fa788127ec8d3ee1af71889c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ole=20Sch=C3=B6nburg?= <ole.schoenburg@gmail.com>
Date: Wed, 3 Mar 2021 09:54:41 +0100
Subject: [PATCH 2/2] subscriber: improve write_padded performance with impl
 Trait

Co-authored-by: Eliza Weisman <eliza@buoyant.io>
---
 tracing-subscriber/src/fmt/format/pretty.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tracing-subscriber/src/fmt/format/pretty.rs b/tracing-subscriber/src/fmt/format/pretty.rs
index 5fb557eeff..af6919107c 100644
--- a/tracing-subscriber/src/fmt/format/pretty.rs
+++ b/tracing-subscriber/src/fmt/format/pretty.rs
@@ -241,7 +241,7 @@ impl<'a> PrettyVisitor<'a> {
         Self { style, ..self }
     }
 
-    fn write_padded(&mut self, value: &dyn fmt::Debug) {
+    fn write_padded(&mut self, value: &impl fmt::Debug) {
         let padding = if self.is_empty {
             self.is_empty = false;
             ""