Fix macro hygiene

`concat!` -> `$crate::__macro_support::concat!`

Author: teohhanhui

tracing/src/lib.rs

@@ -931,6 +931,7 @@ pub mod subscriber;
 #[doc(hidden)]
 pub mod __macro_support {
     pub use crate::callsite::Callsite;
+    pub use crate::stdlib::concat;
     use crate::stdlib::{
         fmt,
         sync::atomic::{AtomicUsize, Ordering},

tracing/src/macros.rs

@@ -592,7 +592,7 @@ macro_rules! event {
         if $crate::level_enabled!($lvl) {
             use $crate::__macro_support::*;
             static CALLSITE: $crate::__macro_support::MacroCallsite = $crate::callsite2! {
-                name: concat!(
+                name: $crate::__macro_support::concat!(
                     "event ",
                     file!(),
                     ":",
@@ -639,7 +639,7 @@ macro_rules! event {
         if $crate::level_enabled!($lvl) {
             use $crate::__macro_support::*;
             static CALLSITE: $crate::__macro_support::MacroCallsite = $crate::callsite2! {
-                name: concat!(
+                name: $crate::__macro_support::concat!(
                     "event ",
                     file!(),
                     ":",
@@ -2171,7 +2171,7 @@ macro_rules! __tracing_log {
 macro_rules! __mk_format_string {
     // === base case ===
     (@ { $(,)* $($out:expr),* $(,)* } $(,)*) => {
-        concat!( $($out),*)
+        $crate::__macro_support::concat!( $($out),*)
     };
 
     // === recursive case (more tts), ===

tracing/src/stdlib.rs

@@ -13,6 +13,8 @@ pub(crate) use std::*;
 #[cfg(not(feature = "std"))]
 pub(crate) use self::no_std::*;
 
+pub use core::concat;
+
 #[cfg(not(feature = "std"))]
 mod no_std {
     // We pre-emptively export everything from libcore/liballoc, (even modules