From a7a68370a72cc553c8ca983fe593062235360b9b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@commure.com>
Date: Sat, 21 Jul 2018 15:56:37 -0700
Subject: [PATCH] Change `eprintln!()`

Address #30143 as well. `writeln!()` hasn't been changed.
---
 src/libstd/macros.rs | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index 49de9f802716..f06b8f621f26 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -217,10 +217,17 @@ macro_rules! eprint {
 /// ```
 #[macro_export]
 #[stable(feature = "eprint", since = "1.19.0")]
+#[allow_internal_unstable]
 macro_rules! eprintln {
     () => (eprint!("\n"));
-    ($fmt:expr) => (eprint!(concat!($fmt, "\n")));
-    ($fmt:expr, $($arg:tt)*) => (eprint!(concat!($fmt, "\n"), $($arg)*));
+    ($($arg:tt)*) => ({
+        #[cfg(not(stage0))] {
+            ($crate::io::_eprint(format_args_nl!($($arg)*)));
+        }
+        #[cfg(stage0)] {
+            eprint!("{}\n", format_args!($($arg)*))
+        }
+    })
 }
 
 #[macro_export]