avoid intermediate allocations in show_error macro

Author: RalfJung

cargo-miri/src/main.rs

@@ -11,7 +11,7 @@ mod version;
 
 use std::{env, iter};
 
-use crate::{phases::*, util::*};
+use crate::phases::*;
 
 fn main() {
     // Rustc does not support non-UTF-8 arguments so we make no attempt either.

cargo-miri/src/util.rs

@@ -14,13 +14,13 @@ use serde::{Deserialize, Serialize};
 
 pub use crate::arg::*;
 
-pub fn show_error(msg: &str) -> ! {
+pub fn show_error(msg: &impl std::fmt::Display) -> ! {
     eprintln!("fatal error: {msg}");
     std::process::exit(1)
 }
 
 macro_rules! show_error {
-    ($($tt:tt)*) => { show_error(&format!($($tt)*)) };
+    ($($tt:tt)*) => { crate::util::show_error(&format_args!($($tt)*)) };
 }
 
 /// The information to run a crate with the given environment.

src/bin/miri.rs

@@ -152,13 +152,13 @@ impl rustc_driver::Callbacks for MiriBeRustCompilerCalls {
     }
 }
 
-fn show_error(msg: &str) -> ! {
+fn show_error(msg: &impl std::fmt::Display) -> ! {
     eprintln!("fatal error: {msg}");
     std::process::exit(1)
 }
 
 macro_rules! show_error {
-    ($($tt:tt)*) => { show_error(&format!($($tt)*)) };
+    ($($tt:tt)*) => { show_error(&format_args!($($tt)*)) };
 }
 
 fn init_early_loggers() {