Ensure panic! messages are only formatted once

rust-lang · Oct 2, 2023 · 3a6ff98 · 3a6ff98
1 parent 98d7379
commit 3a6ff98
Showing 1 changed file with 13 additions and 13 deletions.
diff --git a/library/std/src/panicking.rs b/library/std/src/panicking.rs
@@ -252,20 252,20 @@ fn default_hook(info: &PanicInfo<'_>) {
  let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
 
  let write = |err: &mut dyn crate::io::Write| {
- // Use the panic message directly if available, otherwise take it from
- // the payload.
- if let Some(msg) = info.message() {
- let _ = writeln!(err, "thread '{name}' panicked at {location}:\n{msg}");
  // The std panic runtime always sets a `&str` or `String` payload for `panic!` and related
  // macros with the formatted message.
  // We try using the payload first to avoid formatting the message twice.
  let msg: &dyn fmt::Display = if let Some(s) = info.payload().downcast_ref::<&'static str>()
  {
  s
  } else if let Some(s) = info.payload().downcast_ref::<String>() {
  s
  } else if let Some(msg) = info.message() {
  msg
  } else {
- let msg = if let Some(s) = info.payload().downcast_ref::<&'static str>() {
- *s
- } else if let Some(s) = info.payload().downcast_ref::<String>() {
- &s[..]
- } else {
- "Box<dyn Any>"
- };
- let _ = writeln!(err, "thread '{name}' panicked at {location}:\n{msg}");
- }
  &"Box<dyn Any>"
  };
  let _ = writeln!(err, "thread '{name}' panicked at {location}:\n{msg}");
 
  static FIRST_PANIC: AtomicBool = AtomicBool::new(true);