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Document why cannot use concat! in dbg!

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Co-authored-by: Miguel Ojeda <ojeda@users.noreply.github.com>
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Lzu Tao 2021-01-21 01:42:37 +00:00
parent a4cbb44ae2
commit d0c1405564
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4
library/std/src/macros.rs
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@ -282,6 +282,10 @@ macro_rules! eprintln {
#[macro_export] #[macro_export]
#[stable(feature = "dbg_macro", since = "1.32.0")] #[stable(feature = "dbg_macro", since = "1.32.0")]
macro_rules! dbg { macro_rules! dbg {
// NOTE: We cannot use `concat!` to make a static string as a format argument
// of `eprintln!` because `file!` could contain a `{` or
// `$val` expression could be a block (`{ .. }`), in which case the `eprintln!`
// will be malformed.
() => { () => {
$crate::eprintln!("[{}:{}]", $crate::file!(), $crate::line!()); $crate::eprintln!("[{}:{}]", $crate::file!(), $crate::line!());
}; };