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| author | Mara Bos <m-ou.se@m-ou.se> | 2021-01-22 14:30:17 +0000 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2021-01-22 14:30:17 +0000 |
| commit | 81a60b7aa8dca83e2c9543390cf116016192871a (patch) | |
| tree | e12d9cae433f85c9956060f2380fba91b0bf9bfc | |
| parent | 2ceee724270f2186e5e85acff49acd35bf8a652a (diff) | |
| parent | d0c1405564024d109ec22b130584d74fcb82d153 (diff) | |
| download | rust-81a60b7aa8dca83e2c9543390cf116016192871a.tar.gz rust-81a60b7aa8dca83e2c9543390cf116016192871a.zip | |
Rollup merge of #81233 - lzutao:dbg, r=KodrAus
Document why not use concat! in dbg! macro
Original title: Reduce code generated by `dbg!` macro
The expanded code before/after: <https://rust.godbolt.org/z/hE3j95>.
---
We cannot use `concat!` since `file!` could contains `{` or the expression is a block (`{ .. }`).
Using it will generated malformed format strings.
So let's document this reason why we don't use `concat!` macro at all.
| -rw-r--r-- | library/std/src/macros.rs | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/library/std/src/macros.rs b/library/std/src/macros.rs index 5a70aa070e8..e466f315152 100644 --- a/library/std/src/macros.rs +++ b/library/std/src/macros.rs @@ -282,6 +282,10 @@ macro_rules! eprintln { #[macro_export] #[stable(feature = "dbg_macro", since = "1.32.0")] 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!()); }; |