diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs index 14b266a43441d..9eba76cc04a64 100644 --- a/src/libstd/macros.rs +++ b/src/libstd/macros.rs @@ -314,6 +314,22 @@ macro_rules! eprintln { /// You can also use `dbg!()` without a value to just print the /// file and line whenever it's reached. /// +/// Finally, if you want to `dbg!(..)` multiple values, it will treat them as +/// a tuple (and return it, too): +/// +/// ``` +/// assert_eq!(dbg!(1usize, 2u32), (1, 2)); +/// ``` +/// +/// However, a single argument with a trailing comma will still not be treated +/// as a tuple, following the convention of ignoring trailing commas in macro +/// invocations. You can use a 1-tuple directly if you need one: +/// +/// ``` +/// assert_eq!(1, dbg!(1u32,)); // trailing comma ignored +/// assert_eq!((1,), dbg!((1u32,))); // 1-tuple +/// ``` +/// /// [stderr]: https://en.wikipedia.org/wiki/Standard_streams#Standard_error_(stderr) /// [`debug!`]: https://docs.rs/log/*/log/macro.debug.html /// [`log`]: https://crates.io/crates/log @@ -333,7 +349,12 @@ macro_rules! dbg { tmp } } - } + }; + // Trailing comma with single argument is ignored + ($val:expr,) => { dbg!($val) }; + ($($val:expr),+ $(,)?) => { + ($(dbg!($val)),+,) + }; } /// Awaits the completion of an async call. diff --git a/src/test/ui/rfc-2361-dbg-macro/dbg-macro-expected-behavior.rs b/src/test/ui/rfc-2361-dbg-macro/dbg-macro-expected-behavior.rs index f1b73ee115db1..e2a7ac349ecd5 100644 --- a/src/test/ui/rfc-2361-dbg-macro/dbg-macro-expected-behavior.rs +++ b/src/test/ui/rfc-2361-dbg-macro/dbg-macro-expected-behavior.rs @@ -54,6 +54,17 @@ fn test() { 7331 })); assert_eq!(foo, 42); + + // Test trailing comma: + assert_eq!(("Yeah",), dbg!(("Yeah",))); + + // Test multiple arguments: + assert_eq!((1u8, 2u32), dbg!(1, + 2)); + + // Test multiple arguments + trailing comma: + assert_eq!((1u8, 2u32, "Yeah"), dbg!(1u8, 2u32, + "Yeah",)); } fn validate_stderr(stderr: Vec) { @@ -85,6 +96,17 @@ fn validate_stderr(stderr: Vec) { "before", ":51] { foo += 1; eprintln!(\"before\"); 7331 } = 7331", + + ":59] (\"Yeah\",) = (", + " \"Yeah\",", + ")", + + ":62] 1 = 1", + ":62] 2 = 2", + + ":66] 1u8 = 1", + ":66] 2u32 = 2", + ":66] \"Yeah\" = \"Yeah\"", ]); }