error[internal]: left behind trailing whitespace

[LittleGuest]

Hi, I'm having a problem with cargo fmt , like this：

error[internal]: left behind trailing whitespace
 --> /playground/src/main.rs:5:5:1
  |
5 |         
  | ^^^^^^^^
  |

warning: rustfmt has failed to format. See previous 1 errors.

code looks like this:

fn main() {
    let a = Some(1);
    let Some(a) = a else{
        panic!("none");
        
    };
    println!("{a}");
}

rustc 1.65.0
rustfmt 1.5.1-stable (897e3755 2022-11-02)

[ytmimi]

Thanks for reaching out. rustfmt doesn't handle let-else formatting because the rules for how it should be formatted are still being discussed in rust-lang/style-team#165

Because rustfmt doesn't format let-else statements the code is left as is by rustfmt, which means the trailing whitespace that exists in the original snippet is also left alone, triggering the internal error that you're seeing. In this case the internal error is rustfmts way of letting you know that there's trailing whitespace in the text of your program that requires manual intervention to remove.

You might also want to follow #4914 to keep track of the implementation on the rustfmt side once the rules have been codified in the fmt-rfc linked above.