panic: left behind trailing whitespace

[35VLG84]

Hello rustfmt team,

Following code will cause panic with stable (1.86.0) and nightly (as 2025-04-25) rustc / rustfmt.

The MRE is also available here: https://github.com/35VLG84/rustfmt-ice as there is a space character which is triggering the ICE.

Here is the stacktrace: rustc-ice-2025-04-25T14_25_14-537623.txt It's also available in the above repository.

MRE

There is a space at the end of the second line (after '¶').
If you remove that space, then the ICE goes away.
Same is true if the comment or the last test line is removed.

fn main() {
    let m = matches!(
        c,
        | 'a' | '¶'
        | 'b' // abc
        | '¿'
    );
}

od -c src/main.rs

0000000   f   n       m   a   i   n   (   )       {  \n
0000020   l   e   t       m       =       m   a   t   c   h   e   s   !
0000040   (  \n                                   c   ,  \n
0000060                       |       '   a   '       |       ' 302 266
0000100   '      \n                                   |       '   b   '
0000120       /   /       a   b   c  \n
0000140   |       ' 302 277   '  \n                   )   ;  \n   }  \n
0000160

Thank you for working with rustfmt, it's really nice and helpful tool!

[35VLG84]

Also if the '¶' is changed to ascii char, the ICE goes away. But even then rustfmt fails to format the code.

error[internal]: left behind trailing whitespace
....
warning: rustfmt has failed to format. See previous 1 errors.