Panic with `wrap_comments` and non-ascii character at comment wrap boundary

[TOETOE55]

There is a piece of code in my project like:

fn main() {
    if xxx {
        let xxx = xxx
            .into_iter()
            .filter(|(xxx, xxx)| {
                if let Some(x) = Some(1) {
                    // xxxxxxxxxxxxxxxxxx, xxxxxxxxxxxx, xxxxxxxxxxxxxxxxxxxx xxx xxxxxxx, xxxxx xxx
                    // xxxxxxxxxx. xxxxxxxxxxxxxxxx，xxxxxxxxxxxxxxxxx xxx xxxxxxx
                    // 是sdfadsdfxxxxxxxxx，sdfaxxxxxx_xxxxx_masdfaonxxx，
                    if false {
                        return true;
                    }
                }
                false
            })
            .collect();
    }
}

When I execute cargo fmt, I got an error:

thread 'main' panicked at 'index out of bounds: the len is 48 but the index is 18446744073709551615', src/tools/rustfmt/src/string.rs:285:27
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

The rustfmt.toml is the following:

wrap_comments = true

I can't understand why a few lines of comments can make fmt crash...

[calebcartwright]

It's not related to having comments nor the quantity of lines of comments, but the fact that there's a non-ascii char at a comment line boundary.

Do you have wrap_comments enabled and/or any other non-default config options set?

(Edit - i see you do have wrap_comments enabled, missed that on the first read!)