rustfmt stops formatting after line comment following `..` in a struct pattern

I wondered why suddenly only half of my file got formatted and boiled down the code to the following MWE:

fn main() {
match e { // this line still gets formatted
        MyStruct {
            field_a,
            .. // this comment here apparently causes trouble
        } => (),
_ => (), // this line is no longer formatted
    };
}

Notably, rustfmt does not complain, it just ignores everything after the offending comment and formats the file only up to that point.

I saw that there are already many open issues revolving around comments, so my apologies if this exact issue has been reported before.

Start by running rustfmt on the Rust MWE in the issue and inspect its comment-handling behavior around the .. in the struct pattern. Trace where formatting stops after the line comment, then add a regression test showing that the entire input is formatted rather than silently truncated.