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

[laikoni]

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.

[ytmimi]

The issue here is that rewrite_struct_pat doesn't have any comment recovery code defined for trailing comments after the ... rustfmt errs on the side of caution here and refuses to rewrite the entire match expression because it realizes that if it went ahead with the rewirte it would remove the // this comment here apparently causes trouble comment.

In order to resolve this one we might consider taking a similar approach to rewrite_struct_lit, which is a similar function, for rewriting structs, but doesn't seem to suffer from this trailing comment problem because rewrite_struct_lit considers the .. as part of the struct fields that it needs to rewrite, while rewrite_struct_pat sort of bolts on the .. handling after rewriting the struct fields. @calebcartwright I'd appreciate getting your take on this idea.

intput:

fn main() {
  let x =  MyStruct {
            field_a,
            .. // this comment here apparently causes trouble
        };
}

output:

fn main() {
    let x = MyStruct {
        field_a,
        .. // this comment here apparently causes trouble
    };
}