Allow a rest pattern before closing brace when destructuring

[Kolsky]

Example for a struct:

let Self {
    x,
    y,
.. } = self;

match x {
    Variant::A {
        a,
        b,
    .. } => { /* snip */ }
    _ => todo!(),
}

Currently a .. is placed either on a separate line, or, in case of match and/or a short list of required fields, right after the trailing comma, all on the same line. I also think the above style may serve the best for the same purpose that a trailing commas are intended for. Please consider, thanks.

[calebcartwright]

Thank you for reaching out. I will leave this open for a bit on the off chance that someone strongly interested in this style is willing to submit an implementation for consideration, but it's highly unlikely that the rustfmt team will ever implement ourselves.

rustfmt's core purpose is to reformat code according to the Rust Style Guide and rustfmt's default formatting must always adhere to that spec. Configuration options are supported in rustfmt primarily to address some of the areas where there's large pockets of disagreement (e.g. tabs vs. spaces). We're generally open to considering new options beyond those, but we have to then evaluate the associated burden on the codebase, maintenance, bug surface, etc. and whether the corresponding style is something desired by a sizeable portion of our user base or a more personal esoteric style.