dead code lint should say "never constructed" for variants that are matched on but never constructed

[pnkfelix]

mod a {
    #[deriving(Show)]
    pub enum E {
        Variant1,
        Variant2,
    }
}

fn main() {
    let x = a::E::Variant1;
    let y = match x {
        a::E::Variant1 => 1i,
        a::E::Variant2 => 2i,
    };
    println!("Hello world: {}", (x, y));
}

produces:

<anon>:5:9: 5:17 warning: variant is never used: `Variant2`, #[warn(dead_code)] on by default
<anon>:5         Variant2,
                 ^~~~~~~~

[pnkfelix]

(arguably this may be a feature, since the arm associated with the pattern here is nontheless never used.)

@pnkfelix Yeah, this was intentional although I'm going to reopen this as I think we can do better on the wording. Used is indeed misleading, constructed is what the lint is proving.

[steveklabnik]

Triage: still an issue today. Updated code:

mod a {
    #[derive(Debug)]
    pub enum E {
        Variant1,
        Variant2,
    }
}

fn main() {
    let x = a::E::Variant1;
    let y = match x {
        a::E::Variant1 => 1,
        a::E::Variant2 => 2,
    };
    println!("Hello world: {:?}", (x, y));
}

[nox]

Could we get some action on that? Seems important, with all the ergonomics stuff going on.