Unused variable `result` without variable result (for loop)

[tbu-]

Code:

fn main() {
    for _ in match return () {
        () => Some(0),
    } {}
}

Warning:

$ rustc a.rs
a.rs:2:5: 4:9 warning: unused variable: `result`, #[warn(unused_variables)] on by default
a.rs:2     for _ in match return () {
a.rs:3         () => Some(0),
a.rs:4     } {}

Playpen

It probably has something to do with for loop desugaring.

[mitaa]

I think this should be marked "E-Easy"

Relevant code is in src/librustc_front/lowering.rs.
Prefixing the variable name with an underscore should probably be enough to fix this
(and a testcase in src/test/run-pass)

[durka]

E-easy‽ I'd like to try this one.