Unused variables inside `for` are not detected

[huonw]

fn main() {
    for _ in range(1i, 101) {
        let x = ();
        match () {
            a => {}
        }
    }
}

compiles without a peep, even though x and a are unused. Commenting out the for gives the expected output:

<anon>:3:13: 3:14 warning: unused variable: `x`, #[warn(unused_variable)] on by default
<anon>:3         let x = ();
                     ^
<anon>:5:13: 5:14 warning: unused variable: `a`, #[warn(unused_variable)] on by default
<anon>:5             a => {}
                     ^

[hirschenberger]

I think this an be closed

[alexcrichton]

Thanks @hirschenberger (fixed in #18014)