Missing shadowing diagnostic with "@" in pattern-match

[eefriedman]

fn main() {
  match Some(1) { None @ _ => { } };
  //let None = 1;
}

<anon>:2:19: 2:27 warning: unused variable: `None`, #[warn(unused_variables)] on by default
<anon>:2   match Some(1) { None @ _ => { } };
                           ^~~~~~~~

This is accepted, but probably shouldn't be. (A normal declaration of a variable named None is rejected.)

[eefriedman]

Related testcase:

fn main() {
    const C: u8 = 1;
    match 1 {
        C @ 2 => { println!("{}", C); }
        _ => {}
    };
}

<anon>:4:9: 4:14 warning: unused variable: `C`, #[warn(unused_variables)] on by default
<anon>:4         C @ 2 => { println!("{}", C); }
                 ^~~~~
Switch constants must all be same type as switch value!
  switch i32 %3, label %match_else [
    i8 1, label %match_case
  ]
LLVM ERROR: Broken function found, compilation aborted!
playpen: application terminated with error code 1

[Aatch]

That second case is unrelated. (And really weird, I'm not even sure how that's happening!)