rustc successfully compiles functions with duplicate argument names

[chris-morgan]

fn foo(a: int, a: bool) {
    println(fmt!("%?", a));
}
fn main() {
    foo(42, false);
}

I expect this to fail to compile on account of the duplicated argument name. Instead:

<anon>:1:7: 1:8 warning: unused variable: `a` [-W unused-variable (default)]
<anon>:1 fn foo(a: int, a: bool) {
                ^

And running it writes false. The first argument is wholly inaccessible.

[huonw]

Triage: still an issue.

[sanxiyn]

Still an issue. Ping @cmr.

Seems like a dupe of #17568 (which is a superset of this issue, hence this one should be closed).

And as #17568 is now fixed, I'm closing this.