Nightly version ignores allow(unused)

[jo-so]

The current nightly version (rustc 1.21.0-nightly (df511d5 2017-08-14)) warns about an unused variable, even if it's flagged with allow(). The stable version doesn't do so.

fn main() {
    #[allow(unused_variables)] let x = 12;
    let y = 11;
}

warning: unused variable: `x`
 --> src/main.rs:2:36
  |
2 |     #[allow(unused_variables)] let x = 12;
  |                                    ^
  |
  = note: #[warn(unused_variables)] on by default

https://play.rust-lang.org/?gist=9b81da266dd1f4383760de35d94f7ff6&version=nightly

[Mark-Simulacrum]

cc @alexcrichton -- would this have been fixed by #43841? Not sure if that's present in this nightly.

[alexcrichton]

Hm no this was not fixed by #43841, I don't know offhand what might cause this, would have to investigate.

[nikomatsakis]

triage: P-high

@alexcrichton, took the liberty of assigning you since it seems likely related to the changes to lint handling.