Given the following code

#![warn(warnings, unused)]

fn main() {
    let x = 13;
}

running rustc -A unused test.rs shows a warning that x is unused as expected (since the module scope takes precedence over the command-line arguments). However, rustc -A warnings prints nothing.

This is caused by the following special handling:

The FIXME already describes the problem, but I haven't found an open issue for this.

The special case was introduced by this commit as part of #21248. Looks like it is a hack needed to silence some otherwise unsilenceable warnings -- but I am not sure if the hack is still needed, or if there isn't a better way to do this.