FN unused_unit: function headers in where clauses

[matthiaskrgr]

trait tr {
    fn func<F>(f: F)
    where
        F: FnOnce() -> (); // false negative
}

struct A {}

fn main() {}

impl tr for A {
    fn func<F>(f: F)
    where
        F: FnOnce() -> (), // false negative
    {
    }
}

Clippy does not report any of the -> ()s.

clippy 0.0.212 (9912925 2020-05-10)