unused_qualification removes generic params

[matthiaskrgr]

I tried this code:

// run-pass

#![feature(unsized_fn_params)]

use std::ops;
use std::ops::Index;

pub struct A;

impl ops::Index<str> for A {
    type Output = ();
    fn index(&self, _: str) -> &Self::Output {
        &()
    }
}

rustc --force-warn unused-qualifications

warning: unnecessary qualification
  --> ./tests/ui/unsized-locals/unsized-index.rs:10:6
   |
10 | impl ops::Index<str> for A {
   |      ^^^^^^^^^^^^^^^
   |
   = note: requested on the command line with `--force-warn unused-qualifications`
help: replace it with the unqualified path
   |
10 | impl Index for A {
   |      ~~~~~

Somehow the generic info gets lost completely? :S

[matthiaskrgr]

#112729 cc @jieyouxu

[asquared31415]

Minimized and not requiring nightly:

#![warn(unused_qualifications)]

mod inner {
    pub trait Trait<T> {}
}

// the import needs to be here for the lint to show up
#[allow(unused_imports)]
use inner::Trait;

impl inner::Trait<u8> for () {}

playground

[jieyouxu]

Thanks for the ping, investigating