unused_unsafe gives wrong reason

[main--]

pub unsafe fn outer() {
    fn inner() {
        unsafe { /* unnecessary */ }
    }
    
    inner()
}

warning: unnecessary `unsafe` block
 --> src/main.rs:3:9
  |
1 | pub unsafe fn outer() {
  | --------------------- because it's nested under this `unsafe` fn
2 |     fn inner() {
3 |         unsafe { /* unnecessary */ }
  |         ^^^^^^ unnecessary `unsafe` block
  |
  = note: #[warn(unused_unsafe)] on by default

The unsafe block is clearly unnecessary, but it being inside a safe function which is nested in an unsafe function is clearly not the reason. Playpen

[ExpHP]

fix looks trivial, I think I got this

[ExpHP]

More specifically, I believe librustc_mir::transform::check_unsafety::is_enclosed should return None as soon as it encounters a safe fn.