Misleading suggestion for unused shorthand field pattern

[andersk]

use std::ops::Range;
fn range_end(Range { start, end }: Range<u32>) -> u32 {
    end
}

gives

warning: unused variable: `start`
 --> test.rs:2:22
  |
2 | fn range_end(Range { start, end }: Range<u32>) -> u32 {
  |                      ^^^^^
  |
  = note: #[warn(unused_variables)] on by default
  = note: to avoid this warning, consider using `_start` instead

You can’t just change start to _start here, of course—we should suggest start: _ instead.

[Mark-Simulacrum]

#47390 has more discussion, so I'll close in favor of that. Thanks!