`warn(needless_borrow)` creates false positive when using `derive(Debug)`

[U007D]

Note: false positive is only emitted when #[derive(Debug)] attribute is present:

#[derive(Debug)]  // must be present to get false positive
pub struct Crowd<'a> {
    people: &'a [usize],
}

gives

   Compiling playground v0.0.1 (file:///playground)
warning: this pattern creates a reference to a reference
 --> src/main.rs:7:5
  |
7 |     people: &'a [usize],
  |     ^^^^^^^^^^^^^^^^^^^ help: change this to: `people: &'a [usize]`
  |
note: lint level defined here
 --> src/main.rs:2:9
  |
2 | #![warn(needless_borrow)]
  |         ^^^^^^^^^^^^^^^
  = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.195/index.html#needless_borrow

warning: this pattern creates a reference to a reference
 --> src/main.rs:7:5
  |
7 |     people: &'a [usize],
  |     ^^^^^^^^^^^^^^^^^^^ help: change this to: `people: &'a [usize]`
  |
  = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.195/index.html#needless_borrow

    Finished dev [unoptimized + debuginfo] target(s) in 0.66 secs

playground example

[phansch]

Looks like the macro check in check_pat of needless_borrow is not working because of rust-lang/rust#49154.

Also: #2651