explicit_auto_deref could suggest variale with borrows

[matthiaskrgr]

Description

The op_ref lint already does this:

warning: needlessly taken reference of left operand
   --> crates/rust-analyzer/src/reload.rs:582:51
    |
582 |             if dummy_replace.iter().any(|replace| &**replace == name) {
    |                                                   ----------^^^^^^^^
    |                                                   |
    |                                                   help: use the left value directly: `**replace`
    |
    = note: `#[warn(clippy::op_ref)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#op_ref

IMO its easier to understand if the span and the suggestion includes the borrows

so

warning: deref which would be done by auto-deref
   --> crates/rust-analyzer/src/handlers.rs:981:41
    |
981 |         snap.analysis.rename(position, &*params.new_name)?.map_err(to_proto::rename_error)?;
    |                                         ^^^^^^^^^^^^^^^^ help: try this: `params.new_name`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#explicit_auto_deref

could become

warning: deref which would be done by auto-deref
   --> crates/rust-analyzer/src/handlers.rs:981:41
    |
981 |         snap.analysis.rename(position, &*params.new_name)?.map_err(to_proto::rename_error)?;
    |                                        ^^^^^^^^^^^^^^^^^ help: try this: `&params.new_name`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#explicit_auto_deref

Version

clippy 0.1.64 (f2d9393 2022-07-02)

Additional Labels

No response

[msfjarvis]

I think I have a similar case (let me know if it should be a separate issue), but I'm not sure if it's actually a bad diagnostic or just me holding it wrong. Given this code:

use once_cell::sync::Lazy;

static BASE_URL: Lazy<String> =
    Lazy::new(|| std::env::var("BASE_URL").expect("BASE_URL must be defined"));

fn main() {
    function(&**BASE_URL);
}

fn function(url: &str) {
    let _ = url;
}

The emitted diagnostic is this:

warning: deref which would be done by auto-deref
 --> src/repro.rs:7:15
  |
7 |     function(&**BASE_URL);
  |               ^^^^^^^^^^ help: try this: `BASE_URL`

At a first glance one might change this invocation to function(BASE_URL) which obviously fails, because when you do a double take you'll see what is really being suggested is function(&BASE_URL). This is probably intentionally so, but it is a bit confusing nonetheless. It'd be great if the diagnostic could look something like this instead:

warning: deref which would be done by auto-deref
 --> src/repro.rs:7:15
  |
7 |     function(&**BASE_URL);
  |              ^^^^^^^^^^^ help: try this: `&BASE_URL`

[Jarcho]

I originally had it that way and I don't remember why I switched it. It had something to do with how the lint pass was implemented.

Related question, how does the suggestion look with &mut *x just suggesting x. e.g.

function(&mut **x)
              ^^^ help: try this: `x`

This one looks fine to me unlike a immutable borrow.

Edit: I guess #9127 answers that question.