needless_borrow track through function call

Summary

Currently, the needless_borrow check is described as:

What it does
Checks for address of operations (&) that are going to be dereferenced immediately by the compiler.

This misses cases where we have borrows earlier in a function that aren't used. For example,

pub struct S;

pub fn f(_: &S) {}

pub fn g() {
    let s = &&S;
    f(s);
}

pub fn h() {
    let s = S;
    f(&&s);
}

In the above example, needless_borrow is triggered on function h, but not on function g.

Lint Name

needless_borrow

Reproducer

Can use same example code block given above and verify that the needless_borrow warning is triggered on function h but not on function g:

pub struct S;

pub fn f(_: &S) {}

pub fn g() {
    let s = &&S;
    f(s);
}

pub fn h() {
    let s = S;
    f(&&s);
}

Version

rustc 1.67.1 (d5a82bbd2 2023-02-07)
cargo 1.67.1 (8ecd4f20a 2023-01-10)

System information:
 Server Version: 20.10.18
 Storage Driver: overlay2
  Backing Filesystem: xfs
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Kernel Version: 5.15.0-1030-aws
 Operating System: Ubuntu 20.04.5 LTS
 OSType: linux
 Architecture: x86_64

Start with the needless_borrow lint and the supplied Rust reproducer. Trace how the borrow is followed through the f(s) call, then verify completion by checking that g is diagnosed as well as h.