arc_with_non_send_sync warns on the caller of a function instead of the function itself

Summary

This happens when we have a function that expects Arc<NonSendSync>. It generates a warning on the calls to the function (more specifically when the Arcs are constructed), but the user cannot fix this warning if this function is provided by a library because they need the library to fix their function first.

Lint Name

arc_with_non_send_sync

Reproducer

I tried this code:

use std::sync::Arc;

fn library_func(_param: Arc<*const ()>) {
    todo!();
}

fn main() {
    library_func(Arc::new(&() as *const ()));
}

I saw this happen:

warning: usage of an `Arc` that is not `Send` and `Sync`
 --> src/main.rs:8:18
  |
8 |     library_func(Arc::new(&() as *const ()));
  |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `Arc<*const ()>` is not `Send` and `Sync` as `*const ()` is neither `Send` nor `Sync`
  = help: if the `Arc` will not used be across threads replace it with an `Rc`
  = help: otherwise make `*const ()` `Send` and `Sync` or consider a wrapper type such as `Mutex`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#arc_with_non_send_sync
  = note: `#[warn(clippy::arc_with_non_send_sync)]` on by default

I expected to see this happen:

warning: usage of an `Arc` that is not `Send` and `Sync`
 --> src/main.rs:3:17
  |
3 |     fn library_func(_param: Arc<*const ()>)
  |                     ^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `Arc<*const ()>` is not `Send` and `Sync` as `*const ()` is neither `Send` nor `Sync`
  = help: if the `Arc` will not used be across threads replace it with an `Rc`
  = help: otherwise make `*const ()` `Send` and `Sync` or consider a wrapper type such as `Mutex`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#arc_with_non_send_sync
  = note: `#[warn(clippy::arc_with_non_send_sync)]` on by default

Version

rustc 1.78.0 (9b00956e5 2024-04-29)
binary: rustc
commit-hash: 9b00956e56009bab2aa15d7bff10916599e3d6d6
commit-date: 2024-04-29
host: aarch64-apple-darwin
release: 1.78.0
LLVM version: 18.1.2

Additional Labels

No response

Start by locating the implementation and tests for the arc_with_non_send_sync lint, then run the supplied reproducer with the library function and its Arc<*const ()> parameter. The change is done when the warning points to the function parameter rather than the caller's Arc::new expression, with coverage for the reported case.