needless_borrow emitted on expression that changes types when `&` is removed

Summary

The error after clippy --fix, this should compile in my opinion. It does compile without the curly braces around guard. It is not a clippy false positive if this is considered a rustc bug.

error[E0308]: mismatched types
 --> src/main.rs:6:17
  |
6 |     function(&{ guard });
  |                 ^^^^^ expected `()`, found `Ref<'_, ()>`
  |
  = note: expected unit type `()`
                found struct `std::cell::Ref<'_, ()>`

Lint Name

needless_borrow

Reproducer

I tried this code:

fn function(_: &()) {}

fn main() {
    let refcell = core::cell::RefCell::new(());
    let guard = refcell.borrow();
    function(&&{ guard }); // two &
}

I saw this happen:

"failed to automatically apply fixes suggested by rustc"

I expected to see this happen:

I expected the result after clippy --fix to compile

fn function(_: &()) {}

fn main() {
    let refcell = core::cell::RefCell::new(());
    let guard = refcell.borrow();
    function(&{ guard }); // one &
}

Version

rustc 1.85.0 (4d91de4e4 2025-02-17)
binary: rustc
commit-hash: 4d91de4e48198da2e33413efdcd9cd2cc0c46688
commit-date: 2025-02-17
host: x86_64-unknown-linux-gnu
release: 1.85.0
LLVM version: 19.1.7

Additional Labels

@rustbot label I-suggestion-causes-error

Start by running the supplied Rust reproducer with the needless_borrow lint and clippy --fix, then inspect the lint's fix suggestion and the resulting type error. Done means the suggested fix no longer changes the expression's type unexpectedly and the fixed reproducer compiles, or the issue is confirmed to be a rustc problem.