needless_borrow false negative on fn that takes AsRef<..> and gets &var

Lint name: needless_borrow

I tried this code:

I wonder if the lint should warn on passing &arg to a function that takes AsRef<..> where the & would not be needed

#![warn(clippy::needless_borrow)]

pub fn main() {
    fn is_hello<T: AsRef<str>>(s: T) {
        assert_eq!("hello", s.as_ref());
    }
    let s: &String = &"hello".to_string();

    is_hello(&&&&s); // warn?
    is_hello(&s); // warn?
    is_hello(s); // ok
    is_hello(&"hello"); // warn?
    is_hello("hello"); // ok
}

Meta

• cargo clippy -V: clippy 0.1.52 (9c09c1f 2021-02-26)
• rustc -Vv:

rustc 1.52.0-nightly (9c09c1f7c 2021-02-26)
binary: rustc
commit-hash: 9c09c1f7cfcf9de0522bcd1cfda32b552195c464
commit-date: 2021-02-26
host: x86_64-unknown-linux-gnu
release: 1.52.0-nightly
LLVM version: 11.0.1

Start by reproducing the Rust example with the needless_borrow lint and run Clippy against each marked call to confirm the false negatives. Trace the lint implementation and existing regression tests, then add coverage for the unnecessary borrows involving AsRef<str> and make the expected warnings match the intended behavior.