redundant_clone: false negative with unneeded ref

Lint name:

I tried this code:

fn opt_string() -> Option<String> {
    Some(String::from("hello world"))
}

fn main() {
    let s: String = match opt_string() {
        Some(ref string) => string.clone(), // we take a ref here so we have to clone()
        // but actually  opt_string() returns an owned value and we could consume it
        _ => String::new(),
    };

    // this could be:

    let _s_better: String = match opt_string()  {
        Some(string) => string,
        _ => String::new(),
    };
    
    assert_eq!("hello world".to_string(), s);
}

Meta

• cargo clippy -V: clippy 0.1.54 (8cf990c 2021-05-15)
• rustc -Vv:

rustc 1.54.0-nightly (8cf990c9b 2021-05-15)
binary: rustc
commit-hash: 8cf990c9b5c59f25c806fad9f4466f9d6509bbea
commit-date: 2021-05-15
host: x86_64-unknown-linux-gnu
release: 1.54.0-nightly
LLVM version: 12.0.1

Start by reproducing the Rust snippet with the redundant_clone lint enabled through cargo clippy. Compare the reported behavior with the ownership shown in the example, then locate the lint implementation and its existing tests. Done means the false negative is covered by a regression test and the lint correctly identifies the unnecessary reference and clone.