false negative unused_mut

[matthiaskrgr]

struct SomeStruct {
	path: std::path::PathBuf,
}

impl SomeStruct {
	fn path_exists(&mut self) -> bool { // false negative unused_mut
		// path.exists() does not need mutable reference:
		// pub fn exists(&self) -> bool { ... } 
		self.path.exists()
	}
}

fn main() {
    let mut s = SomeStruct { path: std::path::PathBuf::from("/tmp/a"), };
    println!("{}", s.path_exists());
}

[zackmdavis]

I'm pretty sure the unused-mut lint is specifically about the mut mutability modifier keyword (as in let mut a = ...). Changing &mut to & where possible sounds like a candidate Clippy lint?

[scottmcm]

I think this is by design, since that's not a let mut, and there are potential reasons for an API to take &uniq even if it only calls shared stuff (or nothing).

[zackmdavis]

jinx

[sanxiyn]

This is rust-lang/rust-clippy#1230. I agree it is out of scope for built-in unused_mut lint. Closing.