False positive for clone_on_copy

[vallentin]

I've encountered a false positive, when calling .clone() on a field of a struct. Followed by calling a method (&self) that takes a closure, which borrows the original struct.

I encountered it using the glfw crate, and boils down to the following:

// glfw: Glfw + Copy
window.glfw.clone().with_primary_monitor(|_, _| {
    println!("{:?}", window.get_size());
});

Clippy suggests removing .clone() since Glfw implements Copy.

using clone on a Copy type

help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#clone_on_copy
help: try removing the clone call: window.glfwclippy(clippy::clone_on_copy)

However, that doesn't work, since it would reborrow window.

error[E0502]: cannot borrow window.glfw as mutable because it is also borrowed as immutable

---

Here's two minimal, reproducible examples.

Example 1

let mut i = 0;

fn foo<F>(_: &i32, mut f: F) where F: FnMut() {
    f();
}

foo(&i.clone(), || {
    i += 1;
});

println!("{}", i);

Example 2

#[derive(Clone, Copy, Debug)]
struct Foo(i32);

impl Foo {
    fn bar<F>(&self, mut f: F) where F: FnMut() {
        f();
    }
}

let mut foo = Foo(0);

foo.clone().bar(|| {
    foo.0 += 1;
});

println!("{:?}", foo);

I'm aware that changing &self to self and removing .clone() works. However, that would require me to modify glfw.

Version: clippy 0.0.212 (082cfa7 2019-06-07)