clippy::non_canonical_clone_impl: non-canonical implementation of `clone` on a `Copy` type

What you see

warning: non-canonical implementation of `clone` on a `Copy` type
 --> main.rs:7:29
  |
7 |       fn clone(&self) -> Self {
  |  _____________________________^
8 | |         Self(self.0)
9 | |     }
  | |_____^ help: change this to: `{ *self }`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#non_canonical_clone_impl
  = note: `#[warn(clippy::non_canonical_clone_impl)]` on by default

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

If both Clone and Copy are implemented, they must agree. This can done by dereferencing self in Clone’s implementation, which will avoid any possibility of the implementations becoming out of sync.

Code that is most likely wrong or useless. Warns by default.

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

#[derive(Eq, PartialEq)]
struct A(u32);

impl Clone for A {
    fn clone(&self) -> Self {
        Self(self.0)
    }
}

impl Copy for A {}

Write this instead

#[derive(Eq, PartialEq)]
struct A(u32);

impl Clone for A {
    fn clone(&self) -> Self {
        *self
    }
}

impl Copy for A {}

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

#[allow(clippy::non_canonical_clone_impl)]
fn my_function() { /* ... */ }

[lints.clippy]
non_canonical_clone_impl = "allow"

cargo clippy -- -A clippy::non-canonical-clone-impl

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.