Why derive(Copy, Clone) is different with derive(Clone) + impl Copy

Hi, I've encountered an unexpected but explainable case, that

#[derive(Clone)]
enum A {
    A = 1,
    B = 2,
    C = 3,
}
impl Copy for A {}

#[derive(Clone, Copy)]
enum B {
    A = 1,
    B = 2, 
    C = 3,
}

Expanded code as

impl ::core::clone::Clone for A {
    #[inline]
    fn clone(self: &Self)
        ->
            A {
            match (&*self,) {
                    (&A::A,) => A::A,
                    (&A::B,) => A::B,
                    (&A::C,) => A::C,
                }
        }
}

impl ::core::clone::Clone for B {
    #[inline]
    fn clone(self: &Self) -> B { { *self } }
}

Note that, both A and B have Copy trait, but their derived Clone impl is quite different.

playground: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=90807b18bd71f650eb68ed0dec06f749 click Show HIR and hit run.