Rust error E0205: #### Note: this error code is no longer emitted by the compiler

The compiler team's explanation

Note: this error code is no longer emitted by the compiler.

An attempt to implement the Copy trait for an enum failed because one of the variants does not implement Copy. To fix this, you must implement Copy for the mentioned variant. Note that this may not be possible, as in the example of

enum Foo {
    Bar(Vec<u32>),
    Baz,
}

impl Copy for Foo { }

This fails because Vec<T> does not implement Copy for any T.

Here's another example that will fail:

#[derive(Copy)]
enum Foo<'a> {
    Bar(&'a mut bool),
    Baz,
}

This fails because &mut T is not Copy, even when T is Copy (this differs from the behavior for &T, which is always Copy).

From rustc --explain E0205 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.