The Copy trait was implemented on a type with a Drop implementation.
Erroneous code example:
#[derive(Copy)]
struct Foo; // error!
impl Drop for Foo {
fn drop(&mut self) {
}
}RunExplicitly implementing both Drop and Copy trait on a type is currently
disallowed. This feature can make some sense in theory, but the current
implementation is incorrect and can lead to memory unsafety (see
issue #20126), so it has been disabled for now.