rustc starts describing trait bounds and pointing at complicated library internals instead of just saying to add #[derive(Clone)]

Code

#[derive(Clone)]
enum Necessity<T> {
    Optional(T),
    Mandatory(T),
}

struct Element<T> {
    attributes: Vec<Necessity<T>>,
    children: Vec<Necessity<Element<T>>>,
}

impl<T: std::clone::Clone> Element<T> {
    fn clone(&self) {
        let _ = self.children.clone();
    }
}

fn main() {
    println!("Hello, world!");
}

Current output

Compiling rust_issue v0.1.0 (/home/seeb/rust/rust_issue)
error[E0599]: the method `clone` exists for struct `Vec<Necessity<Element<T>>>`, but its trait bounds were not satisfied
   --> src/main.rs:14:31
    |
2   | enum Necessity<T> {
    | ----------------- doesn't satisfy `Necessity<Element<T>>: Clone`
...
14  |         let _ = self.children.clone();
    |                               ^^^^^ method cannot be called on `Vec<Necessity<Element<T>>>` due to unsatisfied trait bounds
    |
   ::: /home/seeb/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:396:1
    |
396 | pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
    | ------------------------------------------------------------------------------------------------ doesn't satisfy `Vec<Necessity<Element<T>>>: Clone`
    |
    = note: the following trait bounds were not satisfied:
            `Necessity<Element<T>>: Clone`
            which is required by `Vec<Necessity<Element<T>>>: Clone`
help: consider annotating `Necessity<Element<T>>` with `#[derive(Clone)]`
    |
2   + #[derive(Clone)]
3   | enum Necessity<T> {
    |

For more information about this error, try `rustc --explain E0599`.
error: could not compile `rust_issue` (bin "rust_issue") due to previous error

Desired output

help: consider annotating `Element<T>` with `#[derive(Clone)]`
    |
7   + #[derive(Clone)]
8   | struct Element<T> {
    |

Rationale and extra context

No response

Other cases

No response

Anything else?

No response

Reproduce the E0599 diagnostic with the example in src/main.rs and compare the current and desired suggestions. Start by tracing the trait-bound output involving Vec in alloc/src/vec/mod.rs; done when the help points to deriving Clone for Element rather than Necessity<Element>.