Require T: Copy for hint::select_unpredictable

[Amanieu]

The current implementation doesn't call the drop the value that is not selected. This could be fixed in the future but for now it is sufficient to limit this to Copy types.

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[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

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---- library/core/src/hint.rs - hint::select_unpredictable (line 764) stdout ----
error[E0277]: the trait bound `&mut Vec<i32>: Copy` is not satisfied
   --> library/core/src/hint.rs:773:18
    |
12  |     let bucket = hint::select_unpredictable(hash % 2 == 0, bucket_one, bucket_two);
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `&mut Vec<i32>`
    |
    = note: `Copy` is implemented for `&Vec<i32>`, but not for `&mut Vec<i32>`
note: required by a bound in `std::hint::select_unpredictable`
   --> /checkout/library/core/src/hint.rs:783:32
    |
783 | pub fn select_unpredictable<T: Copy>(condition: bool, true_val: T, false_val: T) -> T {
    |                                ^^^^ required by this bound in `select_unpredictable`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.

[workingjubilee]

need to fix an example, looks like

[joboet]

I don't think this is a good idea as it also forbids the usage of select_unpredictable with mutable references.

[Amanieu]

Closing in favor of #139977 which fixes drop handling.