Uplift `clippy::{drop,forget}_{ref,copy}` lints by Urgau · Pull Request #109732...

This PR aims at uplifting the clippy::drop_ref, clippy::drop_copy, clippy::forget_ref and clippy::forget_copy lints.

Those lints are/were declared in the correctness category of clippy because they lint on useless and most probably is not what the developer wanted.

drop_ref and forget_ref

The drop_ref and forget_ref lint checks for calls to std::mem::drop or std::mem::forget with a reference instead of an owned value.

Example

let mut lock_guard = mutex.lock();
std::mem::drop(&lock_guard) // Should have been drop(lock_guard), mutex
// still locked
operation_that_requires_mutex_to_be_unlocked();

Explanation

Calling drop or forget on a reference will only drop the reference itself, which is a no-op. It will not call the drop or forget method on the underlying referenced value, which is likely what was intended.

drop_copy and forget_copy

The drop_copy and forget_copy lint checks for calls to std::mem::forget or std::mem::drop with a value that derives the Copy trait.

Example

let x: i32 = 42; // i32 implements Copy
std::mem::forget(x) // A copy of x is passed to the function, leaving the
                    // original unaffected

Explanation

Calling std::mem::forget does nothing for types that implement Copy since the value will be copied and moved into the function on invocation.

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Followed the instructions for uplift a clippy describe here: #99696 (review)

cc @m-ou-se (as T-libs-api leader because the uplifting was discussed in a recent meeting)

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