Clippy should warn against redundant calls to `Option::as_ref` on `Option<&_>`

What it does

Option::as_ref is used to convert &Option<T> to Option<&T>. Clippy should warn against using this function when T is already a reference type, unless the destination type requires Option<&&T> for some reason.

Advantage

Code cleanliness and brevity. Sometimes redundant calls to as_ref can arise if you refactor a variable from being owned to being passed by reference.

Drawbacks

No response

Example

fn my_fn(value: Option<&T>) {
    value.as_ref().map(...)
}

Could be written as:

fn my_fn(value: Option<&T>) {
    value.map(...)
}

Start by locating Clippy's existing lint entry points and tests for Option method patterns; the issue's example provides the initial case to inspect. Done means redundant as_ref calls on Option<&T> are warned about, while cases requiring Option<&&T> remain allowed.