lint suggestion: `manual_unwrap_unchecked`

What it does

Essentially: search for cases where hint::unreachable_unchecked is used when Option::unwrap_unchecked or Result::unwrap_unchecked could be preferred.

Advantage

No response

Drawbacks

No response

Example

A bunch from a hashbrown PR: https://github.com/rust-lang/hashbrown/pull/693/changes

But to inline a here, the main cases are:

---

if some_result.is_err() {
    unsafe { unreachable_unchecked() }
}
if some_option.is_none() {
    unsafe { unreachable_unchecked() }
}

becomes

unsafe { some_result.unwrap_unchecked() };
unsafe { some_option.unwrap_unchecked() };

---

let value1 = match some_result {
    Ok(ok) => ok,
    Err(_) => unsafe { unwrap_unchecked() }
};
let value2 = match some_option {
    Some(some) => some,
    None => unsafe { unwrap_unchecked() }
};

becomes

let value1 = unsafe { some_result.unwrap_unchecked() };
let value2 = unsafe { some_option.unwrap_unchecked() };

---

let Ok(value1) = some_result else {
    unsafe { unwrap_unchecked() }
};
let Some(value2) = some_option else {
    unsafe { unwrap_unchecked() }
};

becomes:

let value1 = unsafe { some_result.unwrap_unchecked() };
let value2 = unsafe { some_option.unwrap_unchecked() };

Comparison with existing lints

Clippy has lots of manual_(method) lints, so, this fits right in with those.

Additional Context

No response

Start by comparing the three Rust examples in the issue with Clippy’s existing manual_* lints. Trace how those lints are implemented and tested, then determine how the proposed lint should recognize the Result and Option cases. Done means the lint consistently suggests unwrap_unchecked in the described patterns without suggesting unsafe transformations outside their valid cases.