await_holding_borrow - like await_holding_lock, but for RefCell

[lylythechosenone]

What it does

This lint should warn users attempting to hold a RefCell's Ref or RefMut guards across an await point.

Advantage

Even in a single-threaded environment, external code can run during awaits. This code may attempt to borrow the same RefCell, causing a panic.

Drawbacks

Holding a borrow may be intentional, although it likely isn't.

Example

async {
    let my_cell: RefCell<_> = /* divine it from somewhere */;
    let my_borrow = my_cell.borrow();
    some_future().await;
    println!("The value is {}!", *my_borrow);
}

There is no trivial improvement to this code. Some examples of a fix might be

• moving the println! before the await;
• wrapping the value in an Rc, cloning it, and dropping the borrow before the await;
• or simply removing the borrow (and println!).

[Jarcho]

There's await_holding_invalid_type to handle that. Will require configuring the lint.

[dwrensha]

Is this the same as https://rust-lang.github.io/rust-clippy/master/index.html#/await_holding_refcell_ref ?