implicit_await_with_async_drop.md

Implicit await with async drop

Consider this code:

async fn foo(input: &QueryInput) -> anyhow::Result<()> {
    let db = DatabaseHandle::connect().await;
    let query = assemble_query(&input)?;
    let results = db.perform_query(query).await;
    while let Some(result) = results.next().await? {
        ...
    }
}

Now let us assume that DatabaseHandle implements AsyncDrop to close the connection. There are numerous points here where db could be dropped (e.g., each use of ?). At each of those points, there is effectively an implicit await similar to AsyncDrop::async_drop(db).await. It seems clear that users should not be required to manually write those things, but it is also a weakening of the existing .await contract (that all blocking points are visible).