⚠️ Yield-safe lint

Use-case

Some types should not be held across a "yield" bound. A typical example is a MutexGuard:

async fn example(x: &Lock<u32>) {
    let data = x.lock().unwrap();
    something().await;
    *data += 1;
}

async fn something() { }

In practice, a lot of these issues are avoided because MutexGuard is not Send, but single-thread runtimes hit these issues.

Types where this would apply

• MutexGuard for mutexes, read-write locks
• Guards for ref-cells
• Things that might use these types internally and wish to bubble it up

Precedent and related questions

• The #[must_use] lint on types, we would want their design to work very closely.
• Non-async-friendly functions like sleep or task::block_on.