Checking playground v0.0.1 (/playground) warning: future cannot be sent between threads safely --> src/main.rs:12:14 | 12 | async fn f() { | ^ future returned by `f` is not `Send` | note: the lint level is defined here --> src/main.rs:1:9 | 1 | #![warn(clippy::future_not_send)] | ^^^^^^^^^^^^^^^^^^^^^^^ note: future is not `Send` as this value is used across an await --> src/main.rs:16:16 | 13 | let a = SomethingNotSend; | - has type `SomethingNotSend` which is not `Send` ... 16 | other().await; | ^^^^^^ await occurs here, with `a` maybe used later ... 20 | } | - `a` is later dropped here = note: `SomethingNotSend` doesn't implement `std::marker::Send` = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#future_not_send warning: call to `std::mem::drop` with a value that does not implement `Drop`. Dropping such a type only extends its contained lifetimes --> src/main.rs:15:9 | 15 | drop(a); | ^^^^^^^ | = note: `#[warn(clippy::drop_non_drop)]` on by default note: argument has type `SomethingNotSend` --> src/main.rs:15:14 | 15 | drop(a); | ^ = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#drop_non_drop warning: `playground` (bin "playground") generated 2 warnings Finished dev [unoptimized + debuginfo] target(s) in 0.50s 

play.rust-lang.org Build using the Nightly version: 1.63.0-nightly (2022-06-03 a6b8c6954829669a5c4f) Clippy 0.1.63 (2022-06-03 a6b8c69)