error[E0277]: `impl Future` cannot be sent between threads safely --> $DIR/auto-with-drop_tracking_mir.rs:25:13 | LL | is_send(foo()); | ------- ^^^^^ `impl Future` cannot be sent between threads safely | | | required by a bound introduced by this call | = help: the trait `Send` is not implemented for `impl Future` note: required by a bound in `is_send` --> $DIR/auto-with-drop_tracking_mir.rs:24:24 | LL | fn is_send(_: impl Send) {} | ^^^^ required by this bound in `is_send` error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0277`.