error[E0277]: `Sender` cannot be shared between threads safely --> $DIR/issue-70935-complex-spans.rs:13:45 | LL | fn foo(tx: std::sync::mpsc::Sender) -> impl Future + Send { | ^^^^^^^^^^^^^^^^^^ `Sender` cannot be shared between threads safely | = help: the trait `Sync` is not implemented for `Sender` = note: required for `&Sender` to implement `Send` note: required because it's used within this closure --> $DIR/issue-70935-complex-spans.rs:17:13 | LL | baz(|| async{ | ^^ note: required because it's used within this `async fn` body --> $DIR/issue-70935-complex-spans.rs:10:67 | LL | async fn baz(_c: impl FnMut() -> T) where T: Future { | ___________________________________________________________________^ LL | | } | |_^ = note: required because it captures the following types: `ResumeTy`, `impl Future`, `()` note: required because it's used within this `async` block --> $DIR/issue-70935-complex-spans.rs:16:16 | LL | async move { | ________________^ LL | | baz(|| async{ LL | | foo(tx.clone()); LL | | }).await; LL | | } | |_____^ error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.