error[E0308]: mismatched types --> $DIR/issue-111011.rs:10:23 | LL | foo(async move || {}); | ^^ expected `Box<_>`, found `async` closure body | = note: expected struct `Box<_>` found `async` closure body `[async closure body@$DIR/issue-111011.rs:10:23: 10:25]` = note: for more on the distinction between the stack and the heap, read https://doc.rust-lang.org/book/ch15-01-box.html, https://doc.rust-lang.org/rust-by-example/std/box.html, and https://doc.rust-lang.org/std/boxed/index.html error[E0308]: mismatched types --> $DIR/issue-111011.rs:11:9 | LL | bar(async move || {}); | --- ^^^^^^^^^^^^^^^^ expected `Box _>`, found closure | | | arguments to this function are incorrect | = note: expected struct `Box<(dyn FnOnce() -> _ + 'static)>` found closure `{closure@$DIR/issue-111011.rs:11:9: 11:22}` = note: for more on the distinction between the stack and the heap, read https://doc.rust-lang.org/book/ch15-01-box.html, https://doc.rust-lang.org/rust-by-example/std/box.html, and https://doc.rust-lang.org/std/boxed/index.html note: function defined here --> $DIR/issue-111011.rs:7:4 | LL | fn bar(x: Box X>) {} | ^^^ ------------------------- help: store this in the heap by calling `Box::new` | LL | bar(Box::new(async move || {})); | +++++++++ + error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0308`.