#![feature(rustc_attrs, stmt_expr_attributes)] fn foo(_: u32, _: u32) {} fn bar(_: u32) {} fn main() { #[rustc_box] Box::new(1); // OK #[rustc_box] Box::pin(1); //~ ERROR `#[rustc_box]` attribute used incorrectly #[rustc_box] foo(1, 1); //~ ERROR `#[rustc_box]` attribute used incorrectly #[rustc_box] bar(1); //~ ERROR `#[rustc_box]` attribute used incorrectly #[rustc_box] //~ ERROR `#[rustc_box]` attribute used incorrectly #[rustfmt::skip] Box::new(1); }