tests/ui/issues/issue-11515.rs

struct Test {
    func: Box<dyn FnMut() + 'static>,
}



fn main() {
    let closure: Box<dyn Fn() + 'static> = Box::new(|| ());
    let test = Box::new(Test { func: closure }); //~ ERROR trait upcasting coercion is experimental [E0658]
}