rust/tests/ui/feature-gates/feature-gate-impl_trait_in_fn_trait_return.rs

fn f() -> impl Fn() -> impl Sized { || () }
//~^ ERROR `impl Trait` is not allowed in the return type of `Fn` trait bounds
fn g() -> &'static dyn Fn() -> impl Sized { &|| () }
//~^ ERROR `impl Trait` is not allowed in the return type of `Fn` trait bounds

fn main() {}