tests/ui/feature-gates/feature-gate-cfg-boolean-literals.rs

#[cfg(true)] //~ ERROR `cfg(true)` is experimental
fn foo() {}

#[cfg_attr(true, cfg(false))] //~ ERROR `cfg(true)` is experimental
//~^ ERROR `cfg(false)` is experimental
fn foo() {}

fn main() {
    cfg!(false); //~ ERROR `cfg(false)` is experimental
}