src/test/ui/borrowck/borrowck-use-uninitialized-in-cast-trait.rs

// Variation on `borrowck-use-uninitialized-in-cast` in which we do a
// trait cast from an uninitialized source. Issue #20791.

trait Foo { fn dummy(&self) { } }
impl Foo for i32 { }

fn main() {
    let x: &i32;
    let y = x as *const dyn Foo; //~ ERROR [E0381]
}