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// Well-formedness of nested opaque types, i.e. `impl Sized` in
// `type Outer = impl Trait<Assoc = impl Sized>`.
// See the comments below.
//
// revisions: pass pass_sound fail
// [pass] check-pass
// [pass_sound] check-fail
// [fail] check-fail
#![feature(type_alias_impl_trait)]
struct IsStatic<T: 'static>(T);
trait Trait<In> {
type Out;
fn get(&self) -> Result<Self::Out, ()> {
Err(())
}
}
impl<T> Trait<&'static T> for () {
type Out = IsStatic<T>;
}
// The hidden type for `impl Sized` is `IsStatic<T>`, which requires `T: 'static`.
// We know it is well-formed because it can *only* be referenced as a projection:
// <OuterOpaque<T> as Trait<&'static T>>::Out`.
// So any instantiation of the type already requires proving `T: 'static`.
#[cfg(pass)]
mod pass {
use super::*;
type OuterOpaque<T> = impl Trait<&'static T, Out = impl Sized>;
fn define<T>() -> OuterOpaque<T> {}
}
// Test the soundness of `pass` - We should require `T: 'static` at the use site.
#[cfg(pass_sound)]
mod pass_sound {
use super::*;
type OuterOpaque<T> = impl Trait<&'static T, Out = impl Sized>;
fn define<T>() -> OuterOpaque<T> {}
fn test<T>() {
let outer = define::<T>();
let _ = outer.get(); //[pass_sound]~ ERROR `T` may not live long enough
}
}
// Similar to `pass` but here `impl Sized` can be referenced directly as
// InnerOpaque<T>, so we require an explicit bound `T: 'static`.
#[cfg(fail)]
mod fail {
use super::*;
type InnerOpaque<T> = impl Sized; //[fail]~ ERROR `T` may not live long enough
type OuterOpaque<T> = impl Trait<&'static T, Out = InnerOpaque<T>>;
fn define<T>() -> OuterOpaque<T> {}
}
fn main() {}
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