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//@ check-pass
//@ known-bug: #84591
trait Subtrait<'a, 'b, R>: Supertrait<'a, 'b> {}
trait Supertrait<'a, 'b> {
fn convert<T: ?Sized>(x: &'a T) -> &'b T;
}
fn need_hrtb_subtrait<'a_, 'b_, S, T: ?Sized>(x: &'a_ T) -> &'b_ T
where
S: for<'a, 'b> Subtrait<'a, 'b, &'b &'a ()>,
{
need_hrtb_supertrait::<S, T>(x)
// This call works and drops the implied bound `'a: 'b`
// of the where-bound. This means the where-bound can
// now be used to transmute any two lifetimes.
}
fn need_hrtb_supertrait<'a_, 'b_, S, T: ?Sized>(x: &'a_ T) -> &'b_ T
where
S: for<'a, 'b> Supertrait<'a, 'b>,
{
S::convert(x)
}
struct MyStruct;
impl<'a: 'b, 'b> Supertrait<'a, 'b> for MyStruct {
fn convert<T: ?Sized>(x: &'a T) -> &'b T {
x
}
}
impl<'a, 'b> Subtrait<'a, 'b, &'b &'a ()> for MyStruct {}
fn extend_lifetime<'a, 'b, T: ?Sized>(x: &'a T) -> &'b T {
need_hrtb_subtrait::<MyStruct, T>(x)
}
fn main() {
let d;
{
let x = "Hello World".to_string();
d = extend_lifetime(&x);
}
println!("{}", d);
}
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