rust/tests/ui/wf/wf-fn-def-check-sig-2.rs

// Regression test for #84533 involving higher-ranked regions
// in the return type.
use std::marker::PhantomData;

fn foo<'c, 'b, 'a>(_: &'c ()) -> (&'c (), PhantomData<&'b &'a ()>) {
    (&(), PhantomData)
}

fn extend_lifetime<'a, 'b, T: ?Sized>(x: &'a T) -> &'b T {
    let f = foo;
    f.baz(x)
    //~^ ERROR lifetime may not live long enough
}

trait Foo<'a, 'b, T: ?Sized> {
    fn baz(self, s: &'a T) -> &'b T;
}
impl<'a, 'b, R, F, T: ?Sized> Foo<'a, 'b, T> for F
where
    F: for<'c> Fn(&'c ()) -> (&'c (), R),
    R: ProofForConversion<'a, 'b, T>,
{
    fn baz(self, s: &'a T) -> &'b T {
        self(&()).1.convert(s)
    }
}

trait ProofForConversion<'a, 'b, T: ?Sized> {
    fn convert(self, s: &'a T) -> &'b T;
}
impl<'a, 'b, T: ?Sized> ProofForConversion<'a, 'b, T> for PhantomData<&'b &'a ()> {
    fn convert(self, s: &'a T) -> &'b T {
        s
    }
}

fn main() {
    let d;
    {
        let x = "Hello World".to_string();
        d = extend_lifetime(&x);
    }
    println!("{}", d);
}