#![feature(nll)]

trait DebugWith<Cx: ?Sized> {
    fn debug_with<'me>(&'me self, cx: &'me Cx) -> DebugCxPair<'me, Self, Cx> {
        DebugCxPair { value: self, cx }
    }

    fn fmt_with(&self, _cx: &Cx, _fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result;
}

struct DebugCxPair<'me, Value: ?Sized, Cx: ?Sized>
where
    Value: DebugWith<Cx>,
{
    value: &'me Value,
    cx: &'me Cx,
}

trait DebugContext { }

struct Foo {
    bar: Bar
}

impl DebugWith<dyn DebugContext> for Foo {
    fn fmt_with(&self, cx: &dyn DebugContext, _fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let Foo { bar } = self;
        bar.debug_with(cx);
        Ok(())
    }
}

struct Bar { }

impl DebugWith<dyn DebugContext> for Bar {
    fn fmt_with(&self, _cx: &dyn DebugContext, _fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        Ok(())
    }
}

fn main() { }