Code: ``` trait Aaa {} impl<'a> Aaa for &'a mut Aaa + 'a {} struct Bar<'a> { writer: &'a mut Aaa + 'a, } fn baz(_: &mut Aaa) { } fn foo<'a>(mut bar: Bar<'a>) { baz(&mut bar.writer); } fn main() { } ``` ``` error: internal compiler error: trying to take the sizing type of Aaa+'a, an unsized type ```