trait DebugInfoOffsetLocation<'tcx, Bx> {
fn deref(&self, bx: &mut Bx) -> Self;
fn layout(&self) -> TyAndLayout<'tcx>;
fn project_field(&self, bx: &mut Bx, field: Field) -> Self;
fn downcast(&self, bx: &mut Bx, variant: VariantIdx) -> Self;
}