Function fold_trait_adaptation 

pub fn fold_trait_adaptation<'new, 'src, F: Fold<'src> + ?Sized>(
    folder: &mut F,
    arena: &'new Bump,
    adaptation: &TraitAdaptation<'_, 'src>,
) -> TraitAdaptation<'new, 'src>

Folds a trait insteadof/as adaptation.