syntax_data: {"ast_node_type":"function","tokens":[{"end":88,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn upcast_from(from: ty::Binder<'tcx, TraitRef<'tcx>>, _tcx: TyCtxt<'tcx>) -> Self {
context_before: impl<'tcx> UpcastFrom<TyCtxt<'tcx>, ty::Binder<'tcx, TraitRef<'tcx>>> for PolyTraitPredicate<'tcx> {
context_after:         from.map_bound(|trait_ref| TraitPredicate {