syntax_data: {"ast_node_type":"function","tokens":[{"end":79,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn upcast_from(from: PolyTraitPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
context_before: impl<'tcx> UpcastFrom<TyCtxt<'tcx>, PolyTraitPredicate<'tcx>> for Predicate<'tcx> {
context_after:         from.map_bound(|p| PredicateKind::Clause(ClauseKind::Trait(p))).upcast(tcx)