syntax_data: {"ast_node_type":"function","tokens":[{"end":56,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn upcast_from(from: TraitRef<I>, _tcx: I) -> Self {
context_before: impl<I: Interner> UpcastFrom<I, TraitRef<I>> for TraitPredicate<I> {
context_after:         TraitPredicate { trait_ref: from, polarity: PredicatePolarity::Positive }