syntax_data: {"ast_node_type":"variable","tokens":[{"end":50,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let p: Predicate<'tcx> = from.upcast(tcx);
context_before:     fn upcast_from(from: PolyTraitPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
context_after:         p.expect_clause()