syntax_data: {"ast_node_type":"variable","tokens":[{"end":43,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let unnormalized_upcast_principal =
context_before:         let source_principal = a_data.principal().unwrap().with_self_ty(tcx, a_ty);
context_after:             util::supertraits(tcx, source_principal).nth(idx).unwrap();