syntax_data: {"ast_node_type":"other","tokens":[{"end":67,"kind":"keyword","start":0,"text":"a_data:"}]}
source_snippet:         a_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
context_before:         unnormalized_upcast_principal: ty::PolyTraitRef<'tcx>,
context_after:         b_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,