syntax_data: {"ast_node_type":"variable","tokens":[{"end":86,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                     let hr_source_principal = upcast_principal.map_bound(|trait_ref| {
context_before:                 ty::ExistentialPredicate::Trait(target_principal) => {
context_after:                         ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)