syntax_data: {"ast_node_type":"other","tokens":[{"end":70,"kind":"keyword","start":0,"text":"ty::ExistentialPredicate::Trait(target_principal)"}]}
source_snippet:                 ty::ExistentialPredicate::Trait(target_principal) => {
context_before:                 // with the target (b_ty).
context_after:                     let hr_source_principal = upcast_principal.map_bound(|trait_ref| {