syntax_data: {"ast_node_type":"other","tokens":[{"end":67,"kind":"keyword","start":0,"text":"ty::ExistentialPredicate::Trait(trait_ref)"}]}
source_snippet:                     ty::ExistentialPredicate::Trait(trait_ref) => {
context_before:                 match predicate.as_ref().skip_binder() {
context_after:                         // Use a type that can't appear in defaults of type parameters.