syntax_data: {"ast_node_type":"other","tokens":[{"end":52,"kind":"keyword","start":0,"text":"a_is_expected:"}]}
source_snippet:                                 a_is_expected: true,
context_before:                             ty::Binder::dummy(ty::PredicateKind::Subtype(ty::SubtypePredicate {
context_after:                                 a,