syntax_data: {"ast_node_type":"other","tokens":[{"end":21,"kind":"keyword","start":0,"text":"fn_def_id:"}]}
source_snippet:     fn_def_id: DefId,
context_before:     predicates: &'a mut Vec<ty::Clause<'tcx>>,
context_after:     bound_vars: &'tcx ty::List<ty::BoundVariableKind>,