syntax_data: {"ast_node_type":"other","tokens":[{"end":20,"kind":"keyword","start":0,"text":"def:"}]}
source_snippet:     def: LocalDefId,
context_before:     tcx: TyCtxt<'tcx>,
context_after: ) -> Result<Option<ty::EarlyBinder<'tcx, ty::Const<'tcx>>>, ErrorGuaranteed> {