syntax_data: {"ast_node_type":"other","tokens":[{"end":27,"kind":"keyword","start":0,"text":"impl_def_id:"}]}
source_snippet:         impl_def_id: DefId,
context_before:         obligation: &PolyTraitObligation<'tcx>,
context_after:     ) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> {