syntax_data: {"ast_node_type":"other","tokens":[{"end":34,"kind":"keyword","start":0,"text":"overlap_mode:"}]}
source_snippet:         overlap_mode: OverlapMode,
context_before:         impl_def_id: DefId,
context_after:     ) -> Result<Option<FutureCompatOverlapError<'tcx>>, OverlapError<'tcx>> {