syntax_data: {"ast_node_type":"other","tokens":[{"end":48,"kind":"keyword","start":0,"text":"extra_data:"}]}
source_snippet:         extra_data: &mut PatternExtraData<'tcx>,
context_before:         match_pairs: &mut Vec<MatchPairTree<'tcx>>,
context_after:         place: PlaceBuilder<'tcx>,