syntax_data: {"ast_node_type":"function","tokens":[{"end":98,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn lower_opt_pattern(&mut self, pat: Option<&'tcx hir::Pat<'tcx>>) -> Option<Box<Pat<'tcx>>> {
context_after:         pat.map(|p| self.lower_pattern(p))