syntax_data: {"ast_node_type":"other","tokens":[{"end":77,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // Out-parameters collecting extra data to be reapplied by the caller
context_before:         expr: Option<&'tcx hir::PatExpr<'tcx>>,
context_after:         ascriptions: &mut Vec<Ascription<'tcx>>,