syntax_data: {"ast_node_type":"impl","tokens":[{"end":56,"kind":"keyword","start":0,"text":"mut"}]}
source_snippet:         mut normalize: impl FnMut(Ty<'tcx>) -> Ty<'tcx>,
context_before:         mut ty: Ty<'tcx>,
context_after:         // This is currently used to allow us to walk a ValTree