{"ast_node_type":"impl","tokens":[{"end":70,"kind":"keyword","start":0,"text":"mut"}]}
        mut handle_opaque_cast_and_subtype: impl FnMut(T) -> Ty<'tcx>,
        mut handle_field: impl FnMut(Ty<'tcx>, Option<VariantIdx>, FieldIdx, T) -> Ty<'tcx>,
    ) -> PlaceTy<'tcx>