{"ast_node_type":"impl","tokens":[{"end":73,"kind":"keyword","start":0,"text":"mut"}]}
    mut region_var_origin: impl FnMut(RegionVid) -> RegionVariableOrigin,
    region_constraints: &RegionConstraintData<'tcx>,
    mut universe_of_region: impl FnMut(RegionVid) -> UniverseIndex,