Function free_fns_for_struct 

fn free_fns_for_struct(
    tcx: TyCtxt<'_>,
    struct_def_id: DefId,
) -> Vec<(DefId, Vec<Local>)>

Collect the free functions in the struct’s own module that take a &Struct / &mut Struct parameter. Rust privacy is module-scoped, so only those can reach a private raw field. Each entry pairs the function with the parameter locals that carry the struct reference.