Function get_all_mutable_methods 

pub fn get_all_mutable_methods(
    tcx: TyCtxt<'_>,
    src_def_id: DefId,
) -> HashSet<DefId>

Find &mut self methods (mutators) on the same struct as src_def_id.

For std types the mutators are located among the std library’s public functions; for user types they are the struct’s inherent &mut self methods.