To suppress compiler warnings for unused parameters and locals, you prefix the name with an underscore.

Many users don't want to allow leading underscores in their variable names globally. Of course you can restrict that to parameters, but that will still allow a leading underscore for used parameters.

The rule should support restricting the leading underscore to only parameters that are really unused.
This could be achieved by either using the type checker or making use of the upcoming functionality intsutils to track all uses of an identifier.