unused-argument

Flag a function parameter that is never read in its body. Every signature form is covered — long, short (f(x) = ...), anonymous, and do. All-underscore names (_, __) follow Julia’s throwaway convention and are skipped, and stub methods whose body is a single placeholder expression — a literal (f(x) = 0), nothing, or an error(...)/throw(...) call — are exempt. Because methods that dispatch on an argument’s type without reading its value are common, this rule is disabled by default; enable it with --select unused-argument.

factor is accepted but never used:

function scale(x, factor)
    2 * x
end

warning: unused-argument
 --> example.jl:1:19
  |
1 | function scale(x, factor)
  |                   ^^^^^^ function argument `factor` is never used