duplicate-formal

Flag a function defined with two parameters of the same name. R raises a runtime error (repeated formal argument); this catches it statically.

Two parameters named x:

f <- function(x, x) x

error: duplicate-formal
 --> example.R:1:18
  |
1 | f <- function(x, x) x
  |                  ^ parameter `x` is declared more than once in this function
  = help: Rename one of the parameters.