Function dots_check 

fn dots_check(formals: &str, class: Option<&str>, indent: &str) -> String

The check a method with formals makes before it reads its index (#2174): dots = empty’s statement (DotsPolicy::r_check), which refuses every argument in ... on the generic’s call (the method’s frame), with the formal each one most likely meant. class is an R expression for the classes in front, the type’s field_error classes.