formalCoverage.R

formalCoverage <- function(fn) {
  formalz <<- formals(fn)
  bod <<- as.character(body(fn))
  
  formal_present <- function(formal) {
    formal_dots_escaped <<- gsub(".", "\\.", formal, fixed = TRUE)
    
    any(grepl(pattern = paste0("(?:\\b|\\s)", formal_dots_escaped, "(?:\\b|\\s)"),
              x = bod,
              perl = TRUE))
  }
  formals_present <<- vapply(names(formalz), formal_present, FALSE)
  
  if (!all(formals_present)) {
    names(formals_present)[!formals_present]
  }
}