I read this as if the last line is not empty, add one (if trailing_empty_line). However, if you have already 5 empty lines, that won't remove 4. You can also just c/p the ensure_last_n_empty() from {styler}:

ensure_last_n_empty <- function(x, n = 1) {
  if (all(x == "")) {
    return("")
  }
  x <- c(x, "", "")
  x <- x[seq(1, length(x) - which(rev(x) != "")[1] + 1L)]
  c(x, rep("", n))
}

styler:::ensure_last_n_empty("hi")
#> [1] "hi" ""
styler:::ensure_last_n_empty(c("hi", ""))
#> [1] "hi" ""
styler:::ensure_last_n_empty(c("hi", "", ""))
#> [1] "hi" ""

^{Created on 2021-12-28 by the reprex package (v2.0.1)}

Thanks for pointing to styler:::ensure_last_n_empty(). I actually tried it, but I wonder if we should regard removing trailing empty lines as part of styler rather than languageserver?

The current release does not remove any trailing empty lines, and the latest dev removes all trailing empty lines. I think it might make some sense to leave it to styler to determine whether it is appropriate to remove all trailing empty lines? Looks like it should be subject to user preference and should be customizable via styler some how, if possible. On languageserver side, we only need to ensure there is at least a trailing empty line to make things work (e.g. .Rprofile).

Ok, makes sense. {styler} dev does remove these additional lines, so with the next CRAN release, people will have this functionality anyways. Thanks for looking into it @renkun-ken, appreciate it that you help fix a problem that is fundamentally not a {languageserver}, but a {styler} problem. 👍