Function to delete all comments from a buffer, without moving them to kill ring

Question

I need to be able to remove all comments from a buffer from elisp code. For now, I am using:

(goto-char (point-min))
(comment-kill (count-lines (point-min) (point-max)))

However, comment-kill is an interactive function, and its primary usage is to delete one comment at a time. Additionally, it has annoying visible side-effects, since it adds all the comments it killed to the kill-ring.

Is there a function allowing to delete (not kill) some or all comments from a buffer?

Answer 1

In general, there's nothing wrong with using commands as part of elisp code. Those functions which are only meant for interactive use will (or should) warn you about that. See next-line for instance.

In order to delete, instead of killing, just make sure the kill-ring isn't changed:

(goto-char (point-min))
(let (kill-ring)
  (comment-kill (count-lines (point-min) (point-max))))

Answer 2

@Malabarba's answer looks like the simplest and most elegant solution. However, if you do this enough that it warrants its own function, you can also adapt comment-kill to delete without modifying the kill ring. Here's the source code of comment-kill with the single-line change to define comment-delete:

(defun comment-delete (arg)
  "Delete the first comment on this line, if any.  Don't touch
the kill ring.  With prefix ARG, delete comments on that many
lines starting with this one."
  (interactive "P")
  (comment-normalize-vars)
  (dotimes (_i (prefix-numeric-value arg))
    (save-excursion
      (beginning-of-line)
      (let ((cs (comment-search-forward (line-end-position) t)))
    (when cs
      (goto-char cs)
      (skip-syntax-backward " ")
      (setq cs (point))
      (comment-forward)
      ;; (kill-region cs (if (bolp) (1- (point)) (point))) ; original
      (delete-region cs (if (bolp) (1- (point)) (point)))  ; replace kill-region with delete-region
      (indent-according-to-mode))))
    (if arg (forward-line 1))))

And here's a function (NB: minimally tested) that provides some additional functionality, allowing you to delete comments on the current line, in the active region, or in the entire buffer:

(defun comment-delete-dwim (beg end arg)
  "Delete comments without touching the kill ring.  With active
region, delete comments in region.  With prefix, delete comments
in whole buffer.  With neither, delete comments on current line."
  (interactive "r\nP")
  (let ((lines (cond (arg
                      (count-lines (point-min) (point-max)))
                     ((region-active-p)
                      (count-lines beg end)))))
    (save-excursion
      (when lines
        (goto-char (if arg (point-min) beg)))
      (comment-delete (or lines 1)))))

I haven't checked performance issues, but perhaps there's a tiny bump from not touching the kill ring. Regardless, I doubt you'll notice performance problems unless you're working with a truly massive buffer. But since you're unlikely to use this function very frequently, it seems like it would not be worth the effort to work on optimization.