Move point to just before end of a comment

Question

Given that the point is right in front of a comment, how do I move it to the end of the comment, but before the comment end markers?

For example:

• for a C++ // xxx comment, I would like to move the point to the end of the line
• for C-style /* xxx */ comments I would like to move the point to right before the second *.

To complicate matters, I would like this to be mode independent. Also, I would like the solution to be based on the syntax table, as there are major modes that don't set up the comment-related regex variables properly.

Starting points:

• The function forward-comment can move the point the after the comment end marker, but I want it to stop before the comment end marker
• The syntax table can define three kinds of comments at the same time (where the b and c flags indicate that character is part of alternative comment kinds). When the point is inside a comment, the function syntax-ppss can tell which kind of comment it is.

Answer 1

This can be done, although Emacs doesn't seem to provide useful info about multi-line comment ends, so it needs a hard coded check for */.

(defun my-end-of-comment ()
  (interactive)
  (let ((state (syntax-ppss))
        (point-init (point)))

    ;; We may be at the comment start, which isn't considered a comment.
    (unless (nth 4 state)
      (save-excursion
        (skip-syntax-forward "^-")
        (let ((state-test (syntax-ppss)))
          (when (and (nth 4 state-test) (<= point-init (nth 8 state-test)))
            (setq state state-test)))))

    (when (nth 4 state)
      (let ((start (nth 8 state)))
        (goto-char start)
        (forward-comment 1)
        (skip-syntax-backward ">")
        ;; Hard code '*/' for C.
        (when (looking-back "\\*\\/")
          (forward-char -2))))))