Question

I usually use Geany or Hi-Tide under Debian (GNU/Linux) for firmware development, mainly C (but also reading old assembler). I document code using single-line comments, and it really annoys me when I retype something and have to manually re-break every following line to keep it in the 80-character margin.

Is there a text editor that can re-wrap consecutive single-line comments (and do this automatically while I type)? That is, given:

/// This is a really long line that should have been wrapped at "that" but was not.
/// This sentence is in the same
/// paragraph as the last.

…I want an editor that will re-wrap this to

/// This is a really long line that
/// should have been wrapped at "that"
/// but was not. This sentence is in
/// the same paragraph as the last.

…preferably doing this sensibly while I type.

I’ve tried:

• Hi-Tide (based on Eclipse 3.3)
• Geany
• jEdit
• UniversalIndentGUI + a bunch of prettifiers (I couldn’t find any formatters that worked, and it’s not a great workflow either)
• GVim – next line begins //should have been… instead of /// should have been…

Update: just to elaborate on my accepted answer – I’ve gone with the snapshot emacs and an extra filladapt mode was also required

Answer 1

In Emacs, to start automatic wrapping, enter auto-fill-mode. To set the line width, run C-u ⟨columns⟩ C-x f.
Emacs, or really CC Mode, will anticipate your commenting structure, so that typing
/// This is a really long line that shoul will result in

/// This is a really long line that
/// shoul‸

And you can refill a paragraph at any time with M-q.

If you want to do refills automatically with each keypress, well there may well be some interal command or third-party library out there, but off-hand you can use this elisp code:

;;; Can't advise SELF-INSERT-COMMAND, so create a wrapper procedure.
(defun self-insert-refill (n)
  (interactive "p")
  (self-insert-command n))

;;; Advise SELF-INSERT-REFILL to execute FILL-PARAGRAPH after every
;;; keypress, but *only* if we're inside a comment
(defadvice self-insert-refill (after refill-paragraph)
  (let ((face (or (get-char-property (point) 'read-face-name)
                  (get-char-property (point) 'face))) )

    (if (and (eq face 'font-lock-comment-face)
             (not (string= " " (this-command-keys))))  ; Spaces would get deleted on refill.
        (fill-paragraph))))

(ad-activate 'self-insert-refill)

(add-hook 'c-mode-hook
  ;; Remap SELF-INSERT-COMMAND to be SELF-INSERT-REFILL.
  (local-set-key [remap self-insert-command] 'self-insert-refill) ))

This is probably not very robust or in keeping with best-practice, and likely not wholly satisfactory, as it won’t work for general editing, e.g. C-d and backspace, and it slows down the editor somewhat, but it’s a start.