Re: "Soft" indent with visual-line-mode?

[Stephen Berman <stephen.berman@gmx.net>]

On Wed, 9 Sep 2009 13:53:58 -0400 Tim Stewart <tim@stoo.org> wrote:

> Hello Emacs Help,
>
> I like the idea of using longlines-mode or visual-line-mode to spend less time
> formatting code as I write.  However, it is not useful to me  when the wrapped
> lines start in the first column and break up the flow  of the code.
>
> As an example, this is what I get now with a line that is indented 4 spaces.
> This is all one line, wrapped by the editor for me:
>
>     This is a test of the emergency broadcast system.  This is only a test. In
> the event of a real emergency, your head would have exploded.
>
> And this is what I want:
>
>     This is a test of the emergency broadcast system.  This is only a test. In
>     the event of a real emergency, your head would have exploded.
>
> I've heard this referred to as a "soft" indent.  I believe that Visual
> SlickEdit 9 and Kate both support this feature if you'd like other  examples.
>
> Does anyone know of a feature or add-on for Emacs that can accomplish this?
> I've scoured the 'Tubes and can't find anything.

The following code might do what you want, though it might need some
tweaking.  (To use it, evaluate it and call the minor mode manually or
add it to appropriate mode hooks.)

Steve Berman

(defun srb-adaptive-indent (beg end)
  "Indent the region between BEG and END with adaptive filling."
  (goto-char beg)
  (while
      (let ((lbp (line-beginning-position))
	    (lep (line-end-position)))
	(put-text-property lbp lep 'wrap-prefix (fill-context-prefix lbp lep))
	(search-forward "\n" end t))))

(define-minor-mode srb-adaptive-wrap-mode
  "Wrap the buffer text with adaptive filling."
  :lighter ""
  (save-excursion
    (save-restriction
      (widen)
      (let ((buffer-undo-list t)
	    (inhibit-read-only t)
	    (mod (buffer-modified-p)))
	(if srb-adaptive-wrap-mode
	    (progn
	      (setq word-wrap t)
	      (unless (member '(continuation) fringe-indicator-alist)
	      	(push '(continuation) fringe-indicator-alist))
	      (jit-lock-register 'srb-adaptive-indent))
	  (jit-lock-unregister 'srb-adaptive-indent)
	  (remove-text-properties (point-min) (point-max) '(wrap-prefix pref))
	  (setq fringe-indicator-alist
	  	(delete '(continuation) fringe-indicator-alist))
	  (setq word-wrap nil))
	(restore-buffer-modified-p mod)))))